Revisiting the optical signatures of BODIPY with ab initio tools

Abstract

BODIPY dyes constitute one of the most efficient class of fluorescent molecules, yet their absorption and emission signatures are hardly predictable with theoretical tools. Here, we use a robust Time-Dependent Density Functional Theory approach that simultaneously accounts for solvent and vibrational effects, in order to simulate the optical properties of a large panel of BODIPY derivatives. In particular, this contribution is focussed on the accurate determination of both the 0–0 energies and vibronic shapes, that allow meaningful comparisons between experimental measurements and theoretical simulations. It turns out that Truhlar's M06-2X functional is well suited for modelling the variations of the 0–0 energies induced by side groups, modifications of the skeleton, stiffening or extension of the π-path. Indeed, while the absolute mean deviation remains quite sizeable, the determination coefficient between experimental and theoretical energies is exceptionally large (R² = 0.98), highlighting the robustness of the proposed approach. In addition, for most BODIPYs, theory is able to accurately reproduce vibrationally resolved bands. The developed protocol was successfully applied to provide insights for both pH and ion sensors. It also allowed the understanding of the optical behaviours of a series of BODIPY dimers and NIR dyes. This constitutes an unprecedented investigation of several BODIPY dyes both in terms of the number of treated molecules (more than sixty) and of the reliability of the predictions.