Co-reporter:Anouck M. Champsaur, Jaeeun Yu, Xavier Roy, Daniel W. Paley, Michael L. Steigerwald, Colin Nuckolls, and Christopher M. Bejger
ACS Central Science September 27, 2017 Volume 3(Issue 9) pp:1050-1050
Publication Date(Web):August 30, 2017
DOI:10.1021/acscentsci.7b00328
We describe a new approach to synthesize two-dimensional (2D) nanosheets from the bottom-up. We functionalize redox-active superatoms with groups that can direct their assembly into multidimensional solids. We synthesized Co6Se8[PEt2(4-C6H4COOH)]6 and found that it forms a crystalline assembly. The solid-state structure is a three-dimensional (3D) network in which the carboxylic acids form intercluster hydrogen bonds. We modify the self-assembly by replacing the reversible hydrogen bonds that hold the superatoms together with zinc carboxylate bonds via the solvothermal reaction of Co6Se8[PEt2(4-C6H4COOH)]6 with Zn(NO3)2. We obtain two types of crystalline materials using this approach: one is a 3D solid and the other consists of stacked layers of 2D sheets. The dimensionality is controlled by subtle changes in reaction conditions. These 2D sheets can be chemically exfoliated, and the exfoliated, ultrathin 2D layers are soluble. After they are deposited on a substrate, they can be imaged. We cast them onto an electrode surface and show that they retain the redox activity of the superatom building blocks due to the porosity in the sheets.
Co-reporter:Margarita Milton, Qian Cheng, Yuan Yang, Colin Nuckolls, Raúl Hernández Sánchez, and Thomas J. Sisto
Nano Letters December 13, 2017 Volume 17(Issue 12) pp:7859-7859
Publication Date(Web):November 10, 2017
DOI:10.1021/acs.nanolett.7b04131
This manuscript presents a working redox battery in organic media that possesses remarkable cycling stability. The redox molecules have a solubility over 1 mol electrons/liter, and a cell with 0.4 M electron concentration is demonstrated with steady performance >450 cycles (>74 days). Such a concentration is among the highest values reported in redox flow batteries with organic electrolytes. The average Coulombic efficiency of this cell during cycling is 99.868%. The stability of the cell approaches the level necessary for a long lifetime nonaqueous redox flow battery. For the membrane, we employ a low cost size exclusion cellulose membrane. With this membrane, we couple the preparation of nanoscale macromolecular electrolytes to successfully avoid active material crossover. We show that this cellulose-based membrane can support high voltages in excess of 3 V and extreme temperatures (−20 to 110 °C). These extremes in temperature and voltage are not possible with aqueous systems. Most importantly, the nanoscale macromolecular platforms we present here for our electrolytes can be readily tuned through derivatization to realize the promise of organic redox flow batteries.Keywords: ferrocene; organic electrolyte; perylene diimide; Redox flow battery; size-exclusion membrane;
Co-reporter:Margarita Milton, Qian Cheng, Yuan Yang, Colin Nuckolls, Raúl Hernández Sánchez, and Thomas J. Sisto
Nano Letters December 13, 2017 Volume 17(Issue 12) pp:7859-7859
Publication Date(Web):November 10, 2017
DOI:10.1021/acs.nanolett.7b04131
This manuscript presents a working redox battery in organic media that possesses remarkable cycling stability. The redox molecules have a solubility over 1 mol electrons/liter, and a cell with 0.4 M electron concentration is demonstrated with steady performance >450 cycles (>74 days). Such a concentration is among the highest values reported in redox flow batteries with organic electrolytes. The average Coulombic efficiency of this cell during cycling is 99.868%. The stability of the cell approaches the level necessary for a long lifetime nonaqueous redox flow battery. For the membrane, we employ a low cost size exclusion cellulose membrane. With this membrane, we couple the preparation of nanoscale macromolecular electrolytes to successfully avoid active material crossover. We show that this cellulose-based membrane can support high voltages in excess of 3 V and extreme temperatures (−20 to 110 °C). These extremes in temperature and voltage are not possible with aqueous systems. Most importantly, the nanoscale macromolecular platforms we present here for our electrolytes can be readily tuned through derivatization to realize the promise of organic redox flow batteries.Keywords: ferrocene; organic electrolyte; perylene diimide; Redox flow battery; size-exclusion membrane;
Co-reporter:Timothy A. Su, Jonathan R. Widawsky, Haixing Li, Rebekka S. Klausen, James L. Leighton, Michael L. Steigerwald, Latha Venkataraman, and Colin Nuckolls
Journal of the American Chemical Society December 11, 2013 Volume 135(Issue 49) pp:18331-18334
Publication Date(Web):November 21, 2013
DOI:10.1021/ja410656a
Here we demonstrate for the first time that strained silanes couple directly to gold electrodes in break-junction conductance measurements. We find that strained silicon molecular wires terminated by alkyl sulfide aurophiles behave effectively as single-molecule parallel circuits with competing sulfur-to-sulfur (low G) and sulfur-to-silacycle (high G) pathways. We can switch off the high conducting sulfur-to-silacycle pathway by altering the environment of the electrode surface to disable the Au–silacycle coupling. Additionally, we can switch between conductive pathways in a single molecular junction by modulating the tip–substrate electrode distance. This study provides a new molecular design to control electronics in silicon-based single molecule wires.
Co-reporter:Anouck M. Champsaur, Cécile Mézière, Magali Allain, Daniel W. Paley, Michael L. Steigerwald, Colin Nuckolls, and Patrick Batail
Journal of the American Chemical Society August 30, 2017 Volume 139(Issue 34) pp:11718-11718
Publication Date(Web):August 22, 2017
DOI:10.1021/jacs.7b07279
Here we disclose a simple route to nanoscopic 2D woven structures reminiscent of the methods used to produce macroscopic textiles. We find that the same principles used in macroscopic weaving can be applied on the nanoscale to create two-dimensional molecular cloth from polymeric strands, a molecular thread. The molecular thread is composed of Co6Se8(PEt3)4L2 superatoms that are bridged with L = benzene bis-1,4-isonitrile to form polymer strands. As the superatoms that make up the polymer chain are electrochemically oxidized, they are electrostatically templated by a nanoscale anion, the tetragonal Lindqvist polyoxometalate Mo6O192–. The tetragonal symmetry of the dianionic template creates a nanoscale version of the box weave. The crossing points in the weave feature π-stacking of the bridging linker. By examining the steps in the weaving process with single crystal X-ray diffraction, we find that the degree of polymerization at the crossing points is crucial in the cloth formation. 2D nanoscale cloth will provide access to a new generation of smart, multifunctional materials, coatings, and surfaces.
Co-reporter:Yu Zhong, Thomas J. Sisto, Boyuan Zhang, Kiyoshi Miyata, X.-Y. Zhu, Michael L. Steigerwald, Fay Ng, and Colin Nuckolls
Journal of the American Chemical Society April 26, 2017 Volume 139(Issue 16) pp:5644-5644
Publication Date(Web):April 18, 2017
DOI:10.1021/jacs.6b13089
This Communication describes a new molecular design that yields ultranarrowband organic photodetectors. The design is based on a series of helically twisted molecular ribbons as the optoelectronic material. We fabricate charge collection narrowing photodetectors based on four different helical ribbons that differ in the wavelength of their response. The photodetectors made from these materials have narrow spectral response with full-width at half maxima of <20 nm. The devices reported here are superior by approximately a factor of 5 to those from traditional organic materials due to the narrowness of their response. Moreover, the active layers for the helical ribbon-based photodetectors are solution-cast but have performance that is comparable to the state-of-the-art narrowband photodetectors made from methylammonium lead trihalide perovskite single crystals. The ultranarrow bandwidth for detection results from the helical ribbons’ high absorption coefficient, good electron mobility, and sharp absorption edges that are defined by the twisted molecular conformation.
Co-reporter:Timothy A. Su, Haixing Li, Rebekka S. Klausen, Nathaniel T. Kim, Madhav Neupane, James L. Leighton, Michael L. Steigerwald, Latha Venkataraman, and Colin Nuckolls
Accounts of Chemical Research April 18, 2017 Volume 50(Issue 4) pp:1088-1088
Publication Date(Web):March 27, 2017
DOI:10.1021/acs.accounts.7b00059
ConspectusThis Account provides an overview of our recent efforts to uncover the fundamental charge transport properties of Si–Si and Ge–Ge single bonds and introduce useful functions into group 14 molecular wires. We utilize the tools of chemical synthesis and a scanning tunneling microscopy-based break-junction technique to study the mechanism of charge transport in these molecular systems. We evaluated the fundamental ability of silicon, germanium, and carbon molecular wires to transport charge by comparing conductances within families of well-defined structures, the members of which differ only in the number of Si (or Ge or C) atoms in the wire. For each family, this procedure yielded a length-dependent conductance decay parameter, β. Comparison of the different β values demonstrates that Si–Si and Ge–Ge σ bonds are more conductive than the analogous C–C σ bonds. These molecular trends mirror what is seen in the bulk.The conductance decay of Si and Ge-based wires is similar in magnitude to those from π-based molecular wires such as paraphenylenes However, the chemistry of the linkers that attach the molecular wires to the electrodes has a large influence on the resulting β value. For example, Si- and Ge-based wires of many different lengths connected with a methyl–thiomethyl linker give β values of 0.36–0.39 Å–1, whereas Si- and Ge-based wires connected with aryl–thiomethyl groups give drastically different β values for short and long wires. This observation inspired us to study molecular wires that are composed of both π- and σ-orbitals. The sequence and composition of group 14 atoms in the σ chain modulates the electronic coupling between the π end-groups and dictates the molecular conductance. The conductance behavior originates from the coupling between the subunits, which can be understood by considering periodic trends such as bond length, polarizability, and bond polarity.We found that the same periodic trends determine the electric field-induced breakdown properties of individual Si–Si, Ge–Ge, Si–O, Si–C, and C–C bonds. Building from these studies, we have prepared a system that has two different, alternative conductance pathways. In this wire, we can intentionally break a labile, strained silicon–silicon bond and thereby shunt the current through the secondary conduction pathway. This type of in situ bond-rupture provides a new tool to study single molecule reactions that are induced by electric fields. Moreover, these studies provide guidance for designing dielectric materials as well as molecular devices that require stability under high voltage bias.The fundamental studies on the structure/function relationships of the molecular wires have guided the design of new functional systems based on the Si- and Ge-based wires. For example, we exploited the principle of strain-induced Lewis acidity from reaction chemistry to design a single molecule switch that can be controllably switched between two conductive states by varying the distance between the tip and substrate electrodes. We found that the strain intrinsic to the disilaacenaphthene scaffold also creates two state conductance switching. Finally, we demonstrate the first example of a stereoelectronic conductance switch, and we demonstrate that the switching relies crucially on the electronic delocalization in Si–Si and Ge–Ge wire backbones. These studies illustrate the untapped potential in using Si- and Ge-based wires to design and control charge transport at the nanoscale and to allow quantum mechanics to be used as a tool to design ultraminiaturized switches.
Co-reporter:Edison Castro;Dr. Thomas J. Sisto;Elkin L. Romero;Fang Liu;Samuel R. Peurifoy;Jue Wang; Xiaoyang Zhu; Colin Nuckolls; Luis Echegoyen
Angewandte Chemie International Edition 2017 Volume 56(Issue 46) pp:14648-14652
Publication Date(Web):2017/11/13
DOI:10.1002/anie.201706895
AbstractTwo cove-edge graphene nanoribbons hPDI2-Pyr-hPDI2 (1) and hPDI3-Pyr-hPDI3 (2) are used as efficient electron-transporting materials (ETMs) in inverted planar perovskite solar cells (PSCs). Devices based on the new graphene nanoribbons exhibit maximum power-conversion efficiencies (PCEs) of 15.6 % and 16.5 % for 1 and 2, respectively, while a maximum PCE of 14.9 % is achieved with devices based on [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). The interfacial effects induced by these new materials are studied using photoluminescence (PL), and we find that 1 and 2 act as efficient electron-extraction materials. Additionally, compared with PC61BM, these new materials are more hydrophobic and have slightly higher LUMO energy levels, thus providing better device performance and higher device stability.
Co-reporter:Haixing Li;Timothy A. Su;María Camarasa-Gómez;Dr. Daniel Hernangómez-Pérez;Simon E. Henn;Dr. Vladislav Pokorný;Caravaggio D. Caniglia;Michael S. Inkpen; Richard Korytár;Dr. Michael L. Steigerwald; Colin Nuckolls; Ferdin Evers and; Latha Venkataraman
Angewandte Chemie International Edition 2017 Volume 56(Issue 45) pp:14145-14148
Publication Date(Web):2017/11/06
DOI:10.1002/anie.201708524
AbstractWe report that the single-molecule junction conductance of thiol-terminated silanes with Ag electrodes are higher than the conductance of those formed with Au electrodes. These results are in contrast to the trends in the metal work function Φ(Ag)<Φ(Au). As such, a better alignment of the Au Fermi level to the molecular orbital of silane that mediates charge transport would be expected. This conductance trend is reversed when we replace the thiols with amines, highlighting the impact of metal–S covalent and metal–NH2 dative bonds in controlling the molecular conductance. Density functional theory calculations elucidate the crucial role of the chemical linkers in determining the level alignment when molecules are attached to different metal contacts. We also demonstrate that conductance of thiol-terminated silanes with Pt electrodes is lower than the ones formed with Au and Ag electrodes, again in contrast to the trends in the metal work-functions.
