Singlet-triplet energy separation in divalent seven-membered cyclic conjugated compounds C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb

Abstract

The electronic and thermal energy differences, ΔE(t-s); enthalpy differences, ΔH(t-s); and free energy differences between the singlet and triplet states, ΔG(t-s), were calculated for C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb at the B3LYP/6-311++G (3df, 2p) level. The singlet-triplet splitting, G s-t, of C6H6C, C6H6Si, C6H6Ge, C6H6Sn, and C6H6Pb generally increased from C6H6C toward C6H6Pb. The most stable tautomers and conformers were suggested for the singlet and triplet states of C6H6M (M = C, Si, Ge, Sn and Pb). The geometrical parameters were calculated and discussed.