Insight into the optical properties of meso-pentafluorophenyl(PFP)-BODIPY: An attractive platform for functionalization of BODIPY dyes

Abstract

The pentafluorophenyl (PFP) moiety is an important and versatile substituent in the chemistry of BODIPYs, porphyrins and corroles. The widespread use of PFP meso-substituted compounds, as intermediates in the synthesis of more complex pyrrole derivatives, is the motivation behind this work, which investigates the optical properties of the meso-PFP-BODIPY from a theoretical point of view. From the panoply of computational tools available for this purpose, we have considered the MS-CASPT2//CASSCF multiconfigurational protocol, and other monoreference methods, including time dependent density functional theory, TD-DFT, the second order approximate couple cluster, CC2, and the algebraic diagrammatic construction scheme of the polarization propagator in its second order, ADC(2). We have identified ADC(2) as the most suited method for the characterization of the absorption properties of BODIPYs. Besides its computational efficiency and the small dependence shown towards the basis set flexibility, the results obtained with this method are independent from the preexisting knowledge of the system and its properties to be calculated by the user. In general, all the methods evaluated show a good performance when compared with experimental results, especially if implicit solvent effects are taken into account, delivering errors which amount to 0.05 eV. Finally, we discuss the effect of the electron-withdrawing PFP substituent at the meso-position on the absorption and emission energies of the boron-dipyrromethene core. The comparison of the PFP-substituted and core BODIPY spectroscopic properties reveals that this substituent red-shifts both the absorption and the emission of the parent dye. On the one hand, the incorporation of this substituent was found to reduce the HOMO-LUMO gap, and on the other it induces a strong destabilization of the electronic ground state along the global coordinate leading the system from the Franck-Condon region to the position of the first excited state, S1, minimum, suggesting a lower S1/S0 internal conversion funnel compared to the parent BODIPY compound.