Spectroscopic and Theoretical Determination of the Electronic Structure of Thiazyl Chains and Extrapolation to Poly(sulfur nitride), (SN)x: A Contribution to the Study of Conducting Polymers

Abstract

The filled and empty level structures of the thiazyl chains R−NSN−R and (R−NSN)2S, with R = Si(CH3)3, are investigated by means of ultraviolet photoelectron and electron transmission spectroscopy. The spectral features are interpreted with the support of ab initio Hartree−Fock (HF)/6-31G* and semiempirical AM1 calculations, within the Koopmans' theorem approximation, and with density functional theory, using the orbital energies of the transition state electronic configuration. Post-HF calculations with infinite-order coupled-cluster expansion are employed to evaluate the first vertical electron affinity value of R−NSN−R, with R = H and CH3. The experimental and theoretical results obtained for the thiazyl chains, as well as those for trans-oligoethenes, are extrapolated in order to evaluate the first ionization energy and electron affinity values for the corresponding (ideal) gas-phase polymers. Poly(sulfur nitride) is predicted to possess a smaller ionization energy and a sizeably higher electron affinity than those of trans-polyacetylene, with a consequent greatly reduced highest occupied molecular orbital−lowest unoccupied molecular orbital energy gap, in agreement with its highly conductive nature.