Tuning Electronic Structures of Carbazole‐Cyanostyrene Molecules to Achieve Dual‐State Emission for Trace Water Analysis, Picric Acid Sensing, and Reversible Mechanofluorochromism

Dual‐state emissive (DSE) materials with efficient emission both in solution and in the solid state can be used in complex environments. In this work, we demonstrate the synthesis of DSE materials by finely tuning the electronic structures of luminogens. Four carbazole‐cyanostyrene compounds with different terminal groups, i. e., CZ‐Ph‐H without additional substituent, CZ‐Ph‐TA with an N,N‐dimethylamino functional group, CZ‐Ph‐CN with a cyano group, and CZ‐Ph‐TB with a t‐butyl group, have been synthesized and their photophysical properties are fully investigated by spectroscopic studies, theoretical calculations, and crystallographic analysis. Interestingly, while CZ‐Ph‐H, CZ‐Ph‐CN, and CZ‐Ph‐TB are aggregation‐induced emissive (AIE) molecules only showing strong emission in the aggregated states (aggregate suspension and solid powder), CZ‐Ph‐TA is a DSE molecule showing strong emission in both dilute solution and aggregated states. In addition, CZ‐Ph‐TA could serve as a fluorescent probe for trace water analysis in organic solvents and picric acid (PA) detection in both dilute solution and aggregate suspension. CZ‐Ph‐TA also exhibits reversible mechanofluorochromism with a spectral shift of 21 nm. The synthesis of the N,N‐dimethylamino‐substituted molecule with excellent photophysical properties represents an important attempt to achieve DSE by finely tuning the electronic structures of molecules. Fine‐tuning: A dual‐state luminogen (DSEgen) with bright fluorescence in both dilute solution and the solid state has been synthesized by finely tuning molecular electronic structures. The DSEgen shows multifunctionality, including water sensing, picric acid detection, and mechanofluorochromism.