1,1′-Binaphthyl Consisting of Two Donor-π-Acceptor Subunits: A General Skeleton for Temperature-Dependent Dual Fluorescence

Temperature-dependent dual fluorescence with the anti-Kasha's rule is of great interest, but is a very challenging property to achieve in small organic molecules. The highly sensitive temperature-dependent dual fluorescence of 2,2 '-bis(dimethylamino)-6,6 '-bis(dimesitylboryl)-1,1 '-binaphthyl (BNMe2-BNaph), which essentially consists of two donor-pi-acceptor (D-pi-A) subunits, inspired the exploration of the importance of its structural features and the general utility of this molecular design. The reference compound MBNMe2-BNaph, which lacks one electron-accepting Mes(2)B, is found to show less sensitive temperature-dependent dual fluorescence, suggesting that the structure of BNMe2-Bnaph, consisting of two symmetrical D-pi-A subunits, is very important for achieving highly sensitive temperature-dependent dual fluorescence. In addition, it is found that another two 1,1 '-binaphthyls, CHONMe2-BNaph and CNNMe2-BNaph, which also consist of two D-pi-A subunits with Mes(2)B groups replaced by CHO and CN, respectively, also show temperature-dependent dual fluorescence, with the fluorescence changing in a similar manner to BNMe2-BNaph, indicating the general utility of the current molecular design for temperature-dependent dual fluorescence. Furthermore, the temperature-dependent dual fluorescence behaviors, such as the relative intensities of the two emission bands, the separation of the two emissions bands, and the sensitivity of the fluorescence intensity ratio to temperature, are greatly influence by the electron acceptors.