Co-reporter:Hasti Amiri, Kenneth L. Shepard, Colin NuckollsRaúl Hernández Sánchez
Nano Letters 2017 Volume 17(Issue 2) pp:
Publication Date(Web):January 19, 2017
DOI:10.1021/acs.nanolett.6b04967
Here we report on the ion conductance through individual, small diameter single-walled carbon nanotubes. We find that they are mimics of ion channels found in natural systems. We explore the factors governing the ion selectivity and permeation through single-walled carbon nanotubes by considering an electrostatic mechanism built around a simplified version of the Gouy–Chapman theory. We find that the single-walled carbon nanotubes preferentially transported cations and that the cation permeability is size-dependent. The ionic conductance increases as the absolute hydration enthalpy decreases for monovalent cations with similar solid-state radii, hydrated radii, and bulk mobility. Charge screening experiments using either the addition of cationic or anionic polymers, divalent metal cations, or changes in pH reveal the enormous impact of the negatively charged carboxylates at the entrance of the single-walled carbon nanotubes. These observations were modeled in the low-to-medium concentration range (0.1–2.0 M) by an electrostatic mechanism that mimics the behavior observed in many biological ion channel-forming proteins. Moreover, multi-ion conduction in the high concentration range (>2.0 M) further reinforces the similarity between single-walled carbon nanotubes and protein ion channels.Keywords: Ion channel; multi-ion conduction; nanofluidic device; single-walled carbon nanotubes;
Co-reporter:Anouck M. Champsaur, Alexandra Velian, Daniel W. Paley, Bonnie Choi, Xavier Roy, Michael L. Steigerwald, and Colin Nuckolls
Nano Letters 2016 Volume 16(Issue 8) pp:5273-5277
Publication Date(Web):July 13, 2016
DOI:10.1021/acs.nanolett.6b02471
In this study, we have developed a method to create Co6Se8 superatoms in which we program the metal–ligand bonds. We exclusively form the Co6Se8 core under simple reaction conditions with a facile separation of products that contain differential substitution of the core. The combination of Co2(CO)8 and PR3 with excess Se gives the differentially and directionally substituted superatoms, Co6Se8(CO)x(PR3)(6–x). The CO groups on the superatom can be exchanged quantitatively with phosphines and isonitriles. Substitution of the CO allows us to manipulate the type and length of chemical bridge between two redox-active superatomic centers in order to modulate intersuperatomic coupling. Linking two superatoms together allows us to form the simplest superatom molecule: a diatomic molecule. We extend the superatom molecule concept to link three superatoms together in a linear arrangement to form acyclic triatomic molecules. These superatom molecules have a rich electrochemical profile and chart a clear path to a whole family of superatom molecules with new and unusual collective properties.Keywords: nanoscale atoms; nanoscale building blocks; superatom molecules; Superatoms;
Co-reporter:Jaeeun Yu, Chul-Ho Lee, Delphine Bouilly, Minyong Han, Philip Kim, Michael L. Steigerwald, Xavier Roy, and Colin Nuckolls
Nano Letters 2016 Volume 16(Issue 5) pp:3385-3389
Publication Date(Web):April 15, 2016
DOI:10.1021/acs.nanolett.6b01152
This study describes a new and simple approach to dope two-dimensional transition metal dichalcogenides (TMDCs) using the superatom Co6Se8(PEt3)6 as the electron dopant. Semiconducting TMDCs are wired into field-effect transistor devices and then immersed into a solution of these superatoms. The degree of doping is determined by the concentration of the superatoms in solution and by the length of time the films are immersed in the dopant solution. Using this chemical approach, we are able to turn mono- and few-layer MoS2 samples from moderately to heavily electron-doped states. The same approach applied on WSe2 films changes their characteristics from hole transporting to electron transporting. Moreover, we show that the superatom doping can be patterned on specific areas of TMDC films. To illustrate the power of this technique, we demonstrate the fabrication of a lateral p–n junction by selectively doping only a portion of the channel in a WSe2 device. Finally, encapsulation of the doped films with crystalline hydrocarbon layers stabilizes their properties in an ambient environment.
Co-reporter:Bonnie Choi, Jaeeun Yu, Daniel W. Paley, M. Tuan Trinh, Maria V. Paley, Jessica M. Karch, Andrew C. Crowther, Chul-Ho Lee, Roger A. Lalancette, Xiaoyang Zhu, Philip Kim, Michael L. Steigerwald, Colin Nuckolls, and Xavier Roy
Nano Letters 2016 Volume 16(Issue 2) pp:1445-1449
Publication Date(Web):February 1, 2016
DOI:10.1021/acs.nanolett.5b05049
Traditional atomic van der Waals materials such as graphene, hexagonal boron-nitride, and transition metal dichalcogenides have received widespread attention due to the wealth of unusual physical and chemical behaviors that arise when charges, spins, and vibrations are confined to a plane. Though not as widespread as their atomic counterparts, molecule-based two-dimensional (2D) layered solids offer significant benefits; their structural flexibility will enable the development of materials with tunable properties. Here we describe a layered van der Waals solid self-assembled from a structure-directing building block and C60 fullerene. The resulting crystalline solid contains a corrugated monolayer of neutral fullerenes and can be mechanically exfoliated. The absorption spectrum of the bulk solid shows an optical gap of 390 ± 40 meV that is consistent with thermal activation energy obtained from electrical transport measurement. We find that the dimensional confinement of fullerenes significantly modulates the optical and electronic properties compared to the bulk solid.
Co-reporter:Delphine Bouilly, Jason Hon, Nathan S. Daly, Scott Trocchia, Sefi Vernick, Jaeeun Yu, Steven Warren, Ying Wu, Ruben L. Gonzalez Jr., Kenneth L. Shepard, and Colin Nuckolls
Nano Letters 2016 Volume 16(Issue 7) pp:4679-4685
Publication Date(Web):June 7, 2016
DOI:10.1021/acs.nanolett.6b02149
A new approach to synthetic chemistry is performed in ultraminiaturized, nanofabricated reaction chambers. Using lithographically defined nanowells, we achieve single-point covalent chemistry on hundreds of individual carbon nanotube transistors, providing robust statistics and unprecedented spatial resolution in adduct position. Each device acts as a sensor to detect, in real-time and through quantized changes in conductance, single-point functionalization of the nanotube as well as consecutive chemical reactions, molecular interactions, and molecular conformational changes occurring on the resulting single-molecule probe. In particular, we use a set of sequential bioconjugation reactions to tether a single-strand of DNA to the device and record its repeated, reversible folding into a G-quadruplex structure. The stable covalent tether allows us to measure the same molecule in different solutions, revealing the characteristic increased stability of the G-quadruplex structure in the presence of potassium ions (K+) versus sodium ions (Na+). Nanowell-confined reaction chemistry on carbon nanotube devices offers a versatile method to isolate and monitor individual molecules during successive chemical reactions over an extended period of time.
Co-reporter:Boyuan Zhang, M. Tuan Trinh, Brandon Fowler, Melissa Ball, Qizhi Xu, Fay Ng, Michael L. Steigerwald, X.-Y. ZhuColin Nuckolls, Yu Zhong
Journal of the American Chemical Society 2016 Volume 138(Issue 50) pp:16426-16431
Publication Date(Web):December 12, 2016
DOI:10.1021/jacs.6b10276
Organic photodetectors (OPDs) are attractive for their high optical absorption coefficient, broad wavelength tunability, and compatibility with lightweight and flexible devices. Here we describe a new molecular design that enables high performance organic photodetectors. We use a rigid, conjugated macrocycle as the electron acceptor in devices to obtain high photocurrent and low dark current. We make a direct comparison between the devices made with the macrocyclic acceptor and an acyclic control molecule; we find that the superior performance of the macrocycle originates from its rigid, conjugated, and cyclic structure. The macrocycle’s rigid structure reduces the number of charged defects originating from deformed sp2 carbons and covalent defects from photo/thermoactivation. With this molecular design, we are able to suppress dark current density while retaining high responsivity in an ultrasensitive nonfullerene OPD. Importantly, we achieve a detectivity of ∼1014 Jones at near zero bias voltage. This is without the need for extra carrier blocking layers commonly employed in fullerene-based devices. Our devices are comparable to the best fullerene-based photodetectors, and the sensitivity at low working voltages (<0.1 V) is a record for nonfullerene OPDs.
Co-reporter:Haixing Li, Nathaniel T. Kim, Timothy A. Su, Michael L. Steigerwald, Colin Nuckolls, Pierre Darancet, James L. Leighton, and Latha Venkataraman
Journal of the American Chemical Society 2016 Volume 138(Issue 49) pp:16159-16164
Publication Date(Web):November 18, 2016
DOI:10.1021/jacs.6b10700
The stability of chemical bonds can be studied experimentally by rupturing single molecule junctions under applied voltage. Here, we compare voltage-induced bond rupture in two Si–Si backbones: one has no alternate conductive pathway whereas the other contains an additional naphthyl pathway in parallel to the Si–Si bond. We show that in contrast to the first system, the second can conduct through the naphthyl group when the Si–Si bond is ruptured using an applied voltage. We investigate this voltage induced Si–Si bond rupture by ab initio density functional theory calculations and molecular dynamics simulations that ultimately demonstrate that the excitation of molecular vibrational modes by tunneling electrons leads to homolytic Si–Si bond rupture.
Co-reporter:Melissa Ball, Yu Zhong, Brandon Fowler, Boyuan Zhang, Panpan Li, Grisha Etkin, Daniel W. Paley, John Decatur, Ankur K. Dalsania, Hexing Li, Shengxiong Xiao, Fay Ng, Michael L. Steigerwald, and Colin Nuckolls
Journal of the American Chemical Society 2016 Volume 138(Issue 39) pp:12861-12867
Publication Date(Web):September 26, 2016
DOI:10.1021/jacs.6b05474
Here, we compare analogous cyclic and acyclic π-conjugated molecules as n-type electronic materials and find that the cyclic molecules have numerous benefits in organic photovoltaics. This is the first report of such a direct comparison. We designed two conjugated cycles for this study. Each comprises four subunits: one combines four electron-accepting, redox-active, diphenyl-perylenediimide subunits, and the other alternates two electron-donating bithiophene units with two diphenyl-perylenediimide units. We compare the macrocycles to acyclic versions of these molecules and find that, relative to the acyclic analogs, the conjugated macrocycles have bathochromically shifted UV–vis absorbances and are more easily reduced. In blended films, macrocycle-based devices show higher electron mobility and good morphology. All of these factors contribute to the more than doubling of the power conversion efficiency observed in organic photovoltaic devices with these macrocycles as the n-type, electron transporting material. This study highlights the importance of geometric design in creating new molecular semiconductors. The ease with which we can design and tune the electronic properties of these cyclic structures charts a clear path to creating a new family of cyclic, conjugated molecules as electron transporting materials in optoelectronic and electronic devices.
Co-reporter:Timothy A. Su; Haixing Li; Rebekka S. Klausen; Jonathan R. Widawsky; Arunabh Batra; Michael L. Steigerwald; Latha Venkataraman
Journal of the American Chemical Society 2016 Volume 138(Issue 24) pp:7791-7795
Publication Date(Web):June 14, 2016
DOI:10.1021/jacs.6b04394
While the single-molecule conductance properties of π-conjugated and σ-conjugated systems have been well-studied, little is known regarding the conductance properties of mixed σ–π backbone wires and the factors that control their transport properties. Here we utilize a scanning tunneling microscope-based break-junction technique to study a series of molecular wires with π–σ–π backbone structures, where the π-moiety is an electrode-binding thioanisole ring and the σ-moiety is a triatomic α–β–α chain composed of C, Si, or Ge atoms. We find that the sequence and composition of group 14 atoms in the α–β–α chain dictates whether electronic communication between the aryl rings is enhanced or suppressed. Placing heavy atoms at the α-position decreases conductance, whereas placing them at the β-position increases conductance: for example, the C–Ge–C sequence is over 20 times more conductive than the Ge–C–Ge sequence. Density functional theory calculations reveal that these conductance trends arise from periodic trends (i.e., atomic size, polarizability, and electronegativity) that differ from C to Si to Ge. The periodic trends that control molecular conductance here are the same ones that give rise to the α and β silicon effects from physical organic chemistry. These findings outline a new molecular design concept for tuning conductance in single-molecule electrical devices.
Co-reporter:Haixing Li, Marc H. Garner, Zhichun Shangguan, Qianwen Zheng, Timothy A. Su, Madhav Neupane, Panpan Li, Alexandra Velian, Michael L. Steigerwald, Shengxiong Xiao, Colin Nuckolls, Gemma C. Solomon and Latha Venkataraman
Chemical Science 2016 vol. 7(Issue 9) pp:5657-5662
Publication Date(Web):30 May 2016
DOI:10.1039/C6SC01360K
Here we examine the impact of ring conformation on the charge transport characteristics of cyclic pentasilane structures bound to gold electrodes in single molecule junctions. We investigate the conductance properties of alkylated cyclopentasilane cis and trans stereoisomers substituted in the 1,3-position with methylthiomethyl electrode binding groups using both the scanning tunneling microscope-based break junction technique and density functional theory based ab initio calculations. In contrast with the linear ones, these cyclic silanes yield lower conductance values; calculations reveal that the constrained dihedral geometries occurring within the ring are suboptimal for σ-orbital delocalization, and therefore, conductance. Theoretical calculations reproduce the measured conductance trends for both cis and trans isomers and find several distinct conformations that are likely to form stable molecular junctions at room temperature. Due to the weakened σ-conjugation in the molecule, through-space interactions are found to contribute significantly to the conductance. This manuscript details the vast conformational flexibility in cyclopentasilanes and the tremendous impact it has on controlling conductance.
