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

摘要

An attempt has been made to generate a triangulene derivative (3), the first non-Kekule polynuclear aromatic hydrocarbon. By oxidizing a corresponding precursor in a toluene solution by p-chloranil, the desired ground-state triplet species in the rigid matrix was identified by ESR spectroscopy. The spin Hamiltonian parameters were determined by spectral simulation as S = 1, g = 2.003, |D/hc| = 0.0073 cm~(-1), |E/hc| approx 0 cm~(-1). The mean inter-spin distance was estimated to be 5.64 A 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 triplet ESR spectra, but the partial exposure of reactive carbon sites with the largest spin density causes the intermolecular chemical-bond formations. The band structure calculations have been carried out for triangulene-based high-spin polymeric systems, demonstrating the generation of a flat #pi#-nonbonding crystal orbital, which delocalizes on the whole system. The flat band with N-fold degeneracy accommodates N ferromagnetically exchange-coupled spins in the ground state.