High-Spin Blatter's Triradicals.

Area of Science:

• Quantum chemistry
• Materials science
• Organic chemistry

Background:

• Organic triradicals with quartet ground states are key for molecular magnets and spintronics.
• Previous broken-symmetry DFT (BS-DFT) methods overestimated energy gaps compared to experiments.
• A Blatter's radical-based triradical exhibits low-lying doublet states and a quartet ground state.

Purpose of the Study:

• To accurately compute doublet-quartet energy gaps for a Blatter's radical-based triradical.
• To investigate and improve upon traditional BS-DFT limitations.
• To propose and computationally model new triradicals for experimental synthesis.

Main Methods:

• Employed various *ab initio* methods, including spin-constraint broken-symmetry DFT (CBS-DFT).
• Utilized state-averaged CASSCF and NEVPT2 computations to address spin-contamination and multireference issues.
• Performed calculations using a series of active spaces for high accuracy.

Main Results:

• Calculated energy gaps show strong agreement with experimental values, overcoming BS-DFT overestimation.
• Confirmed the quartet ground state for the prototypical triradical and two newly proposed analogues.
• Demonstrated the effectiveness of advanced *ab initio* methods for accurate electronic structure determination.

Conclusions:

• Accurate *ab initio* methods provide reliable energy gap values for organic triradicals.
• The studied triradicals, including new designs, possess quartet ground states suitable for advanced applications.
• Computational modeling is essential for guiding experimental synthesis and characterization of novel high-spin molecules.