Electronic properties and aromaticity of substituted diphenylfulvenes in the ground (S0) and excited (T1) states

In the present account, we investigate electronic properties of diphenylfulvene and its derivatives substituted in phenyl rings. The results were compared with the analogous properties of fulvene and its derivatives with the same substituents at the exocyclic carbon atom. All properties were evaluated and compared in the ground electronic S0 state and in the first excited T1 triplet state. These properties are dipole moments, charges, number of π electrons, and aromaticity of the fulvenic, five-membered ring in the two sets of compounds. The latter property was estimated by the harmonic oscillator model for aromaticity (HOMA) index and, for the fulvenes group, by the calculation of aromatic stabilization energy in both electronic states. It was also investigated whether Baird's rule alone can account for the aromaticity differences in the two electronic states.