David H. Waldeck

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Name: Waldeck, David

Organization: University of Pittsburgh , USA

Department: Department of Chemistry

Title: Professor(PhD)

TOPICS

Physical Chemistry

Material Chemistry

self-assembled monolayers

Chemicals
References

Effects of the Backbone and Chemical Linker on the Molecular Conductance of Nucleic Acid Duplexes

Co-reporter:Edward Beall, Selma Ulku, Chaoren Liu, Emil Wierzbinski, Yuqi Zhang, Yookyung Bae, Peng Zhang, Catalina Achim, David N. Beratan, and David H. Waldeck

Journal of the American Chemical Society May 17, 2017 Volume 139(Issue 19) pp:6726-6726

Publication Date(Web):April 23, 2017

DOI:10.1021/jacs.7b02260

Scanning tunneling microscope break junction measurements are used to examine how the molecular conductance of nucleic acids depends on the composition of their backbone and the linker group to the electrodes. Molecular conductances of 10 base pair long homoduplexes of DNA, aeg-PNA, γ-PNA, and a heteroduplex of DNA/aeg-PNA with identical nucleobase sequence were measured. The molecular conductance was found to vary by 12 to 13 times with the change in backbone. Computational studies show that the molecular conductance differences between nucleic acids of different backbones correlate with differences in backbone structural flexibility. The molecular conductance was also measured for duplexes connected to the electrode through two different linkers, one directly to the backbone and one directly to the nucleobase stack. While the linker causes an order-of-magnitude increase in the overall conductance for a particular duplex, the differences in the electrical conductance with backbone composition are preserved. The highest molecular conductance value, 0.06G0, was measured for aeg-PNA duplexes with a base stack linker. These findings reveal an important new strategy for creating longer and more complex electroactive, nucleic acid assemblies.

Chirality Control of Electron Transfer in Quantum Dot Assemblies

Co-reporter:Brian P. Bloom, Brittney M. Graff, Supriya Ghosh, David N. Beratan, and David H. Waldeck

Journal of the American Chemical Society July 5, 2017 Volume 139(Issue 26) pp:9038-9038

Publication Date(Web):June 13, 2017

DOI:10.1021/jacs.7b04639

Electron spin and molecular chirality are emerging as factors that can be used effectively to direct charge flow at the molecular scale. We report order of magnitude effects of molecular chirality on electron-transfer rates between quantum dots (QDs) in chiral QD assemblies. Indeed, both the circular polarization of the light that excites the electron donor and the imprinted chirality of the acceptor QDs affect the dot-to-dot electron-transfer kinetics. We define a polarization for the electron-transfer rate constant and show that it correlates with the strength of the acceptor QD circular dichroism (CD) spectrum. These findings imply that the CD strength of the QD exciton transition(s) may be used as a predictor for the spin-dependent electron transfer, indicating that chiral imprinting of the dots may lie at the origin of this phenomenon.

Charge and spin transport through nucleic acids

Co-reporter:David N. Beratan, Ron Naaman, David H. Waldeck

Current Opinion in Electrochemistry 2017 Volume 4, Issue 1(Volume 4, Issue 1) pp:

Publication Date(Web):1 August 2017

DOI:10.1016/j.coelec.2017.08.017

•Backbone fluctuations enhance the conductance by one to two orders of magnitude.•Electronic coherence persists across 5 (or more) nucleobase pairs in DNA, depending on base sequence.•Transient or “flickering resonance” among DNA bases establishes extended range coherence.•DNA's helical base stacking establishes spin selectivity for transmitted electrons.Recent developments in our understanding of charge and spin transport through nucleic acid duplexes are discussed. Particular emphasis is placed on recent findings that point to the importance of nucleobase fluctuations, transient but extended length-scale electronic coherence, and chiral-induced spin selectivity.Download high-res image (110KB)Download full-size image

Spin Selective Charge Transport through Cysteine Capped CdSe Quantum Dots

Co-reporter:Brian P. Bloom, Vankayala Kiran, Vaibhav Varade, Ron Naaman, and David. H. Waldeck

Nano Letters 2016 Volume 16(Issue 7) pp:4583-4589

Publication Date(Web):June 23, 2016

DOI:10.1021/acs.nanolett.6b01880

This work demonstrates that chiral imprinted CdSe quantum dots (QDs) can act as spin selective filters for charge transport. The spin filtering properties of chiral nanoparticles were investigated by magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements and magnetoresistance measurements. The mCP-AFM measurements show that the chirality of the quantum dots and the magnetic orientation of the tip affect the current–voltage curves. Similarly, magnetoresistance measurements demonstrate that the electrical transport through films of chiral quantum dots correlates with the chiroptical properties of the QD. The spin filtering properties of chiral quantum dots may prove useful in future applications, for example, photovoltaics, spintronics, and other spin-driven devices.

