Structure and Dynamics of Triplet States

Photosynthesis. In the photosynthetic process light energy is absorbed by carotenoids and bacteriochlorophylls and transferred to photosynthetic reaction centers. Time-resolved vibrational methods, including transient RR and TR techniques, are well-suited to elucidate the structure and dynamics of the excited (singlet and triplet) states of these chromophores. Nanosecond and picosecond transient RR studies of carotenoid excited states have been conducted by Atkinson and co-workers ... 

Elsewhere in this volume Millhauser et al. have discussed the application of nitroxide electron paramagnetic resonance (EPR) spin labels to the study of the structure and dynamics of biopolymers. Another type of EPR spin label that also is useful for investigating biopolymer systems is provided by the photoexcited triplet state of an intrinsic chromophore, because a triplet state carries electronic paramagnetism. A major advantage of the photoexcited triplet state of an intrinsic chromophore over an extrinsic spin label such as a nitroxide adduct is the relatively small structural perturbation caused by the former, which consists only of a localized electronic excitation. Although not as widely exploited as fluorescence, the phosphorescence of proteins, originating from the photoexcited triplet state, has received a great deal of attention. EPR afficionados have a natural attraction to photoexcited triplet states that dates back to the... 

We have provided experimental evidence demonstrating the very different behaviour of triplet states of aromatic carbonyls in lignin and in dilute solution. These differences result, we believe, from the very restricted motion within the lignin structure relative to fluid solution. By using oxygen saturated samples rather than air saturated samples, we have been able to.establish for the first time that dynamic quenching by oxygen occurs within TMP. 

In the present chapter aimed at the smdents and postgraduates first of all, as well as at the beginners in this field, we consider thoroughly the dynamic Jahn-Teller effect for the 3d (3d ) ions in the octahedral (tetrahedral) impurity centers. Energy level structure of the orbital triplet T2 and interaction of its states with the... 

The Trstate CTI in spheroidene was found to be much less efficient than that in /2-carotene, which facilitated the examination of triplet-state dynamics by time-resolved absorption spectroscopy. Scheme 3.5 shows the configurations of the all-trans and cis isomers of spheroidene. The all-trans isomer consists of an open conjugated chain (n= 10) shifted to the left in the entire carbon skeleton, to which a pair of large peripheral groups are attached at both ends. Concerning the position of the ds-bend, the 13 -ds and 9-cis isomers can be classified into peripheral-ds isomers, whereas the 13-ds and 15-ds isomers are central-ds isomers. Concerning the structure of the cis bend, 13 -ds, 9-cis, and 13-ds isomers are methylated cis iso-... 

This chapter covered the use of excited states as probes for dynamic studies involving supramolecular stmctures. It was shown that excited singlet and triplet states provide complementary capabilities for these studies. Micelles are the best characterized structures, and most of the methodology currently in use was developed when studying these supramolecular systems. Other self-assemblies, such as vesicles and bile salt aggregates, have been studied to some extent, but the dynamics of guest complexation has not been fully described and will undoubtedly be explored in the future. Cyclodextrins are widely employed as... 

We begin with a brief survey of the fine structure characteristics of a ligand-centered phosphorescent triplet state. This is followed by some considerations concerning the ODMR experiment and finally we review results of recent ODMR investigations with focus on the information regarding structure and dynamics complementary to optical work. 

The analysis of CIDNP effects allows information to be obtained on the structure and reactivity of active short-lived (from nanoseconds to microseconds) paramagnetic species (free radicals and radical ions, triplet excited molecules), and on molecular dynamics in the radical pair. The analysis makes it possible to distinguish between the bulk and in-cage stages of complex chemical reactions. CIDNP data also provide information on the multiplicities of reacting states, which is of utmost importance for understanding photochemical processes. 

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