To enhance computational efficiency, we compared PPP-CI results with those obtained at the PPP-RASCI level, which eliminates potentially negligible high-energy configurations by restricting the number of holes/particles in the lower and higher HF-MOs. This limitation reduces the overall number of configurations, making RASCI more computationally efficient than CISDT. We started by selecting a subset of MOs to span the active RAS2 space, where all possible electron excitations are considered (reduced full-CI or CASCI). This active space should include the most chemically relevant MOs for the system. For 3T triangulenes, we used a RAS2 subspace containing the doubly degenerate HOMO and the next 4 virtual molecular orbitals, totaling 4 electrons in 6 MOs (see Fig. and).