Ab initio and first principles theoretical investigations of triplet-triplet fluorescence in trimethylenemethane biradicals

Abstract

Theoretical studies on triplet-triplet (T1 → T0) fluorescence of the arylated trimethylenemethane (TMM) biradicals, 32, were carried out using post-Hartree-Fock ab initio and various first principles density functional theory methods. Analysis of optimized geometries including bond alternations and spin distributions indicates that the triplet ground (32) and excited (32∗) states of these biradicals have aromatic and quinoidal characteristics, respectively. Inspection of their calculated electronic structures shows that, in comparison to 32, one of the spins in 32∗ is more delocalized onto arene-rings linked to the TMM framework.