Unraveling excited state dynamics and photophysical properties for a series of phenol-quinoline derivatives by controlling hydrogen bond geometry

Abstract

As a “site-specific” interaction, the hydrogen bonds play an important role in optical properties. Therefore, we used the time dependent density functional theory to study the excited state dynamics and photophysical properties of a series of phenol-quinoline derivatives (1-3 compounds) by controlling the hydrogen bond geometry. The calculated geometric parameters and reduced density gradient results show that the intramolecular hydrogen bond distance is inversely proportional to the hydrogen bond strength. Meanwhile, potential energy curves shows that the stronger the hydrogen bond strength, the smaller the energy barriers in the ground (S0) and excited (S1) states. In particular, we use not only the linear response solvation model but also the state-specific (SS) solvation model for the PES in the S1 state. The results show that the SS solvation model better establishes the relationship between the hydrogen bond strength and the energy barrier in the S1 state. In addition, increasing the dihedral angle of intramolecular hydrogen bond leads to more obvious intramolecular charge transfer during excitation transition. Moreover, we also found that the dihedral angle affects the excited state dynamics and the fluorescence emission properties. Our theoretical results indicate that the fluorescence quenching pathway of the 3 compound is caused by the photoinduced electron transfer process, which is different from the experimentally proposed non-radiative deactivation by conical intersections.