Tuning the Singlet-Triplet Energy Gap in a Non-Kekule Series by Designed Structural Variation. The Singlet States of N-Substituted-3,4-dimethylenepyrrole Biradicals

摘要

Semiempirical quantum chemical calculations (AM1/CI and PM3/CI) confirm the qualitative perturbational prediction that electron-withdrawing groups on the ring nitrogen of a 3, 4-dimethylenepyrrole should diminish the energy separation of the singlet and triplet and triplet states to near zero. Syntheses of a series of precursors of such biradicals have been developed.