Skeletal motions

Although 130 is undoubtedly less rigid than its lower double-bond homolog (123h), skeletal motion must still be sufficiently restricted so... 

The separation into a vibrational and an electronic part is implied by the Placzek polarizability theory. The further analysis of vibrational motions has in the past typically been accomplished by calculating the vibrational energy distribution in valence coordinates. For the large-scale skeletal motions often important in ROA, and for relating Raman and ROA scattering cross-sections to the vibrational motions of structural parts of an entity, a different approach is needed. 

As we have discussed in depth elsewhere, despite the similarities in the structures of hypericin and hypocrellin, which are centered about the perylene quinone nucleus, their excited-state photophysics exhibit rich and varied behavior. The H-atom transfer is characterized by a wide range of time constants, which in certain cases exhibit deuterium isotope effects and solvent dependence. Of particular interest is that the shortest time constant we have observed for the H-atom transfer is 10 ps. This is exceptionally long for such a process, 100 fs being expected when the solute H atom does not hydrogen bond to the solvent [62]. That the transfer time is so long in the perylene quinones has been attributed to the identification of the reaction coordinate with skeletal motions of the molecule [48, 50]. 

A simple view of the effect of placing a dye molecule on a surface is that adsorption inhibits some of the low frequency skeletal motions which contribute to the radiationless decay of D to the ground state (internal conversion). Thus, it is easy to understand how adsorption of rhodamine B can lead to a lifetime which is longer than in solution, just as the solution lifetime increases significantly with solvent viscosity (15,26). We have taken Tj to be 1/k and recall, somewhat reassuringly, that T2 was the same on glass and on both semiconductors. 

Skeletal motions can also induce transitions from the lowest excited singlet state to the lowest triplet state (intersystem crossing). Thus, changes in k may be due not only to internal conversion but also to Intersystem crossing. It should be noted that Injection can also take place from the triplet state, as discussed by Spltler et al. (29). 

Reduction of Donor-Acceptor Distance by Skeletal Motions... 

Interferometers made far-IR spectroscopy possible, and enabled observation of lattice vibrations of crystals, low-frequency skeletal motions of organics and... 

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