Co-reporter:Melissa Ball, Yu Zhong, Ying Wu, Christine Schenck, Fay Ng, Michael Steigerwald, Shengxiong Xiao, and Colin Nuckolls
Accounts of Chemical Research 2015 Volume 48(Issue 2) pp:267
Publication Date(Web):December 19, 2014
DOI:10.1021/ar500355d
This Account describes a body of research in the design, synthesis, and assembly of molecular materials made from strained polycyclic aromatic molecules. The strain in the molecular subunits severely distorts the aromatic molecules away from planarity. We coined the term “contorted aromatics” to describe this class of molecules. Using these molecules, we demonstrate that the curved pi-surfaces are useful as subunits to make self-assembled electronic materials. We have created and continue to study two broad classes of these “contorted aromatics”: discs and ribbons. The figure that accompanies this conspectus displays the three-dimensional surfaces of a selection of these “contorted aromatics”.The disc-shaped contorted molecules have well-defined conformations that create concave pi-surfaces. When these disc-shaped molecules are substituted with hydrocarbon side chains, they self-assemble into columnar superstructures. Depending on the hydrocarbon substitution, they form either liquid crystalline films or macroscopic cables. In both cases, the columnar structures are photoconductive and form p-type, hole- transporting materials in field effect transistor devices. This columnar motif is robust, allowing us to form monolayers of these columns attached to the surface of dielectrics such as silicon oxide. We use ultrathin point contacts made from individual single-walled carbon nanotubes that are separated by a few nanometers to probe the electronic properties of short stacks of a few contorted discs. We find that these materials have high mobility and can sense electron-deficient aromatic molecules.The concave surfaces of these disc-shaped contorted molecules form ideal receptors for the molecular recognition and assembly with spherical molecules such as fullerenes. These interfaces resemble ball-and-socket joints, where the fullerene nests itself in the concave surface of the contorted disc. The tightness of the binding between the two partners can be increased by creating more hemispherically shaped contorted molecules. Given the electronic structure of these contorted discs and the fullerenes, this junction is a molecular version of a p–n junction. These ball-and-socket interfaces are ideal for photoinduced charge separation. Photovoltaic devices containing these molecular recognition elements demonstrate approximately two orders of magnitude increase in charge separation.The ribbon-shaped, contorted molecules can be conceptualized as ultranarrow pieces of graphene. The contortion causes them to wind into helical ribbons. These ribbons can be formed into the active layer of field effect transistors. We substitute the ribbons with di-imides and therefore are able to transport electrons. Furthermore, these materials absorb light strongly and have ideal energetic alignment of their orbitals with conventional p-type electronic polymers. In solar cells, these contorted ribbons with commercial donor polymers have record efficiencies for non-fullerene-based solar cells. An area of interest for future exploration is the merger of these highly efficient contorted ribbons with the well-defined interfaces of the ball-and-socket materials.
Co-reporter:Timothy A. Su; Haixing Li; Vivian Zhang; Madhav Neupane; Arunabh Batra; Rebekka S. Klausen; Bharat Kumar; Michael L. Steigerwald; Latha Venkataraman
Journal of the American Chemical Society 2015 Volume 137(Issue 38) pp:12400-12405
Publication Date(Web):September 16, 2015
DOI:10.1021/jacs.5b08155
While the electrical conductivity of bulk-scale group 14 materials such as diamond carbon, silicon, and germanium is well understood, there is a gap in knowledge regarding the conductivity of these materials at the nano and molecular scales. Filling this gap is important because integrated circuits have shrunk so far that their active regions, which rely so heavily on silicon and germanium, begin to resemble ornate molecules rather than extended solids. Here we unveil a new approach for synthesizing atomically discrete wires of germanium and present the first conductance measurements of molecular germanium using a scanning tunneling microscope-based break-junction (STM-BJ) technique. Our findings show that germanium and silicon wires are nearly identical in conductivity at the molecular scale, and that both are much more conductive than aliphatic carbon. We demonstrate that the strong donor ability of C–Ge σ-bonds can be used to raise the energy of the anchor lone pair and increase conductance. Furthermore, the oligogermane wires behave as conductance switches that function through stereoelectronic logic. These devices can be trained to operate with a higher switching factor by repeatedly compressing and elongating the molecular junction.
Co-reporter:Haixing Li; Timothy A. Su; Vivian Zhang; Michael L. Steigerwald; Colin Nuckolls;Latha Venkataraman
Journal of the American Chemical Society 2015 Volume 137(Issue 15) pp:5028-5033
Publication Date(Web):February 12, 2015
DOI:10.1021/ja512523r
Here we study the stability and rupture of molecular junctions under high voltage bias at the single molecule/single bond level using the scanning tunneling microscope-based break-junction technique. We synthesize carbon-, silicon-, and germanium-based molecular wires terminated by aurophilic linker groups and study how the molecular backbone and linker group affect the probability of voltage-induced junction rupture. First, we find that junctions formed with covalent S–Au bonds are robust under high voltage and their rupture does not demonstrate bias dependence within our bias range. In contrast, junctions formed through donor–acceptor bonds rupture more frequently, and their rupture probability demonstrates a strong bias dependence. Moreover, we find that the junction rupture probability increases significantly above ∼1 V in junctions formed from methylthiol-terminated disilanes and digermanes, indicating a voltage-induced rupture of individual Si–Si and Ge–Ge bonds. Finally, we compare the rupture probabilities of the thiol-terminated silane derivatives containing Si–Si, Si–C, and Si–O bonds and find that Si–C backbones have higher probabilities of sustaining the highest voltage. These results establish a new method for studying electric field breakdown phenomena at the single molecule level.
Co-reporter:Melissa Ball; Brandon Fowler; Panpan Li; Leo A. Joyce; Fang Li; Taifeng Liu; Daniel Paley; Yu Zhong; Hexing Li; Shengxiong Xiao; Fay Ng; Michael L. Steigerwald
Journal of the American Chemical Society 2015 Volume 137(Issue 31) pp:9982-9987
Publication Date(Web):July 30, 2015
DOI:10.1021/jacs.5b05698
We present here a new design motif for strained, conjugated macrocycles that incorporates two different aromatics into the cycle with an −A–B–A–B– pattern. In this study, we demonstrate the concept by alternating electron donors and acceptors in a conjugated cycle. The donor is a bithiophene, and the acceptor is a perylene diimide derivative. The macrocycle formed has a persistent elliptiform cavity that is lined with the sulfur atoms of the thiophenes and the π-faces of the perylene diimide. Due to the linkage of the perylene diimide subunits, the macrocycles exist in both chiral and achiral forms. We separate the three stereoisomers using chiral high-performance liquid chromatography and study their interconversion. The mechanism for interconversion involves an “intramolecular somersault” in which one of the PDIs rotates around its transverse axis, thereby moving one of its diimide heads through the plane of the cavity. These unusual macrocycles are black in color with an absorption spectrum that spans the visible range. Density functional theory calculations reveal a photoinduced electron transfer from the bithiophene to the perylene diimide.
Co-reporter:Qishui Chen; M. Tuan Trinh; Daniel W. Paley; Molleigh B. Preefer; Haiming Zhu; Brandon S. Fowler; X.-Y. Zhu; Michael L. Steigerwald
Journal of the American Chemical Society 2015 Volume 137(Issue 38) pp:12282-12288
Publication Date(Web):September 16, 2015
DOI:10.1021/jacs.5b06258
We describe the synthesis of two conjugated macrocycles that are formed from the end-to-end linking of stilbenes. We have named these macrocycles cyclostilbenes. The two cyclostilbene isomers created in this study differ in the configuration of the double bond in their subunits. These macrocycles are formed selectively through a stepwise reductive elimination from a tetraplatinum precursor and subsequent photoisomerization. Single-crystal X-ray diffraction reveals the formation of channel architectures in the solid state that can be filled with guest molecules. The cyclostilbene macrocycles emit blue light with fluorescence quantum yields that are high (>50%) and have photoluminescence lifetimes of ∼0.8–1.5 ns. The breadth and large Stokes shift in fluorescence emission, along with broad excited-state absorption, result from strong electronic–vibronic coupling in the strained structures of the cyclostilbenes.
Co-reporter:M. Tuan Trinh
The Journal of Physical Chemistry C 2015 Volume 119(Issue 3) pp:1312-1319
Publication Date(Web):December 22, 2014
DOI:10.1021/jp512650g
Singlet fission, the splitting of one singlet into two triplets, can potentially increase the efficiency of optoelectronic devices beyond conventional limits. Among the singlet fission molecules discovered to date, two mechanisms have emerged: intra- or intermolecular singlet fission. Here we show a combined intra- to intermolecular singlet fission mechanism in the model system of diphenyl-dicyano-oligoene (DPDC). Excitation of DPDC to the first optically bright state leads to the ultrafast formation of an intramolecular triplet pair, which decays in 40 ps in the solution phase but can also split competitively in 30 ps into two long-lived triplets (2×T1) on adjacent molecules in solid films. These findings suggest a design principle for efficient singlet fission: the independent tuning of singlet–triplet pair coupling and triplet pair splitting from intra- and intermolecular interactions, respectively.
Co-reporter:Chul-Ho Lee;Theanne Schiros;Elton J. G. Santos;Bumjung Kim;Kevin G. Yager;Seok Ju Kang;Sunwoo Lee;Jaeeun Yu;Kenji Watanabe;Takashi Taniguchi;James Hone;Efthimios Kaxiras;Philip Kim
Advanced Materials 2014 Volume 26( Issue 18) pp:2812-2817
Publication Date(Web):
DOI:10.1002/adma.201304973
Co-reporter:Yu Zhong ; M. Tuan Trinh ; Rongsheng Chen ; Wei Wang ; Petr P. Khlyabich ; Bharat Kumar ; Qizhi Xu ; Chang-Yong Nam ; Matthew Y. Sfeir ; Charles Black ; Michael L. Steigerwald ; Yueh-Lin Loo ; Shengxiong Xiao ; Fay Ng ; X.-Y. Zhu
Journal of the American Chemical Society 2014 Volume 136(Issue 43) pp:15215-15221
Publication Date(Web):October 14, 2014
DOI:10.1021/ja5092613
We report an efficiency of 6.1% for a solution-processed non-fullerene solar cell using a helical perylene diimide (PDI) dimer as the electron acceptor. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor–acceptor interfaces, indicating that charge carriers are created from photogenerated excitons in both the electron donor and acceptor phases. Light-intensity-dependent current–voltage measurements suggested different recombination rates under short-circuit and open-circuit conditions.
Co-reporter:Michael A. Novak ; Sumedh Surwade ; Jason Prokop ; Kirill Bolotin ; James Hone ; Louis Brus ; Colin Nuckolls ;Haitao Liu
Journal of the American Chemical Society 2014 Volume 136(Issue 24) pp:8536-8539
Publication Date(Web):May 28, 2014
DOI:10.1021/ja503821s
This paper reports a high-throughput, label-free technique to visualize individual carbon nanotubes (CNTs) on a silicon wafer using a conventional optical microscope. We show that individual CNTs can locally enhance the rate of vapor-phase HF etching of SiO2 to produce a SiO2 trench that is several to several tens of nanometers in depth. The trench is visible under an optical microscope due to a change in the optical interference in the SiO2 layer, allowing the location of an individual CNT to be determined. With this technique, we demonstrate high-throughput Raman characterization and reactivity studies on individual CNTs.
Co-reporter:Yu Zhong ; Bharat Kumar ; Seokjoon Oh ; M. Tuan Trinh ; Ying Wu ; Katherine Elbert ; Panpan Li ; Xiaoyang Zhu ; Shengxiong Xiao ; Fay Ng ; Michael L. Steigerwald
Journal of the American Chemical Society 2014 Volume 136(Issue 22) pp:8122-8130
Publication Date(Web):May 20, 2014
DOI:10.1021/ja503533y
We describe the design and synthesis of a new graphene ribbon architecture that consists of perylenediimide (PDI) subunits fused together by ethylene bridges. We created a prototype series of oligomers consisting of the dimer, trimer, and tetramer. The steric congestion at the fusion point between the PDI units creates helical junctions, and longer oligomers form helical ribbons. Thin films of these oligomers form the active layer in n-type field effect transistors. UV–vis spectroscopy reveals the emergence of an intense long-wavelength transition in the tetramer. From DFT calculations, we find that the HOMO–2 to LUMO transition is isoenergetic with the HOMO to LUMO transition in the tetramer. We probe these transitions directly using femtosecond transient absorption spectroscopy. The HOMO–2 to LUMO transition electronically connects the PDI subunits with the ethylene bridges, and its energy depends on the length of the oligomer.
