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

摘要

Theoretical studies on triplet-triplet (T-1 -> T-0) fluorescence of the arylated trimethylenemethane (TMM) biradicals, (3)2(center dot center dot), 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 ((3)2(center dot center dot)) and excited ((3)2(center dot center dot)*) states of these biradicals have aromatic and quinoidal characteristics, respectively. Inspection of their calculated electronic structures shows that, in comparison to (3)2(center dot center dot), one of the spins in (3)2(center dot center dot)* is more delocalized onto arene-rings linked to the TMM framework.