On the Computation of Adiabatic Energies in Aza-Boron-Dipyrromethene Dyes.

We have simulated the optical properties of Aza-Boron-dipyrromethene (Aza-BODIPY) dyes and, more precisely, the 0-0 energies as well as the shape of both absorption and fluorescence bands, thanks to the computation of vibronic couplings. To this end, time-dependent density functional theory (TD-DFT) calculations have been carried out with a systematic account of both vibrational and solvent effects. In a first step, we assessed different atomic basis sets, a panel of global and range-separated hybrid functionals as well as different solvent models (linear-response, corrected linear-response, and state-specific). In this way, we have defined an accurate yet efficient protocol for these dyes. In a second stage, several simulations have been carried out to investigate acidochromic and complexation effects, as well as the impact of side groups on the topology of the optical bands. In each case, theory is able to accurately reproduce experimental results and the proposed protocol is consequently useful to design new dyes featuring improved properties.