Conformational Regulations to Realize Modifiable ESIPT (Excited-State Intramolecular Proton Transfer) by Intermolecular Interactions

Abstract

Regulating the changes of molecular conformations is crucial yet challenging for manipulating the multiple-responsive emissions in excited-state intramolecular proton transfer (ESIPT) materials. In this work, we explored the specific emission regulations 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 with different crystallization conformations. It is unique that the crystals obtained in dimethylformamide (BDIBD-DMF) and methanol (BDIBD-MeOH) exhibit single emission band, which corresponds to the green and red emission from keto1st and keto2nd excited state, respectively, while the crystals obtained in acetone (BDIBD-ACE) display dual emissions from both states, manifesting an overall yellow color. A comprehensive theoretical study verifies that the modified intermolecular interactions due to different crystallization conformations regulate the emissions via affecting the energy barrier of dual-ESIPT procedures. The above results provide concrete understandings for the regulation of excited state emissions by ground state conformational changes in ESIPT processes, as well as unique insights into the design and application of novel ESIPT emission materials.