Electron Transfer in Nanoparticle Dyads Assembled on a Colloidal Template

Co-reporter:Brittney M. Graff, Brian P. Bloom, Emil Wierzbinski, and David H. Waldeck

Journal of the American Chemical Society 2016 Volume 138(Issue 40) pp:13260-13270

Publication Date(Web):September 16, 2016

DOI:10.1021/jacs.6b06991

This work shows how to create covalently bound nanoparticle dyad assemblies on a colloidal template and studies photoinduced charge transfer in them. New results are reported for how the electron-transfer rate changes with the inter-nanoparticle distance and the energy band offset of the nanoparticles (reaction Gibbs energy). The experimental findings show that the distance dependence is consistent with an electron tunneling mechanism. The dependence of the rate on the energy band offset is found to be consistent with Marcus theory, as long as one performs a sum over final electronic states. These results indicate that our understanding of electron transfer in molecular donor–bridge–acceptor assemblies can be translated to describe nanoparticle–bridge–nanoparticle assemblies.

Eliminating Fermi-level pinning in PbS quantum dots using an alumina interfacial layer

Co-reporter:Brian P. Bloom, Madu N. Mendis, Emil Wierzbinski and David H. Waldeck

Journal of Materials Chemistry A 2016 vol. 4(Issue 4) pp:704-712

Publication Date(Web):23 Dec 2015

DOI:10.1039/C5TC03945B

Through a systematic approach we show that the insertion of a thin alumina layer in between a PbS QD layer and an Au substrate can eliminate Fermi level pinning. In this study band edge energies of different sized PbS QD monolayers with different cross-linkers were measured by using ultraviolet photoelectron spectroscopy and electrochemistry. When PbS QDs were immobilized directly on the Au, the measured valence band maximum was found to be insensitive to changes in the QD size or cross-linker indicating Fermi level pinning of the QD valence band to the Au Fermi level. After insertion of a thin film of alumina in between the PbS quantum dot monolayer film and the Au substrate, the measured valence band position revealed a shift that depended on ligand and QD size. These results identify a general method for eliminating Fermi level pinning in QDs and an approach for predictably controlling the energetics at QD–metal interfaces which is beneficial for improving the performance of QD based solar cells.

Through-Solvent Tunneling in Donor–Bridge–Acceptor Molecules Containing a Molecular Cleft

Co-reporter:B. M. Graff, D. N. Lamont, M. F. L. Parker, B. P. Bloom, C. E. Schafmeister, and D. H. Waldeck

The Journal of Physical Chemistry A 2016 Volume 120(Issue 30) pp:6004-6013

Publication Date(Web):July 12, 2016

DOI:10.1021/acs.jpca.6b05624

Photoinduced electron transfer is used to investigate the solvent-mediated electron tunneling between electron donor and acceptor groups in polar solvents. Bis-peptide scaffolds are used to control the spatial positioning of electron donor and acceptor groups and create a molecular cleft. The photoinduced electron transfer is studied for two different cleft sizes, and the electronic coupling is found to be controlled by the nature of the solvent and the ability of the molecular cleft to accommodate it, as well as interact directly with it. These studies demonstrate the importance of electron tunneling through nonbonded contacts and reveal a strategy for examining such tunneling pathways in polar solvents.

Identifying the Correct Host–Guest Combination To Sensitize Trivalent Lanthanide (Guest) Luminescence: Titanium Dioxide Nanoparticles as a Model Host System

Co-reporter:Arijita Chakraborty, Gouranga H. Debnath, Nayan Ranjan Saha, Dipankar Chattopadhyay, David H. Waldeck, and Prasun Mukherjee

The Journal of Physical Chemistry C 2016 Volume 120(Issue 41) pp:23870-23882

Publication Date(Web):September 22, 2016

DOI:10.1021/acs.jpcc.6b08421

This work develops a rationale for effective sensitization of trivalent lanthanide cation (Ln3+) luminescence in a semiconductor nanoparticle by examining the luminescence characteristics of Ln3+ dopants in titanium dioxide nanoparticles [Ti(Ln)O2] [Ln = praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), or ytterbium (Yb)], as a representative model system. For excitation of the TiO2 host at 350 nm the intraconfigurational 4f–4f sharp luminescence bands are observed for the Nd, Sm, Eu, Ho, Er, Tm, and Yb incorporated (doped) nanoparticles, and no such luminescence is observed for the Pr, Gd, Tb, and Dy containing nanoparticles. While host sensitized luminescence of lanthanide ions dominate the emission in the Nd and Sm incorporated nanoparticles, the host sensitization effect is less pronounced for the Eu and Yb containing systems, and for the Ho, Er, and Tm doped nanocrystals only a subset of the dopant ions’ luminescence bands is sensitized. The experimental observations of the host sensitized Ln3+ luminescence properties in the [Ti(Ln)O2] nanoparticles can be rationalized by considering that the dopant ions act as charge traps in the host lattice and associated environment induced luminescence quenching effects. Using these results, an energy offset between the trap site and the nanoparticle’s band edge that will generate an optimal host sensitized dopant emission is proposed. The approach presented necessarily improves over a combinatorial approach to select the host and dopant moieties, with the benefit of providing physicochemical insight regarding the nature of photophysical processes in a given host (semiconductor nanoparticle)–guest (Ln3+) composite system.

