α‐Cyano Triaryl[3]radialene: Unsymmetrical Stereo‐configuration, Clustering‐enhanced Excimer Emission, and Radical‐involved Multimodal Information Switching.

[3]Radialene has a peculiar topology and cross‐conjugation system, representing a unique molecular scaffold in organic materials. Herein, we report a special class of stereoisomeric α‐cyano triaryl[3]radialenes (CTRs) that show concentration‐caused quenching in solution but emit red‐shifted and enhanced luminescence in the crystalline state. Clustering of multiple cyano groups and their through‐space interactions with the [3]radialene ring significantly extend π‐electron communication meanwhile rigidifying the propeller conformation multivalently, thus playing a key role behind the state‐dependent luminescence. These radialenes with a substantial electron affinity undergo a reversible electron transfer transition to anionic radicals with good stability, showing switching of photoabsorption, photoluminescence and electron spin resonance (ESR) signal. We also established proof‐of‐concept applications of CTRs for multimodal information encryption and chemical sensing. [ABSTRACT FROM AUTHOR]