A TD‐DFT investigation of the photo‐induced excited state intramolecular proton transfer dynamics for the novel 5,5′‐(9,9‐dihexyl‐9H‐fluorene‐2,7‐diyl)bis(2‐benzo[d]thiazol‐2‐yl)phenol) system

Abstract

AbstractDensity functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods are adopted to explore the ground‐state and excited‐state intramolecular double hydrogen bonding interactions as well as the excited state intramolecular proton transfer (ESIPT) mechanism for 5,5′‐(9,9‐dihexyl‐9H‐fluorene‐2,7‐diyl)bis(2‐benzo[d]thiazol‐2‐yl)phenol) (abbreviated as Ia) system. The simulated electronic spectra of the Ia system (ie, absorption and fluorescence spectra) are reappeared by experimental results, which reveals the reasonability and correctness of the calculated theory adopted in this work. We firstly verify that the dual intramolecular hydrogen bonds of Ia should be enhanced in the first excited state via geometrical parameters (ie, bond lengths and bond angles) and infrared (IR) vibrational spectra. Then, insights into the photo‐excitation aspects, we confirm that the charge redistribution facilitates the ESIPT tendency. Particularly, the increased electronic densities around proton acceptors could play important roles in attracting proton H2 and H5 atoms for the Ia system. At last, via constructing potential energy surfaces (PESs), we clearly clarify the excited state intramolecular single proton transfer mechanism for the Ia system. This work not only clarifies the detailed ESIPT mechanism for the novel Ia system and makes up for the deficiencies in previous experiment but also promotes a deeper understanding about the excited state behaviors involved in multiple hydrogen bonding interactions.