Co-reporter:Anup Kumar Singh and Kothandam Krishnamoorthy
Langmuir November 21, 2017 Volume 33(Issue 46) pp:13401-13401
Publication Date(Web):October 31, 2017
DOI:10.1021/acs.langmuir.7b02728
Rylene imides (RIs) self-assemble into various nanostructures. Often, the synthesis of unsymmetrical RIs (URIs) is required to achieve nanostructures. However, the synthesis of URIs is nontrivial. Thus, a structurally similar alternative is desirable. iso-Indigo (i-indigo) has a π core and lactam rings that are structurally similar to the RIs. Unsymmetrical iso-indigo (i-indigo) can be easily synthesized by condensing oxindole and isatin. We have synthesized a series of unsymmetrical i-indigo molecules. In these molecules, the π–π interaction, hydrogen bonding, and van der Waals interactions are in operation. Because of these, the molecules self-assemble into spheres, fibers, and dahlia flower morphologies. If the hydrogen bonding interaction is disrupted, then all of them form fibers. Control experiments indicate that the complete absence of hydrogen bonding is deleterious to self-assembly. We also show that the lower analogs of i-indigo are not sufficient to form self-assembled nanostructures.
Co-reporter:Bhanprakash Jain, Kothandam Krishnamoorthy
Materials Today Energy 2017 Volume 5(Volume 5) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.mtener.2017.06.004
•Large ion trapping to improve charge storage.•Polyphenols for large area electrode preparation.•High specific capacitance and power density in PEDOT.Poly(3,4-ethylenedioxythiophene) (PEDOT) is a stable conducting polymer, hence its dispersion is widely used in commercial devices. However, PEDOT's charge storage properties are not impressive. Thus, improvement in charge storage properties of PEDOT will render the possibility of fabricating stable energy storage devices such as supercapacitors. A fundamentally different approach is required to achieve this objective. We envisioned that the charge storage property of PEDOT can be improved by trapping large anions. These ions would facilitate better ion transport into the PEDOT matrix from the electrolyte and increase the efficiency of supercapacitors. Furthermore, a large anion such as triiodide is relatively immobile in the polymer matrix, hence we hypothesize the ions to be trapped in the polymer. To test this hypothesis, triiodide trapped PEDOT based supercapacitors are fabricated on paper substrates. A 1 cm2 triiodide incorporated PEDOT based supercapacitor exhibited a specific capacitance of 486 F/g. On the other hand, PEDOT without triiodide incorporation exhibited a specific capacitance of 221 F/g. Indeed, a device with an area of 32 cm2 exhibited a specific capacitance of 476 F/g.
Co-reporter:Kamal Prakash, Shweta Manchanda, Vediappan Sudhakar, Nidhi Sharma, Muniappan Sankar, Kothandam Krishnamoorthy
Dyes and Pigments 2017 Volume 147(Volume 147) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.dyepig.2017.07.053
•Facile synthesis of β-functionalized “push-pull” porphyrins and their characterization.•The Soret and Q bands of Zn(II) porphyrin dyes were red-shifted (30–35 nm) and broadened as compared to ZnTPP.•The fluorescence quenching, decrement in quantum yield and lifetime reflected intramolecular charge transfer from donor to acceptor.•The HOMO-LUMO energy levels of Zn(II) porphyrin dyes suggest the feasibility of facile electron-transfer in DSSC.•ZnT(Mes)P(CN-COOH) displayed η = 3.13% whereas co-sensitization of this dye with N719 dye increased PCE up to 5.35%.Three new β-substituted “push-pull” Zn(II) porphyrin dyes with various electron donors at meso-positions and cyanoacetic acid as acceptor at β-position have been designed and synthesized. These porphyrins have been characterized by UV-Vis, Fluorescence, 1H NMR and 13C NMR spectroscopic techniques and cyclic voltammetric studies. The Soret and Q band of Zn(II) porphyrin dyes were found to be red-shifted (30–35 nm) as compared to ZnTPP. The fluorescence quenching and the decrement in quantum yield and lifetime suggest intramolecular charge