Theoretical study on influence of geometry controlling over the excited-state intramolecular proton transfer of 10-hydroxybenzo[h]quinoline and its derivatives

•Calculated electronic spectra of HBQ agree with experiments.•Geometry changes lead to different electronic spectra.•Potential energy surfaces indicate that proton transfer is more favorable in the excited-state.•Excited-state intramolecular proton transfer (ESIPT) is ultrafast within 100fs.•The twisting skeleton is initiated after ESIPT, leading to low fluorescence of tautomer.