Abstract
Highly excited electronic states of pyrene in ethanol solution and the relaxation processes in the S1 singlet state are investigated by femtosecond transient absorption spectroscopy. UV excitation at 290 nm is utilized to excite the molecule in some vibronic level of S6 state. From this state internal conversion (IC) takes place and the build‐up of S1 population has been observed to be completed in the first 2–3 ps, with a time constant of about 400 fs. The evolution of the absorption spectra occurring on a longer time scale is attributed to the vibrational cooling in the S1 state which is completed in about 25–30 ps. The transient absorption spectrum is interpreted with the aid of semiempirical calculations.
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