The first non-Kekule polynuclear aromatic high-spin hydrocarbon: Generation of a triangulene derivative and band structure calculation of triangulene-based high-spin hydrocarbons

An attempt has been made to generate a triangulene derivative (3), the firs t non-Kekule polynuclear aromatic hydrocarbon. By oxidizing a corresponding precursor in a toluene solution by p-chloranil, the desired ground-state t ripler species in the rigid matrix was identified by ESR spectroscopy. The spin Hamiltonian parameters were determined by spectral simulation as S = I , g = 2.003, \D/hc\ = 0.0073 cm(-1) \E/hc\ - 0 cm(-1). The mean inter-spin distance was estimated to be 5.64 Angstrom by a point-dipolar approximation , being in consistent with the spin-delocalized nature of triangulene 3. It has turned out that 3 is stable enough to give the tripler ESR spectra, bu t the partial exposure of reactive carbon sites with the largest spin densi ty causes the intermolecular chemical-bond formations. The band structure c alculations have been carried out for triangulene-based high-spin polymeric systems, demonstrating the generation of a flat pi -nonbonding crystal orb ital, which delocalizes on the whole system. The fiat band with N-fold dege neracy accommodates N ferromagnetically exchange-coupled spins in the groun d state.