transfer from donor to acceptor. Zn porphyrins exhibited anodic shift in their first redox potentials (0.03–0.11 V) as compared to ZnTPP. The HOMO-LUMO energy levels of Zn porphyrin dyes were compared with the conduction band of TiO2 and the electrolyte I−/I3−. The HOMO levels of all the dyes are sufficiently higher than the energy level of electrolyte I−/I3− and LUMO levels significantly lower than the conduction band of TiO2 which reflect the feasibility of facile electron-transfer. ZnT(Mes)P(CN-COOH) has been co-sensitized with N719 dye to further improve the PCE efficiency. These dyes displayed power conversion efficiency (PCE) of η = 1.72–3.13% where co-sensitized ZnT(Mes)P(CN-COOH) (N719) dye demonstrated maximum PCE efficiency up to 5.35%, with a Jsc of 11.8 mA cm−2, a Voc of 630 mV and a fill factor (FF) of 72% due to better light harvesting capacity.β-Functionalized “push-pull porphyrin” dyes have been designed, synthesized and studied for DSSC applications. These dyes displayed power conversion efficiency (PCE) of η = 1.72–3.13% where co-sensitized ZnT(Mes)P(CN-COOH)(N719) dye demonstrated maximum PCE efficiency up to 5.35%, with a Jsc of 11.8 mA cm−2, a Voc of 630 mV and a fill factor (FF) of 0.72.Download high-res image (324KB)Download full-size image
Co-reporter:Manik E. Bhosale;Abhik Banerjee
RSC Advances (2011-Present) 2017 vol. 7(Issue 21) pp:12659-12662
Publication Date(Web):2017/02/21
DOI:10.1039/C6RA27662H
A conjugated polymer comprising heterocycles was prepared and carbonized to obtain carbon with interlayer spacings between 0.42 and 0.37 nm and exhibited a specific capacity of 250 mA h g−1.
Co-reporter:Vediappan Sudhakar;Arulraj Arulkashmir
Chemical Communications 2017 vol. 53(Issue 49) pp:6629-6632
Publication Date(Web):2017/06/16
DOI:10.1039/C7CC03276E
Dye regeneration was improved by using an optimum quantity of graphene, which was dispersed in a polymer that suppresses back electron transfer. Using this approach, DSSCs with an efficiency of 10.4% have been fabricated.
Co-reporter:Chayanika Das, Soumyajyoti ChatterjeeGuruswamy Kumaraswamy, Kothandam Krishnamoorthy
The Journal of Physical Chemistry C 2017 Volume 121(Issue 6) pp:
Publication Date(Web):January 26, 2017
DOI:10.1021/acs.jpcc.6b12822
Design and fabrication of rechargeable energy storage devices that are robust to mechanical deformation is essential for wearable electronics. We report the preparation of compressible supercapacitors that retain their specific capacitance after large compression and that recover elastically after at least a hundred compression–expansion cycles. Compressible supercapacitors are prepared using a facile, scalable method that readily yields centimeter-scale macroporous objects. We ice template a solution of polyethylenimine in green tea extract to prepare a macroporous cross-linked polymer gel (PG) whose walls are impregnated with green tea derived polyphenols. As the PG is insulating, we impart conductivity by deposition of gold on it. Gold deposition is done in two steps: first, silver nanoparticles are formed on the PG walls by in situ reduction by polyphenols and then gold films are deposited on these walls. Gold coated PGs (GPGs) were used as electrodes to deposit poly(3,4-ethylenedioxythiophene) as a pseudocapacitive material. The specific capacitance of PEDOT coated GPGs (PGPG) was found to be 253 F/g at 1 A/g. PGPG could be compressed and expanded over a hundred cycles without any suffering mechanical failure or loss of capacitative performance. The capacitance was found to be 243 F/g upon compressing the device to 25% of its original size (viz. compressive strain = 75%). Thus, even large compression does not affect the device performance. This device shows power and energy densities of 2715 W/kg and 22 Wh/kg, respectively, in the uncompressed state. The macroporous nature of PGPG makes it possible to fill the PGPG pores with gel electrolyte. We report that the gel electrolyte filled supercapacitor exhibited a specific capacitance of 200 F/g, which increased by 4% upon 75% compression.
