Predicting Magnetic Coupling and Spin-Polarization Energy in Triangulene Analogues

Abstract

Triangulene and its analogue metal-free magnetic systems have garnered increasing attention since their discovery. Predicting the magnetic coupling and spin-polarization energy with quantitative accuracy is beyond the predictive power of today’s density functional theory (DFT) due to their intrinsic multireference character. Herein, we create a benchmark dataset of 25 magnetic systems with nonlocal spin densities, including the triangulene monomer, dimer, and their analogues. We calculate the magnetic coupling (J) and spin-polarization energy (ΔE spin) of these systems using complete active space self-consistent field (CASSCF) and coupled-cluster methods as high-quality reference values. This reference data is then used to benchmark 22 DFT functionals commonly used in material science. Our results show that, while some functionals consistently correctly predict the qualitative character of the ground state, achieving quantitative accuracy with small relative errors is currently not feasible. PBE0, M06-2X, and MN15 are predicting the correct electronic ground state for all systems investigated here and also have the lowest mean absolute error for predicting both ΔE spin (0.34, 0.32, and 0.31 eV) and J (11.74, 12.66, and 10.64 meV). They may therefore also serve as starting points for higher-level methods such as the GW or the random phase approximation. As other functionals fail for the prediction of the ground state, they cannot be recommended for metal-free magnetic systems.

Magnetic Coupling Control in Triangulene Dimers

“… The molecules of the TRI-series (including TRI-TRI, TRI-CC-TRI, TRI-CCCC-TRI, and TRI-Ph-TRI) have four unpaired electrons, while the other dimers constructed by monoradicals have two spins. We optimized the structures of these radicals as free molecules and calculated their magnetic properties at the PBE0/def2-TZVP level with the Gaussian 16 package , (see computational details for more information; for validation see ref ). We find that all of them have OSS ground states and thus AFM interactions between the monomers (Table and Figure a).…”

The role of electrostatic potential in the translocation of triangulene across membranes

“… 12–14 Yu created a benchmark dataset of 25 magnetic systems with nonlocal spin densities that can more accurately predict electronic ground state for triangulene analogues. 15 Shen introduced a new intramolecular radical–radical coupling approach and successfully synthesize two fused triangulene dimers efficiently. 16 Arikawa synthesized a kinetically-stabilized nitrogen-doped triangulene cation derivative.…”

“…14 According to the calculation of density functional theory (DFT), the derivatives of triangulene have high affinity for DNA helix. [20][21][22][23] Nevertheless, there are different mechanisms in healthy tissues and tumours. Unlike the nontoxic buckled form in healthy tissues, in tumours with relatively low pH values, the derivatives can intercalate DNA double stranded base pairs in a planar form to disrupt biological processes, showing their potential anti-cancer properties.…”