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

Abstract

Gas-phase photoelectron spectroscopy and theoretical calculations are used to study the electronic structure of 1,2-dichalcogenins. Photoelectron spectra are reported for 1,2-dithiin, 3,6-dimethyl-1,2-dithiin, 3,6-diisopropyl-1,2-dithiin, 3,6-di-tert-butyl-1,2-dithiin, 2-selenathiin, 1,2-diselenin, 3,6-dimethyl-1,2-diselenin, and 3,6-di-tert-butyl-1,2-diselenin and are assigned on the basis of (a) trends in ionization cross sections as the ionization photon energy is varied and (b) shifts of the ionizations as chemical substitutions are made. The calculated properties of 1,2-dithiin and 3,6-dimethyl-1,2-dithiin are compared to experimental results. The first four filled frontier valence orbitals are associated with orbitals that can be described as being primarily carbon π and chalcogen lone pair in character. Comparison of spectra collected with He I, He II, and Ne I ionization sources for each compound indicate that there is a large degree of mixing of chalcogen and carbon character through most of the valence orbitals. The highest occupied molecular orbital of the selenium-containing compounds has more chalcogen character than the highest occupied molecular orbital of the 1,2-dithiins. The photoelectron spectra of 1,2-dithiin and 1,2-diselenin contain a sharp ionization that corresponds to removal of an electron from an orbital that is predominantly chalcogen−chalcogen σ bonding in character. The narrow ionization profile indicates fairly weak chalcogen−chalcogen σ bonding in this orbital, which would result in a corresponding weakly antibonding chalcogen−chalcogen σ* orbital. Computational results show that an orbital that is primarily S−S σ* in character is the lowest unoccupied molecular orbital of 1,2-dithiin, and electronic transition calculations show a low-energy HOMO-to-LUMO transition that can be described as a π/lone pair-to-σ* transition that explains the unusual color of 1,2-dichalcogenins.

Investigation of metal–dithiolate fold angle effects: Implications for molybdenum and tungsten enzymes

“…The specific assignment of the ionizations can be made by comparison of the spectra to those of related molecules and by comparison of the relative ionization intensities as the source energy is varied (21). From previous experimental studies (20,50) and calculations of atomic photoionization cross-sections (51), it is expected that ionizations from orbitals with significant Ti 3d or Mo 4d contributions will increase in intensity compared with ionizations of primarily S 3p character when data collected with a HeII photon source is compared with data collected with a HeI photon source. Mixing of metal and sulfur character in orbitals will result in smaller changes in relative intensities of ionizations being observed.…”

Electronic excitation of sulfur-organic compounds - performance of time-dependent density functional theory

“…As detailed elsewhere [29], the TDDFT study of 33 predicts p 3 r à andp 3p à type transitions which determine the NUV/vis spectrum. Although the CIS calculation of 31 resulted in a ®rst absorption band at 350 nm rather than the 450 nm found experimentally [29,60], the nature of the transition is the same as in TDDFT calculations [29].…”

“…The longest-wavelength absorption of the meropolymethinetype dyes 1,2-dithiol-2,2-ylidene acetaldehyde (57), 4-(1,3-benzodithiol-2-ylidene)cylohexadien-1-one (58) and the syn-pyramidalized 2-(thioxanthen-9-ylidene)indane-1,3-dione (59) are calculated at wavelengths too short ( Table 2). The erratic blueshift of the calculated wavelengths of the color bands increases in passing from the tetrathiaporphyrine dication (60) to the bisthienylmethinium cation (61) to the open-chain polymethine dye 62. The error in the calculation of the red±blue colored 62 amounts to about 0.74 eV.…”

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)

“…Some of these hexa-heterocycle systems have been intensively investigated [1]. Two of these 1,2-dichalcogenins, dithiin, and diselenin and their derivatives have been synthesized and/or extracted from plants [2][3][4][5][6][7][8].…”