MULTIRESONANT 4-WAVE-MIXING IN DIPHENYLOCTATETRAENE DOPED BIBENZYL CRYSTALS

A diphenyloctatetraene (DPOT) doped bibenzyl crystal is a model system for studying the spectroscopic properties of polyenes because the wel l-defined local environment of the DPOT eliminates most of the inhomog eneous broadening that obscures many transitions. The spectra of the t hree DPOT sites in this host are measured with site-selective laser sp ectroscopy to define the vibrational, electronic, and vibronic states of the S-0, S-1, and S-2 electronic states. Multiply resonant four-wav e mixing spectra were then obtained using a coherent anti-Stokes Raman spectroscopy method (CARS) for a series of different laser frequencie s in order to define the CARS excitation profile (CEP). The CEP profil e of the C=C and C-C stretch vibrations showed strong enhancement of t he four-wave mixing from the S-2 State but only the C=C stretch mode h ad observable enhancement from the S-1 state. Contrary to previous stu dies in pentacene, azulene, and perylene, DPOT did not exhibit enhance ment of vibronic transitions that would permit mode selective or site- selective nonlinear spectroscopy. (C) 1995 American Institute of Physi cs.