Tuning Photophysical Properties and ESIPT Mechanism of 10‐Hydroxybenzo[ <i>h</i> ]Quinoline by Ring‐Annelation Modification:A Theoretical Study

Abstract The ring‐annelation modification of phenyl and naphthyl on excited‐state intramolecular proton transfer (ESIPT) and photophysical properties of seven 10‐hydroxybenzo[h]quinoline (HBQ) derivatives were investigated by density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations. Potential energy curve (PEC) analysis suggests that proton transfer is more probable in the excited state for all studied molecules. In particular, for HBQ, HBQ‐B, HBQ‐C, HBQ‐D, HBQ‐C‐2, the ESIPT can occur spontaneously. Naphthyl both at the 8, 9‐position and 2, 3‐position of HBQ are unfavorable for the formation of keto form tautomer in excite state. Absorption and fluorescence spectra analyses demonstrate that the absorption and emission wavelength increase with extending the conjugation effect. It also found that 3, 4 ‐position of HBQ is very important for near‐infrared emission.