The geometry relaxation and photodeactivation from the S2 state of dibenzofuran studied by ultrafast spectroscopy
Dibenzofuran (DBF) has attracted much attention from scientists recently since it is applied as a photoluminescence material and pharmaceutically active compound. Since the polychlorinated derivatives are highly toxic and manifest photostability in the environment. Femtosecond transient absorption spectroscopy associated with quantum chemical calculations are employed to investigate the ultrafast excited state dynamics of dibenzofuran from the S 2 state in 1,4-dioxane and ethanol, respectively. Following excitation at a wavelength of 266 nm, the S 2 state is firstly populated in the Franck–Condon region and preserves the planar molecular structure of the ground state. The observed increase of the transient absorption spectra of the excited state within the first several picoseconds indicates a geometry relaxation occurring on the S 2 potential energy surface. The subsequent kinetic traces of excited state absorption show that the S 2 state in the adiabatic region decays to the S 1 state through a fast internal conversion, followed by intersystem crossing to the T 1 state with a decay time of tens and hundreds of picoseconds in ethanol and 1,4-dioxane, respectively. Finally, the deactivation processes from the S 1 or T state are slow and take place on a time scale of about 20 ns.
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