Regulating the excited-state intramolecular dual proton transfer process and multiple fluorescence of 2,5-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene-1,4-diol by expanding π-conjugation

A new fluorescent chromophore with double hydrogen bonds, 2,5-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene-1,4-diol (BDIBD), has recently been reported experimentally, which can achieve full-color panel luminescence in different solvents. It is hypothesized that this phenomenon may be triggered by the excited-state double proton transfer process, but lacking specific theoretical details. Enlightened by the excellent photophysical characteristics of organic molecules containing the π-extended units, we mainly discuss the effects of expanding π-conjugation on multiple fluorescence and the excited-state intramolecular dual proton transfer (ESIDPT) of this molecule using density functional theory and time-dependent density functional theory methods to explore the possibility of much broadened optical responses and full-color display. Three BDIBD derivatives are obtained by expanding the π-conjugated groups. The theoretical details of the multiple fluorescence emitted by BDIBD are given in detail and it is found that the photophysical properties of BDIBD with expanding π-conjugation are also significantly altered. The results show that expanding π-conjugation have a significant impact on the ESIDPT process of BDIBD chromophore, promoting the first proton transfer and inhibiting the second proton transfer process, respectively. This work proposes that the expanding π-conjugation can modulate the ESIDPT process and multiple fluorescence, providing some thoughts for designing and developing novel fluorescent chromophores experimentally in the future. • By expanding π-conjugation, BDIBD and its derivatives exhibit the excellent photophysical properties. • All BDIBD and its derivatives can undergo the ESIDPT process and the dual proton transfer is a stepwise process. • Expanding π-conjugation can modulate the kinetic process of ESIDPT in BDIBD by promoting the 1 st PT and inhibiting the 2 nd PT process.