Theoretical spectroscopy of a NIR-absorbing benziphthalocyanine dye

Abstract

Benziphthalocyanines are (Yanai et al. in Chem Phys Lett 393:51–57, 2004) phthalocyanines in which one isoindoline unit has been replaced by a phenyl ring. In this study, we focus on a macrocycle of this family recently synthesized by Uchiyama and co-workers (Toriumi et al. Angew Chem Int Ed 53:7814–7818, 2014), and composed of three indoline units (substituted with 2,6-diisopropylphenyl-oxy groups) and one resorcinol unit. We aim at characterizing the possible tautomers to evaluate whether this compound might exist as a mixture of several forms or not. To reach our goals, we use state-of-the-art ab initio theories, i.e., Time-Dependent Density Functional Theory coupled with a refined solvation model (the Polarizable Continuum Model) as well as post-Hartree Fock approaches. We first investigate the stability, the structure and the aromaticity of the possible tautomers before analyzing their spectroscopic signatures. Using an approach going beyond the vertical approximation, we compare experimental and theoretical 0–0 energies and band shapes. This study allows us to point out the dominant presence of the quinoidal form as well as to unravel the vibronic contributions responsible for the specific shape of the optical spectrum.