Triplet state spectroscopy

Monkman AP, Burrows HD, Miguel MD, Hamblett I, Navaratnam S (2001) Triplet state spectroscopy of conjugated polymers studied by pulse radiolysis. Synthetic Metals 116(l-3) 75-79... 

Typical singlet lifetimes are measured in nanoseconds while triplet lifetimes of organic molecules in rigid solutions are usually measured in milliseconds or even seconds. In liquid media where drfifiision is rapid the triplet states are usually quenched, often by tire nearly iibiqitoiis molecular oxygen. Because of that, phosphorescence is seldom observed in liquid solutions. In the spectroscopy of molecules the tenn fluorescence is now usually used to refer to emission from an excited singlet state and phosphorescence to emission from a triplet state, regardless of the actual lifetimes. 

Fessenden R W and Verma N C 1976 Time resolved electron spin resonance spectroscopy. III. Electron spin resonance emission from the hydrated electron. Possible evidence for reaction to the triplet state J. Am. Chem. Soc. 98 243-4... 

Many early studies in ESR spectroscopy were concerned with anions, cations and triplet states derived from conjugated molecules. The unpaired electron(s)... 

McGlynn, S. P., Azumi, T., and Kinoshita, M. (1969). Molecular Spectroscopy of the Triplet State , Prentice Hall, Englewood Cliffs, N.J. 

Fujii, R. et al., Cis-to-trans isomerization of spheroidene in the triplet state as detected by time-resolved absorption spectroscopy, J. Phys. Chem. A, 106, 2410, 2002. Montenegro, M.A. et al., Model studies on the photosensitized isomerization of bixin, J. Agric. Food Chem., 52, 367, 2004. 

The functionalization of zinc porphyrin complexes has been studied with respect to the variation in properties. The structure and photophysics of octafluorotetraphenylporphyrin zinc complexes were studied.762 Octabromoporphyrin zinc complexes have been synthesized and the effects on the 11 NMR and redox potential of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraarylporphyrin were observed.763 The chiral nonplanar porphyrin zinc 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin was synthesized and characterized.764 X-ray structures for cation radical zinc 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin and the iodinated product that results from reaction with iodine and silver(I) have been reported.765 Molecular mechanics calculations, X-ray structures, and resonance Raman spectroscopy compared the distortion due to zinc and other metal incorporation into meso dialkyl-substituted porphyrins. Zinc disfavors ruffling over doming with the total amount of nonplanar distortion reduced relative to smaller metals.766 Resonance Raman spectroscopy has also been used to study the lowest-energy triplet state of zinc tetraphenylporphyrin.767... 

The paramagnetism of the triplet state can be observed by electron spin resonance spectroscopy. This is perhaps the most reliable means of determining the existence of a triplet state since the ESR signals can be predicted using the following Hamiltonian operator ... 

Wild, U. P. Characterization of Triplet States by Optical Spectroscopy. 55, 1-47 (1975). 

Seminal studies on the dynamics of proton transfer in the triplet manifold have been performed on HBO [109]. It was found that in the triplet states of HBO, the proton transfer between the enol and keto tautomers is reversible because the two (enol and keto) triplet states are accidentally isoenergetic. In addition, the rate constant is as slow as milliseconds at 100 K. The results of much slower proton transfer dynamics in the triplet manifold are consistent with the earlier summarization of ESIPT molecules. Based on the steady-state absorption and emission spectroscopy, the changes of pKa between the ground and excited states, and hence the thermodynamics of ESIPT, can be deduced by a Forster cycle [65]. Accordingly, compared to the pKa in the ground state, the decrease of pKa in the... 

Photosensitization of diaryliodonium salts by anthracene occurs by a photoredox reaction in which an electron is transferred from an excited singlet or triplet state of the anthracene to the diaryliodonium initiator.13"15,17 The lifetimes of the anthracene singlet and triplet states are on the order of nanoseconds and microseconds respectively, and the bimolecular electron transfer reactions between the anthracene and the initiator are limited by the rate of diffusion of reactants, which in turn depends upon the system viscosity. In this contribution, we have studied the effects of viscosity on the rate of the photosensitization reaction of diaryliodonium salts by anthracene. Using steady-state fluorescence spectroscopy, we have characterized the photosensitization rate in propanol/glycerol solutions of varying viscosities. The results were analyzed using numerical solutions of the photophysical kinetic equations in conjunction with the mathematical relationships provided by the Smoluchowski16 theory for the rate constants of the diffusion-controlled bimolecular reactions. 

The transient triplet carbene formed from irradiation of DABA in benzene can be observed to react with styrene. For this process laser spectroscopy reveals a bimolecular rate constant (ksty) equal to 1.2 x 107M-1s-1. The product of the reaction is the expected cyclopropane. This observation clearly supports the spectral assignment of the carbene made above. When deuteriated a-methylstyrene is substituted for styrene as a trap for the carbene, the cyclopropane that results is a 1 1 mixture of stereoisomers, (20) (Table 6). This finding indicates that BA is reacting in this sequence exclusively from its ground triplet state. 

---