Co-reporter:Arulraj Arulkashmir;Vediappan Sudhakar ;Kotham Krishnamoorthy
Advanced Energy Materials 2016 Volume 6( Issue 9) pp:
Publication Date(Web):
DOI:10.1002/aenm.201502334
Recombination of charges residing in the TiO2 and redox electrolyte is one of the factors affecting the efficiency of dye sensitized solar cells (DSSCs). To circumvent this recombination, inorganic oxide barrier layers and organic silanes have been coated on TiO2/dyes. Due to the insulating nature of these layers, the efficiency increase is not very impressive. Conducting polymers with different band edges are used to suppress the charge recombination. Amongst the four polymers that are used as barrier layers, a polymer with a highest occupied molecular orbital energy at −5.8 eV and lowest unoccupied molecular orbital at −3.1 eV is found to increase the electron life time at TiO2 and decrease the charge recombination. The electron life time is found to be 88 ms. In addition to the long electron life time, the recombination resistance of this polymer is also high (91 Ω). This resistance is 18% higher than that measured for DSSCs without polymer barrier layer. These factors impact the efficiency of DSSCs. DSSCs fabricated with this polymer as barrier layer exhibit an efficiency of 9.2%, which is 22% higher than that of DSSCs without polymer barrier layer.
Co-reporter:Chayanika Das and Kothandam Krishnamoorthy
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 43) pp:29504
Publication Date(Web):October 7, 2016
DOI:10.1021/acsami.6b10431
Flexible microsupercapacitors (MSCs) are needed to power ultrasmall wearable electronic devices. Silk cocoons comprise microfibers of silk, which is an attractive natural resource to fabricate MSCs. These fibers are insulators; hence, they must be converted to conducting surfaces. Polyphenols from green tea have been used as a protective layer that also acted as a reducing agent for silver ions. The reduction of silver ions resulted in the formation of silver nanoparticles that subsequently reduced gold ions to gold. The gold film imparts conductivity to the silk fiber without affecting the mechanical strength of the silk fiber. The mechanical strength of uncoated silk fiber and gold coated silk fiber were found to be 5.2 and 5 GPa, respectively. A pseudocapacitive polymer, poly(3,4-ethylenedioxythiophene), was used as the active material to fabricate MSCs. The MSCs showed an impressive gravimetric capacitance of 500 F/g and areal capacitance of 62 mF/cm2. The power and energy densities were calculated to be 2458 W/kg and 44 Wh/kg, respectively. The device was coiled on a cylinder, and the performance of the device was found to be same as that of the uncoiled device. To demonstrate that the approach is not specific to silk, we also coated gold on cotton fibers using the protocol used to coat gold on silk. Coiled and uncoiled supercapacitors were fabricated using PEDOT coated cotton fibers. The gravimetric capacitance was found to be 250 F/g with energy and power densities of 5.5 Wh/kg and 1118 W/kg, respectively. We have also demonstrated that the devices can be connected in parallel and series to improve the performance of the miniaturized devices.Keywords: cotton fibers; gold coated cotton threads; microsupercapacitors; silk fibers
Co-reporter:Arulraj Arulkashmir and Kothandam Krishnamoorthy
Chemical Communications 2016 vol. 52(Issue 17) pp:3486-3489
Publication Date(Web):22 Jan 2016
DOI:10.1039/C5CC09603K
A transparent, conducting and low surface energy surface was prepared by disassembly of anionic micelles, which altered the orientation of the donor polymer and imparted gradation between the donor and acceptor. This configuration increased the solar cell device efficiency.
Co-reporter:Manik E. Bhosale, Rajith Illathvalappil, Sreekumar Kurungot and Kothandam Krishnamoorthy
Chemical Communications 2016 vol. 52(Issue 2) pp:316-318
Publication Date(Web):22 Oct 2015
DOI:10.1039/C5CC08148C
Conjugated porous polymers were used as precursors to prepare nitrogen and sulphur doped carbon atoms, which were then used for oxygen reduction and energy storage.
Co-reporter:Ravi Kumar, Muniappan Sankar, Vediappan Sudhakar and Kothandam Krishnamoorthy
New Journal of Chemistry 2016 vol. 40(Issue 7) pp:5704-5713
Publication Date(Web):11 Jan 2016
DOI:10.1039/C5NJ02610E
We have designed and synthesized a series of simple cost-effective ‘push–pull’ Zn(II) porphyrin dyes containing various electron donors such as 2-thienyl, pyrenyl, phenyl, 4′-bromophenyl, 4′-tbutylphenyl and 4′-carboxyphenyl acceptor moieties in three steps. Their optical absorption spectra, electrochemical redox and photovoltaic properties have been investigated in detail. The overall power conversion efficiencies (η) of DSSCs based on these dyes are in the range of 2.1 to 4.2% and highly depend on their donor moiety. The incorporation of trans-10,20-dimesityl groups is highly beneficial for preventing the π–π aggregation among the porphyrin moieties, thus favorably suppressing the charge recombination and intermolecular interaction. Among all, pyrenyl appended Zn(II) porphyrin has exhibited a higher power conversion efficiency of 4.2% under 1 sun illumination due to the extended π-conjugation and electron donating ability of the pyrenyl moiety.