Co-reporter:Zhixing Chen ; Daniel W. Paley ; Lu Wei ; Andrew L. Weisman ; Richard A. Friesner ; Colin Nuckolls ;Wei Min
Journal of the American Chemical Society 2014 Volume 136(Issue 22) pp:8027-8033
Publication Date(Web):May 21, 2014
DOI:10.1021/ja502706q
Vibrational imaging such as Raman microscopy is a powerful technique for visualizing a variety of molecules in live cells and tissues with chemical contrast. Going beyond the conventional label-free modality, recent advance of coupling alkyne vibrational tags with stimulated Raman scattering microscopy paves the way for imaging a wide spectrum of alkyne-labeled small biomolecules with superb sensitivity, specificity, resolution, biocompatibility, and minimal perturbation. Unfortunately, the currently available alkyne tag only processes a single vibrational “color”, which prohibits multiplex chemical imaging of small molecules in a way that is being routinely practiced in fluorescence microscopy. Herein we develop a three-color vibrational palette of alkyne tags using a 13C-based isotopic editing strategy. We first synthesized 13C isotopologues of EdU, a DNA metabolic reporter, by using the newly developed alkyne cross-metathesis reaction. Consistent with theoretical predictions, the mono-13C (13C≡12C) and bis-13C (13C≡13C) labeled alkyne isotopologues display Raman peaks that are red-shifted and spectrally resolved from the originally unlabeled (12C≡12C) alkynyl probe. We further demonstrated three-color chemical imaging of nascent DNA, RNA, and newly uptaken fatty-acid in live mammalian cells with a simultaneous treatment of three different isotopically edited alkynyl metabolic reporters. The alkyne vibrational palette presented here thus opens up multicolor imaging of small biomolecules, enlightening a new dimension of chemical imaging.
Co-reporter:Seok Ju Kang;Gwan-Hyoung Lee;Young-Jun Yu;Yue Zhao;Bumjung Kim;Kenji Watanabe;Takashi Taniguchi;James Hone;Philip Kim
Advanced Functional Materials 2014 Volume 24( Issue 32) pp:5157-5163
Publication Date(Web):
DOI:10.1002/adfm.201400348
Enhancing the device performance of single crystal organic field effect transistors (OFETs) requires both optimized engineering of efficient injection of the carriers through the contact and improvement of the dielectric interface for reduction of traps and scattering centers. Since the accumulation and flow of charge carriers in operating organic FETs takes place in the first few layers of the semiconductor next to the dielectric, the mobility can be easily degraded by surface roughness, charge traps, and foreign molecules at the interface. Here, a novel structure for high-performance rubrene OFETs is demonstrated that uses graphene and hexagonal boron nitride (hBN) as the contacting electrodes and gate dielectric layer, respectively. These hetero-stacked OFETs are fabricated by lithography-free dry-transfer method that allows the transfer of graphene and hBN on top of an organic single crystal, forming atomically sharp interfaces and efficient charge carrier-injection electrodes without damage or contamination. The resulting heterostructured OFETs exhibit both high mobility and low operating gate voltage, opening up new strategy to make high-performance OFETs and great potential for flexible electronics.
Co-reporter:Arunabh Batra, Pierre Darancet, Qishui Chen, Jeffrey S. Meisner, Jonathan R. Widawsky, Jeffrey B. Neaton, Colin Nuckolls, and Latha Venkataraman
Nano Letters 2013 Volume 13(Issue 12) pp:6233-6237
Publication Date(Web):November 25, 2013
DOI:10.1021/nl403698m
We demonstrate a new method of achieving rectification in single molecule devices using the high-bias properties of gold–carbon bonds. Our design for molecular rectifiers uses a symmetric, conjugated molecular backbone with a single methylsulfide group linking one end to a gold electrode and a covalent gold–carbon bond at the other end. The gold–carbon bond results in a hybrid gold-molecule “gateway” state pinned close to the Fermi level of one electrode. Through nonequilibrium transport calculations, we show that the energy of this state shifts drastically with applied bias, resulting in rectification at surprisingly low voltages. We use this concept to design and synthesize a family of diodes and demonstrate through single-molecule current–voltage measurements that the rectification ratio can be predictably and efficiently tuned. This result constitutes the first experimental demonstration of a rationally tunable system of single-molecule rectifiers. More generally, the results demonstrate that the high-bias properties of “gateway” states can be used to provide additional functionality to molecular electronic systems.
Co-reporter:Jian Zhu ; Jinguo Wang ; Fujian Lv ; Shengxiong Xiao ; Colin Nuckolls ;Hexing Li
Journal of the American Chemical Society 2013 Volume 135(Issue 12) pp:4719-4721
Publication Date(Web):March 18, 2013
DOI:10.1021/ja401334j
We describe the use of benzyl alcohols in a solvothermal/alcoholysis reaction to form nanocrystalline sheets of anatase titania. By tuning the reaction conditions, we adjust the size of the nanosheets. The type and density of benzyl groups that decorate the basal plane of the titania sheets control the self-assembly into layered structures. These layered materials can be grown from solid substrates to create iridescent thin films that reflect specific wavelengths of visible light.
Co-reporter:Seok Ju Kang ; Seokhoon Ahn ; Jong Bok Kim ; Christine Schenck ; Anna M. Hiszpanski ; Seokjoon Oh ; Theanne Schiros ; Yueh-Lin Loo
Journal of the American Chemical Society 2013 Volume 135(Issue 6) pp:2207-2212
Publication Date(Web):January 30, 2013
DOI:10.1021/ja308628z
This work explores the formation of well-defined molecular p–n junctions in solution-processed self-assembled heterojunction solar cells using dodecyloxy-substituted contorted hexabenzocoronene (12-c-HBC) as a donor material and phenyl-C70-butyric acid methyl ester (PC70BM) as an acceptor. We find that the contorted 12-c-HBC molecules effectively assemble in solution to form a nested structure with the ball-shaped PC70BM. The result is a self-assembled molecular-scale p–n junction. When this well-defined p–n junction is embedded in active films, we can make efficient self-assembled solar cells with minimal amounts of donor material relative to the acceptor. The power conversion efficiency is drastically enhanced by the mode of donor and acceptor assembly within the film.
Co-reporter:Shengxiong Xiao, Seok Ju Kang, Ying Wu, Seokhoon Ahn, Jong Bok Kim, Yueh-Lin Loo, Theo Siegrist, Michael L. Steigerwald, Hexing Li and Colin Nuckolls
Chemical Science 2013 vol. 4(Issue 5) pp:2018-2023
Publication Date(Web):08 Mar 2013
DOI:10.1039/C3SC50374G
We describe here the synthesis and electronic device properties of a new type of polycyclic aromatic molecule, the contorted octabenzocircumbiphenyl (c-OBCB). Contorted polycyclic aromatic hydrocarbons (PAHs) are promising small active molecules for organic devices. We present two different methods to synthesize c-OBCB derivatives that allow the smooth incorporation of functional groups. The material has a highly contorted exterior with six 4-helicenes and two 5-helicenes around the exterior of the expanded core of the aromatic. With appropriate sidechains, the material is soluble in common organic solvents and forms thin films. In thin films, the tetradodecyloxy-substituted c-OBCB self-assembles to form the active layer in organic field effect transistors. It is a hole transporting organic semiconductor. In the transistors, the c-OBCB forms good contact with source and drain contacts made from graphene. The c-OBCB self-assembles into a heterojunction from solution with phenyl-C70-butyric acid methyl ester (PC70BM). We observed power conversion efficiencies of ∼2.9 % under 100 mW cm−2 illumination at a 1:4 weight ratio of the c-OBCB relative to PC70BM. The c-OBCB is shape complementary to the ball shaped PC70BM.
Co-reporter:Daniel W. Paley;Danielle F. Sedbrook;Dr. John Decatur; Felix R. Fischer;Dr. Michael L. Steigerwald; Colin Nuckolls
Angewandte Chemie 2013 Volume 125( Issue 17) pp:
Publication Date(Web):
DOI:10.1002/ange.201302115
Co-reporter:Daniel W. Paley;Danielle F. Sedbrook;Dr. John Decatur; Felix R. Fischer;Dr. Michael L. Steigerwald; Colin Nuckolls
Angewandte Chemie International Edition 2013 Volume 52( Issue 17) pp:
Publication Date(Web):
DOI:10.1002/anie.201302115
Co-reporter:Dr. Shengxiong Xiao;Dr. Seok Ju Kang;Yu Zhong;Shengguo Zhang;Dr. Amy M. Scott;Dr. Alberto Moscatelli; Nicholas J. Turro;Dr. Michael L. Steigerwald; Hexing Li; Colin Nuckolls
Angewandte Chemie International Edition 2013 Volume 52( Issue 17) pp:4558-4562
Publication Date(Web):
DOI:10.1002/anie.201300209
Co-reporter:Daniel W. Paley;Danielle F. Sedbrook;Dr. John Decatur; Felix R. Fischer;Dr. Michael L. Steigerwald; Colin Nuckolls
Angewandte Chemie International Edition 2013 Volume 52( Issue 17) pp:4591-4594
Publication Date(Web):
DOI:10.1002/anie.201300758
Co-reporter:Daniel W. Paley;Danielle F. Sedbrook;Dr. John Decatur; Felix R. Fischer;Dr. Michael L. Steigerwald; Colin Nuckolls
Angewandte Chemie 2013 Volume 125( Issue 17) pp:4689-4692
Publication Date(Web):
DOI:10.1002/ange.201300758
Co-reporter:Xavier Roy;Chul-Ho Lee;Andrew C. Crowther;Christine L. Schenck;Tiglet Besara;Roger A. Lalancette;Theo Siegrist;Peter W. Stephens;Louis E. Brus;Michael L. Steigerwald;Philip Kim
Science 2013 Volume 341(Issue 6142) pp:157-160
Publication Date(Web):12 Jul 2013
DOI:10.1126/science.1236259
Ionic Materials via Charged Clusters
The formation of salts from atomic and small molecular ions could in principle be replicated with larger inorganic clusters. However, many clusters are stabilized by organic ligands that create a barrier for charge transfer reactions to create ions. Roy et al. (p. 157, published online 6 June; see the Perspective by Batail) now report that chromium, cobalt, and nickel selenide and telluride clusters form materials by charge transfer with C60. The Co and Cr clusters formed a layered structure analogous to CdI2, while the Ni cluster formed a structure related to NaCl.
Co-reporter:Sriharsha V. Aradhya, Jeffrey S. Meisner, Markrete Krikorian, Seokhoon Ahn, Radha Parameswaran, Michael L. Steigerwald, Colin Nuckolls, and Latha Venkataraman
Nano Letters 2012 Volume 12(Issue 3) pp:1643-1647
Publication Date(Web):February 21, 2012
DOI:10.1021/nl2045815
Electronic factors in molecules such as quantum interference and cross-conjugation can lead to dramatic modulation and suppression of conductance in single-molecule junctions. Probing such effects at the single-molecule level requires simultaneous measurements of independent junction properties, as conductance alone cannot provide conclusive evidence of junction formation for molecules with low conductivity. Here, we compare the mechanics of the conducting para-terminated 4,4′-di(methylthio)stilbene and moderately conducting 1,2-bis(4-(methylthio)phenyl)ethane to that of insulating meta-terminated 3,3′-di(methylthio)stilbene single-molecule junctions. We simultaneously measure force and conductance across single-molecule junctions and use force signatures to obtain independent evidence of junction formation and rupture in the meta-linked cross-conjugated molecule even when no clear low-bias conductance is measured. By separately quantifying conductance and mechanics, we identify the formation of atypical 3,3′-di(methylthio)stilbene molecular junctions that are mechanically stable but electronically decoupled. While theoretical studies have envisaged many plausible systems where quantum interference might be observed, our experiments provide the first direct quantitative study of the interplay between contact mechanics and the distinctively quantum mechanical nature of electronic transport in single-molecule junctions.
Co-reporter:Zhenfeng Bian ; Jian Zhu ; Jinguo Wang ; Shengxiong Xiao ; Colin Nuckolls ;Hexing Li
Journal of the American Chemical Society 2012 Volume 134(Issue 4) pp:2325-2331
Publication Date(Web):January 3, 2012
DOI:10.1021/ja210270m
Described here is a new and highly general strategy for multiple-template (multitemplate) patterning. This process is significant because it allows us to create various unusual shapes such as solid spheres, yolk–shell spheres, flowerlike particles, and structured nanocomponents. Alcoholysis of the metal–organic precursors with mixtures of glycerol and various amounts of ethanol followed by calcination yields oxides. The glycerol plays the dual role of hierarchically assembling the metal–organic composites and stabilizing the structures during the subsequent conversions. Furthermore, we demonstrate for the first time that these metal–organic composites can be converted into oxides, nitrides, and highly graphitized carbon nanostructures. We show that these yolk–shell structures display superior photocatalytic activity and electrochemical properties.
Co-reporter:Daniel T. Chase ; Aaron G. Fix ; Seok Ju Kang ; Bradley D. Rose ; Christopher D. Weber ; Yu Zhong ; Lev N. Zakharov ; Mark C. Lonergan ; Colin Nuckolls ;Michael M. Haley
Journal of the American Chemical Society 2012 Volume 134(Issue 25) pp:10349-10352
Publication Date(Web):June 14, 2012
DOI:10.1021/ja303402p
Herein we report the synthesis and characterization of a series of 6,12-diarylindeno[1,2-b]fluorenes (IFs). Functionalization with electron donor and acceptor groups influences the ability of the IF scaffold to undergo two-electron oxidation and reduction to yield the corresponding 18- and 22-π-electron species, respectively. A single crystal of the pentafluorophenyl-substituted IF can serve as an active layer in an organic field-effect transistor (OFET). The important finding is that the single-crystal OFET yields an ambipolar device that is able to transport holes and electrons.
