Photophysical properties of 3-hydroxyphthalimide fluorophores based on the ESIPT mechanism: A theoretical study

By adopting the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods, the excited state intramolecular charge transfer (ESIPT) processes and photophysical properties of 3-OHPht-Pyr and 3-OHPht-Iquin with different substituents (pyridine and isoquinoline) are studied. The results indicate that 3-OHPht-Pyr is more prone to the ESIPT process accompanied by molecular twisting compared to 3-OHPht-Iquin. Moreover, the differences in twisting angles and trends result in the differences of the fluorescence peaks of the two molecules. It is worth noting that the Stokes shifts of the two molecules can reach 170 nm and 220 nm, respectively.