Co-reporter:Sashi Debnath;Saumya Singh;Anjan Bedi;Kotham Krishnamoorthy;Sanjio S. Zade
Journal of Polymer Science Part A: Polymer Chemistry 2016 Volume 54( Issue 13) pp:1978-1986
Publication Date(Web):
DOI:10.1002/pola.28064
ABSTRACT
To study the effect of site-selective copolymerization of borondipyrromethene (BODIPY) with acetylene on the structural and optoelectronic properties, three copolymers P1–P3 were synthesized by the Sonogashira cross-coupling of BODIPY units with diacetylene and bromine capping through all the possible linkages: α-α (P1), α-β (P2), and β-β (P3). The optoelectronic properties of the polymers were investigated systematically to understand the effect of site-selective polymerization. The HOMO levels of the polymers were significantly tuned from P1 to P3 with negligible change in the LUMO levels. Broadening of absorption spectra from P3 to P1 was observed because of increase in the extent of conjugation. Additionally, the charge transport properties of these polymers in organic thin-film transistors (OTFTs) revealed that P1 and P3 exhibited only p-type mobility, whereas P2 exhibited electron mobility. Notably, the further investigations of the surface morphology of polymer films by atomic force microscopy (AFM) unveiled that comb like nanostructural arrangements in P3 was beneficial for the charge-carrier mobility over the circular arrangements in P1 and P2. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1978–1986
Co-reporter:Saumya Singh, Sundaresan Chithiravel, and Kothandam Krishnamoorthy
The Journal of Physical Chemistry C 2016 Volume 120(Issue 46) pp:26199-26205
Publication Date(Web):October 26, 2016
DOI:10.1021/acs.jpcc.6b08225
Copolymers of 4,4-difluoro-4-borata-3a-azonia-4a-aza-s-indacene (BODIPY) and diketopyrrolopyrrole (DPP) were synthesized. The BODIPY has a permanent dipole and the DPP has a quadrupole. The dipole and the quadrupole in the monomers are expected to bring the polymers closer and to improve the charge-transport properties. By judicious choice of these monomers, the electron wave function is evenly distributed through the molecules. However, we notice that the torsional angle at the connecting point of BODIPY and DPP is a function of the methyl moieties at the β, β′ position of the BODIPY. We found that the polymer comprising DPP and BODIPY without methyl moiety at β, β′ position showed a torsional angle of 27°, the lowest among the three polymers studied in this work. The absorption spectrum of the polymer showed transitions because of vibronic coupling indicating linearity along the polymer backbone. The band gap of the polymer was found to be 1.2 eV. The thermally stable polymer showed an ambipolar charge transport of 0.01 cm2/(V s).
Co-reporter:Manik E. Bhosale and Kothandam Krishnamoorthy
Chemistry of Materials 2015 Volume 27(Issue 6) pp:2121
Publication Date(Web):February 27, 2015
DOI:10.1021/cm5046786
Organic lithium batteries are attractive because of the possibility of fabricating lightweight and flexible devices. However, the organic lithium batteries have a few drawbacks. The specific capacity is usually lower than the theoretical capacity, which further decreases upon cycling. Often, the specific capacity is very low compared to theoretical capacity while discharging the battery at moderate and high C rates. To circumvent this issue, we chemically reduced carboxylic acid functionality substituted perylene diimide (benzoic-PDI) with hydrazine. Indeed, we found that the rate of redox reaction as well as the conductivity of the benzoic-PDI increased upon chemical reduction. The battery comprising reduced benzoic-PDI exhibits 100% Coulombic efficiency and specific capacity while discharging at 20C. The battery also exhibits very high specific energy (213 Wh/kg) and specific power (8548 W/kg). The control experiments confirm our hypothesis of using chemical reduction to improve the performance of organic lithium battery.
Co-reporter:Chayanika Das, Bhanprakash Jain and Kothandam Krishnamoorthy
Chemical Communications 2015 vol. 51(Issue 58) pp:11662-11664
Publication Date(Web):08 Jun 2015
DOI:10.1039/C5CC03108G
Polyphenols from green tea were used to electrolessly deposit gold on silk cocoons (SCs) and nanoporous aluminum oxide (AAO) templates. The gold coated cocoons were used as electrodes in supercapacitors and showed a capacitance as high as 254 F g−1 and a specific power of 2287 W kg−1. A metal coated AAO template was used for molecular separation.
