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Nitin Chattopadhyay - One of the best experts on this subject based on the ideXlab platform.
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differential forster resonance energy transfer from the Excimers of poly n vinylcarbazole to coumarin 153
Journal of Physical Chemistry B, 2012Co-Authors: Debanjana Ghosh, Nilashis Nandi, Nitin ChattopadhyayAbstract:Photophysics of the nonconjugated vinyl polymer poly(N-vinylcarbazole) (PNVC) has been explored in the presence of coumarin 153 (C153) exploiting steady state and time-resolved fluorometric techniques. Dual emission from the two distinct Excimers of PNVC adds importance to the study and makes it interesting. The study substantiates the occurrence of Forster resonance energy transfer (FRET) from PNVC to C153. The differential involvement of the two Excimers in the energy transfer process has been established. Considering the fact that FRET is a long distance dipole induced phenomenon, this differential effect has been rationalized from a difference in the dipole moments of the two Excimers. Determination of the quenching constants reveals an order of magnitude more quenching of the high energy Excimer than the low energy one in the presence of the quencher C153.
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characterization of the Excimers of poly n vinylcarbazole using tranes
Journal of Luminescence, 2011Co-Authors: Debanjana Ghosh, Nitin ChattopadhyayAbstract:Time-resolved emission spectra (TRES) and time-resolved area normalized emission spectra (TRANES) are exploited to characterize the Excimers of poly(N-vinylcarbazole) (PNVC) in toluene and water. The time-resolved study together with the steady state measurements, decipher the fluorescence of the system containing pendant carbazole moieties in the polymer backbone unambiguously. Isoemissive point in the TRANES establishes that there are only two Excimers of PNVC, the partially overlapped Excimer emitting at high energy and the sandwich type Excimer emitting at lower energy, and they are formed exclusively in the photoexcited state. The study substantiates an equilibrium between the two Excimers.
Zbigniew Szamel - One of the best experts on this subject based on the ideXlab platform.
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The nature of trapping sites and recombination centres in PVK and PVKPBD electroluminescent matrices seen by spectrally resolved thermoluminescence
Journal of Physics D: Applied Physics, 2010Co-Authors: Ireneusz Glowacki, Zbigniew SzamelAbstract:Two electroluminescent polymer matrices: poly(N-vinylcarbazole) (PVK) and PVK with 40 wt % of 2-tert-butylphenyl-5-biphenyl–1, 3, 4-oxadiazole (PBD) were studied using spectrally resolved thermoluminescence (SRTL) in temperature range 15-325 K. The comparison of the SRTL results with the electroluminescence (EL) spectra has allowed identifying the localized (trapping) sites and the radiative recombination centres present in the investigated matrices. In the neat PVK films deep traps with a depth about 200 meV, related to triplet Excimers dominate, while in the PVK–PBD (40 wt %) blend films the traps that are related to triplet exciplexes formed by the carbazole groups and the PBD molecules dominate. Depth of the traps in the PVK–PBD blend is somewhat lower than that in the neat PVK. An analysis of the EL spectra shows that in the PVK and in the PVK–PBD blend the dominant radiative centres are singlet Excimers and singlet exciplexes, respectively. However in the neat PVK some contributions of the triplet monomer and the triplet Excimer states in the electroluminescence were also detected.
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The nature of trapping sites and recombination centres in PVK and PVK–PBD electroluminescent matrices seen by spectrally resolved thermoluminescence
Journal of Physics D: Applied Physics, 2010Co-Authors: Ireneusz Glowacki, Zbigniew SzamelAbstract:Two electroluminescent polymer matrices poly(N-vinylcarbazole) (PVK) and PVK with 40 wt% of 2-tert-butylphenyl-5-biphenyl–1,3,4-oxadiazole (PBD) were studied using spectrally resolved thermoluminescence (SRTL) in the temperature range 15–325 K. The comparison of the SRTL results with the electroluminescence (EL) spectra has allowed identification of the localized (trapping) sites and the radiative recombination centres present in the investigated matrices. In the neat PVK films deep traps with a depth about 200 meV, related to triplet Excimers dominate, while in the PVK–PBD (40 wt%) blend films the traps that are related to triplet exciplexes formed by the carbazole groups and the PBD molecules dominate. Depth of the traps in the PVK–PBD blend is somewhat lower than that in the neat PVK. An analysis of the EL spectra shows that in the PVK and in the PVK–PBD blend the dominant radiative centres are singlet Excimers and singlet exciplexes, respectively. However, in the neat PVK some contributions of the triplet monomer and the triplet Excimer states in the EL were also detected.
Edward C. Lim - One of the best experts on this subject based on the ideXlab platform.
