All calculations were performed using a def2-TZVP basis set. The supplementary basis sets (jbas and cbas) were always of the same quality as the regular ones. routines. It enables one to carry out a full LVC parametrization 62 of the PES using both the BSE@GW and TD-DFT levels of theory. The computation of the overlap matrix was also performed in SHARC's WFOVERLAP module. Our LVC model included the lowest 10 singlet (including the singlet ground state) and 14 triplet states. We opted for a def2-TZVP basis set as we observed that the BSE@GW calculations demonstrate a high sensitivity to basis set quality (see Fig. in the ESI ). Both the RI and TDA were employed and the first 49 core molecular orbitals were discarded to calculate the wave function overlaps. For this, a wave function truncation threshold of 0.998 was chosen. The same convergence criteria and grid settings for the BSE@GW calculations were chosen as those used for the spectra calculations. For this model, we used a displacement factor of 0.05. To calculate the GW quasiparticle energies, contour deformation techniques (CD) were used with an orbital range of [157,177] for which the correlation part of the self-energy was calculated. The eigenvalue-only self-consistent GW scheme (evGW) was used to converge quasiparticle energies. The range-separated functional LC-BLYP(α = 0.2, ω = 0.08) was used as a starting point.