Showing papers on "Excimer published in 1974"
TL;DR: A new (optical) method of diffusion measurement is described which allows the determination of the coefficient of lateral diffusion, Ddiff, of aromatic molecules in the hydrophobic region of lipid bilayers using pyrene as a fluorescence probe.
368 citations
TL;DR: In this article, a statistical model based on the rotational isomeric state approximation is used to formulate an expression for the fraction of excimer forming sites in the solid systems, which is consistent with an activated exciton migration to preformed excimer sites.
Abstract: Excimer formation has been examined in solid films of poly(2‐vinylnaphthalene) (P2VN) and polystyrene (PS) as a function of sample temperature from 373 to 4.2°K and film preparation temperature between 373 and 295°K. The concentration of suitable excimer forming sites in the solid state is fixed by the temperature at which the film is cast. A statistical model based on the rotational isomeric state approximation is used to formulate an expression for the fraction of excimer forming sites in the solid systems. This model makes use of the excimer site conformation energy, found to be 2500 cal for P2VN. Excimer sampling in solid solution is shown to be consistent with an activated exciton migration to preformed excimer sites. The mechanism for this process is attributed to a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. A semianalytical expression for the enhancement of the excitation migration is developed which has the same general form as the experimental results. The effective vibrational frequency is found to be 157 cm−1 for PS and 84 cm−1 for P2VN.
86 citations
01 Dec 1974
TL;DR: In this article, a general method for evaluation of equilibrium geometries and vibronic transition intensities of crystalline excimers is described, which provides realistic potential surfaces which include, in addition to the α electron surfaces, also the repulsive hard core of the α electrons and the effect of the crystal potential.
Abstract: A general method for evaluation of equilibrium geometries and vibronic transition intensities of crystalline excimers is described. The method provides realistic potential surfaces which include, in addition to the α electron surfaces, also the repulsive hard core of the α electrons and the effect of the crystal potential. The method is applied to the study of the potential surfaces of the pyrene excimer, both in the crystal and in the gas phase. The method is also used for a direct evaluation of the vibronic structure of the excimer emission. The calculations reproduce the main experimentally observed properties including the structureless envelope of the emission band and the temperature dependence of its line width.
76 citations
TL;DR: In this paper, the emission properties of various carbazole double molecules in solution have been investigated, and the 1,3-bis(N−carbazolyl) propane, a useful model coumpound for poly(N·vinylcarbazole), was studied in detail.
Abstract: The emission properties of various carbazole ``double'' molecules in solution have been investigated. One compound in particular, namely 1,3‐bis(N‐carbazolyl) propane, a useful model coumpound for poly(N‐vinylcarbazole), has been studied in detail. Both steady state and transient measurements are utilized to determine rate and thermodynamic parameters for the formation of intramolecular excimers. Results on other model coumpounds in which the carbazole groups are symmetrically or unsymmetrically attached to the 1,3 positions of a propane chain are used to offer qualitative insight regarding the geometry of the intramolecular excimer state.
62 citations
TL;DR: In this paper, the pyrene excimer fluorescence seen in poly(methyl methacrylate) at high concentrations does not arise from microcrystallites but from pairs of molecules close to the excimer configuration.
Abstract: It is shown that the pyrene excimer fluorescence seen in poly(methyl methacrylate) at high concentrations does not arise from microcrystallites but from pairs of molecules close to the excimer configuration. The yield of this fluorescence is enhanced by aggregation. The aggregation is caused by an attraction between ground state molecules due to long range dispersion forces (van der Waals forces). These forces also account for an observed broadening and red shift in the absorption.
50 citations
TL;DR: In this paper, the time development in the nanosecond range of the intramolecular excimer fluorescence of 1,3-dinaphthylpropane was studied using a single-photon counting technique.
40 citations
TL;DR: In this paper, the excited equilibrium state of charge transfer molecular complexes in polar solvents is described by the use of the nonlinear Schrodinger equation presented in our previous paper.
Abstract: The excited equilibrium state of molecular complex in solution is described by the use of the nonlinear Schrodinger equation presented in our previous paper. The excited equilibrium state of charge-transfer molecular complex or the equilibrium state of exciplex in polar solvents is quite polar and quite different from the excited Franck-Condon state, and has large tendency to dissociate to solvated ions. These theoretical results are confirmed by the laser photolysis experiments on the excited states of the molecular complexes.
