Density functional theory study of silole‐fused tetramethyleneethane biradicals with orbital interactions

Abstract

The geometries, energy gap between singlet and triplet states (S–T gap), electronic transitions, and molecular orbitals of the diphenyl derivative of the silole‐fused tetramethyleneethane (TME) (3,4‐dimethylenesilole) biradical 7•• were determined by using the density functional theory method at the unrestricted Becke, three‐parameter, Lee–Yang–Parr/cc‐pVDZ level. In a manner similar to that of the parent TME biradical, the S–T gap of 7•• is small. The wavelengths of electronic transitions of 37•• (λET = 450 nm) are calculated to be different from that of 17•• (λET = 673 nm). These differences are attributed to interactions between orbitals of the two allyl radical moieties, especially, the existence of double σ*–π* conjugation, that is, π*–σ*–π* conjugation, that takes place in the silole subunit. Copyright © 2011 John Wiley & Sons, Ltd.

Diradicals

“…The singlet-ground-state diradical DR69 was observed at λ max = 661 nm . DFT computational predictions of the ground-state spin multiplicity and electronic properties, including excitation energies, were obtained for silole-fused TME diradical DR70 . The singlet state was found to be the ground-state spin multiplicity with an energy difference of 3.8 kcal mol –1 .…”