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

Author:
Wu, Jie, Cheng, Yangyang, Lan, Jingbo, Wu, Di, Qian, Shengyou, Yan, Lipeng, He, Zhen, Li, Xiaoyu, Wang, Kai, Zou, Bo, You, Jingsong
Source:
Journal of the American Chemical Society 2016 v.138 no.39 pp. 12803-12812
ISSN:
1520-5126
Subject:
chemical bonding, engineering, fluorescent dyes, isomers, prediction, pyrimidines, screening
Abstract:
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.
Agid:
5560514