Two-Photon Circular Dichroism of an Axially Dissymmetric Diphosphine Ligand with Strong Intramolecular Charge Transfer

In this article we report on the study of the polarization dependent two-photon absorption (TPA) of (S)-(+)-(1,1'-binaphthalene-2,2'-diyl)bis(diphenylphosphine) (S-BINAP) in solution, and the theoretical-experimental analysis of its two-photon circular dichroism (TPCD) spectrum. The comparative examination of the following two correlation functionals, using the 6-31G* basis set, showed that the Coulomb attenuated method variant of the Becke's three-parameter exchange and the Lee-Yang-Parr (CAM-B3LYP) is more reliable than B3LYP in molecules such as S-BINAP, a heteroaromatic diphosphine chiral ligand with strong intramolecular charge transfer. To access the theoretical TPCD spectra, we employed time dependent density functional theory (TD-DFT) at the mentioned level of theory and over the first 40 electronic excited states including solvent effects by means of the polarizable continuum model (PCM). The extended calculation on twice as many electronic excited states in vacuo proved to be crucial for the correct assignment of the experimental bands. TPA measurements were performed in the femtosecond regime and over a broad spectral range using the double L-scan technique.