A scanning tunneling microscope break junction method with continuous bias modulation

Co-reporter:Edward Beall, Xing Yin, David H. Waldeck and Emil Wierzbinski

Nanoscale 2015 vol. 7(Issue 36) pp:14965-14973

Publication Date(Web):19 Aug 2015

DOI:10.1039/C5NR04649A

Single molecule conductance measurements on 1,8-octanedithiol were performed using the scanning tunneling microscope break junction method with an externally controlled modulation of the bias voltage. Application of an AC voltage is shown to improve the signal to noise ratio of low current (low conductance) measurements as compared to the DC bias method. The experimental results show that the current response of the molecule(s) trapped in the junction and the solvent media to the bias modulation can be qualitatively different. A model RC circuit which accommodates both the molecule and the solvent is proposed to analyze the data and extract a conductance for the molecule.

Driving charge separation for hybrid solar cells: photo-induced hole transfer in conjugated copolymer and semiconductor nanoparticle assemblies

Co-reporter:Y. Wang, K. Liu, P. Mukherjee, D. A. Hines, P. Santra, H. Y. Shen, P. Kamat and D. H. Waldeck

Physical Chemistry Chemical Physics 2014 vol. 16(Issue 11) pp:5066-5070

Publication Date(Web):28 Jan 2014

DOI:10.1039/C3CP55210A

This work reports on the use of an internal electrostatic field to facilitate charge separation at inorganic–organic interfaces, analogous to those in hybrid solar cells. Systematic charge transfer studies show that the donor–acceptor charge transfer rate is highly sensitive to the direction of the internal electric field.

Luminescence Quenching by Photoinduced Charge Transfer between Metal Complexes in Peptide Nucleic Acids

Co-reporter:Xing Yin, Jing Kong, Arnie De Leon, Yongle Li, Zhijie Ma, Emil Wierzbinski, Catalina Achim, and David H. Waldeck

The Journal of Physical Chemistry B 2014 Volume 118(Issue 30) pp:9037-9045

Publication Date(Web):June 27, 2014

DOI:10.1021/jp5027042

A new scaffold for studying photoinduced charge transfer has been constructed by connecting a [Ru(Bpy)3]2+ donor to a bis(8-hydroxyquinolinate)2 copper [CuQ2] acceptor through a peptide nucleic acid (PNA) bridge. The luminescence of the [Ru(Bpy)3]2+* donor is quenched by electron transfer to the [CuQ2] acceptor. Photoluminescence studies of these donor-bridge-acceptor systems reveal a dependence of the charge transfer on the length and sequence of the PNA bridge and on the position of the donor and acceptor in the PNA. In cases where the [Ru(Bpy)3]2+ can access the π base stack at the terminus of the duplex, the luminescence decay is described well by a single exponential; but if the donor is sterically hindered from accessing the π base stack of the PNA duplex, a distribution of luminescence lifetimes for the donor [Ru(Bpy)3]2+* is observed. Molecular dynamics simulations are used to explore the donor-PNA-acceptor structure and the resulting conformational distribution provides a possible explanation for the distribution of electron transfer rates.

A Three-Step Kinetic Model for Electrochemical Charge Transfer in the Hopping Regime

Co-reporter:Xing Yin, Emil Wierzbinski, Hao Lu, Silvia Bezer, Arnie R. de Leon, Kathryn L. Davis, Catalina Achim, and David H. Waldeck

The Journal of Physical Chemistry A 2014 Volume 118(Issue 35) pp:7579-7589

Publication Date(Web):May 9, 2014

DOI:10.1021/jp502826e

Single-step nonadiabatic electron tunneling models are widely used to analyze electrochemical rates through self-assembled monolayer films (SAMs). For some systems, such as nucleic acids, long-range charge transfer can occur in a “hopping” regime that involves multiple charge transfer events and intermediate states. This report describes a three-step kinetic scheme to model charge transfer in this regime. Some of the features of the three-step model are probed experimentally by changing the chemical composition of the SAM. This work uses the three-step model and a temperature dependence of the charge transfer rate to extract the charge injection barrier for a SAM composed of a 10-mer peptide nucleic acid that operates in the hopping regime.

Seedless CTAB mediated growth of anisotropic nanoparticles and nanoparticle clusters on nanostructured plasmonic templates

Co-reporter:Matthew J. Kofke, Emil Wierzbinski and David H. Waldeck

Journal of Materials Chemistry A 2013 vol. 1(Issue 41) pp:6774-6781

Publication Date(Web):05 Sep 2013

DOI:10.1039/C3TC31431F

A seedless method for the synthesis of novel noble metal nanostructures has been developed. The method employs alkanethiol self-assembled monolayer (SAM) functionalized submicron apertures or surface bound colloidal nanoparticles as a template, and it is derived from surfactant mediated anisotropic Au nanoparticle synthesis with cetyltrimethylammonium bromide (CTAB) in solution (M. Grzelczak, et al., Chem. Soc. Rev. 2008, 37, 1783). Nanoparticle nucleation and growth is found to depend on the chain length of the alkanethiol, with short chain SAMs showing little nanoparticle growth. As compared to solution phase nanoparticle synthesis/growth, the addition of Ag+ and I− shape directing ions to the growth solution have a relatively minor effect on the templated growth process. When applied to 80 nm Au nanoparticles immobilized on an ITO surface, this methodology resulted in oligomeric Au nanostructures with asymmetric geometries. To highlight the wide applicability of this approach, Ag and Pd nanoparticles were grown within submicron apertures also, and they displayed features that are distinct from those of Au. The results suggest that the interaction between CTAB and the alkanethiol monolayer template surface is key to the nanostructure growth.

