A Novel Strategy to Design and Construct AIE‐active Mechanofluorochromic Materials via Regulation of Molecular Structure.

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 (ΦTM‐2=13.73 % and ΦTM‐3=36.21 %), whereas TM‐1 and TM‐4 exhibit the opposite properties (ΦTM‐1=1.48 % and ΦTM‐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(ΦTM‐2<ΦTM‐3, ΦTM‐1<ΦTM‐4). Significantly, TM‐2 and TM‐3 also exhibited reversible mechanochromic behavior (Emission red shifts: ΔλTM‐2=43 nm and ΔλTM‐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. [ABSTRACT FROM AUTHOR]