High-Spin Blatter’s Triradicals

Abstract

Robust organic triradicals with high-spin quartet ground-state provide promising applications in molecular magnets, spintronics, etc. In this context, a triradical based on Blatter’s radical has been synthesized recently possessing two doublet-quartet energy gaps with 70% occupation of quartet ground state at room temperature. The traditional broken-symmetry (BS)-DFT computed energy gaps are reported to be somewhat overestimated in comparison to the experimentally observed values. In this work, we have employed different ab initio methods on this prototypical system to obtain more accurate doublet-quartet energy gaps for this triradical. The spin constraint broken symmetry (CBS)-DFT method has been used to reduce the overestimation of energy gaps from BS-DFT. To address the issues of spin-contamination and multi-reference nature of low-spin states affecting the DFT methods, we have computed the energy gaps using appropriately state-averaged CASSCF and NEVPT2 computations. Using a series of active spaces, our calculations are shown to provide quite accurate values in concordance with the experimentally observed results. Further, we have proposed and modeled another three triradicals based on Blatter’s radical which are of interest for experimental synthesis and characterization. Our computations show that all these triradicals also have quartet ground state with similar energy difference between the excited doublet states.