A Postsynthetic Modification of II–VI Semiconductor Nanoparticles to Create Tb3+ and Eu3+ Luminophores

Co-reporter:Prasun Mukherjee, Robin F. Sloan, Chad M. Shade, David H. Waldeck, and Stéphane Petoud

The Journal of Physical Chemistry C 2013 Volume 117(Issue 27) pp:14451-14460

Publication Date(Web):June 4, 2013

DOI:10.1021/jp404947x

We describe a novel method for creating luminescent lanthanide-containing nanoparticles in which the lanthanide cations are sensitized by the semiconductor nanoparticle’s electronic excitation. In contrast to previous strategies, this new approach creates such materials by addition of external salt to a solution of fully formed nanoparticles. We demonstrate this postsynthetic modification for the lanthanide luminescence sensitization of two visible emitting lanthanides (Ln), Tb3+ and Eu3+ ions, through ZnS nanoparticles in which the cations were added postsynthetically as external Ln(NO3)3·xH2O salt to solutions of ZnS nanoparticles. The postsynthetically treated ZnS nanoparticle systems display Tb3+ and Eu3+ luminescence intensities that are comparable to those of doped Zn(Ln)S nanoparticles, which we reported previously (J. Phys. Chem. A, 2011, 115, 4031–4041). A comparison with the synthetically doped systems is used to contrast the spatial distribution of the lanthanide ions, bulk versus surface localized. The postsynthetic strategy described in this work is fundamentally different from the synthetic incorporation (doping) approach and offers a rapid and less synthetically demanding protocol for Tb3+:ZnS and Eu3+:ZnS luminophores, thereby facilitating their use in a broad range of applications.

The Effect of Oxygen Heteroatoms on the Single Molecule Conductance of Saturated Chains

Co-reporter:Emil Wierzbinski, Xing Yin, Keith Werling, and David H. Waldeck

The Journal of Physical Chemistry B 2013 Volume 117(Issue 16) pp:4431-4441

Publication Date(Web):October 26, 2012

DOI:10.1021/jp307902v

Single molecule conductance measurements on alkanedithiols and alkoxydithiols (dithiolated oligoethers) were performed using the STM-controlled break junction method in order to ascertain how the oxygen heteroatoms in saturated linear chains impact the molecular conductance. The experimental results show that the difference in conductance increases with chain length, over the range studied. Comparisons with electronic structure calculations and previous work on alkanes indicate that the conductance of the oligoethers is lower than that of alkane chains with the same length. Electronic structure calculations allow the difference in the conductance of these two families of molecules to be traced to differences in the spatial distribution of the molecular orbitals that contribute most to the conductance. A pathway analysis of the electronic coupling through the chain is used to explain how the difference in conductance between the alkane and oligoether molecules depends on the chain length.

Ligand-Induced Changes in the Characteristic Size-Dependent Electronic Energies of CdSe Nanocrystals

Co-reporter:Brian P. Bloom, Liu-Bin Zhao, Yang Wang, and David H. Waldeck , Ruibin Liu, Peng Zhang, and David N. Beratan

The Journal of Physical Chemistry C 2013 Volume 117(Issue 43) pp:22401-22411

Publication Date(Web):August 19, 2013

DOI:10.1021/jp403164w

This work explores the electronic energy of CdSe nanoparticles as a function of nanoparticle (NP) size and capping ligand. Differential pulse voltammetry was used to determine the valence band edge of CdSe NPs that are capped with three different ligands (aniline, thiophenol, and phenylphosphonic acid), and the experimental values are compared with DFT calculations. These results show how the energy position and the size-dependent behavior of the energy bands of CdSe can be modulated by the chemical nature of the capping ligand. The computations underscore how the nature of the highest lying filled states of the nanoparticle can change with ligand type and how this can explain differences between previously reported size-dependent data on similar systems. The findings show that both the ligand and quantum confinement effects should be accounted for in modeling size-dependent effects for different NP–ligand systems.

Enhanced Sensitivity of Delocalized Plasmonic Nanostructures

Co-reporter:Madu N. Mendis, Himadri S. Mandal, and David H. Waldeck

The Journal of Physical Chemistry C 2013 Volume 117(Issue 48) pp:25693-25703

Publication Date(Web):November 19, 2013

DOI:10.1021/jp410000u

This work reports on the observation of a delocalized surface plasmon resonance (DSPR) phenomenon in linear chains of square-shaped silver nanoparticles (NP) as a function of the chain length and the distance between the nanoparticles in the chain. Transmission spectra of the silver nanoparticle chains reveal the emergence of new, red-shifted extinction peaks that depend strongly on the spacing between the nanoparticles and the polarization of the exciting light with respect to the chain axis. As the spacing between the nanoparticles in the linear chain decreases and the number of nanoparticles in the linear chain increases, the strength of the new extinction features increases strongly. These changes can be described by a tight-binding model for the coupled chain, which indicates that the origin of the phenomenon is consistent with an increased coupling between the nanoparticles. FDTD calculations reveal that the electric field is strongly enhanced between the nanoparticles in the chain. The DSPR response is found to be much more sensitive to dielectric changes than the localized surface plasmon resonance (LSPR).

