In the continuous quest for improving TD-DFT methodologies as a tool to predict the photophysical features of solvated chromophores, we investigate two model regioisomers based on the 1,2,3-triazole moiety. Starting from their experimental absorption and emission spectra, key energy differences highlighting the main trends between the two isomers are extracted and used to gauge the accuracy of several levels of theory. RI-CC2 and EOM-CCSD calculations allow us to ascertain that the low energy spectra are not linked to double excitations. In a vacuum, none of these methods nor any of the implemented TD-DFT levels of theory, ranging from global hybrids (PBE0, B3LYP) to range-separated functionals without (CAM-B3LYP, ωB97X) or with dispersion corrections (ωB97X-D), are able to capture the key features that differentiate the two chromophores. Accounting for solvent within a specific PCM model allows us to recover experimental trends, but the dramatic changes occurring when moving from toluene to THF and/or when using different PCM approaches (LR, cLR, SS) suggest that this agreement is probably fortuitous. Even if the ωB97X-D functional combined with the SS-PCM scheme leads to quantitative agreement with experiment, TD-DFT results obtained for 1,2,3-triazole based chromophores need to be treated with caution. We also show that the SS-PCM approach may be useful to test current and novel exchange-correlation functionals against the charge transfer failure.

International audienceWe report the synthesis, the photophysical and the two-photon absorption (2PA) properties of a series of octupolar bipyrimidine-based ligands incorporating N-substituted amines as terminal donor groups. The effect of replacing phenylvinylene π-conjugated linkers by fluorenylvinylene ones was also investigated. The linear absorption spectrum of these compounds is dominated by an intensive charge transfer band which is sensitive to N-substitution and the π-bridge nature. The excitation anisotropy spectrum indicates that this band encompasses multiple S0 → Sn transitions, whose occurrence is well rationalized on the basis of the Frenkel exciton model. The 2PA spectrum also corroborates the presence of several electronic transitions. In apolar or moderately polar medium, excited ligands mainly deactivate through a highly emissive intramolecular charge transfer (ICT) state localized within a single branch of the chromophore. In highly polar medium, the solvent-induced stabilization of the low emissive twisted intramolecular charge transfer (TICT) state leads to a severe quenching of the fluorescence. The same mechanism is observed upon complexation with Zn2+. According to single-crystal X-ray analyses, metal-induced planarization of the bipyrimidine chelating site was observed for the short length ligands. Such a dimensional change from D2d to D2h symmetry leads to a decrease of 2PA cross-sections with respect to the free ligands. A divergent effect is observed for the complex with the long length ligand since the three-dimensional structure is maintained which induces a sizeable increase of the 2PA cross-section with a maximum value of up to 2000 GM