Photophysical properties of azaboradibenzo[6]helicene derivatives

The electronic circular dichroism (CD), UV-Vis absorption and emission spectra, charge transport, and nonlinear optical properties of the novel azaboradibenzo[6]helicene have been investigated by density functional theory (DFT) for the first time. The calculated absorption and emission energies are in good agreement with the experimental ones. The simulated CD spectra nicely reproduce the experimental CD spectra in both excitation energy and rotational strength without any shift or scaling, which can be used to assign its absolute configuration (AC) with high confidence. The electronic transition properties have been assigned and analyzed. The observed CD bands mainly result from exciton-coupling of the ortho-fused aromatic rings. The adiabatic potential energy surface method was used to calculate reorganization energy of the studied compound. The hole reorganization energy is slightly smaller than that of the electron reorganization energy. The largest bond-length changes upon reduction and oxidation are mainly localized on the rings containing B-N bonds. It is found that the photophysical properties of azaboradibenzo[6]helicene can be effectively tuned upon substitution. In view of the second-order polarizability value and intrinsic non-centrosymmetric electronic structure, the studied compounds have the possibility to be excellent second-order nonlinear optical materials.