Voltammetry Can Reveal Differences between the Potential Energy Curve (pec) and Density of States (dos) Models for Heterogeneous Electron Transfer

Co-reporter:David H. Waldeck

The Journal of Physical Chemistry C 2013 Volume 117(Issue 40) pp:20746-20761

Publication Date(Web):September 13, 2013

DOI:10.1021/jp4071532

This work uses the potential energy curve (pec) and density of states (dos) methods to calculate the cyclic voltammogram for a redox adsorbate that undergoes a simple one-electron reversible redox reaction. It extends an earlier treatment for simulation of voltammograms, which used the simple Butler–Volmer kinetics and classic Marcus theory in the nonadiabatic limit, to calculate the voltammogram for an arbitrary electrode–reactant coupling strength. Voltammograms are calculated as a function of the electrode–reactant coupling strength and reorganization energy, and the dependence of the voltammetric peak potentials and normalized peak currents on sweep rate are calculated and compared for the pec and dos methods. Although the pec and dos approaches coincide in the nonadiabatic limit, they deviate very significantly for large electronic couplings, beyond the nonadiabatic limit. The most interesting finding is that the dos voltammetric wave splits into two separated peaks, under some conditions at large coupling strengths.

The Single-Molecule Conductance and Electrochemical Electron-Transfer Rate Are Related by a Power Law

Co-reporter:Emil Wierzbinski, Ravindra Venkatramani, Kathryn L. Davis, Silvia Bezer, Jing Kong, Yangjun Xing, Eric Borguet, Catalina Achim, David N. Beratan, and David H. Waldeck

ACS Nano 2013 Volume 7(Issue 6) pp:5391

Publication Date(Web):May 21, 2013

DOI:10.1021/nn401321k

This study examines quantitative correlations between molecular conductances and standard electrochemical rate constants for alkanes and peptide nucleic acid (PNA) oligomers as a function of the length, structure, and charge transport mechanism. The experimental data show a power-law relationship between conductances and charge transfer rates within a given class of molecules with the same bridge chemistry, and a lack of correlation when a more diverse group of molecules is compared, in contrast with some theoretical predictions. Surprisingly, the PNA duplexes exhibit the lowest charge-transfer rates and the highest molecular conductances. The nonlinear rate–conductance relationships for structures with the same bridging chemistries are attributed to differences in the charge-mediation characteristics of the molecular bridge, energy barrier shifts and electronic dephasing, in the two different experimental settings.Keywords: break junction; charge transport; dephasing; molecular bridge; nucleic acids

Effect of Backbone Flexibility on Charge Transfer Rates in Peptide Nucleic Acid Duplexes

Co-reporter:Emil Wierzbinski ; Arnie de Leon ; Xing Yin ; Alexander Balaeff ; Kathryn L. Davis ; Srinivas Reppireddy ; Ravindra Venkatramani ; Shahar Keinan ; Danith H. Ly ; Marcela Madrid ; David N. Beratan ; Catalina Achim

Journal of the American Chemical Society 2012 Volume 134(Issue 22) pp:9335-9342

Publication Date(Web):April 30, 2012

DOI:10.1021/ja301677z

Charge transfer (CT) properties are compared between peptide nucleic acid structures with an aminoethylglycine backbone (aeg-PNA) and those with a γ-methylated backbone (γ-PNA). The common aeg-PNA is an achiral molecule with a flexible structure, whereas γ-PNA is a chiral molecule with a significantly more rigid structure than aeg-PNA. Electrochemical measurements show that the CT rate constant through an aeg-PNA bridging unit is twice the CT rate constant through a γ-PNA bridging unit. Theoretical calculations of PNA electronic properties, which are based on a molecular dynamics structural ensemble, reveal that the difference in the CT rate constant results from the difference in the extent of backbone fluctuations of aeg- and γ-PNA. In particular, fluctuations of the backbone affect the local electric field that broadens the energy levels of the PNA nucleobases. The greater flexibility of the aeg-PNA gives rise to more broadening, and a more frequent appearance of high-CT rate conformations than in γ-PNA.