Co-reporter:K. P. Prajitha, S. Chithiravel, K. Krishnamoorthy and S. K. Asha
Journal of Materials Chemistry A 2014 vol. 2(Issue 46) pp:9882-9891
Publication Date(Web):02 Oct 2014
DOI:10.1039/C4TC01806K
A homologous series of pentadecyl phenol functionalized perylenebisimide (PBI) terminated with trialkoxy gallate esters was synthesized, where the terminal alkyl chain length was varied from n = 4 to 12 (PBI-En). The thermotropic liquid crystalline (LC) characteristics of the molecules were analyzed using differential scanning calorimetry (DSC), polarized light microscopy (PLM) combined with variable temperature wide angle X-ray diffraction (WXRD) techniques. A clear odd–even oscillation was observed in the melting as well as isotropization enthalpies as a function of alkyl spacer length in the terminal gallate unit, with the even spacers exhibiting higher values. The higher members of the series with n > 8 exhibited thermotropic liquid crystalline textures in the PLM, which remained stable until room temperature. The nature of the LC phase was identified to be columnar rectangular and columnar hexagonal based on detailed analysis of the WXRD pattern recorded in the LC phase. The WXRD pattern of the room temperature LC frozen samples indicated a nearly constant intra columnar stack distance of ∼3.7 Å for all the members. The space-charge-limited current (SCLC) values of the LC frozen sample films were analyzed for dependence of the bulk mobility estimate on the nature of the LC phase. The columnar hexagonal phase exhibited a mobility value one order (10−3 cm2 V−1 s−1) higher than that of crystalline (10−4 cm2 V−1 s−1) and two orders higher than that of columnar rectangular phase (10−5 cm2 V−1 s−1), indicating a strong dependence of packing on bulk mobility.
Co-reporter:Chayanika Das and Kothandam Krishnamoorthy
Chemical Communications 2014 vol. 50(Issue 44) pp:5905-5908
Publication Date(Web):07 Apr 2014
DOI:10.1039/C4CC00841C
Nanotubes with variable hydrophobic interiors were prepared by disassembling anionic micelles in the inner walls of positive charge bearing conjugated polymer nanotubes.
Co-reporter:Arulraj Arulkashmir, Bhanprakash Jain, Jino C. John, Kanak Roy and Kothandam Krishnamoorthy
Chemical Communications 2014 vol. 50(Issue 3) pp:326-328
Publication Date(Web):28 Oct 2013
DOI:10.1039/C3CC45391J
Chemical doping of an electron transporter results in the formation of a radical anion containing semiconductor which showed high electron mobility (13 cm2 V−1 s−1) at low operating voltage (1 V).
Co-reporter:Saumya Singh, Vijay Venugopalan and Kothandam Krishnamoorthy
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 26) pp:13376-13382
Publication Date(Web):22 Apr 2014
DOI:10.1039/C4CP01098A
Judiciously chosen side chains of conjugated molecules have a positive impact on charge transport properties when used as the active material in organic electronic devices. Amongst the side chains, oligoethylene glycols (OEGs) have been relatively unexplored due to their hydrophilic nature. OEGs also affect the smooth film formation of conjugated molecules, which preclude device fabrication. However, X-ray diffraction studies have shown that OEGs facilitate intermolecular contact, which is a desirable property for the fabrication of organic electronic devices. Thus the challenge is to design and synthesize organic solvent soluble and uniform film forming conjugated molecules with OEG side chains. We have designed and synthesized conjugated small molecules (CSMs) comprising BODIPY as acceptor and triphenylamine as donor with an OEG side chain. This molecule forms smooth films when processed from organic solvents. In order to understand the impact of the OEG side chain, we have also synthesized alkyl chain analogs. All the molecules exhibit exactly the same HOMO and LUMO energy levels, but the packing in the solid state is different. CSM with methyl side chains exhibit an inter planar distance of 4.15 Å. Contrary to this, the OEG side chain containing CSM showed an inter planar spacing of 4.30 Å, which is 0.2 Å less than the alkyl side chain comprising CSMs. Please note that the length of the hydrophobic and hydrophilic side chains is the same. Interestingly, the OEG side chain comprising CSM showed two orders of higher hole carrier mobilities compared to all the other derivatives. The same molecule also showed an extremely low threshold voltage of −0.27 V indicating the OEG side chains' favourable interaction between substrate as well as between molecules.
