The S1–S transition of indole and N-deuterated indole: Spectroscopy and picosecond dynamics in the excited state

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Abstract
A vibrational analysis for the excitation and fluorescence spectra of the S1–S0 transition in jet‐cooled indole and N‐deuterated indole is presented. This analysis yields the frequencies for eight low‐lying S1 vibrational modes of both isotopic species. Single vibronic level fluorescence spectra also enable us to refine many of the S0 vibrational frequencies. Quantum interference effects in the energy‐resolved fluorescence decays for one vibrational level of S1 indole are observed as a result of picosecond laser excitation. Through analysis of the fluorescence spectra and the modulated fluorescence decays, the coupling responsible for the quantum beats was found to result from a zero‐order in‐plane mode coupled to a level which is described by several zero‐order out‐of‐plane modes. The effect of the deuterium substitution on the quantum beats is also investigated.