3 years ago

The K-Region in Pyrenes as a Key Position to Activate Aggregation-Induced Emission: Effects of Introducing Highly Twisted N,N-Dimethylamines

The K-Region in Pyrenes as a Key Position to Activate Aggregation-Induced Emission: Effects of Introducing Highly Twisted N,N-Dimethylamines
Gen-ichi Konishi, Kazunobu Igawa, Keiji Morokuma, Satoshi Suzuki, Shunsuke Sasaki
A new design strategy to activate aggregation-induced emission (AIE) in pyrene chromophores is reported. In a previous report, we demonstrated that highly twisted N,N-dialkylamines of anthracene and naphthalene induce drastic AIE when these donors are introduced at appropriate positions to stabilize the S1/S0 minimum energy conical intersection (MECI). In the present study, this design strategy was applied to pyrene: the introduction of N,N-dimethylamine substituents at the 4,5-positions of pyrene, the so-called K-region, are likely to stabilize MECIs. To examine this hypothesis, four novel pyrene derivatives, which contain highly twisted N,N-dimethylamino groups at the 4- (4-Py), 4,5- (4,5-Py), 1- (1-Py), or 1,6-positions (1,6-Py) were tested. The nonradiative transitions of 4,5-Py are highly efficient (knr = 57.1 × 107 s–1), so that its fluorescence quantum yield in acetonitrile decreases to Φfl = 0.04. The solid-state fluorescence of 4,5-Py is efficient (Φfl = 0.49). In contrast, 1,6-Py features strong fluorescence (Φfl = 0.48) with a slow nonradiative transition (knr = 11.0 × 107 s–1) that is subject to severe quenching (Φfl = 0.03) in the solid state. These results underline that the chemistry of the pyrene K-region is intriguing, both from a photophysical perspective and with respect to materials science.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b00996

DOI: 10.1021/acs.joc.7b00996

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