Theoretical study on the relationship between the position of the substituent and the ESIPT fluorescence characteristic of HPIP*

Abstract

The influences of the substituent base position on the excited state intramolecular proton transfer fluorescence properties were explored in 2-(2′-hydroxyphenyl)imidazo[1,2-a]-pyridine (HPIP) and HPIP’s derivatives (5′Br-HPIP and 6′Br-HPIP). And the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were used to calculate the molecule structures. The calculated results showed that the influence of 5′Br-HPIP on the fluorescence intensity is stronger than that of 6′Br-HPIP. The fluorescence emission peak of 5′Br-HPIP occurred a blue shift compared with HPIP, and 6′Br-HPIP exhibited an opposite red shift. The change of the fluorescence emission peak was attributed to the decrease of the energy gap from 6′Br-HPIP to 5′Br-HPIP. Our work on the substituent position influence could be helpful to design and develop new materials.