Coupling Between Electrons and Molecular Vibrations of an Anthracene Single Molecule in a Cyclodextrin(Atomic and Molecular Physics)

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Optical studies of a single anthracene molecule succeeded by using a β-cyclodextrin (CyD) as an isolating cage. The absorption and the fluorescence spectra consist of several vibronic lines with 0.174-0.178eV intervals and are mirror image with each other. In addition, their line shapes vary scarcely between RT and 2 K. These facts indicate that the anthracene molecule is almost free in the β-CyD cage. These spectra are theoretically analyzed by a free-molecule-model in which the electronic excited state couples with the vibrations hw of the molecule with coupling strength s (Haung Rhys factor). Observed spectra are in good agreement with theoretical ones with s = 1.56 and hw = 0.178eV. For the single crystal of anthracene, absorption and fluorescence were also measured. At 2 K, the zero-phonon peak becomes enhanced and the phonon lines becomes sharpened compared with the single molecule case. But at RT, the fluorescence spectrum becomes quite diffused shape. These facts suggest that the exciton can move among anthracene molecules at low temperatures. It falls into a trapped state at RT.
社団法人日本物理学会の論文
2004-11-15