Co-reporter:Satej S. Dharmapurikar, Arulraj Arulkashmir, Chayanika Das, Pooja Muddellu, and Kothandam Krishnamoorthy
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 15) pp:7086
Publication Date(Web):June 28, 2013
DOI:10.1021/am401379a
Small molecules and oligomers can be synthesized with very high purity and precise molecular weights, but they often do not form uniform thin films while processed from solution. Decreased intermolecular contacts between the small molecules are another disadvantage. To increase the intermolecular contacts in small molecules, we have chosen i-indigo, as one of the conjugated molecular units. The electron poor i-indigo has been connected with electron rich triphenylamine to synthesize a donor–acceptor–donor type small molecule. The propeller shaped triphenylamine helps to increase the solubility of the small molecule as well as isotropic charge transport. The intermolecular spacing between the molecules has been found to be low and did not vary as a function of thermal annealing. This implies that the intermolecular contacts between the small molecules are enhanced, and they do not vary as a function of thermal annealing. Organic field effect transistors (OFET) fabricated using a small molecule exhibited a hole carrier mobility (μ) of 0.3 cm2/(V s) before thermal annealing. A marginal increase in μ was observed upon thermal annealing at 150 °C, which has been attributed to changes in thin film morphology. The morphology of the thin films plays an important role in charge transport in addition to the intermolecular spacing that can be modulated with a judicious choice of the conjugated molecular unit.Keywords: hole mobility; i-indigo; organic field effect transistor; quadrupole interaction; small molecules; triphenylamine;
Co-reporter:Arulraj Arulkashmir, Rajashree Y. Mahale, Satej S. Dharmapurikar, Manoj K. Jangid and Kothandam Krishnamoorthy
Polymer Chemistry 2012 vol. 3(Issue 6) pp:1641-1646
Publication Date(Web):30 Apr 2012
DOI:10.1039/C2PY20146A
Metalloporphyrins and metal free porphyrins have been explored as active materials in field effect transistors. Amorphous forms of these porphyrins are preferred over their crystalline analogue due to the ease of solution processability. To achieve solution processability, a metalloporphyrin was anchored on a vinyl polymer by taking advantage of the supramolecular interaction between the metal and the pyridine moiety of the polymer. Non covalent bonding was preferred because it provides an opportunity to better manipulate the polymer's properties compared to its covalent bonding analogue. The binding between the porphyrin and the polymer was optimised in solution and the supramolecular complex was spun on various substrates to form thin films. The porphyrin was found to be uniformly distributed throughout the polymer films contrary to the existing approaches, wherein small molecule phase segregates in the polymer film. Field effect transistors were fabricated using the porphyrin-polymer complex and the device parameters were measured at atmospheric condition. The devices annealed at 80 °C showed hole carrier mobility of 2.0 × 10−4 cm2 V−1 s−1 with charge trapping at the dielectric semiconductor interface. Furthermore, the high carrier mobility observed at low temperature annealing makes this supramolecular complex an attractive candidate to explore in flexible substrates.
Co-reporter:Rajashree Y. Mahale, Arulraj Arulkashmir, Kingshuk Dutta and Kothandam Krishnamoorthy
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 13) pp:4577-4583
Publication Date(Web):03 Feb 2012
DOI:10.1039/C2CP23544G
The impact of electron transfer (ET) from a series of band edge modulated polymers to atmospheric oxygen is examined in connection with substrate oxidation prevention. Polymers with the highest occupied molecular orbital (HOMO) energy level below and above the oxygen energy level were tested and the former showed better efficiency. Furthermore, the oxidation prevention efficiency of a polymer with lower HOMO increased by two orders of magnitude, when the pores on the film were filled with spherical molecules, [6,6]-phenyl-C61-butyric acid methyl ester. We found that the polymer surface hydrophobicity has little or no influence on oxidation prevention. It is interesting to note that a polymer with a hole mobility of 8 × 10−10 cm2 V−1 s−1 showed a two-fold increase in oxidation prevention efficiency compared to a polymer with a hole mobility of 6 × 10−5 cm2 V−1 s−1. Over all, from the concerted approach, we conclude that a polymer devoid of pores with the HOMO energy level below oxygen and low charge carrier mobility is a suitable candidate for prevention of substrate oxidation/corrosion.
