Excitation-Wavelength-Dependent Structure in the Fluorescence Spectra of Bu States of Diphenylpolyenes

Abstract

Experiments have used a tunable picosecond laser to study evolving fluorescence spectra of 1,8-diphenylocta-l,3,5,7-tetraene (DPO) in hexane solution at room temperture. The spectra recorded synchronously (±20 ps) with the irradiation event are analysed in terms of the time-integrated spectra, spectra obtained through a delayed gate, resonance Raman signals and fluorescence from the second excited singlet state. Data are presented to show the dependence of the S2 → S0 spectrum on the excitation wavelength. The spectra clearly show that vibrational relaxation is incomplete on the timescale of the S2 lifetime. On the other hand, the spectral bands show little tendency at room temperature towards line-narrowing effects. This indicates that the rate of molecular site relaxation is at least comparable to the lifetime of the S2 state under these conditions.