Aggregate emission behaviors and reversible mechanofluorochromic properties of α-cyanostilbene functionalized indolo[3,2-b]carbazole derivatives

Abstract

Four novel α-cyanostilbene functionalized indolo[3,2-b]carbazole (ICZ) derivatives (ICZH, ICZF, ICZCH₃ and ICZCF₃) were synthesized to explore the structure–property relationship of intermolecular interaction and molecular packing modes in their fluorescence performances. Fluorescence emission spectra showed that the ICZ derivatives exhibited strong yellow emission in benzene solution. The four compounds have the same solvatochromic effect due to the same π-conjugated core structure. All four compounds showed an aggregation-induced emission enhancement characteristic in tetrahydrofuran–water mixture solution, and the main reason is that the distorted spatial structure of the α-cyanostilbene group effectively avoids intermolecular π–π stacking in aggregation states. Interestingly, only compounds ICZF and ICZCF₃ possessed obvious mechanofluorochromic (MFC) properties; powder XRD, SEM and DSC experimental investigations revealed that the MFC characteristic is based on the synergistic effect of intramolecular planarization and intermolecular J-aggregation stacking after grinding. Our study presents an efficient strategy for understanding photophysical properties and designing more MFC materials.