Charge Transfer through Modified Peptide Nucleic Acids

Co-reporter:Emil Wierzbinski, Arnie de Leon, Kathryn L. Davis, Silvia Bezer, Matthäus A. Wolak, Matthew J. Kofke, Rudy Schlaf, Catalina Achim, and David H. Waldeck

Langmuir 2012 Volume 28(Issue 4) pp:1971-1981

Publication Date(Web):January 4, 2012

DOI:10.1021/la204445u

We studied the charge transfer properties of bipyridine-modified peptide nucleic acid (PNA) in the absence and presence of Zn(II). Characterization of the PNA in solution showed that Zn(II) interacts with the bipyridine ligands, but the stability of the duplexes was not affected significantly by the binding of Zn(II). The charge transfer properties of these molecules were examined by electrochemistry for self-assembled monolayers of ferrocene-terminated PNAs and by conductive probe atomic force microscopy for cysteine-terminated PNAs. Both electrochemical and single molecular studies showed that the bipyridine modification and Zn(II) binding do not affect significantly the charge transfer of the PNA duplexes.

Perfluorinated Aromatic Spacers for Sensitizing Europium(III) Centers in Dinuclear Oligomers: Better than the Best by Chemical Design?

Co-reporter:Dr. Jean-François Lemonnier;Lucille Babel;Dr. Laure Guénée;Dr. Prasun Mukherjee;Dr. David H. Waldeck;Dr. Svetlana V. Eliseeva;Dr. Stéphane Petoud;Dr. Claude Piguet

Angewandte Chemie 2012 Volume 124( Issue 45) pp:11464-11467

Publication Date(Web):

DOI:10.1002/ange.201205082

Perfluorinated Aromatic Spacers for Sensitizing Europium(III) Centers in Dinuclear Oligomers: Better than the Best by Chemical Design?

Co-reporter:Dr. Jean-François Lemonnier;Lucille Babel;Dr. Laure Guénée;Dr. Prasun Mukherjee;Dr. David H. Waldeck;Dr. Svetlana V. Eliseeva;Dr. Stéphane Petoud;Dr. Claude Piguet

Angewandte Chemie International Edition 2012 Volume 51( Issue 45) pp:11302-11305

Publication Date(Web):

DOI:10.1002/anie.201205082

Determination of the Electronic Energetics of CdTe Nanoparticle Assemblies on Au Electrodes by Photoemission, Electrochemical, and Photocurrent Studies

Co-reporter:Yang Wang ; Zuoti Xie ; Gilad Gotesman ; Lei Wang ; Brian P. Bloom ; Tal Z. Markus ; Dan Oron ; Ron Naaman

The Journal of Physical Chemistry C 2012 Volume 116(Issue 33) pp:17464-17472

Publication Date(Web):August 1, 2012

DOI:10.1021/jp306702t

This work explores the electronic states of CdTe semiconductor nanoparticles (NPs) that are immobilized on a polycrystalline Au film through an organic linker (dithiol). The HOMO and LUMO energies of the CdTe NPs were determined by using photoelectron spectroscopy and cyclic voltammetry. The results from these measurements show that the HOMO energy is independent of the nanoparticle size and is pinned to the Fermi level, whereas the LUMO energy changes systematically with the size of the NP. Studies with different capping ligands imply that the dithiol ligand removes surface states and enhances the optoelectronic properties of the NPs.

Optimizing Sensitization Processes in Dinuclear Luminescent Lanthanide Oligomers: Selection of Rigid Aromatic Spacers

Co-reporter:Jean-François Lemonnier ; Laure Guénée ; César Beuchat ; Tomasz A. Wesolowski ; Prasun Mukherjee ; David H. Waldeck ; Kristy A. Gogick ; Stéphane Petoud ;Claude Piguet

Journal of the American Chemical Society 2011 Volume 133(Issue 40) pp:16219-16234

Publication Date(Web):September 1, 2011

DOI:10.1021/ja206806t

This work illustrates a simple approach for optimizing the lanthanide luminescence in molecular dinuclear lanthanide complexes and identifies a particular multidentate europium complex as the best candidate for further incorporation into polymeric materials. The central phenyl ring in the bis-tridentate model ligands L3–L5, which are substituted with neutral (X = H, L3), electron-withdrawing (X = F, L4), or electron-donating (X = OCH3, L5) groups, separates the 2,6-bis(benzimidazol-2-yl)pyridine binding units of linear oligomeric multi-tridentate ligand strands that are designed for the complexation of luminescent trivalent lanthanides, Ln(III). Reactions of L3–L5 with [Ln(hfac)3(diglyme)] (hfac– is the hexafluoroacetylacetonate anion) produce saturated single-stranded dumbbell-shaped complexes [Ln2(Lk)(hfac)6] (k = 3–5), in which the lanthanide ions of the two nine-coordinate neutral [N3Ln(hfac)3] units are separated by 12–14 Å. The thermodynamic affinities of [Ln(hfac)3] for the tridentate binding sites in L3–L5 are average (6.6 ≤ log(β2,1Y,Lk) ≤ 8.4) but still result in 15–30% dissociation at millimolar concentrations in acetonitrile. In addition to the empirical solubility trend found in organic solvents (L4 > L3 ≫ L5), which suggests that the 1,4-difluorophenyl spacer in L4 is preferable, we have developed a novel tool for deciphering the photophysical sensitization processes operating in [Eu2(Lk)(hfac)6]. A simple interpretation of the complete set of rate constants characterizing the energy migration mechanisms provides straightforward objective criteria for the selection of [Eu2(L4)(hfac)6] as the most promising building block.

