| Research Abstract |
The present research project aims to clarifying how and why nonradiative processes in aromatic molecules are influenced by solvents surrounding them through experimental investigations on solvated clusters containing aromatic chromophores. By applying various spectroscopic methods, i.e., multiple laser resonances, massselective photoionization, and ultrafast laser spectroscopy, the following results have been achieved.
1.Hydrated clusters of acridine and 9-acridone have been studied to explore molecular-level correlation between structural motifs in hydrogen-bonding networks and nonradiative processes in the chromophores. Geometries of the hydrates have been determined by comparison of experimental data(band shifts in electronic transitions and fluorescence-detected infrared spectra)with density-functional-theory calculations. Pico-second time-resolved measurements have shown that fluorescence lifetimes depend substantially on cluster sizes as well as hydrogenbonding sites. The microsco
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pic solvation effects have been explained in terms of energetics relating to closely lying(n, π^*)and(π, π^*)states, which are characteristically shifted by hydrogen bonds.
2.Electronic transitions of benzene clusters in the monomer S_1-S_0 region have been reinvestigated. It has been found that previous size-assignments accepted for two decades need to be corrected, based on detailed examination of mass-selective holeburing spectra recorded for various isotopic species of dimer and trimer ion channels. New assignments have been proposed for the benzene trimer and tetramer, which resolve contradictions between experimental and theoretical results reported so far. The present data also provide information on geometry and excitation exchange interactions of the clusters.
3.Geometrical structure of solvated clusters containing 9-cyanoanthracene has been determined by rotational coherence spectroscopy implemented with pico-second time-resolved pump-probe depletion. In particular, structral motif for aprotic solvent molecules, e.g., carbon dioxide, acetonitrile, and fluoroform, has been established for the first time, which will be a solid foundation for discussing the relationship between reaction dynamics and solvation structure in clusters of related cyano-aromatics. Less
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