Co-reporter:Kingshuk Dutta, Rajashree Y. Mahale, Arulraj Arulkashmir, and Kothandam Krishnamoorthy
Langmuir 2012 Volume 28(Issue 26) pp:10097-10104
Publication Date(Web):June 12, 2012
DOI:10.1021/la301760a
Supramolecular complexes involving nanoscopic amphiphilic assemblies (AAs) and polyelectrolytes have been used to prepare a variety of materials, wherein the dynamic AAs retain the structural features, but the polyelectrolytes undergo conformational changes. Here we show that a charge bearing rigid conjugated polymer can alter the structural features and disassemble AAs. We also demonstrate reversible assembly and disassembly of AAs by controlling the number of charges on the rigid polymer. During the disassembly, the guest molecules sequestered in the AAs are released. The rate of release has been modulated by changing the morphology of the charge bearing polymer. Concomitant to the AAs disassembly, the polymer surface becomes hydrophobic due to the binding of the amphiphiles on the charges of the polymer backbone. By controlling the charges on the polymer, the surface wettability was varied gradually from hydrophilic to hydrophobic.
Co-reporter:K. P. Prajitha, S. Chithiravel, K. Krishnamoorthy and S. K. Asha
Journal of Materials Chemistry A 2014 - vol. 2(Issue 46) pp:NaN9891-9891
Publication Date(Web):2014/10/02
DOI:10.1039/C4TC01806K
A homologous series of pentadecyl phenol functionalized perylenebisimide (PBI) terminated with trialkoxy gallate esters was synthesized, where the terminal alkyl chain length was varied from n = 4 to 12 (PBI-En). The thermotropic liquid crystalline (LC) characteristics of the molecules were analyzed using differential scanning calorimetry (DSC), polarized light microscopy (PLM) combined with variable temperature wide angle X-ray diffraction (WXRD) techniques. A clear odd–even oscillation was observed in the melting as well as isotropization enthalpies as a function of alkyl spacer length in the terminal gallate unit, with the even spacers exhibiting higher values. The higher members of the series with n > 8 exhibited thermotropic liquid crystalline textures in the PLM, which remained stable until room temperature. The nature of the LC phase was identified to be columnar rectangular and columnar hexagonal based on detailed analysis of the WXRD pattern recorded in the LC phase. The WXRD pattern of the room temperature LC frozen samples indicated a nearly constant intra columnar stack distance of ∼3.7 Å for all the members. The space-charge-limited current (SCLC) values of the LC frozen sample films were analyzed for dependence of the bulk mobility estimate on the nature of the LC phase. The columnar hexagonal phase exhibited a mobility value one order (10−3 cm2 V−1 s−1) higher than that of crystalline (10−4 cm2 V−1 s−1) and two orders higher than that of columnar rectangular phase (10−5 cm2 V−1 s−1), indicating a strong dependence of packing on bulk mobility.
Co-reporter:Chayanika Das and Kothandam Krishnamoorthy
Chemical Communications 2014 - vol. 50(Issue 44) pp:NaN5908-5908
Publication Date(Web):2014/04/07
DOI:10.1039/C4CC00841C
Nanotubes with variable hydrophobic interiors were prepared by disassembling anionic micelles in the inner walls of positive charge bearing conjugated polymer nanotubes.
Co-reporter:Rajashree Y. Mahale, Arulraj Arulkashmir, Kingshuk Dutta and Kothandam Krishnamoorthy
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 13) pp:NaN4583-4583
Publication Date(Web):2012/02/03
DOI:10.1039/C2CP23544G
The impact of electron transfer (ET) from a series of band edge modulated polymers to atmospheric oxygen is examined in connection with substrate oxidation prevention. Polymers with the highest occupied molecular orbital (HOMO) energy level below and above the oxygen energy level were tested and the former showed better efficiency. Furthermore, the oxidation prevention efficiency of a polymer with lower HOMO increased by two orders of magnitude, when the pores on the film were filled with spherical molecules, [6,6]-phenyl-C61-butyric acid methyl ester. We found that the polymer surface hydrophobicity has little or no influence on oxidation prevention. It is interesting to note that a polymer with a hole mobility of 8 × 10−10 cm2 V−1 s−1 showed a two-fold increase in oxidation prevention efficiency compared to a polymer with a hole mobility of 6 × 10−5 cm2 V−1 s−1. Over all, from the concerted approach, we conclude that a polymer devoid of pores with the HOMO energy level below oxygen and low charge carrier mobility is a suitable candidate for prevention of substrate oxidation/corrosion.
