Propeller Configuration Flipping of the Trivalent Boron-Inducing Substituent Dependence of the Circularly Polarized Luminescence Sign in Triarylborane-Based [7]Helicenes.

We here disclose two triarylborane-based [7]helicenes, which contain a dimesitylboryl or a 2-(dimesitylboryl)phenyl at position 9 of the [7]helicene skeleton. The change in the peripheral substituent from dimesitylboryl to 2-(dimesitylboryl)phenyl induced doubling of |glum| and sign inversion of the circularly polarized luminescence (CPL). The substituent dependence of the CPL sign is reasonably explained by the propeller configuration flipping of boron, which has a significant influence on the chiroptical properties.

Triarylborane-based [5]Helicenes with Full-Color Circularly Polarized Luminescence.

The efficient synthetic route was disclosed to prepare optically active triarylborane-based [5]helicenes, 7B-PhHC and 7B5N-PhHC. Their emission wavelengths are tunable by both the chemical structure modification and the tuning of excited state charge transfer dynamics via selection of appropriate solvents or addition of external F-, enabling the full-color circularly polarized luminescence with moderate to good quantum yields (0.07-0.51) and high luminescence dissymmetry factors (glum > 5 × 10-3).

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-π-acceptor (D-π-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 Mes2 B, is found to show less sensitive temperature-dependent dual fluorescence, suggesting that the structure of BNMe2 -Bnaph, consisting of two symmetrical D-π-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-π-A subunits with Mes2 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.

2,2'-Diamino-6,6'-diboryl-1,1'-binaphthyl: A Versatile Building Block for Temperature-Dependent Dual Fluorescence and Switchable Circularly Polarized Luminescence.

Temperature-dependent dual fluorescence and switchable circularly polarized luminescence (CPL) are two highly pursued but challenging properties for small organic molecules (SOMs). We herein disclose a triarylborane π-system based on a 2,2'-diamino-6,6'-diboryl-1,1'-binaphthyl scaffold that can serve as a versatile building block for achieving these two properties by simply choosing different amino groups. BNMe2 -BNaph with less bulky dimethylamino groups displays temperature-dependent dual fluorescence, and can thus be used as a highly sensitive ratiometric fluorescence thermometer. On the other hand, BNPh2 -BNaph with bulky diphenylamino groups exhibits intense fluorescence in both solution and in the solid state. A change of solvent from nonpolar cyclohexane to highly polar MeCN not only shifts the CPL position to much longer wavelength but also inverts the CPL sign. In addition, the complexation of BNPh2 -BNaph with fluoride greatly enhances the CPL intensity.

Modification of [5]Helicene with Dimesitylboryl: One Way To Enhance the Fluorescence Efficiency.

The efficient synthetic route was disclosed to prepare structurally asymmetric [5]helicenes, which are substituted with either BMes2 (7B-HC) or both BMes2 and NMe2 (8B5NMe2-HC, 7B5NMe2-HC). Compared with the parent [5]helicene, these compounds show greatly enhanced fluorescence. In addition, they still retain fairly strong fluorescence in the solid state. Moreover, the complexation of 8B5NMe2-HC and 7B5NMe2-HC with fluoride can induce significant blue shift in fluorescence and the formed complexes are also highly fluorescent.