Investigating XC-functionals towards describing experimentally relevant excited state properties of NIR-BODIPY derivatives†

Abstract

The predictive and analytical power of time-dependent density functional theory (TD-DFT) has been instrumental in the design and mechanistic understanding of numerous organic chromophores. Yet, the widely popular boron-dipyrromethene (BODIPY) dye class suffers from notorious TD-DFT accuracy issues undermining the serviceability of the technique. Highly-correlated wave function approaches are much better at reproducing photophysical properties but become computationally unviable when making the push towards larger near-infrared (NIR) active structures. In an effort to find the protocol most capable at helping experimentalists design and analyze novel NIR BODIPYs, we have benchmarked 11 global or range-separated hybrid exchange-correlation functionals (XCFs) with different amounts of Hartree-Fock exchange. By relating both transition energies and oscillator strengths, first through a set of resolution-of-the-identity second-order coupled cluster (riCC2) calculations and then directly to experiment, it is revealed which XCFs behave most consistently and whether the Tamm-Dancoff approximation is best employed.