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Why Do Simple Molecules with “Isolated” Phenyl Rings Emit Visible Light?

Zhang, Haoke, Zheng, Xiaoyan, Xie, Ni, He, Zikai, Liu, Junkai, Leung, Nelson L. C., Niu, Yingli, Huang, Xuhui, Wong, Kam Sing, Kwok, Ryan T. K., Sung, Herman H. Y., Williams, Ian D., Qin, Anjun, Lam, Jacky W. Y., Tang, Ben Zhong
Journal of the American Chemical Society 2017 v.139 no.45 pp. 16264-16272
aromatic compounds, ethane, fluorescence, fluorescent dyes
π-Bonds connected with aromatic rings were generally believed as the standard structures for constructing highly efficient fluorophores. Materials without these typical structures, however, exhibited only low fluorescence quantum yields and emitted in the ultraviolet spectral region. In this work, three molecules, namely bis(2,4,5-trimethylphenyl)methane, 1,1,2,2-tetrakis(2,4,5-trimethylphenyl)ethane, and 1,1,2,2-tetraphenylethane, with nonconjugated structures and isolated phenyl rings were synthesized and their photophysical properties were systematically investigated. Interestingly, the emission spectra of these three molecules could be well extended to 600 nm with high solid-state quantum yields of up to 70%. Experimental and theoretical analyses proved that intramolecular through-space conjugation between the “isolated” phenyl rings played an important role for this abnormal phenomenon.