Pyrene meets 2-(2-hydroxyphenyl)benzothiazole: Creation of highly efficient solid-state monomeric emitter for organic light-emitting diode

Strong intermolecular vibronic interactions often induce aggregation-caused quenching (ACQ) in dyes. Appending sterically bulky substituents or propeller-shaped moieties at the periphery of the dye molecule to impede these undesirable interactions is a traditional strategy for converting ACQ to aggregation-induced emission (AIE). Herein, we synthesized a highly planar molecule (HBT-Py) by conjugating 2-(2-hydroxyphenyl)benzothiazole (an excited-state intramolecular proton transfer (ESIPT)-active dye) to pyrene (a typical fluorophore undergoing ACQ due to excimer formation). Although strong p-p interactions still exist between the pyrene moieties in its crystalline state, HBT-Py exhibits strong monomeric solid-state fluorescence and also behaves as an efficient emitter in its light-emitting diode. The experimental observations and theoretical calculations demonstrate that the ability to undergo ESIPT is pivotal for the AIE in HBT-Py. Hence, this study presents a new method to impart excellent emission properties in the aggregated state of molecules that are originally planar and susceptible to ACQ.