Co-reporter:Jeffrey S. Meisner ; Seokhoon Ahn ; Sriharsha V. Aradhya ; Markrete Krikorian ; Radha Parameswaran ; Michael Steigerwald ; Latha Venkataraman
Journal of the American Chemical Society 2012 Volume 134(Issue 50) pp:20440-20445
Publication Date(Web):November 21, 2012
DOI:10.1021/ja308626m
We study the effects of molecular structure on the electronic transport and mechanical stability of single-molecule junctions formed with Au point contacts. Two types of linear conjugated molecular wires are compared: those functionalized with methylsulfide or amine aurophilic groups at (1) both or (2) only one of its phenyl termini. Using scanning tunneling and atomic force microscope break-junction techniques, the conductance of mono- and difunctionalized molecular wires and its dependence on junction elongation and rupture forces were studied. Charge transport through monofunctionalized wires is observed when the molecular bridge is coupled through a S–Au donor–acceptor bond on one end and a relatively weak Au−π interaction on the other end. For monofunctionalized molecular wires, junctions can be mechanically stabilized by installing a second aurophilic group at the meta position that, however, does not in itself contribute to a new conduction pathway. These results reveal the important interplay between electronic coupling through metal−π interactions and quantum mechanical effects introduced by chemical substitution on the conjugated system. This study affords a strategy to deterministically tune the electrical and mechanical properties through molecular wires.
Co-reporter:Rebekka S. Klausen ; Jonathan R. Widawsky ; Michael L. Steigerwald ; Latha Venkataraman
Journal of the American Chemical Society 2012 Volume 134(Issue 10) pp:4541-4544
Publication Date(Web):February 21, 2012
DOI:10.1021/ja211677q
Bulk silicon, the bedrock of information technology, consists of the deceptively simple electronic structure of just Si–Si σ bonds. Diamond has the same lattice structure as silicon, yet the two materials have dramatically different electronic properties. Here we report the specific synthesis and electrical characterization of a class of molecules, oligosilanes, that contain strongly interacting Si–Si σ bonds, the essential components of the bulk semiconductor. We used the scanning tunneling microscope-based break-junction technique to compare the single-molecule conductance of these oligosilanes to those of alkanes. We found that the molecular conductance decreases exponentially with increasing chain length with a decay constant β = 0.27 ± 0.01 Å–1, comparable to that of a conjugated chain of C═C π bonds. This result demonstrates the profound implications of σ conjugation for the conductivity of silicon.
Co-reporter:Theanne Schiros;Stefan Mannsfeld;Chien-yang Chiu;Kevin G. Yager;James Ciston;Alon A. Gorodetsky;Matteo Palma;Zac Bullard;Theodore Kramer;Dean Delongchamp;Daniel Fischer;Ioannis Kymissis;Michael F. Toney
Advanced Functional Materials 2012 Volume 22( Issue 6) pp:1167-1173
Publication Date(Web):
DOI:10.1002/adfm.201102572
Abstract
This paper shows how the self-assembled interlocking of two nanostructured materials can lead to increased photovoltaic performance. A detailed picture of the reticulated 6-DBTTC/C60 organic photovoltaic (OPV) heterojunction, which produces devices approaching the theoretical maximum for these materials, is presented from near edge X-ray absorption spectroscopy (NEXAFS), X-ray photoelectron spectroscopy (XPS), Grazing Incidence X-ray diffraction (GIXD) and transmission electron microscopy (TEM). The complementary suite of techniques shows how self-assembly can be exploited to engineer the interface and morphology between the cables of donor (6-DBTTC) material and a polycrystalline acceptor (C60) to create an interpenetrating network of pure phases expected to be optimal for OPV device design. Moreover, we find that there is also a structural and electronic interaction between the two materials at the molecular interface. The data show how molecular self-assembly can facilitate 3-D nanostructured photovoltaic cells that are made with the simplicity and control of bilayer device fabrication. The significant improvement in photovoltaic performance of the reticulated heterojunction over the flat analog highlights the potential of these strategies to improve the efficiency of organic solar cells.
Co-reporter:Jeffrey S. Meisner, Danielle F. Sedbrook, Markrete Krikorian, Jun Chen, Aaron Sattler, Matthew E. Carnes, Christopher B. Murray, Michael Steigerwald and Colin Nuckolls
Chemical Science 2012 vol. 3(Issue 4) pp:1007-1014
Publication Date(Web):06 Jan 2012
DOI:10.1039/C2SC00770C
We describe the synthesis and characterization of a new class of cyano-functionalized oligoenes and their derivatives. We have made the vinylogous series of α,ω-diphenyl-μ,ν-dicyano-oligoenes (DPDCn) comprised of each odd-numbered member from 3 to 13 linear conjugated olefins. Installing cyano groups onto the oligoene backbone lowers HOMO and LUMO energies by up to ∼0.7 eV, thereby stabilizing the molecule with respect to oxidative decomposition; this exemplifies a new approach to the stabilization of conjugated oligoenes. UV-vis absorption spectra and redox potentials across the DPDCn series reveal that the molecular band gap ranges from 2.80 to 1.75 eV. This gap can be further tuned by the facile installation of a variety of aryl end-groups. The choice of end-groups also greatly affects the physical properties such as solubility and the solid-state packing. We also present the longest oligoene crystal structure reported to date. Moreover, we find that the prototypical linear structure makes oligoenes suitable as molecular wires and connectors in the bottom-up construction of nanoscale architectures. As a proof of concept, carboxylic acid terminated oligoenes were used to position 10-nm Fe3O4 nanoparticles on a GaAs (100) substrate.
Co-reporter:Hanfei Wang, Natalie B. Muren, David Ordinario, Alon A. Gorodetsky, Jacqueline K. Barton and Colin Nuckolls
Chemical Science 2012 vol. 3(Issue 1) pp:62-65
Publication Date(Web):20 Oct 2011
DOI:10.1039/C1SC00772F
This study creates a device where the DNA is electronically integrated to serve as both the biological target and electrical transducer in a CNT–DNA–CNT device. We detect DNA binding and methylation by the methyltransferase M.SssI at the single molecule level. We demonstrate sequence-specific, reversible binding of M.SssI and protein-catalyzed methylation that alters the protein-binding affinity of the device. This device, which relies on the exquisite electrical sensitivity of DNA, represents a unique route for the specific, single molecule detection of enzymatic activity.
Co-reporter:Seokhoon Ahn, Sriharsha V. Aradhya, Rebekka S. Klausen, Brian Capozzi, Xavier Roy, Michael L. Steigerwald, Colin Nuckolls and Latha Venkataraman
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 40) pp:13841-13845
Publication Date(Web):09 Jul 2012
DOI:10.1039/C2CP41578J
We characterize electron transport across Au–molecule–Au junctions of heterogeneous carboxyl and methyl sulfide terminated saturated and conjugated molecules. Low-bias conductance measurements are performed using the scanning tunneling microscopy based break-junction technique in the presence of solvents and at room temperature. For a series of alkanes with 1–4 carbon atoms in the hydrocarbon chain, our results show an exponential decrease in conductance with increasing molecule length characterized by a decay constant of 0.9 ± 0.1 per methylene group. Control measurements in pH 11 solutions and with COOMe terminations suggest that the carboxylic acid group binds through the formation of a COO−–Au bond. Simultaneous measurements of conductance and force across these junctions yield a rupture force of 0.6 ± 0.1 nN, comparable to that required to rupture a Au–SMe bond. By establishing reliable, in situ junction formation, these experiments provide a new approach to probe electronic properties of carboxyl groups at the single molecule level.
Co-reporter:Dr. Seok Ju Kang;Dr. Jong Bok Kim;Chien-Yang Chiu;Dr. Seokhoon Ahn;Dr. Theanne Schiros;Stephanie S. Lee;Dr. Kevin G. Yager;Dr. Michael F. Toney; Yueh-Lin Loo; Colin Nuckolls
Angewandte Chemie International Edition 2012 Volume 51( Issue 34) pp:8594-8597
Publication Date(Web):
DOI:10.1002/anie.201203330
Co-reporter:Dr. Xavier Roy;Christine L. Schenck;Dr. Seokhoon Ahn; Roger A. Lalancette; Latha Venkataraman; Colin Nuckolls;Dr. Michael L. Steigerwald
Angewandte Chemie International Edition 2012 Volume 51( Issue 50) pp:12473-12476
Publication Date(Web):
DOI:10.1002/anie.201206301
Co-reporter:Dr. Xavier Roy;Christine L. Schenck;Dr. Seokhoon Ahn; Roger A. Lalancette; Latha Venkataraman; Colin Nuckolls;Dr. Michael L. Steigerwald
Angewandte Chemie International Edition 2012 Volume 51( Issue 50) pp:
Publication Date(Web):
DOI:10.1002/anie.201209203
Co-reporter:Dr. Seok Ju Kang;Dr. Jong Bok Kim;Chien-Yang Chiu;Dr. Seokhoon Ahn;Dr. Theanne Schiros;Stephanie S. Lee;Dr. Kevin G. Yager;Dr. Michael F. Toney; Yueh-Lin Loo; Colin Nuckolls
Angewandte Chemie 2012 Volume 124( Issue 34) pp:8722-8725
Publication Date(Web):
DOI:10.1002/ange.201203330
Co-reporter:Danielle F. Sedbrook, Daniel W. Paley, Michael L. Steigerwald, Colin Nuckolls, and Felix R. Fischer
Macromolecules 2012 Volume 45(Issue 12) pp:5040-5044
Publication Date(Web):June 13, 2012
DOI:10.1021/ma300876q
We describe here a well-behaved initiator for ring-opening alkyne metathesis polymerization (ROAMP) of dibenzocyclooctynes. The reaction produces living polymers with low polydispersities and predictable molecular weights. We activate the well-known alkyne metathesis precatalyst, [(N(tBu)Ar)3Mo≡CCH2CH3], with phenolic ligands that have σ-electron donating substituents. We show that the chelating ability of these ligands as well as the nature of the propagating molybdenum center have dramatic effects on the outcome of the polymerization reaction.
Co-reporter:Seok Ju Kang;Bumjung Kim;Keun Soo Kim;Yue Zhao;Zheyuan Chen;Gwan Hyoung Lee;James Hone;Philip Kim
Advanced Materials 2011 Volume 23( Issue 31) pp:3531-3535
Publication Date(Web):
DOI:10.1002/adma.201101570
Co-reporter:Jeffrey S. Meisner, Masha Kamenetska, Markrete Krikorian, Michael L. Steigerwald, Latha Venkataraman, and Colin Nuckolls
Nano Letters 2011 Volume 11(Issue 4) pp:1575-1579
Publication Date(Web):March 17, 2011
DOI:10.1021/nl104411f
Controlling electron transport through a single-molecule device is key to the realization of nanoscale electronic components. A design requirement for single molecule electrical devices is that the molecule must be both structurally and electrically connected to the metallic electrodes. Typically, the mechanical and electrical contacts are achieved by the same chemical moiety. In this study, we demonstrate that the structural role may be played by one group (for example, a sulfide) while the electrical role may be played by another (a conjugated chain of C═C π-bonds). We can specify the electrical conductance through the molecule by modulating to which particular site on the oligoene chain the electrode binds. The result is a device that functions as a potentiometer at the single-molecule level.
Co-reporter:Brycelyn M. Boardman ; Jonathan R. Widawsky ; Young S. Park ; Christine L. Schenck ; Latha Venkataraman ; Michael L. Steigerwald
Journal of the American Chemical Society 2011 Volume 133(Issue 22) pp:8455-8457
Publication Date(Web):May 3, 2011
DOI:10.1021/ja201334s
Understanding the electrical properties of semiconducting quantum dot devices have been limited due to the variability of their size/composition and the chemistry of ligand/electrode binding. Furthermore, to probe their electrical conduction properties and its dependence on ligand/electrode binding, measurements must be carried out at the single dot/cluster level. Herein we report scanning tunneling microscope based break junction measurements of cobalt chalcogenide clusters with Te, Se and S to probe the conductance properties. Our measured conductance trends show that the Co–Te based clusters have the highest conductance while the Co-S clusters the lowest. These trends are in very good agreement with cyclic voltammetry measurements of the first oxidation potentials and with density functional theory calculations of their HOMO–LUMO gaps.
