The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been inter...

We present a new method to measure the triplet exciton diffusion length in organic semiconductors. N,N'-di-[(1-naphthyl)-N,N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPD) has been used as a model system. Triplet excitons are injected into a thin film of NPD by a phosphorescent thin film, which is optically excited and forms a sharp interface with the NPD layer. The penetration profile of the tri...

The IR-dyes, having the absorption maximum in the range of 600 nm to 1100 nm, are expected to have very low triplet e nergy level. The triplet-triplet (T-T) absorption spectra and decay characteris tics have becn invcstigated for four IR laser dyes, namely, IR-140, IR-144, Q-Switch I and Q-Switch 5. Triplet state of these IR dyes are generated by electron pulse radiolysis in benzene-benzonitril...

We have used two-photon photoemission to probe the dynamics of the long-lived triplet excitons in pristine and photo-oxidized lms of poly[2-methoxy,5-(2'-ethylhexoxy)-1,4-phenylenevinylene] (MEH-PPV). We use a rate equation model to explain the intensity dependence of the total photoelectron yield in terms of the relaxation dynamics of the triplet excitons. Observations of the pristine lms indi...

A method is described for obtaining the rate constant of the photodegradation process of fluorophores illuminated by a focused laser beam. The explicit kinetic equations, describing the population dynamics of excited singlet and triplet states, are averaged over the illuminated volume to describe the resulting fluorescence signal. The illumination is modulated at frequencies from 1 Hz to 100 Hz...

Although oxygen is a powerful oxidant, the triplet ground state of dioxygen constitutes a kinetic barrier for oxidation of biological molecules, which are mostly singlet state (1). However, the unpaired orbitals of dioxygen can sequentially accommodate single electrons to yield O2 ., H2O2, the very reactive zOH, and water (Fig. 1, Reaction 1). The oxidative potential of atmospheric oxygen is ma...

Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H](2-) after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to...

The mechanism for the reaction of the cyanogen radical (CN) with the cyanomidyl radical (HNCN) has been investigated theoretically. The electronic structure information of the singlet and triplet potential energy surfaces (PESs) is obtained at the B3LYP/6-311+G(3df,2p) level, and the single-point energies are refined at the CCSD(T)/6-311+G(3df,2p) level as well as by multilevel MCG3-MPWB method...

This paper presents a density functional theory (DFT)/time-dependent DFT (TD-DFT) study on the lowest lying singlet and triplet excited states of 20 selected polybrominateddiphenyl ether (PBDE) congeners, with the solvation effect included in the calculations using the polarized continuum model (PCM). The results obtained showed that for most of the brominated diphenyl ether (BDE) congeners, th...

The decomposition of 1,2-dioxetanone into a CO(2) molecule and into an excited state formaldehyde molecule was studied in condensed phase, using a density functional theory approach. Singlet and triplet ground and excited states were all included in the calculations. The calculations revealed a novel mechanism for the chemiluminescence of this compound. The triplet excitation can be explained b...