The biradical character of 1,2-dithiin and its valence isomers

Pseudo Jahn-Teller origin of instability of planar configurations of hexa-heterocycles. Application to compounds with 1,2- and 1,4-C4X2 skeletons (X = O, S, Se, Te)

“…TD-DFT and CASPT2 calculations for 1,2-dithiin predicted a weak long-wavelength transition in the visible region [13]. For this molecule photochemistry and magnetic chemical shift experiments were performed [14], and vibrational frequency calculations were also carried out [15]. Photoelectron spectra and electronic structure of 1,2-dithiin, 1,2-diselenin and their derivatives are also reported [1,3,8].…”

Gas-Phase Photoelectron Spectroscopic and Theoretical Studies of 1,2-Dichalcogenins: Ionization Energies, Orbital Assignments, and an Explanation of Their Color

“…3 The dithiin ring is a theoretically interesting 8πelectron antiaromatic system that has been studied computationally. [3][4][5][6][7][8][9][10][11][12] Despite the absence of a normal chromophore, 1,2-dithiins are brightly colored reddish-orange compounds that absorb in the visible near 450 nm. An early quantum mechanical calculation 4 assigned the visible transitions in the spectrum of 1,2dithiin to a weak π-to-π* transition, but this calculation used a planar geometry that is unreliable, given the twisted geometry of 1,2-dithiin revealed by the microwave spectrum 13 and later calculations.…”

“…Thiarubrine A, 1a , thiarubrine B, 1b , and related compounds occur naturally in plants such as those of the Compositae ( Asteraceae ) family. , They show a wide range of biological activity both in the dark and in the light, including potent antifungal, antibacterial, antitumor, and nematocidal activity . The dithiin ring is a theoretically interesting 8π-electron antiaromatic system that has been studied computationally. − …”

“…Despite the absence of a normal chromophore, 1,2-dithiins are brightly colored reddish-orange compounds that absorb in the visible near 450 nm. An early quantum mechanical calculation 4 assigned the visible transitions in the spectrum of 1,2-dithiin to a weak π-to-π* transition, but this calculation used a planar geometry that is unreliable, given the twisted geometry of 1,2-dithiin revealed by the microwave spectrum and later calculations. − A more recent ab initio study 8 using the variation-perturbation CIPSI method calculated the energy of the first excited singlet states of 1,2-dithiin and assigned the visible transition to a 1 B (HOMO to LUMO) transition, but no explanation has been given for the unusual energy of this transition.…”

Ionization Energies and Dyson Orbitals of 1,2-Dithiin

“…The former have demonstrated the extensive antiviral, antifungal, antibacterial, and nematocidal properties of thiarubrines A and B . The syntheses of 1,2-dithiin pigments and the antibiotic activity of these compounds in darkness and in light have been widely investigated. , Theoretical interest issues from the possible antiaromaticity of six-member, eight-electron rings, tautomerism pertaining to ring-opened forms, and the stability of variational ansätze. − Configuration interaction calculations on the lowest excited states have provided explanations for the redness of 1,2-dithiin in terms of wave functions dominated by excited determinants where an electron is promoted from one of the highest occupied molecular orbitals of the ground state to the lowest unoccupied molecular orbital. , Gas-phase, photoelectron spectra (PES) of 1,2-dichalcogenins 11 have been interpreted in terms of Hartree−Fock molecular orbitals and their energies.…”