Bright mechanoluminescence and dramatically different mechanofluorochromic behaviors of tetraarylimidazoles by slight modulation of substituent structure

Abstract

Three tetraarylimidazoles IMDMA, IMCZ and IMDPA by respective introduction of dimethylaminophenyl, N-carbazoly-phenyl and diphenylaminophenyl at N1 atom on imidazole core are prepared and their photophysical properties in both solution and solid state are investigated. The bright mechanoluminescence can be readily observed on these crystals, and a mechanism that polar molecular couples rather than space groups should be truly responsible for mechanoluminescence is elaborated in this work and it is verified to be effective on these imidazoles and many crystals in other reports. Interestingly, the slight modulation of substituent structures correspondingly results in red-shifted, no-shifted and blue-shifted emission on IMDPA, IMCZ and IMDMA under force stimuli. The reason for such sharply differentiated mechanofluorochrism is revealed to be flexibility difference of substituents in aid of theoretical calculations and crystallography. This work presents a very appropriate system to understand the structure-packing-property relationship.