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.