Opposite mechanoluminescence behavior of two isomers with different linkage positions

Two isomers of mm-TPE(PI)(2) and pp-TPE(PI)(2), constructed by the two same aromatic blocks of tetraphenylethene and phenanthro[9,10-d]imidazole, exhibit totally different mechanoluminescence, as a result of the ignorable different linkage positions on the tetraphenylethene moiety. Detailed analysis and theoretical calculations demonstrate the structure-packing-property relationship of organic mechanoluminescent luminogens, with the emphasis on the important role of molecular packing in the solid state.