34 citations
TL;DR: In this paper, the authors show that 4-thiouridine (4TU) exhibits a weak unusual luminescence, the quantum yield of which is 3 × 10-4 at 25°C.
Abstract: — In bidistilled water, 4-thiouridine (4TU) exhibits a weak unusual luminescence, the quantum yield of which is 3 × 10-4 at 25°C. The excitation spectrum corresponds well to the 4TU absorption spectrum. The emission lies at longer wavelengths (Λmax 550 nm) than the 4TU phosphorescence observed at 77 K (Λmax, 470–480 nm). From the emission signal obtained after an excitation flash of 3 ns half-width, an “apparent” rate constant for the radiative deactivation process, shorter than 5 × 106 s, can be inferred. The 300 K emission is efficiently quenched by halides and by oxygen: quenching involves a long-lived intermediate (⋍ 200 ns).
Clearly the emissive state X is populated through the S0-S1 electronic transition ππ* of 4TU. The nature of X cannot be unambiguously determined: it cannot be an excimer but can be either the 4TU triplet state or another chemical state distinct from the 4TU excited singlet or triplet states.
An interesting finding is that the 300 K emission and the ability of 4TU to photoreact are related: they are quenched with the same efficiency by halide anions. This indicates that quenching occurs at the same long-lived intermediate species, which is either a precursor of the emitter or the emitter itself.
32 citations
TL;DR: In this paper, the excited states of CO, H 2 O and NH 3 have been calculated by the singly excited configuration interaction method using two large basis sets, one of which contained diffuse functions in order to describe Rydberg states.
31 citations
TL;DR: In this article, the authors investigated the efficiency of vacuum ultraviolet generation for solid Ar, Kr and Xe excited by 10-30 kV electrons. And they found that the presence of trace amounts of O2was found to cause energy transfer from the excimer bands to longer wavelengths.
31 citations
TL;DR: In this article, a previous report to the effect that the self-sensitised photo-peroxidation of 1,3-diphenylisobenzofuran in solution proceeds at a rate independent of acceptor concentration when this is very low has been confirmed and interpreted in terms of a re-encounter of O 2 1 Δ g and ground state acceptor molecules generated in the same triplet-triplet annihilation act.
TL;DR: In this article, the use of magnetic field effects in delayed fluorescence (DF) and electrogenerated chemiluminescence (ECL) studies to obtain information about the involvement of triplet state species in reactions leading to the production of monomeric and dimeric (excimer or exciplex) excited states is described.
TL;DR: In this article, a theoretical treatment of the collisional ionization of a highly excited atom with a molecule is improved by use of the exact form factor of the hydrogen atom in highly excited states.
TL;DR: In this article, the fluorescence emission spectra and fluorescence decay times of amorphous films prepared by evaporation of a number of aromatic hydrocarbons on to a substrate cooled with liquid nitrogen were measured.
TL;DR: In this article, a statistical model for the excimer forming site fraction in fluid and rigid solutions of poly(4-vinylbiphenyl) (PVBP) over the temperature range 373-77°K was presented.
Abstract: Excimer formation has been examined in fluid and rigid solutions of poly(4‐vinylbiphenyl) (PVBP) over the temperature range 373–77°K. The concentration of suitable excimer‐forming sites is fixed by the temperature at which the film is cast. A statistical model for the excimer‐forming site fraction was previously developed for poly(2‐vinylnaphthalene) (P2VN) and is now shown to satisfactorily fit the PVBP data, using the excimer site conformation energy of 800 cal. Furthermore, as was previously demonstrated for P2VN and polystyrene (PS), excimer sampling in the rigid solution is shown to arise from an activated exciton migration to preformed excimer sites. The proposed mechanism for this process involves a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. An effective vibrational frequency for this process has been determined to be 150±30 cm−1 for PVBP. Finally, excimer sampling mechanisms for fluid and rigid solutions are compared in terms of qualitative potential energy concepts.
TL;DR: In this paper, a series of aromatic hydrocarbons was quenched by the addition of fumaronitrile, which is consistent with the charge-transfer or electron-transfer mechanism.