Co-reporter:Chien-Yang Chiu, Bumjung Kim, Alon A. Gorodetsky, Wesley Sattler, Sujun Wei, Aaron Sattler, Michael Steigerwald and Colin Nuckolls
Chemical Science 2011 vol. 2(Issue 8) pp:1480-1486
Publication Date(Web):18 May 2011
DOI:10.1039/C1SC00156F
We detail a general method for the synthesis of dibenzotetrathienocoronenes and elucidate their solid state structures in crystals and co-crystals. The contorted dibenzotetrathienocoronene (c-DBTTC) is a tetrathiophene-fused version of the previously studied contorted hexabenzocoronenes (c-HBC). The synthesis detailed here is simple and provides easy access to this important class of materials. We have found that these materials display molecular flexibility and tunable supramolecular self-assembly properties in the solid state by shifting molecular conformations between two different conformations. Depending on the conditions under which a c-DBTTC-containing material crystallizes, the c-DBTTC adopts either the “up-down” or the “butterfly” conformation. When grown from the vapor phase, crystals of the unsubstituted c-DBTTC show the molecule only in the up-down conformation, and it packs into dense crystals containing columnar arrays with close intracolumnar packing. The packing is controlled by the inherent molecular corrugation of the three-dimensional core and sulfur–sulfur interactions. When grown as co-crystals with electron acceptors from solution, the butyl-substituted c-DBTTC either adopts the butterfly conformation when the electron acceptor is small enough to be completely enveloped (TCNQ) or the up-down conformation when the electron acceptor is relatively large (C60). When grown from organic solvent crystals of the butyl-substituted c-DBTTC contain molecules of the solvent as the only guest, and we observe both conformations of the c-DBTTC. Controlling the supramolecular structure is the key to developing these materials for electronic applications.
Co-reporter:Adam C. Whalley, Kyle N. Plunkett, Alon A. Gorodetsky, Christine L. Schenck, Chien-Yang Chiu, Michael L. Steigerwald and Colin Nuckolls
Chemical Science 2011 vol. 2(Issue 1) pp:132-135
Publication Date(Web):11 Oct 2010
DOI:10.1039/C0SC00470G
This article describes the synthesis of a new type of bowl-shaped polycyclic aromatic hydrocarbon. These bowls are formed by joining the proximal carbons of contorted hexabenzocoronenes. These methods begin to tap a wealth of structural diversity available from these core structures. The bowl-shaped hydrocarbons more easily accept electrons than their contorted hexabenzocoronene precursors and associate strongly with C70.
Co-reporter:Yueh-Lin Loo, Anna M. Hiszpanski, Bumjung Kim, Sujun Wei, Chien-Yang Chiu, Michael L. Steigerwald, and Colin Nuckolls
Organic Letters 2010 Volume 12(Issue 21) pp:4840-4843
Publication Date(Web):October 5, 2010
DOI:10.1021/ol102016m
Fluorinated, contorted hexabenzocoronenes (HBCs) have been synthesized in a facile manner via Suzuki−Miyaura coupling of fluorinated phenyl boronic acids followed by photocyclization and Scholl cyclization. In addition to the molecular conformation observed in previous HBC derivatives, close-contact fluorine−fluorine intramolecular interactions result in a metastable conformation not previously observed. Heating the metastable HBCs above 100 °C irreversibly converts them to the stable conformation, suggesting that the metastable conformation arises from a kinetically arrested state during cyclization.
Co-reporter:Dr. Felix R. Fischer ; Colin Nuckolls
Angewandte Chemie International Edition 2010 Volume 49( Issue 40) pp:7257-7260
Publication Date(Web):
DOI:10.1002/anie.201003549
Co-reporter:Dr. Alon A. Gorodetsky;Chien-Yang Chiu;Dr. Theanne Schiros;Dr. Matteo Palma;Marshall Cox;Zhang Jia;Wesley Sattler; Ioannis Kymissis;Dr. Michael Steigerwald; Colin Nuckolls
Angewandte Chemie International Edition 2010 Volume 49( Issue 43) pp:7909-7912
Publication Date(Web):
DOI:10.1002/anie.201004055
Co-reporter:Dr. Alon A. Gorodetsky;Chien-Yang Chiu;Dr. Theanne Schiros;Dr. Matteo Palma;Marshall Cox;Zhang Jia;Wesley Sattler; Ioannis Kymissis;Dr. Michael Steigerwald; Colin Nuckolls
Angewandte Chemie 2010 Volume 122( Issue 43) pp:8081-8084
Publication Date(Web):
DOI:10.1002/ange.201004055
Co-reporter:Noah J. Tremblay;Alon A. Gorodetsky Dr.;Marshall P. Cox;Theanne Schiros Dr.;Bumjung Kim;Rachel Steiner;Zachary Bullard;Aaron Sattler;Woo-Young So Dr.;Yoshimitsu Itoh Dr.;Michael F. Toney Dr.;Hirohito Ogasawara Dr.;Arthur P. Ramirez ;Ioannis Kymissis Dr.;Michael L. Steigerwald Dr.
ChemPhysChem 2010 Volume 11( Issue 4) pp:799-803
Publication Date(Web):
DOI:10.1002/cphc.200900941
Co-reporter:Noah J. Tremblay;Alon A. Gorodetsky Dr.;Marshall P. Cox;Theanne Schiros Dr.;Bumjung Kim;Rachel Steiner;Zachary Bullard;Aaron Sattler;Woo-Young So Dr.;Yoshimitsu Itoh Dr.;Michael F. Toney Dr.;Hirohito Ogasawara Dr.;Arthur P. Ramirez ;Ioannis Kymissis Dr.;Michael L. Steigerwald Dr.
ChemPhysChem 2010 Volume 11( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/cphc.201090016
Co-reporter:Haitao Liu ; Sunmin Ryu ; Zheyuan Chen ; Michael L. Steigerwald ; Colin Nuckolls ;Louis E. Brus
Journal of the American Chemical Society 2009 Volume 131(Issue 47) pp:17099-17101
Publication Date(Web):November 10, 2009
DOI:10.1021/ja9043906
We demonstrate a photochemical reaction between graphene and benzoyl peroxide. This reaction introduces spatially localized defects into the graphene basal plane. The reactivity of the single-layer graphene is ∼14 times higher than that of the double-layer graphene. Our result suggests that photoexcited graphene transfers a hot electron to benzoyl peroxide and induces its decomposition to a phenyl radical.
Co-reporter:Haitao Liu ; Michael L. Steigerwald
Journal of the American Chemical Society 2009 Volume 131(Issue 47) pp:17034-17035
Publication Date(Web):June 2, 2009
DOI:10.1021/ja903333s
We show that carbon nanotubes (CNTs) accelerate the wet etching of silicon dioxide in a strong alkaline solution. This catalytic effect is due to the spontaneous adsorption of hydroxide on the surface of the CNTs. Such adsorption creates an electrical double layer around the CNTs within which the concentration of hydroxide is higher than the bulk value. Our result suggests that the electrical double layer can be used to pattern nanoscale features. Fabrication of SiO2 trenches with ∼60 nm lateral resolution is demonstrated.
Co-reporter:Alon A. Gorodetsky, Marshall Cox, Noah J. Tremblay, Ioannis Kymissis and Colin Nuckolls
Chemistry of Materials 2009 Volume 21(Issue 18) pp:4090
Publication Date(Web):August 26, 2009
DOI:10.1021/cm9016134
Co-reporter:Xuefeng Guo and Colin Nuckolls
Journal of Materials Chemistry A 2009 vol. 19(Issue 31) pp:5470-5473
Publication Date(Web):23 Apr 2009
DOI:10.1039/B900331M
We present a universal lithographic methodology for creating single molecule devices based on single-walled carbon nanotubes as point contacts. These contacts are formed by electron beam lithography and precise oxygen plasma etching. Through robust amide linkages, functional molecular bridges with diamines are covalently wired into carboxylic acid-functionalized nanogaps to afford single molecule devices with desired functionalities.
Co-reporter:Kyle N. Plunkett, Kamil Godula, Colin Nuckolls, Noah Tremblay, Adam C. Whalley and Shengxiong Xiao
Organic Letters 2009 Volume 11(Issue 11) pp:2225-2228
Publication Date(Web):April 24, 2009
DOI:10.1021/ol9001834
Contorted hexabenzocoronenes (HBCs) have been synthesized in an expedited manner utilizing a double Barton-Kellogg olefination reaction and a subsequent Scholl cyclization. The scope of both transformations was investigated using a series of pentacene quinones and double olefin precursors. The utility of these reactions to help create functionalized and oligomeric HBCs in a rapid manner is demonstrated.
Co-reporter:Matthew Carnes;Daniela Buccella;JudyY.-C. Chen;ArthurP. Ramirez Dr.;NicholasJ. Turro ;Michael Steigerwald Dr.
Angewandte Chemie 2009 Volume 121( Issue 2) pp:296-300
Publication Date(Web):
DOI:10.1002/ange.200804435
Co-reporter:Matthew Carnes;Daniela Buccella;JudyY.-C. Chen;ArthurP. Ramirez Dr.;NicholasJ. Turro ;Michael Steigerwald Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 2) pp:290-294
Publication Date(Web):
DOI:10.1002/anie.200804435
Co-reporter:Matthew Carnes;Daniela Buccella;JudyY.-C. Chen;ArthurP. Ramirez Dr.;NicholasJ. Turro ;Michael Steigerwald Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/anie.200990098
No abstract is available for this article.
Co-reporter:Song Liu;Jianming Li;Qian Shen;Yang Cao;Xuefeng Guo ;Guoming Zhang;Chaoqun Feng;Jin Zhang ;Zhongfan Liu ;MichaelL. Steigerwald Dr.;Dongsheng Xu
Angewandte Chemie International Edition 2009 Volume 48( Issue 26) pp:4759-4762
Publication Date(Web):
DOI:10.1002/anie.200901018
Co-reporter:Matthew Carnes;Daniela Buccella;JudyY.-C. Chen;ArthurP. Ramirez Dr.;NicholasJ. Turro ;Michael Steigerwald Dr.
Angewandte Chemie 2009 Volume 121( Issue 19) pp:
Publication Date(Web):
DOI:10.1002/ange.200990100
No abstract is available for this article.
Co-reporter:Shengxiong Xiao;Xuefeng Guo;Matthew Myers;Qian Miao;Michael L. Steigerwald
PNAS 2009 Volume 106 (Issue 3 ) pp:691-696
Publication Date(Web):2009-01-20
DOI:10.1073/pnas.0807596106
This study reports a general methodology for making stable high-performance photosensitive field effect transistors (FET)
from self-assembled columns of polycyclic aromatic hydrocarbons by using single-walled carbon nanotubes (SWNTs) as point contacts.
In particular, the molecules used in this work are liquid crystalline materials of tetra(dodecyloxy)hexabenzocoronenes (HBCs)
that are able to self-organize into columnar nanostructures with a diameter similar to that of SWNTs and then form nanoscale
columnar transistors. To rule out potential artifacts, 2 different structural approaches were used to construct devices. One
approach is to coat thin films of HBCs onto the devices with the SWNT–metal junctions protected by hydrogensilsesquioxane
resin (HSQ), and the other is to place a droplet of HBC exactly on the nanogaps of SWNT electrodes. Both types of devices
showed typical FET behaviors, indicating that SWNT–molecule–SWNT nanojunctions are responsible for the electrical characteristics
of the devices. After thermally annealing the devices, HBC molecules assembled into columnar structures and formed more efficacious
transistors with increased current modulation and higher gate efficiency. More interestingly, when the devices were exposed
to visible light, photocurrents with an on/off ratio of >3 orders of magnitude were observed. This study demonstrates that
stimuli-responsive nanoscale transistors have the potential applications in ultrasensitive devices for environmental sensing
and solar energy harvesting.
Co-reporter:Alina K. Feldman, Michael L. Steigerwald, Xuefeng Guo and Colin Nuckolls
Accounts of Chemical Research 2008 Volume 41(Issue 12) pp:1731
Publication Date(Web):September 18, 2008
DOI:10.1021/ar8000266
As the top-down fabrication techniques for silicon-based electronic materials have reached the scale of molecular lengths, researchers have been investigating nanostructured materials to build electronics from individual molecules. Researchers have directed extensive experimental and theoretical efforts toward building functional optoelectronic devices using individual organic molecules and fabricating metal−molecule junctions. Although this method has many advantages, its limitations lead to large disagreement between experimental and theoretical results. This Account describes a new method to create molecular electronic devices, covalently bridging a gap in a single-walled carbon nanotube (SWNT) with an electrically functional molecule. First, we introduce a molecular-scale gap into a nanotube by precise oxidative cutting through a lithographic mask. Now functionalized with carboxylic acids, the ends of the cleaved carbon nanotubes are reconnected with conjugated diamines to give robust diamides. The molecular electronic devices prepared in this fashion can withstand and respond to large environmental changes based on the functional groups in the molecules. For example, with oligoanilines as the molecular bridge, the conductance of the device is sensitive to pH. Similarly, using diarylethylenes as the bridge provides devices that can reversibly switch between conjugated and nonconjugated states. The molecular bridge can perform the dual task of carrying electrical current and sensing/recognition through biological events such as protein/substrate binding and DNA hybridization. The devices based on DNA can measure the difference in electrical properties of complementary and mismatched strands. A well-matched duplex DNA 15-mer in the gap exhibits a 300-fold lower resistance than a duplex with a GT or CA mismatch. This system provides an ultrasensitive way to detect single-nucleotide polymorphisms at the individual molecule level. Restriction enzymes can cleave certain cDNA strands assembled between the SWNT electrodes; therefore, these strands maintain their native conformation when bridging the ends of the SWNTs. This methodology for creating novel molecular circuits forges both literal and figurative connections between chemistry, physics, materials science, and biology and promises a new generation of integrated multifunctional sensors and devices.
Co-reporter:Matthew Carnes;Daniela Buccella;John Decatur Dr.;MichaelL. Steigerwald Dr.
