TURBOMOLE was also used for all SCS-CC2 and CC2 singlepoint calculations along the dissociation curves. The frozen-core and resolution of the identity 134 (RI) approximations were employed with appropriate auxiliary basis sets 135 . Coupled cluster singles doubles with perturbative triples excitation correction [CCSDR(3)] calculations for select points along the dissociation curves were carried out with Dalton2016, 137 also utilising the frozen-core approximation. The WFT calculations were used to identify suitable reference data for the subsequent assessment of TD-DFT methods.