Cheranellore Sudha Kartha
Bio: Cheranellore Sudha Kartha is an academic researcher from Cochin University of Science and Technology. The author has contributed to research in topic(s): Diffraction efficiency & HOMO/LUMO. The author has an hindex of 5, co-authored 7 publication(s) receiving 104 citation(s).
20 Jun 2004-Applied Optics
TL;DR: A methylene-blue-sensitized polymer blend of polyvinyl alcohol and polyacrylic acid is fabricated and tested for holographic recording and was found to have good characteristics such as high sensitivity, storage stability, ease of fabrication, and environmental stability.
Abstract: A methylene-blue-sensitized polymer blend of polyvinyl alcohol and polyacrylic acid is fabricated and tested for holographic recording. It was found to have good characteristics such as high sensitivity, storage stability, ease of fabrication, and environmental stability. Optimization of the ratio of polyvinyl alcohol/polyacrylic acid, the sensitizer concentration, pH, energy, diffraction efficiency measurements, etc., have been done. pH is found to have a great influence on the recovery of the dye in this matrix. The results of experimental investigations into the properties of this new material are reported.
23 Apr 2015-New Journal of Chemistry
TL;DR: In this paper, two 3,4-ethylenedioxythiophene (EDOT) based low band gap donor-acceptor (D-A) conjugated copolymers were designed and synthesized via direct arylation, in which the HOMO and LUMO gaps were fine-tuned by the regular insertion of electron deficient units, 2,1,3-benzothiadiazole (BTZ) and 2, 1,3 -benzoselenadiazoles (BTSe), respectively.
Abstract: Two 3,4-ethylenedioxythiophene (EDOT) based low band gap donor–acceptor (D–A) conjugated copolymers were designed and synthesized via direct arylation, in which the HOMO–LUMO gaps were fine-tuned by the regular insertion of electron deficient units, 2,1,3-benzothiadiazole (BTZ) and 2,1,3-benzoselenadiazole (BTSe), respectively. Structural characterization was performed by FT-IR, 1H NMR and XPS. In order to investigate the variation in the energy band structure of the copolymers, quantum-chemical calculation using density functional theory was carried out. The alternating insertion of the chalcogenadiazole unit in the PEDOT (poly(3,4-ethylenedioxythiophene)) lowers the HOMO and LUMO energy levels. As a result, the polymers with a lower band gap compared to that of the homopolymer, PEDOT, were obtained. Optical and electrochemical results confirmed that BTSe is marginally superior to BTZ in EDOT based alternate donor–acceptor copolymers. The present experimental results correlate well with HSE06 level theoretical calculations compared to those with the B3LYP level. Z-scan experiments reveal that the copolymers exhibit a strong nonlinear absorption coefficient and a nonlinear refraction coefficient of the order 10−10 esu and the third-order nonlinear susceptibility is of the order of 10−11 esu. These findings indicated that the EDOT–chalcogenadiazole copolymers can be developed into excellent third-order nonlinear optical materials.
07 Jan 2015-RSC Advances
TL;DR: In this article, the donor-acceptor (D-A) π conjugated copolymer, poly(2,5-(3,4-ethylenedioxythiophene)-alt-2,7-(9,9-dioctylfluorene)) (P(EDOT-FL)), a photoconductive and nonlinear optical material has been synthesized via a direct arylation method using palladium acetate as a catalyst and characterized.
Abstract: The donor–acceptor (D–A) π conjugated copolymer, poly(2,5-(3,4-ethylenedioxythiophene)-alt-2,7-(9,9-dioctylfluorene)) (P(EDOT–FL)), a photoconductive and nonlinear optical material has been synthesized via, a direct arylation method using palladium acetate as a catalyst and characterized. The theoretical studies along with photophysical and electrochemical studies confirmed that the copolymer exhibited a relatively lower band gap (2.29 eV) than that of polyfluorene. The photoconductivity properties of the P(EDOT–FL):PC61BM films under various illuminations were studied and high photosensitivity was observed at 488 nm. The field dependence of the photoconductivity in P(EDOT–FL):PC61BM blend films showed that the films could withstand up to 75 V μm−1 and the photosensitivity at higher electric fields was even greater than two lakh (at 75 V μm−1, the photosensitivity was 289 742). At higher electric fields, the photocurrent entered into micro ampere ranges. The intensity dependence on the photocurrent in these films was also investigated. Third-order nonlinear optical properties of P(EDOT–FL) under nanosecond laser excitation at 532 nm have been studied by a Z-scan technique. The polymer exhibited a high nonlinear absorption and refraction coefficient. The polymer also showed a good optical limiting response at 532 nm. These results provide an avenue for application of P(EDOT–FL) in photo conducting and nonlinear optical devices.
01 Feb 2016-Optical Materials
TL;DR: In this article, the potential of a metal-ion doped panchromatic photopolymer recording material for real-time holographic data storage has been evaluated in the context of holographic transmission gratings.
Abstract: Studies carried out to gauge the potential of a metal-ion doped panchromatic photopolymer recording material for application in real-time holographic data storage is presented. The photopolymer films are spin coated on glass plates to ensure better surface uniformity. Volume holographic transmission gratings with peak diffraction efficiency of 80% could be stored in the photopolymer films of 100 μm thickness. An efficiency of 70% is achievable even for gratings recorded with exposure energy as low as 10 mJ/cm 2 . A checkerboard pattern data page recorded in the photopolymer film using a defocused 4- f recording geometry could be reconstructed with good image quality. The experimental results illustrate the competency of the developed photopolymer for holographic data storage applications.
