Spectroscopic and theoretical determination of the electronic structure ofthiazyl chains and extrapolation to poly(sulfur nitride), (SN)(x): A contribution to the study of conducting polymers

The filled and empty level structures of the thiazyl chains R-NSN-R and (R- NSN)(2)S, with R = Si(CH3)(3), are investigated by means of ultraviolet pho toelectron and electron transmission spectroscopy. The spectral features ar e interpreted with the support of ab initio Hartree-Fock (HF)/6-31G* and se miempirical AM1 calculations. within the Koopmans' theorem approximation, a nd with density functional theory. using the orbital energies of the transi tion state electronic configuration. Post-HF calculations with infinite-ord er coupled-cluster expansion are employed to evaluate the first vertical el ectron 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 t rans-oligoethenes, are extrapolated in order to evaluate the first ionizati on energy and electron affinity values for the corresponding (ideal) gas-ph ase polymers. Poly(sulfur nitride) is predicted to possess a smaller ioniza tion energy and a sizeably higher electron affinity than those of trans-pol yacetylene, with a consequent greatly reduced highest occupied molecular or bital-lowest unoccupied molecular orbital energy gap, in agreement with its highly conductive nature.