Multifunctional pyrenoimidazole substituted tetraphenylethylene derivatives: Mechanochromism and aggregation-induced emission

Organic molecules having propeller shaped architecture integrated with aggregation induced emission (AIE) fluorophores namely, (E)-4-(10-(2-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)vinyl)-9H-pyreno[4,5-d]imida-zol-9-yl)-1-naphthonitrile (TPE-SPNC) and (E)-4-(10-(2-(4'-(1-cyano-2,2-diphenylvinyl)-[1,1'-biphenyl]-4-yl) vinyl)-9H-pyreno[4,5-d]imidazol-9-yl)-1-naphthonitrile (TPA-SPNC) have been synthesized and explored their mechanofluorochromic (MFC) properties. The thermal, electrochemical and photophysical properties of TPE-SPNC and TPA-SPNC have been analyzed. The pyrenoimidazoles, TPE-SPNC and TPA-SPNC show strong aggregation induced emission (AIE) and reversible mechanochromic behavior. In the aggregated state, the restricted intramolecular rotation (RIR) of phenyl rings of TPE (TPE-SPNC) and TPA (TPA-SPNC) are suppressed which reduced the non-radiative excited state energy loss leading increase of fluorescence intensity. The quantum yield of TPE-SPNC/TPA-SPNC in distinct forms are of 21.89%/49.14% (pristine), 56.90%/66.89% (grinding) and 63.01 %/71.24% (annealing). The powder X-Ray diffraction (PXRD) reveal that the morphological change of these pyrenoimidazoles from crystalline to an amorphous could be attributed for mechanochromism.