Effect of hydrogen bonding on the nonradiative properties of dibenzofuran

Femtosecond time-resolved transient absorption spectroscopy is employed to investigate the ultrafast excited-state dynamics from the S₂ state of dibenzofuran and the hydrogen bonding effect in protic and aprotic solvents. Following the excitation with 266 nm, the initial population on the S₂ state couples to the S₁ state via internal conversion on tens of picoseconds. Afterwards, vibrational energy relaxation (VER) with dozens of picoseconds is determined in all solvents and strongly depended on the polarities of aprotic solvents. And the rising species related with the hydrogen-bonded intermediate S^⁎ state are observed just in ethanol and methanol with the higher Kamlet parameter α. Subsequently, the intersystem crossing from the S₁ state to the triplet manifold is a main deactivation pathway with the decay time of ≫ns. All the relaxation processes exhibit solvent dependence, indicating that hydrogen bonding interaction between solute and solvent enhances VER and significantly influences on the excited state dynamics of dibenzofuran.