Co-reporter:Vediappan Sudhakar, Arulraj Arulkashmir and Kothandam Krishnamoorthy
Chemical Communications 2017 - vol. 53(Issue 49) pp:NaN6632-6632
Publication Date(Web):2017/05/25
DOI:10.1039/C7CC03276E
Dye regeneration was improved by using an optimum quantity of graphene, which was dispersed in a polymer that suppresses back electron transfer. Using this approach, DSSCs with an efficiency of 10.4% have been fabricated.
Co-reporter:Manik E. Bhosale, Rajith Illathvalappil, Sreekumar Kurungot and Kothandam Krishnamoorthy
Chemical Communications 2016 - vol. 52(Issue 2) pp:NaN318-318
Publication Date(Web):2015/10/22
DOI:10.1039/C5CC08148C
Conjugated porous polymers were used as precursors to prepare nitrogen and sulphur doped carbon atoms, which were then used for oxygen reduction and energy storage.
Co-reporter:Arulraj Arulkashmir and Kothandam Krishnamoorthy
Chemical Communications 2016 - vol. 52(Issue 17) pp:NaN3489-3489
Publication Date(Web):2016/01/22
DOI:10.1039/C5CC09603K
A transparent, conducting and low surface energy surface was prepared by disassembly of anionic micelles, which altered the orientation of the donor polymer and imparted gradation between the donor and acceptor. This configuration increased the solar cell device efficiency.
Co-reporter:Chayanika Das, Bhanprakash Jain and Kothandam Krishnamoorthy
Chemical Communications 2015 - vol. 51(Issue 58) pp:NaN11664-11664
Publication Date(Web):2015/06/08
DOI:10.1039/C5CC03108G
Polyphenols from green tea were used to electrolessly deposit gold on silk cocoons (SCs) and nanoporous aluminum oxide (AAO) templates. The gold coated cocoons were used as electrodes in supercapacitors and showed a capacitance as high as 254 F g−1 and a specific power of 2287 W kg−1. A metal coated AAO template was used for molecular separation.
Co-reporter:Arulraj Arulkashmir, Bhanprakash Jain, Jino C. John, Kanak Roy and Kothandam Krishnamoorthy
Chemical Communications 2014 - vol. 50(Issue 3) pp:NaN328-328
Publication Date(Web):2013/10/28
DOI:10.1039/C3CC45391J
Chemical doping of an electron transporter results in the formation of a radical anion containing semiconductor which showed high electron mobility (13 cm2 V−1 s−1) at low operating voltage (1 V).
Co-reporter:Saumya Singh, Vijay Venugopalan and Kothandam Krishnamoorthy
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 26) pp:NaN13382-13382
Publication Date(Web):2014/04/22
DOI:10.1039/C4CP01098A
Judiciously chosen side chains of conjugated molecules have a positive impact on charge transport properties when used as the active material in organic electronic devices. Amongst the side chains, oligoethylene glycols (OEGs) have been relatively unexplored due to their hydrophilic nature. OEGs also affect the smooth film formation of conjugated molecules, which preclude device fabrication. However, X-ray diffraction studies have shown that OEGs facilitate intermolecular contact, which is a desirable property for the fabrication of organic electronic devices. Thus the challenge is to design and synthesize organic solvent soluble and uniform film forming conjugated molecules with OEG side chains. We have designed and synthesized conjugated small molecules (CSMs) comprising BODIPY as acceptor and triphenylamine as donor with an OEG side chain. This molecule forms smooth films when processed from organic solvents. In order to understand the impact of the OEG side chain, we have also synthesized alkyl chain analogs. All the molecules exhibit exactly the same HOMO and LUMO energy levels, but the packing in the solid state is different. CSM with methyl side chains exhibit an inter planar distance of 4.15 Å. Contrary to this, the OEG side chain containing CSM showed an inter planar spacing of 4.30 Å, which is 0.2 Å less than the alkyl side chain comprising CSMs. Please note that the length of the hydrophobic and hydrophilic side chains is the same. Interestingly, the OEG side chain comprising CSM showed two orders of higher hole carrier mobilities compared to all the other derivatives. The same molecule also showed an extremely low threshold voltage of −0.27 V indicating the OEG side chains' favourable interaction between substrate as well as between molecules.
