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

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.