Clear piezochromic behaviors of AIE active organic powders under hydrostatic pressure
A novel diphenylacrylonitrile derivative (Z) 3 (4' (diphenylamino) [1,1' biphenyl] 4 yl) 2 (4 methoxyphenyl) acrylonitrile (b CN TPA) containing a twisted triphenylamine and diphenylacetonitrile was synthesized via Knoevenagel condensation and Suzuki coupling reactions. These molecules exhibited aggregation enhanced emission (AIE) effects. Interestingly, their mechano fluorochromic properties were invisible upon grinding with a pestle. However, when hydrostatic pressure in a diamond anvil cell (DAC) was applied on the crystals of b CN TPA, the distinct piezochromic behaviors of the compound were observed. The fluorescence color changed from light green (530 nm) to red (665 nm) with a significant red shift of 135 nm. The powder X ray diffraction and high pressure Raman studies indicated that the as synthesized and ground samples had the same crystalline structures, while the compressed samples had an evident change in inter molecular interactions. Comparative tests and theoretical analysis further confirmed that the distinct fluorescence behaviors of the desired dye during the different stress conditions were associated with the various inter molecular interactions that existed with adjacent molecules.