To start with, we target the two triangulene structures in Fig. . In recent years, these molecules have been extensively investigated theoretically as prototypical examples of ST inversion. Experimental absorption spectra of both dyes, collected in the 80's, will be exploited to parametrize and validate the PPP model. PPP parameters for C atoms, derived in the 1950s, are well established and transferable among different molecules. Specifically, setting the on-site energy of C atoms to zero, we adopt the standard value for the on-site e-e interaction, U C = 11.26 eV, and for the nearest-neighbor C-C hopping, t = 2.4