Angewandte Chemie 2008 Volume 120( Issue 16) pp:3024-3027
Publication Date(Web):
DOI:10.1002/ange.200704355
Co-reporter:Seokwoo Jeon;Changgu Lee;Jinyao Tang;James Hone
Nano Research 2008 Volume 1( Issue 5) pp:427-433
Publication Date(Web):2008 November
DOI:10.1007/s12274-008-8044-1
A simple method for high-yield, chemical vapor deposition (CVD) synthesis of serpentine carbon nanotubes, employing quartz substrates and a molecular cluster catalyst, is described. The growth mechanism is analyzed by controlled addition of nanoscale barriers, and by mechanical analysis of the curved sections. The serpentine structures are used to study the electrical transport properties of parallel arrays of identical nanotubes, which show three-terminal conductance that scales linearly with the number of nanotube segments.
Co-reporter:Matthew Carnes;Daniela Buccella;John Decatur Dr.;MichaelL. Steigerwald Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 16) pp:2982-2985
Publication Date(Web):
DOI:10.1002/anie.200704355
Co-reporter:Jinyao Tang;Yiliang Wang;Jennifer E. Klare;George S. Tulevski;Shalom J. Wind Dr.
Angewandte Chemie International Edition 2007 Volume 46(Issue 21) pp:
Publication Date(Web):15 MAY 2007
DOI:10.1002/anie.200790092
Coordination chemistry provides a versatile method to form molecular-scale wires between nanoscale electrodes, as S. J. Wind, C. Nuckolls, and co-workers describe in their Communication on page 3892 ff. First, a bifunctional molecule is assembled into a monolayer on the electrode surface such that only one end of the molecule reacts with the electrode, and then a second molecule (e.g. a metal ion, as shown in the picture) is introduced to span the gap between the termini of the closely spaced nanoscale films.
Co-reporter:Jinyao Tang;Yiliang Wang;Jennifer E. Klare;George S. Tulevski;Shalom J. Wind Dr.
Angewandte Chemie 2007 Volume 119(Issue 21) pp:
Publication Date(Web):15 MAY 2007
DOI:10.1002/ange.200790092
Koordinationschemische Methoden wurden zur reversiblen Bildung von molekularen Drähten zwischen nanoskaligen Elektroden genutzt, wie es S. J. Wind, C. Nuckolls und Mitarbeiter in ihrer Zuschrift auf S. 3966 ff. beschreiben. Zuerst wird ein difunktionelles Molekül senkrecht an eine Monoschicht auf der Elektrodenoberfläche geheftet, dann wird ein zweites Molekül eingeführt (z. B. ein Metallion, wie im Bild gezeigt), das die gegenüberliegenden oberflächenmodifizierten Filme chemisch verbrückt.
Co-reporter:Kwang Taeg Rim;Mohamed Siaj;Shengxiong Xiao;Matthew Myers;Vincent D. Carpentier;Li Liu;Chaochin Su;Michael L. Steigerwald;Mark S. Hybertsen;Peter H. McBreen;George W. Flynn
Angewandte Chemie International Edition 2007 Volume 46(Issue 41) pp:
Publication Date(Web):18 SEP 2007
DOI:10.1002/anie.200701117
Bowled over: Hexabenzocoronene (HBC) binds to the surface of a ruthenium crystal through its “radialene” π bonds. Measurements on the product after heating of the HBC–surface complex are consistent with a bowl-shaped molecular fragment that is strongly bound, rim down, to the metal surface. This structure represents a new type of seed that could be used to grow single-walled carbon nanotubes of specific diameter and chirality.
Co-reporter:Jinyao Tang;Yiliang Wang;Jennifer E. Klare;George S. Tulevski;Shalom J. Wind Dr.
Angewandte Chemie International Edition 2007 Volume 46(Issue 21) pp:
Publication Date(Web):7 MAR 2007
DOI:10.1002/anie.200604398
Wire straits: Three-component molecular wires were constructed in situ by first assembling a monolayer of a bifunctional arene on the electrode surfaces, such that only one end of the molecule (thiol) reacts with the electrode. Then, a second molecule was used to chemically bridge the gap between the termini of the films. Coordination chemistry in this context provides a versatile method to reversibly form molecular-scale wires (see picture). EDTA=ethylenediaminetetraacetate.
Co-reporter:Kwang Taeg Rim;Mohamed Siaj;Shengxiong Xiao;Matthew Myers;Vincent D. Carpentier;Li Liu;Chaochin Su;Michael L. Steigerwald;Mark S. Hybertsen;Peter H. McBreen;George W. Flynn
Angewandte Chemie 2007 Volume 119(Issue 41) pp:
Publication Date(Web):18 SEP 2007
DOI:10.1002/ange.200701117
Umgestülpt: Hexabenzocoronen (HBC) lagert sich zunächst über die Radialen-π-Bindungen an die Oberfläche eines Rutheniumkristalls an. Erhitzen überführt diesen Komplexes in eine Struktur, in der ein schalenförmiges Molekülfragment mit dem Rand nach unten stark an die Metalloberfläche bindet. Diese Struktur könnte als neuartiger Keim für das Wachstum einwandiger Kohlenstoffnanoröhren mit definiertem Durchmesser und vorgegebener Chiralität genutzt werden.
Co-reporter:Jinyao Tang;Yiliang Wang;Jennifer E. Klare;George S. Tulevski;Shalom J. Wind Dr.
Angewandte Chemie 2007 Volume 119(Issue 21) pp:
Publication Date(Web):7 MAR 2007
DOI:10.1002/ange.200604398
Molekulare Dreikomponentendrähte wurden in situ hergestellt, indem eine Monoschicht aus difunktionellen Arenen so auf den Elektrodenoberflächen aufgebaut wurde, dass nur ein Molekülende (Thiol) mit der Elektrode reagiert. Danach wird mit einem zweiten Molekül die Lücke zwischen den Film-Enden chemisch überbrückt. Koordinationskomplexe eignen sich hier hervorragend, um Drähte molekularer Größe reversibel zu erzeugen (siehe Bild).
Co-reporter:Xuefeng Guo;Joshua P. Small;Jennifer E. Klare;Yiliang Wang;Meninder S. Purewal;Iris W. Tam;Byung Hee Hong;Robert Caldwell;Limin Huang;Stephen O'Brien;Jiaming Yan;Ronald Breslow;Shalom J. Wind;James Hone;Philip Kim
Science 2006 Vol 311(5759) pp:356-359
Publication Date(Web):20 Jan 2006
DOI:10.1126/science.1120986
Abstract
Molecular electronics is often limited by the poorly defined nature of the contact between the molecules and the metal surface. We describe a method to wire molecules into gaps in single-walled carbon nanotubes (SWNTs). Precise oxidative cutting of a SWNT produces carboxylic acid–terminated electrodes separated by gaps of ≤10 nanometers. These point contacts react with molecules derivatized with amines to form molecular bridges held in place by amide linkages. These chemical contacts are robust and allow a wide variety of molecules to be tested electrically. In addition to testing molecular wires, we show how to install functionality in the molecular backbone that allows the conductance of the single-molecule bridges to switch with pH.
Co-reporter:Xuefeng Guo;Matthew Myers;Shengxiong Xiao;Michael Lefenfeld;Rachel Steiner;George S. Tulevski;Jinyao Tang;Julian Baumert;Frank Leibfarth;James T. Yardley;Michael L. Steigerwald;Philip Kim;
Proceedings of the National Academy of Sciences 2006 103(31) pp:11452-11456
Publication Date(Web):July 19, 2006
DOI:10.1073/pnas.0601675103
This work details a method to make efficacious field-effect transistors from monolayers of polycyclic aromatic hydrocarbons
that are able to sense and respond to their chemical environment. The molecules used in this study are functionalized so that
they assemble laterally into columns and attach themselves to the silicon oxide surface of a silicon wafer. To measure the
electrical properties of these monolayers, we use ultrasmall point contacts that are separated by only a few nanometers as
the source and drain electrodes. These contacts are formed through an oxidative cutting of an individual metallic single-walled
carbon nanotube that is held between macroscopic metal leads. The molecules assemble in the gap and form transistors with
large current modulation and high gate efficiency. Because these devices are formed from an individual stack of molecules,
their electrical properties change significantly when exposed to electron-deficient molecules such as tetracyanoquinodimethane
(TCNQ), forming the basis for new types of environmental and molecular sensors.
Co-reporter:George S. Tulevski;Matt B. Myers;Mark S. Hybertsen;Michael L. Steigerwald
Science 2005 Vol 309(5734) pp:591-594
Publication Date(Web):22 Jul 2005
DOI:10.1126/science.1112767
Abstract
We describe a new strategy for the in situ growth of molecular wires predicated on the synthesis of a trifunctional “primed” contact formed from metal-carbon multiple bonds. The ruthenium-carbon π bond provides structural stability to the molecular linkages under ambient conditions, and density functional calculations indicate the formation of an efficient conduit for charge carriers to pass between the metal and the molecule. Moreover, the metal-carbon π bond provides a chemically reactive site from which a conjugated molecular wire can be grown in situ through an olefin metathesis reaction.
Co-reporter:Q. Miao;M. Lefenfeld;T.-Q. Nguyen;T. Siegrist;C. Kloc;C. Nuckolls
Advanced Materials 2005 Volume 17(Issue 4) pp:
Publication Date(Web):18 JAN 2005
DOI:10.1002/adma.200401251
Linear acenes terminated with quinones demonstrate that electrostatic complementarity is a viable self-assembly motif for organic semiconductors. An organic field-effect transistor with co-facial, head-to-tail stacks with π-surfaces 0.1 Å closer together than the aromatic planes of graphite is fabricated. The field-effect mobilities and ON/OFF current ratios are high enough to be useful in flexible electronic applications.
Co-reporter:Shengxiong Xiao;Matthew Myers;Qian Miao;Sébastien Sanaur;Keliang Pang;Michael L. Steigerwald
Angewandte Chemie 2005 Volume 117(Issue 45) pp:
Publication Date(Web):16 NOV 2005
DOI:10.1002/ange.200590148
Co-reporter:Shengxiong Xiao;Matthew Myers;Qian Miao;Sébastien Sanaur;Keliang Pang;Michael L. Steigerwald
Angewandte Chemie 2005 Volume 117(Issue 45) pp:
Publication Date(Web):20 SEP 2005
DOI:10.1002/ange.200502142
Gefällig gewellt: Beim Design elektronischer Materialien auf der Grundlage nichtplanarer aromatischer Moleküle tritt eine neue Klasse von Hexabenzocoronenen mit deutlich gewellter Struktur in den Vordergrund. Werden vier Alkoxy-Seitenketten eingeführt, so stapeln sich die Moleküle zu unendlich ausgedehnten Säulen (siehe Bild); dieses Material eignet sich als aktive Schicht in Feldeffekttransistoren.
Co-reporter:Shengxiong Xiao, Matthew Myers, Qian Miao, Sébastien Sanaur, Keliang Pang, Michael L. Steigerwald,Colin Nuckolls
Angewandte Chemie International Edition 2005 44(45) pp:7390-7394
Publication Date(Web):
DOI:10.1002/anie.200502142
Co-reporter:Shengxiong Xiao, Matthew Myers, Qian Miao, Sébastien Sanaur, Keliang Pang, Michael L. Steigerwald,Colin Nuckolls
Angewandte Chemie International Edition 2005 44(45) pp:7315
Publication Date(Web):
DOI:10.1002/anie.200590149
Co-reporter:Mark L. Bushey;Thuc-Quyen Nguyen;Wei Zhang;Dana Horoszewski
Angewandte Chemie 2004 Volume 116(Issue 41) pp:
Publication Date(Web):16 SEP 2004
DOI:10.1002/ange.200301678
Das Design, die Synthese und die Selbstorganisation einer neuen Klasse vollständig substituierter Arene, die kolumnare Überstrukturen bilden, werden in diesem Kurzaufsatz detailliert beschrieben. Die Selbstorganisation dieser Moleküle führt zur Bildung von helicalen und polaren Säulen, deren Anordnung mit elektrischen Feldern gesteuert werden kann. In konzentrierten Lösungen ordnen sich die Säulen in helicalen Überstrukturen an, die zirkular polarisiertes Licht im sichtbaren Wellenlängenbereich reflektieren. Durch Schleuderbeschichtung erzeugte Filme bilden, abhängig von der Struktur der verwendeten Seitenketten, entweder polare Monoschichten oder isolierte molekulare Stränge, die rastersondenmikroskopisch beobachtet werden können. Darüber hinaus werden Methoden beschrieben, mit denen diese Mesogene zu monodispersen Oligomeren verknüpft werden können, die sich zu definierten Sekundärkonformationen falten.
Co-reporter:George S. Tulevski;Mark L. Bushey;Jenna L. Kosky;Shane J. T. Ruter
Angewandte Chemie 2004 Volume 116(Issue 14) pp:
Publication Date(Web):24 MAR 2004
DOI:10.1002/ange.200353476
Nestbau: Eine Methode zum Aufbau eines starren Wasserstoffbrückenrezeptors durch simultane Bindung dreier Thiolgruppen an eine Goldoberfläche wird beschrieben (siehe Bild: O rot, C grau, N blau, S gelb, Oberflächengoldatome violett). Derartige Rezeptoren erkennen π-Oberflächen mit komplementärer Größe und Form sowie passendem Wasserstoffbrückenbindungs-Code.
