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Molecular Engineering of Mechano­chromic Materials by Programmed C–H Arylation: Making a Counterpoint in the Chromism Trend

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posted on 07.09.2016, 00:00 by Jie Wu, Yangyang Cheng, Jingbo Lan, Di Wu, Shengyou Qian, Lipeng Yan, Zhen He, Xiaoyu Li, Kai Wang, Bo Zou, Jingsong You
The development of facile methods for screening organic functional molecules through C–H bond activation is a revolutionary trend in materials research. The prediction of mechano­chromism as well as mechano­chromic trends of luminogens is an appealing yet challenging puzzle. Here, we present a strategy for the design of mechano­chromic luminogens based on the dipole moment of donor–acceptor molecules. For this purpose, a highly efficient route to 2,7-diaryl-[1,2,4]­triazolo­[1,5-a]­pyrimidines (2,7-diaryl-TAPs) has been established through programmed C–H arylation, which unlocks a great opportunity to rapidly assemble a library of fluorophores for the discovery of mechano­chromic regularity. Molecular dipole moment can be employed to explain and further predict the mechano­chromic trends. The 2,7-diaryl-TAPs with electron-donating groups on the 2-aryl and electron-withdrawing groups on the 7-aryl possess a relatively small dipole moment and exhibit a red-shifted mechano­chromism. When the two aryls are interchanged, the resulting luminogens have a relatively large dipole moment and display a blue-shifted mechano­chromism. Seven pairs of isomers with opposite mechano­chromic trends are presented as illustrative examples. The aryl-interchanged congeners with a bidirectional emission shift are structurally similar, which provides an avenue for understanding in-depth the mechano­chromic mechanism.

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