We firstly benchmark 22 DFT functionals for the triangulene monomer and dimer, including PBE, BLYP, BP86, ωB97XD, 57 ωB97M-V, 58 HSE06, B2GP-PLYP, 60 PWPB95, 61 B2PLYP, and ωB97X-2 (Table ). This comprehensive selection of functionals covers GGA, meta-GGA, hybrid-GGA, hybrid-meta GGA, range-separated hybrids, and double hybrids. The total energy of CSS, OSS and HS, namely triplet for the monomer and quintet for the dimer, are calculated, and J and ΔEspin are derived. For OSS states, the brokensymmetry approach is employed, while the stability of DFT wavefunction is tested. As in Gaussian 16 it is possible to automatically optimize the wavefunction until it is stable, most of the calculations are performed employing this code, except for SCAN, r 2 SCAN-3c, ωB97M-V, ωB97X-2, B2GP-PLYP, and PWPB95, which are not available in Gaussian 16. Instead, these functionals have been studied using the ORCA 5.0