Isolation and Characterization of the Triradical 1,3,5‐Trimethylenebenzene

Abstract

Hoch symmetrisch ist das Quartett‐Triradikal Trimethylenbenzol, das erstmals isoliert werden konnte (siehe Struktur). Weil es trotz seiner offenschaligen Konfiguration photochemisch stabil ist, stellt es einen vielversprechenden Baustein für magnetische Materialien dar.

Energy Gaps of Polyradicals from an Effective and Transferable Hamiltonian with through-Bond Interactions

“…It is known that these double-degenerate excited states are in fact a Jahn−Teller pair. 54,55 The energy gap predicted is 0.67 eV, which is also within quantum chemistry values.…”

“…We show in Table that our model Hamiltonian correctly predicts a spin quartet ground state with a double-degenerate spin doublet state immediately above. It is known that these double-degenerate excited states are in fact a Jahn–Teller pair. , The energy gap predicted is 0.67 eV, which is also within quantum chemistry values.…”

“…3,54 With few experiments available, it was only recently studied using matrix isolation spectrocopy. 55 Theoretical computations based on CASSCF and CASPT2N found an adiabatic doublet-quartet energy splitting of 0.6−0.7 eV 56,57 that has been corroborated in a recent work based on the DDCI CAS(3,3) methodology. 58 We show in Table 1 that our model Hamiltonian correctly predicts a spin quartet ground state with a double-degenerate spin doublet state immediately above.…”

“…1,3,5,-Trimethylenebenzene ( TriMB on Figure ) is the basis of many high-spin polyradicals described in the literature and has a quartet ground state. , With few experiments available, it was only recently studied using matrix isolation spectrocopy . Theoretical computations based on CASSCF and CASPT2N found an adiabatic doublet-quartet energy splitting of 0.6–0.7 eV , that has been corroborated in a recent work based on the DDCI CAS­(3,3) methodology …”

Characterization and Quantification of Polyradical Character

“…This provides us with reference values for the atomic and diatomic contributions of ⟨ Ŝ 2 ⟩ in the ideal case of three perfectly localized spins for different electronic states. Finally, the spin properties of a number of all σ, all π, and σ–π triradicals such as trimethylenebenzene (TMB), − tridehydrobenzene isomers (TDB), − and dehydro-m-xylylene (DMX), ,, are characterized in detail in their lowest-lying doublet and quartet electronic states. Direct comparison with the appropriate reference values obtained for the model system permit to actually quantify the triradical character of these species.…”