Conformational regulation to realize modifiable ESIPT (excited-state intramolecular proton transfer) through intermolecular interactions

Abstract

Regulating molecular conformation changes is crucial yet challenging for manipulating multiple-responsive emissions in excited-state intramolecular proton transfer (ESIPT) materials. In this work, we explored the specific emission regulation of a dual-ESIPT-active molecule, BDIBD (2,5-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene-1,4-diol), by subtly controlling the ground and excited states through different crystallization conformations. Notably, the crystals obtained in dimethylformamide (BDIBD–DMF) and methanol (BDIBD–MeOH) exhibited a single emission band, corresponding to the green and red emission from the keto^1st and keto^2nd excited states, respectively, while the crystals obtained in acetone (BDIBD–ACE) displayed dual emissions from both states, resulting in an overall yellow color. A comprehensive theoretical study verified that the modified intermolecular interactions, due to different crystallization conformations, regulated emissions by affecting the energy barrier of dual-ESIPT processes. The above results provide a concrete understanding of the regulation of excited-state emissions through ground-state conformational changes in ESIPT processes, as well as unique insights into the design and application of novel ESIPT emission materials.