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A theoretical study of the structure and energetics of stacked dimers of polycyclic aromatic hydrocarbons. Application of INDO 1/S method to singlet Excimers of naphthalene and phenanthrene
Chemical Physics Letters, 1994Co-Authors: Rovshan G. Sadygov, Edward C. LimAbstract:Abstract We show here that, with the incorporation of intermolecular distance dependence of π—σ interactions, the INDO 1/S method promises to be a very useful tool for investigating the structure and energetics of singlet Excimers of polycyclic aromatic hydrocarbons. Application of the method to naphthalene yields binding energies and vertical transition energies (in absorption and in emission) of the singlet Excimer which are in good agreement with experiment. The method also provides a possible explanation for the failure of phenanthrene to exhibit Excimer fluorescence or the self-quenching of the monomer fluorescence.
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Photoassociation and photoinduced charge transfer in bridged diaryl compounds. 6. Intramolecular triplet Excimers of dicarbazolylalkanes and their comparison to an intermolecular triplet Excimer of carbazole
The Journal of Physical Chemistry, 1994Co-Authors: Jianjian Cai, Edward C. LimAbstract:A time-resolved emission study of intramolecular triplet Excimer formation has been carried out for dicarbazolylmethane (DCM) and dicarbazolylpropane (DCP) in fluid solution at room temperature. The triplet Excimer formation was deduced from the comparison of the phosphorescence with the corresponding emission from the intermolecular triplet Excimer of carbazole. It has been found that whereas the triplet Excimer formation in DCP is evident in both polar and nonpolar solvents, the Excimer formation in DCM is observed only in polar solvents at longer delay times. The result indicates that the conformation favored by the triplet Excimer is more readily attainable in DCP than in DCM. The enhancement of the triplet Excimer formation by polar solvent, which is also observed for carbazole, suggests that the triplet Excimers are stabilized (at least in part) by charge resonance interactions. Comparison of the temporal characteristics of the normal delayed fluorescence of DCP with those of the corresponding Excimer phosphorescence suggests that the delayed fluorescence at long delay times is produced by bimolecular annihilation of the intramolecular triplet Excimers. This in turn implies that the excited singlet-state species produced by bimolecular annihilation of the triplet Excimers is unstable and rearranges into monomeric (i.e., non-interacting) conformation prior tomore » its decay by emission of radiation. 16 refs., 7 figs.« less
Debanjana Ghosh - One of the best experts on this subject based on the ideXlab platform.
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differential forster resonance energy transfer from the Excimers of poly n vinylcarbazole to coumarin 153
Journal of Physical Chemistry B, 2012Co-Authors: Debanjana Ghosh, Nilashis Nandi, Nitin ChattopadhyayAbstract:Photophysics of the nonconjugated vinyl polymer poly(N-vinylcarbazole) (PNVC) has been explored in the presence of coumarin 153 (C153) exploiting steady state and time-resolved fluorometric techniques. Dual emission from the two distinct Excimers of PNVC adds importance to the study and makes it interesting. The study substantiates the occurrence of Forster resonance energy transfer (FRET) from PNVC to C153. The differential involvement of the two Excimers in the energy transfer process has been established. Considering the fact that FRET is a long distance dipole induced phenomenon, this differential effect has been rationalized from a difference in the dipole moments of the two Excimers. Determination of the quenching constants reveals an order of magnitude more quenching of the high energy Excimer than the low energy one in the presence of the quencher C153.
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characterization of the Excimers of poly n vinylcarbazole using tranes
Journal of Luminescence, 2011Co-Authors: Debanjana Ghosh, Nitin ChattopadhyayAbstract:Time-resolved emission spectra (TRES) and time-resolved area normalized emission spectra (TRANES) are exploited to characterize the Excimers of poly(N-vinylcarbazole) (PNVC) in toluene and water. The time-resolved study together with the steady state measurements, decipher the fluorescence of the system containing pendant carbazole moieties in the polymer backbone unambiguously. Isoemissive point in the TRANES establishes that there are only two Excimers of PNVC, the partially overlapped Excimer emitting at high energy and the sandwich type Excimer emitting at lower energy, and they are formed exclusively in the photoexcited state. The study substantiates an equilibrium between the two Excimers.
V A Kochelap - One of the best experts on this subject based on the ideXlab platform.
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vibrational relaxation of Excimers
Physics-Uspekhi, 1998Co-Authors: V V Datsyuk, I A Izmailov, V A KochelapAbstract:A review of the vibrational relaxation of Excimers is presented. Various kinetic models used in the literature to interpret experimental data and to model Excimer lasers are discussed. Of these, those based on the Fokker?Planck diffusion equation are the most general due to the essentially nonequilibrium population of the hundreds of high vibrational levels and because of the multiquantum nature of the transitions involved. Numerous manifestations of these important kinetic features are analyzed. The diffusive relaxation concept has led to an overestimate of the influence of vibrational relaxation on Excimer laser parameters, the saturant light flux and quantum yield expressions departing considerably from those commonly used. To gain insight into relaxation physics, considerable attention is given to the determination of kinetic parameters capable of adequately describing the electronic-vibration kinetics. Rate constants for Excimer vibrational relaxation are also given.
