Large Changes in Fluorescent Color and Intensity of Symmetrically Substituted Arylmaleimides Caused by Subtle Structure Modifications

Abstract Herein we report on four diarylmaleimides based on 3‐ or 2‐substituted benzothiophene (M3S or M2S) and benzofuran (M3O or M2O), which show very different emission properties: aggregation‐caused quenching (ACQ), aggregation‐induced emission (AIE), and dual‐state strong emission (DSE) in both solution and solid states. Their emission color in the solid state can be adjusted from green–yellow into red. M2O displays strong red solid‐state emission at 630 nm with a quantum yield of 46.3 %. Single‐crystal X‐ray diffraction analysis confirms that their large distinction in solid‐state emission originates from their different packing structures: hydrogen‐bonded organic frameworks (HOFs) for M3S, a staggered structure for M3O, J‐aggregation for M2S, and weak H‐aggregation for M2O. HOF of M3S and weak H‐aggregation of M2O make them produce inverse‐type piezochromic fluorescence: blueshifted “turn‐on” and redshifted “turn‐off” emission, respectively. These results provide new insight in fluorescence manipulated by subtle structure modification.