Electrochemically Guided Photovoltaic Devices: A Photocurrent Study of the Charge Transfer Directionality between CdTe and CdSe Nanoparticles

Co-reporter:Y. Wang ; L. Wang ;D. H. Waldeck

The Journal of Physical Chemistry C 2011 Volume 115(Issue 37) pp:18136-18141

Publication Date(Web):August 8, 2011

DOI:10.1021/jp205615p

This work reports on the energy level alignment and charge transfer in organized assemblies of CdTe and CdSe nanoparticles (NPs), for both electrochemical systems and in solid-state photovoltaic devices. This work shows how control over the energy level alignment, by manipulation of the size and surface ligands of the CdTe and CdSe NPs, can be combined with control over the NPs spatial arrangement, either by sequential self-assembly onto a Au working electrode of an electrochemical cell or spin-coating onto an ITO substrate of a photovoltaic device, to facilitate photoinduced charge separation (photocurrent). By properly arranging the spatial and energetic hierarchy of the assemblies, the charge transfer direction and its efficiency can be optimized.

Lanthanide Sensitization in II−VI Semiconductor Materials: A Case Study with Terbium(III) and Europium(III) in Zinc Sulfide Nanoparticles

Co-reporter:Prasun Mukherjee, Chad M. Shade, Adrienne M. Yingling, Daniel N. Lamont, David H. Waldeck, and Stéphane Petoud

The Journal of Physical Chemistry A 2011 Volume 115(Issue 16) pp:4031-4041

Publication Date(Web):November 23, 2010

DOI:10.1021/jp109786w

This work explores the sensitization of luminescent lanthanide Tb3+ and Eu3+ cations by the electronic structure of zinc sulfide (ZnS) semiconductor nanoparticles. Excitation spectra collected while monitoring the lanthanide emission bands reveal that the ZnS nanoparticles act as an antenna for the sensitization of Tb3+ and Eu3+. The mechanism of lanthanide ion luminescence sensitization is rationalized in terms of an energy and charge transfer between trap sites and is based on a semiempirical model, proposed by Dorenbos and co-workers (Dorenbos, P. J. Phys.: Condens. Matter2003, 15, 8417−8434; J. Lumin.2004, 108, 301−305; J. Lumin.2005, 111, 89−104. Dorenbos, P.; van der Kolk, E. Appl. Phys. Lett.2006, 89, 061122-1−061122-3; Opt. Mater.2008, 30, 1052−1057. Dorenbos, P. J. Alloys Compd.2009, 488, 568−573; references 1−6.) to describe the energy level scheme. This model implies that the mechanisms of luminescence sensitization of Tb3+ and Eu3+ in ZnS nanoparticles are different; namely, Tb3+ acts as a hole trap, whereas Eu3+ acts as an electron trap. Further testing of this model is made by extending the studies from ZnS nanoparticles to other II−VI semiconductor materials; namely, CdSe, CdS, and ZnSe.

Role of Nucleobase Energetics and Nucleobase Interactions in Single-Stranded Peptide Nucleic Acid Charge Transfer

Co-reporter:Amit Paul ; Silvia Bezer ; Ravindra Venkatramani ; Laura Kocsis ; Emil Wierzbinski ; Alexander Balaeff ; Shahar Keinan ; David N. Beratan ; Catalina Achim

Journal of the American Chemical Society 2009 Volume 131(Issue 18) pp:6498-6507

Publication Date(Web):April 21, 2009

DOI:10.1021/ja9000163

Self-assembled monolayers of single-stranded (ss) peptide nucleic acids (PNAs) containing seven nucleotides (TTTXTTT), a C-terminus cysteine, and an N-terminus ferrocene redox group were formed on gold electrodes. The PNA monomer group (X) was selected to be either cytosine (C), thymine (T), adenine (A), guanine (G), or a methyl group (Bk). The charge transfer rate through the oligonucleotides was found to correlate with the oxidation potential of X. Kinetic measurements and computational studies of the ss-PNA fragments show that a nucleobase mediated charge transport mechanism in the deep tunneling superexchange regime can explain the observed dependence of the kinetics of charge transfer on the PNA sequence. Theoretical analysis suggests that the charge transport is dominantly hole-mediated and takes place through the filled bridge orbitals. The strongest contribution to conductance comes from the highest filled orbitals (HOMO, HOMO-1, and HOMO-2) of individual bases, with a rapid drop off in contributions from lower lying filled orbitals. Our studies further suggest that the linear correlation observed between the experimental charge transfer rates and the oxidation potential of base X arises from weak average interbase couplings and similar stacking geometries for the four TTTXTTT systems.