Abstract: The fluorescence of a series of aromatic hydrocarbons was quenched by the addition of fumaronitrile, which is consistent with the charge-transfer or electron-transfer mechanism. The fluorescence quenching was accompanied by the appearance of a new, broad structureless emission band attributed to the fluorescence from the exciplex in non-polar or slightly polar solvents. In highly polar solvents only quenching of the fluorescence occurred. The energies of the band maxima of the exciplex fluorescences and the magnitude of the ionization potentials of a series of fluorescers showed a good correlation with each other. Solvent and temperature dependence of the exciplex fluorescence was examined and discussed. The present aromatic hydrocarbon-fumaronitrile system also formed a charge-transfer complex in their ground states at relatively high concentrations of each component. The selective excitation of the ground state charge-transfer complex gave rise to the fluorescence emission in a fluid solution at room te...
TL;DR: In this paper, it is shown that by taking into account anhormonicity, it is possible to explain why, in ground-to-excimer absorption in pyrene, the non-phonon peak can be resolved whereas the other peaks are overlapped.
TL;DR: In this paper, the authors measured the phosphorescence spectrum of naphthalene in fluid isooctane solution in the temperature range of 80 to 100°C and ascribe it to the triplet excimer of the triplets.
Abstract: The phosphorescence spectrum of naphthalene has been measured in fluid isooctane solution in the temperature range of 80 to −100°C The spectrum is essentially different from that obtained in rigid solution at 77K, and is ascribable to phosphorescence from the triplet excimer of naphthalene An analysis of the experimental results suggests that the radiative rate constant for the triplet decay is enhanced as a result of the formation of the triplet excimer
TL;DR: In this article, a modified model for excimer absorption and emission is proposed, based on vibrational relaxation to the bath, while invalid for highly excited vibrational levels at low temperatures, is valid at high temperature.
TL;DR: In this article, the fluorescence spectra of poly-α-methylstyrene (PMS) and of copolymers of general structure have been compared, and it is shown that at room temperature in the same solvent, excimer fluorescence is not observed for the condensation copolymer, in agreement with the results obtained by Hirayama on α, ω-diphenylalkanes.
TL;DR: In this article, the authors interpreted the appearance of new broad bands, decreased lifetimes and a marked decrease in the quantum yield of the triplet state of 1:2-benzanthracene as arising from triplet excimer formation.
TL;DR: The large temperature dependence of the fluorescence maximum of (-)-bornyl 9-anthryl-3-propanoate is interpreted in terms of anharmonicity of thermally populated excimer vibrational levels.
TL;DR: In this article, the low-temperature phosphorescence spectrum of poly-3,6-dibromo-N-vinyl carbazole was observed in rigid solution.
Abstract: Excimer phosphorescence is observed in the lowtemperature phosphorescence spectrum of poly-3,6-dibromo-N-vinylcarbazole in rigid solution.
TL;DR: In this paper, the radiative decay processes of the excited monomer singlet and excimer states of o -xylene in solution have been examined as functions of temperature and concentration, and the fluorescence rate constants for both states are independent of temperature.
TL;DR: In this paper, the authors used the Phosphorescence-Microwave Double Resonance (PMDR) technique to study the triplet of hexachlorebenzene (HCB) at 1.6 K and found that the emission is due to a species involving HCB itself.
TL;DR: In this article, the quenching of the first excited singlet states of benzenes subsituted with the F, CH3 and CF3 groups in the vapour phase by O2, NO, diolefins, and simple ketones is reported.
Journal Article•
TL;DR: In this paper, the effect of additive scintillator solutes on the degradation of polyvinyltoluene (PVT) excimer fluorescence arising from the irradiation by uv light has been investigated in monomer-free PVT systems.
Abstract: The protective effect of additive scintillator solutes on the degradation of polyvinyltoluene (PVT) excimer fluorescence arising from the irradiation by uv light has been investigated in monomer-free PVT systems. In these monomer-free systems, the fluorescence degradation of additive solutes is more intense than that of PVT excimer, and the degradation of PVT excimer fluorescence is protected by the addition of small amounts of anthracene or POPOP. The observed fluorescence degradation and protective effect are explained by a quenching model.