Co-reporter:Mark L. Bushey;Thuc-Quyen Nguyen;Wei Zhang;Dana Horoszewski
Angewandte Chemie International Edition 2004 Volume 43(Issue 41) pp:
Publication Date(Web):16 SEP 2004
DOI:10.1002/anie.200301678
This Minireview details the design, synthesis, and self-assembly of a new class of crowded aromatics that form columnar superstructures. The assembly of these subunits produces helical and polar stacks, whose assembly can be directed with electric fields. In concentrated solutions, these self-assembled helical rods exhibit superhelical arrangements that reflect circularly polarized light at visible wavelengths. Depending on the side chains employed, spin-cast films yield either polar monolayers or isolated strands of molecules that can be visualized with scanning probe microscopy. Also detailed herein are methods to link these mesogens together to produce monodisperse oligomers that fold into defined secondary conformations.
Co-reporter:George S. Tulevski;Mark L. Bushey;Jenna L. Kosky;Shane J. T. Ruter
Angewandte Chemie International Edition 2004 Volume 43(Issue 14) pp:
Publication Date(Web):24 MAR 2004
DOI:10.1002/anie.200353476
Nest building: a method to create a rigid hydrogen-bond receptor through the simultaneous binding of three thiol substituent groups to a gold surface is reported (see picture: red=O, gray=C, blue=N, yellow=S, purple=Au surface atom). These receptors are able to distinguish and select for π surfaces with a complementary size, shape, and hydrogen-bonding code.
Co-reporter:Mark L. Bushey;Austin Hwang;Peter W. Stephens
Angewandte Chemie International Edition 2002 Volume 41(Issue 15) pp:
Publication Date(Web):2 AUG 2002
DOI:10.1002/1521-3773(20020802)41:15<2828::AID-ANIE2828>3.0.CO;2-T
Chiral side chains installed into the stacks of overcrowded arenes enforce helical conformations (see picture). The assembly process can be directed with electric fields as a result of a dipole moment parallel to the stacking direction. In concentrated solutions, superhelices emerge that reflect circularly polarized light.
Co-reporter:Mark L. Bushey;Austin Hwang;Peter W. Stephens
Angewandte Chemie 2002 Volume 114(Issue 15) pp:
Publication Date(Web):30 JUL 2002
DOI:10.1002/1521-3757(20020802)114:15<2952::AID-ANGE2952>3.0.CO;2-K
Chirale Seitenketten in den Stapeln sterisch überladener Arene erzwingen Helixkonformationen (siehe Bild). Die Selbstorganisation kann mit elektrischen Feldern gesteuert werden, weil ein Dipolmoment parallel zur Stapelrichtung existiert. In konzentrierten Lösungen bilden sich Überhelices, die circular polarisiertes Licht reflektieren.
Co-reporter:Timothy A. Su ; Jonathan R. Widawsky ; Haixing Li ; Rebekka S. Klausen ; James L. Leighton ; Michael L. Steigerwald ; Latha Venkataraman
Journal of the American Chemical Society () pp:
Publication Date(Web):November 21, 2013
DOI:10.1021/ja410656a
Here we demonstrate for the first time that strained silanes couple directly to gold electrodes in break-junction conductance measurements. We find that strained silicon molecular wires terminated by alkyl sulfide aurophiles behave effectively as single-molecule parallel circuits with competing sulfur-to-sulfur (low G) and sulfur-to-silacycle (high G) pathways. We can switch off the high conducting sulfur-to-silacycle pathway by altering the environment of the electrode surface to disable the Au–silacycle coupling. Additionally, we can switch between conductive pathways in a single molecular junction by modulating the tip–substrate electrode distance. This study provides a new molecular design to control electronics in silicon-based single molecule wires.
Co-reporter:Jeffrey S. Meisner, Danielle F. Sedbrook, Markrete Krikorian, Jun Chen, Aaron Sattler, Matthew E. Carnes, Christopher B. Murray, Michael Steigerwald and Colin Nuckolls
Chemical Science (2010-Present) 2012 - vol. 3(Issue 4) pp:NaN1014-1014
Publication Date(Web):2012/01/06
DOI:10.1039/C2SC00770C
We describe the synthesis and characterization of a new class of cyano-functionalized oligoenes and their derivatives. We have made the vinylogous series of α,ω-diphenyl-μ,ν-dicyano-oligoenes (DPDCn) comprised of each odd-numbered member from 3 to 13 linear conjugated olefins. Installing cyano groups onto the oligoene backbone lowers HOMO and LUMO energies by up to ∼0.7 eV, thereby stabilizing the molecule with respect to oxidative decomposition; this exemplifies a new approach to the stabilization of conjugated oligoenes. UV-vis absorption spectra and redox potentials across the DPDCn series reveal that the molecular band gap ranges from 2.80 to 1.75 eV. This gap can be further tuned by the facile installation of a variety of aryl end-groups. The choice of end-groups also greatly affects the physical properties such as solubility and the solid-state packing. We also present the longest oligoene crystal structure reported to date. Moreover, we find that the prototypical linear structure makes oligoenes suitable as molecular wires and connectors in the bottom-up construction of nanoscale architectures. As a proof of concept, carboxylic acid terminated oligoenes were used to position 10-nm Fe3O4 nanoparticles on a GaAs (100) substrate.
Co-reporter:Shengxiong Xiao, Seok Ju Kang, Ying Wu, Seokhoon Ahn, Jong Bok Kim, Yueh-Lin Loo, Theo Siegrist, Michael L. Steigerwald, Hexing Li and Colin Nuckolls
Chemical Science (2010-Present) 2013 - vol. 4(Issue 5) pp:NaN2023-2023
Publication Date(Web):2013/03/08
DOI:10.1039/C3SC50374G
We describe here the synthesis and electronic device properties of a new type of polycyclic aromatic molecule, the contorted octabenzocircumbiphenyl (c-OBCB). Contorted polycyclic aromatic hydrocarbons (PAHs) are promising small active molecules for organic devices. We present two different methods to synthesize c-OBCB derivatives that allow the smooth incorporation of functional groups. The material has a highly contorted exterior with six 4-helicenes and two 5-helicenes around the exterior of the expanded core of the aromatic. With appropriate sidechains, the material is soluble in common organic solvents and forms thin films. In thin films, the tetradodecyloxy-substituted c-OBCB self-assembles to form the active layer in organic field effect transistors. It is a hole transporting organic semiconductor. In the transistors, the c-OBCB forms good contact with source and drain contacts made from graphene. The c-OBCB self-assembles into a heterojunction from solution with phenyl-C70-butyric acid methyl ester (PC70BM). We observed power conversion efficiencies of ∼2.9 % under 100 mW cm−2 illumination at a 1:4 weight ratio of the c-OBCB relative to PC70BM. The c-OBCB is shape complementary to the ball shaped PC70BM.
Co-reporter:Haixing Li, Marc H. Garner, Zhichun Shangguan, Qianwen Zheng, Timothy A. Su, Madhav Neupane, Panpan Li, Alexandra Velian, Michael L. Steigerwald, Shengxiong Xiao, Colin Nuckolls, Gemma C. Solomon and Latha Venkataraman
Chemical Science (2010-Present) 2016 - vol. 7(Issue 9) pp:NaN5662-5662
Publication Date(Web):2016/05/30
DOI:10.1039/C6SC01360K
Here we examine the impact of ring conformation on the charge transport characteristics of cyclic pentasilane structures bound to gold electrodes in single molecule junctions. We investigate the conductance properties of alkylated cyclopentasilane cis and trans stereoisomers substituted in the 1,3-position with methylthiomethyl electrode binding groups using both the scanning tunneling microscope-based break junction technique and density functional theory based ab initio calculations. In contrast with the linear ones, these cyclic silanes yield lower conductance values; calculations reveal that the constrained dihedral geometries occurring within the ring are suboptimal for σ-orbital delocalization, and therefore, conductance. Theoretical calculations reproduce the measured conductance trends for both cis and trans isomers and find several distinct conformations that are likely to form stable molecular junctions at room temperature. Due to the weakened σ-conjugation in the molecule, through-space interactions are found to contribute significantly to the conductance. This manuscript details the vast conformational flexibility in cyclopentasilanes and the tremendous impact it has on controlling conductance.
Co-reporter:Seokhoon Ahn, Sriharsha V. Aradhya, Rebekka S. Klausen, Brian Capozzi, Xavier Roy, Michael L. Steigerwald, Colin Nuckolls and Latha Venkataraman
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 40) pp:NaN13845-13845
Publication Date(Web):2012/07/09
DOI:10.1039/C2CP41578J
We characterize electron transport across Au–molecule–Au junctions of heterogeneous carboxyl and methyl sulfide terminated saturated and conjugated molecules. Low-bias conductance measurements are performed using the scanning tunneling microscopy based break-junction technique in the presence of solvents and at room temperature. For a series of alkanes with 1–4 carbon atoms in the hydrocarbon chain, our results show an exponential decrease in conductance with increasing molecule length characterized by a decay constant of 0.9 ± 0.1 per methylene group. Control measurements in pH 11 solutions and with COOMe terminations suggest that the carboxylic acid group binds through the formation of a COO−–Au bond. Simultaneous measurements of conductance and force across these junctions yield a rupture force of 0.6 ± 0.1 nN, comparable to that required to rupture a Au–SMe bond. By establishing reliable, in situ junction formation, these experiments provide a new approach to probe electronic properties of carboxyl groups at the single molecule level.
Co-reporter:Xuefeng Guo and Colin Nuckolls
Journal of Materials Chemistry A 2009 - vol. 19(Issue 31) pp:NaN5473-5473
Publication Date(Web):2009/04/23
DOI:10.1039/B900331M
We present a universal lithographic methodology for creating single molecule devices based on single-walled carbon nanotubes as point contacts. These contacts are formed by electron beam lithography and precise oxygen plasma etching. Through robust amide linkages, functional molecular bridges with diamines are covalently wired into carboxylic acid-functionalized nanogaps to afford single molecule devices with desired functionalities.
Co-reporter:Hanfei Wang, Natalie B. Muren, David Ordinario, Alon A. Gorodetsky, Jacqueline K. Barton and Colin Nuckolls
Chemical Science (2010-Present) 2012 - vol. 3(Issue 1) pp:NaN65-65
Publication Date(Web):2011/10/20
DOI:10.1039/C1SC00772F
This study creates a device where the DNA is electronically integrated to serve as both the biological target and electrical transducer in a CNT–DNA–CNT device. We detect DNA binding and methylation by the methyltransferase M.SssI at the single molecule level. We demonstrate sequence-specific, reversible binding of M.SssI and protein-catalyzed methylation that alters the protein-binding affinity of the device. This device, which relies on the exquisite electrical sensitivity of DNA, represents a unique route for the specific, single molecule detection of enzymatic activity.
Co-reporter:Chien-Yang Chiu, Bumjung Kim, Alon A. Gorodetsky, Wesley Sattler, Sujun Wei, Aaron Sattler, Michael Steigerwald and Colin Nuckolls
Chemical Science (2010-Present) 2011 - vol. 2(Issue 8) pp:NaN1486-1486
Publication Date(Web):2011/05/18
DOI:10.1039/C1SC00156F
We detail a general method for the synthesis of dibenzotetrathienocoronenes and elucidate their solid state structures in crystals and co-crystals. The contorted dibenzotetrathienocoronene (c-DBTTC) is a tetrathiophene-fused version of the previously studied contorted hexabenzocoronenes (c-HBC). The synthesis detailed here is simple and provides easy access to this important class of materials. We have found that these materials display molecular flexibility and tunable supramolecular self-assembly properties in the solid state by shifting molecular conformations between two different conformations. Depending on the conditions under which a c-DBTTC-containing material crystallizes, the c-DBTTC adopts either the “up-down” or the “butterfly” conformation. When grown from the vapor phase, crystals of the unsubstituted c-DBTTC show the molecule only in the up-down conformation, and it packs into dense crystals containing columnar arrays with close intracolumnar packing. The packing is controlled by the inherent molecular corrugation of the three-dimensional core and sulfur–sulfur interactions. When grown as co-crystals with electron acceptors from solution, the butyl-substituted c-DBTTC either adopts the butterfly conformation when the electron acceptor is small enough to be completely enveloped (TCNQ) or the up-down conformation when the electron acceptor is relatively large (C60). When grown from organic solvent crystals of the butyl-substituted c-DBTTC contain molecules of the solvent as the only guest, and we observe both conformations of the c-DBTTC. Controlling the supramolecular structure is the key to developing these materials for electronic applications.
Co-reporter:Adam C. Whalley, Kyle N. Plunkett, Alon A. Gorodetsky, Christine L. Schenck, Chien-Yang Chiu, Michael L. Steigerwald and Colin Nuckolls
Chemical Science (2010-Present) 2011 - vol. 2(Issue 1) pp:NaN135-135
Publication Date(Web):2010/10/11
DOI:10.1039/C0SC00470G
This article describes the synthesis of a new type of bowl-shaped polycyclic aromatic hydrocarbon. These bowls are formed by joining the proximal carbons of contorted hexabenzocoronenes. These methods begin to tap a wealth of structural diversity available from these core structures. The bowl-shaped hydrocarbons more easily accept electrons than their contorted hexabenzocoronene precursors and associate strongly with C70.
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