01 Mar 2015-European Polymer Journal
TL;DR: A series of low band gap 3,4-ethylenedioxythiophene (EDOT) and quinoxaline donor-acceptor (D-A) copolymers were designed and their electronic structure and properties were investigated by employing density functional theory in the periodic boundary condition using HSE06 exchange correlation functional and 6-31G basis set.
Abstract: A series of low band gap 3,4-ethylenedioxythiophene (EDOT) and quinoxaline donor–acceptor (D–A) copolymers were designed and their electronic structure and properties were investigated by employing density functional theory in the periodic boundary condition using HSE06 exchange correlation functional and 6-31G basis set. The acceptors investigated were acenaphthylene, phenyl and phenanthrene substituted quinoxaline units. DFT calculations have been performed for both monomers and model oligomers to analyse their electronic properties. The designed copolymers have been synthesized through a simple and facile method. i.e., direct arylation reaction. The photophysical and electrochemical properties of EDOT–quinoxaline copolymers were investigated. The copolymers, P(EDOT-ACEQX), P(EDOT-BZQX), and P(EDOT-PHQX) exhibited theoretical band gap of 1.81, 1.76 and 1.63 eV, respectively using the DFT/HSE06/6-31G calculation and the optical band gap of 1.80, 1.75, and 1.66 eV, respectively, according to the onset edge of lower energy peak of the polymers in solution. Electrochemical studies demonstrated that quinoxaline moieties elevated the HOMO (highest occupied molecular orbital) level and lowered the LUMO (lowest unoccupied molecular orbital) level of the PEDOT (Poly(3,4-ethylenedioxythiophene)) backbone. The theoretical and experimental evaluations revealed the regular alternation of quinoxaline moieties. The band gap of the copolymers was well correlated with the acceptor strength. The experimental results supported the theoretical predictions. The third-order nonlinear optical (NLO) properties of D–A EDOT–quinoxaline copolymers, evaluated by z-scan method with nanosecond laser beam at 532 nm, are reported. Polymers possess strong refractive effect with nonlinear refraction coefficient of −0.47 × 10 −10 , −0.95 × 10 −10 and −0.64 × 10 −10 esu, respectively. Effective third-order nonlinear susceptibilities were calculated to be 0.82 × 10 −11 , 1.46 × 10 −11 and 1.17 × 10 −11 esu, respectively. Polymers showed good optical limiting behavior due to two photon absorption (TPA). The results suggest that EDOT–quinoxaline copolymers are promising materials for third-order nonlinear optical applications.
01 Jan 2008
Abstract: The air electrode, which reduces oxygen (O2), is a critical component in energy generation and storage applications such as fuel cells and metal/air batteries. The highest current densities are achieved with platinum (Pt), but in addition to its cost and scarcity, Pt particles in composite electrodes tend to be inactivated by contact with carbon monoxide (CO) or by agglomeration. We describe an air electrode based on a porous material coated with poly(3,4-ethylenedioxythiophene) (PEDOT), which acts as an O2 reduction catalyst. Continuous operation for 1500 hours was demonstrated without material degradation or deterioration in performance. O2 conversion rates were comparable with those of Pt-catalyzed electrodes of the same geometry, and the electrode was not sensitive to CO. Operation was demonstrated as an air electrode and as a dissolved O2 electrode in aqueous solution.
10 Nov 2016-Chemical Reviews
TL;DR: This Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting and describes the known mechanisms of optical limiting for the different types of materials.
Abstract: The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the functi...
01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg
TL;DR: In this paper, the reversible photoreduction of methylene blue in acrylate media was studied using a benzyl dimethyl ketal photoinitiator upon 365 nm irradiation.
Abstract: The reversible photoreduction of methylene blue in acrylate media is studied here. Methylene blue can be photoreduced using a benzyl dimethyl ketal photoinitiator upon 365 nm irradiation. The photoreduction is due to the interaction of methylene blue with methyl radical which is generated when benzyl dimethyl ketal is photocleaved. The photoreduced polyacrylate sample exhibits reversible photoreduction behavior due to the cyclic processes of oxidation in air and reduction in nitrogen upon UV exposure. Since methylene blue is widely used across many disciplines, our results have many potential applications in sensors, data storage, electronic devices, etc.
TL;DR: A brief review of the optimisation of photopolymer materials for holographic data storage (HDS) applications is described and the key contributions of each work examined and many of the suggestions made for the improvement of the different photopolymers discussed are presented.
Abstract: Photopolymers are very interesting as optically sensitive recording media due to the fact that they are inexpensive, self-processing materials with the ability to capture low-loss, high-fidelity volume recordings of 3D illuminating patterns. We have prepared this paper in part in order to enable the recognition of outstanding issues, which limit in particular the data storage capacity in holographic data storage media. In an attempt to further develop the data storage capacity and quality of the information stored, that is, the material sensitivity and resolution, a deeper understanding of such materials in order to improve them has become ever more crucial. In this paper a brief review of the optimisation of photopolymer materials for holographic data storage (HDS) applications is described. The key contributions of each work examined and many of the suggestions made for the improvement of the different photopolymer material discussed are presented.