A Novel Strategy to Design and Construct AIE‐active Mechanofluorochromic Materials via Regulation of Molecular Structure
Kaibo Zheng, Hui Chen, Yufeng Xiao, Xiang Liu, Jiaying Yan, Nuonuo Zhang
Abstract
Abstract In this work, we first designed and synthesized tetraphenylene‐fused aryl‐imidazole derivatives TM‐1 – 4 via regulation of molecular structure, which were consisted of 1H‐imidazo[4,5‐f][1,10]phenanthroline, 1H‐phenanthro[9,10‐d]imidazole, 4,5‐diphenyl‐1H‐imidazole, 3,3′‐(1H‐imidazole‐4,5‐diyl)dipyridine moieties and AIE‐active tetraphenylethene units, respectively. The results illustrated that TM‐1 – 4 exhibited clear AIE characteristics. Meanwhile, TM‐2 and TM‐3 show excellent solid emission properties (Φ TM‐2 =13.73 % and Φ TM‐3 =36.21 %), whereas TM‐1 and TM‐4 exhibit the opposite properties (Φ TM‐1 =1.48 % and Φ TM‐4 =4.83 %). The multiple rotors (pyridine and benzene ring) causes twisted conformations of the molecule that prevents π‐π stacking and enhances solid emission(Φ TM‐2 <Φ TM‐3 , Φ TM‐1 <Φ TM‐4 ). Significantly, TM‐2 and TM‐3 also exhibited reversible mechanochromic behavior (Emission red shifts: Δλ TM‐2 =43 nm and Δλ TM‐3 =41 nm) with color changes between blue and green emissions. The powder X‐ray diffraction (PXRD) suggested the disordered state of ground sample could be readily returned to an ordered crystalline. Therefore, the mechanochromisms of TM‐2 and TM‐3 are ascribable to the phase transformation between crystal and amorphous structure. The single crystal X‐ray analysis of TM‐2 reveals a twisted conformation for TPE moiety and the absence of π‐π intermolecular stacking. These excellent optical properties of TM‐2 and TM‐3 make them potentially applications in mechanochromic materials and imaging agents.