Effect of Deuterium Substitution on Electron Transfer at Cytochrome c/SAM Interfaces

Co-reporter:Kathryn L. Davis and David H. Waldeck

The Journal of Physical Chemistry B 2008 Volume 112(Issue 39) pp:12498-12507

Publication Date(Web):September 9, 2008

DOI:10.1021/jp803006b

The involvement of protons in the heterogeneous electron transfer between cytochrome c and a gold electrode to which it is attached was studied by comparing the electron transfer rate constants for H2O and D2O solutions. Rate constants were measured as a function of the electrochemical cell solution and the protein incubant solution, i.e., k0(incubant, cell). Two separate isotope effects exist: a cell “isotope effect”, KIEcell = k0(H2O, H2O):k0(H2O, D2O), which is manifest at short time scales (<30 s) and arises from the viscosity difference between H2O and D2O, and an incubant isotope effect, KIEinc= k0(H2O, H2O):k0(D2O, H2O), which is manifest at longer times (>2 h) and results from H/D exchange. The two isotope effects are approximately equal (∼1.2) and a total isotope effect KIEtotal = k0(H2O, H2O):k0(D2O, D2O) can be constructed that is the product of KIEcell and KIEinc. The nature of the electron transfer process, possible coupling to a proton transfer process, and the involvement of specific hydrogens in the transfer mechanism are discussed.

Pendant unit effect on electron tunneling in U-shaped molecules

Co-reporter:Min Liu, Subhasis Chakrabarti, David H. Waldeck, Anna M. Oliver, Michael N. Paddon-Row

Chemical Physics 2006 Volume 324(Issue 1) pp:72-84

Publication Date(Web):9 May 2006

DOI:10.1016/j.chemphys.2005.11.040

Abstract

The electron transfer reactions of three U-shaped donor-bridge-acceptor molecules with different pendant groups have been studied in different solvents as a function of temperature. Analysis of the electron transfer kinetics in nonpolar and weakly polar solvents provides experimental reaction Gibbs energies that are used to parameterize a molecular solvation model. This solvation model is then used to predict energetic parameters in the electron transfer rate constant expression and allow the electronic coupling between the electron donor and electron acceptor groups to be determined from the rate data. The U-shaped molecules differ by alkylation of the aromatic pendant group, which lies in the ‘line-of-sight’ between the donor and acceptor groups. The findings show that the electronic coupling through the pendant group is similar for these molecules.

Protagonists in chemistry

Co-reporter:David H Waldeck

Inorganica Chimica Acta 2005 Volume 358(Issue 10) pp:2841-2843

Publication Date(Web):15 June 2005

DOI:10.1016/j.ica.2004.09.046

Electron-Transfer Dynamics of Cytochrome C: A Change in the Reaction Mechanism with Distance

Co-reporter:Jianjun Wei;Haiying Liu;Dimitri E. Khoshtariya;Hiromichi Yamamoto;Allison Dick Dr.

Angewandte Chemie International Edition 2002 Volume 41(Issue 24) pp:

Publication Date(Web):12 DEC 2002

DOI:10.1002/anie.200290021

Directly linking a gold electrode coated with pyridine-terminated self-assembled monolayers (SAMs) to the redox-active heme unit of cytochrome c has enabled the electron-transfer mechanism to be studied as a function of distance. Comparison of the kinetic data for this system (see graph) with earlier data on COOH-terminated SAMs requires a change in the electron-transfer mechanism with distance from the electrode surface that does not involve large-amplitude conformational rearrangement.

Electron-Transfer Dynamics of Cytochrome C: A Change in the Reaction Mechanism with Distance

Co-reporter:Jianjun Wei;Haiying Liu;Dimitri E. Khoshtariya;Hiromichi Yamamoto;Allison Dick Dr.

Angewandte Chemie 2002 Volume 114(Issue 24) pp:

Publication Date(Web):12 DEC 2002

DOI:10.1002/ange.200290020

Direkte Anknüpfung einer Goldelektrode, die mit Pyridin-terminierten selbstorganisierten Monoschichten (SAMs) belegt ist, an eine redoxaktive Häm-Einheit von Cytochrom c ermöglichte die Untersuchung des Elektronentransfers in Abhängigkeit vom Abstand zwischen Oberfläche und Protein. Anhand der kinetischen Daten dieses Systems (siehe Graph) und älterer Daten zu COOH-terminierten SAMs wurde festgestellt, dass ab einem bestimmten Abstand von der Elektrodenoberfläche ein anderer Elektronentransfermechanismus wirksam ist, der keine umfangreichen konformativen Änderungen erfordert.

Immobilization of cytochrome c at Au electrodes by association of a pyridine terminated SAM and the heme of cytochrome

Co-reporter:Hiromichi Yamamoto, Haiying Liu and David H. Waldeck

Chemical Communications 2001 (Issue 11) pp:1032-1033

Publication Date(Web):09 May 2001

DOI:10.1039/B101767P

Electrochemical methods are used to demonstrate that cytochrome c can be immobilized on electrodes that are coated with self-assembled monolayers of 4-pyridinyl–CO2–(CH2)n –S (n > 6) through interaction between the pyridine terminal unit and the heme of the cytochrome.

Driving charge separation for hybrid solar cells: photo-induced hole transfer in conjugated copolymer and semiconductor nanoparticle assemblies

Co-reporter:Y. Wang, K. Liu, P. Mukherjee, D. A. Hines, P. Santra, H. Y. Shen, P. Kamat and D. H. Waldeck

Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 11) pp:NaN5070-5070

Publication Date(Web):2014/01/28