Dicyanomethylenated Acridone Based Crystals: Torsional Vibration Confinement Induced Emission with Supramolecular Structure Dependent and Stimuli Responsive Characteristics

A series of dicyanomethylenated acridone derivatives, DCNAC-Cn (n = 1, 4, 6) and DPA-DCNAC-C4, are designed and synthesized. They are highly luminescent in the crystalline state but nonemissive in the amorphous state. The interesting crystallization-induced-emission (CIE) behavior is attributed to the restricted torsional vibrations of the molecular skeletons in crystal lattices. DCNAC-Cn-based crystals display obvious molecular-packing-dependent emission properties. The molecular packing of DCNAC-Cn in crystals is easily regulated by modifying the length of alkyl chains, resulting in the tunable emission colors from green to red. A DPA-DCNAC-C4 molecule consisting of a DCNAC acceptor and two diphenylamino donors shows intramolecular charge-transfer (ICT) characteristic and strong near-infrared emission (λem = 707 nm, ΦF = 0.16) in the crystalline state. Mechanical, thermal, and organic-vapor stimuli can reversibly alter the aggregation phases between crystalline and amorphous states. Therefore, this study presents a stimuli-responsive emission on/off switching system with various emission colors (560 to 700 nm).