RESONANCE CARS OF $\alpha, \omega$-DIPHENYLPOLYENES IN THE LOWEST EXCITED SINGLET AND TRIPLET STATES
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Date
1985
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Ohio State University
Abstract
Transient CARS and/or CSRS spectra of $\alpha, \omega$-diphenylbutadiene (DPB), -diphenylhexatriene (DPH) and -diphenyloctatetraene (DPO) in the lowest excited singlet [S$_{1}$] and triplet [T$_{1}$] states have been recorded with the resonance enhancement by the transient $S_{n}-S_{1}$ or $T_{n}-T_{1}$ absorption. The measurement was made on room temperature solutions ($\sim10^{-4}M$) in various solvents, by using temporally coincident exciting (UV) and probe (visible dye) laser pulses of several nsec duration and by scanning a dye laser frequency. The $S_{1}$ and $T_{1}$ signals were distinguished from each other by the different resonant behaviors and by using delayed measurement if necessary. The obtained vibrational frequencies were in fair agreement with those from the two-photon excitation or transient resonance Raman spectra reported for some of the states, but generally more abundant and much better resolved. The assignment and the interpretation of frequency shift from the ground state are discussed by referring to the theoretical calculations. An unusual $\nu_{C=C}$ frequency of $S_{1}$ DPO, as already known in the two-photon spectrum, was observed at $1755 cm^{-1}$ (in n-heptane) with striking resonance enhancement. The anomalous value has been suggested to arise from the vibraonic interaction with the ground state, but does not seem to have been interpreted conclusively. No such anomalous frequencies were detected in the present observation except above. The above frequency was found to be shifted appreciably ($\sim 25 cm^{-1}$) depending upon the solvent in distinction from the other modes, possibly indicating the cause of anomaly. On the other hand, the $S_{1}$ spectrum of DPH showed some different features depending on the solvent polarity. This observation and the marked abundance of $S_{1}$ DPH lines might suggest the conformational variety.""
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Author Institution: Research Laboratory of Resources Utilization, Tokyo Institute of Technology