A computational study of the effects of axial halogen substitutions of boron subphthalocyanines on their electronic spectra in solution and in the solid state.

Non-planar boron subphthalocyanine chloride is a talented photoelectric material and has been widely applied. In this paper, we have investigated the effects of axial halogen substitutions on electronic spectra of boron subphthalocyanines by combining DFT/TDDFT calculations and available experimental data in solution and in the solid state. We utilize long range separated density functional and polarizable continuum model to obtain the electronic structure and absorption spectra. The computed frontier molecular orbital energy matches well with experiment in dichloromethane and the simulated spectra correctly reproduce the trend of experiment in toluene. Furthermore, we model two configurations (convex-to-convex and concave-to-concave) of dimers of boron subphthalocyanines based on experimental structures in thin film: From F to Cl to Br substitution, the simulated wavelength of absorption peaks in the visible region slightly increases; in contrast, the absorption strength decreases. Moreover, our calculated results suggest that the convex-to-convex configurations of dimers may be the main contributors to the absorption spectra of X-BsubPC (X = F, Cl, Br) in thin film, though no experimental spectra of thin film of X-BsubPC (X = F, Br) yet. Finally, we find that CAM-B3LYP is able to reproduce the energy of frontier molecular orbitals quite well.