A TD-DFT investigation of UV spectra of pyranoïdic dyes: A NCM vs PCM comparison

We report the calculation of the UV spectra of more than 40 substituted coumarins and chromones in solution. In particular, two solvent models are compared, the multipolar expansion model (NCM) developed in Nancy and the PCM scheme developed in Pisa and Napoli. All calculations are carried out at the NCM-TDPBE0/6-311G(2d,2p)//NCM-B3LYP/6-311G(2d,2p) and at the PCM-TDDFT/6-311+G(2d,2p)//PCM-DFT/6-311G(2d,2p) levels of theory. For most of the studied coumarin and chromone derivatives, there are at least two allowed excited states corresponding to transitions presenting a strong oscillator strength in the UV region. For the NCM treatment of substituted pyranones, the required accuracy for the design of molecules has been reached (we found a accuracy on the predictive data of 7 nm/0.08 eV for λmax(1) and 9 nm/0.18 eV for λmax(2)). Compared to PCM values, the NCM formalism provides λmax(1) predictions with equivalent accuracy and reliability. For λmax(2), the importance of diffuse functions is clearly demonstrated.