title: Electronic states of 1,6,6a lambda4-trithiapentalene and its 2,5-dimethyl and 2,5-diphenyl derivatives. Ultraviolet-visible linear dichroism spectroscopy and time-dependent density functional theory calculations.
abstract: The electronic transitions of 1,6,6a lambda4-trithiapentalene (TTP) and its 2,5-dimethyl and 2,5-diphenyl derivatives (DMTTP and DPTTP) are investigated by ultraviolet-visible linear dichroism spectroscopy on molecular samples partially aligned in stretched polyethylene, and by time-dependent density functional theory calculations (TD-B3LYP/6-31G*). The theoretical predictions are in good agreement with the observed polarization spectra, allowing a detailed assignment of observed transitions to calculated electronic states. According to the theoretical results, sigma-sigma* excitations involving orbitals associated with the unique S-S-S three-center bonding in the TTP ring system play a fundamental role in the description of low-lying electronic states. The visible absorption band close to 20,000 cm(-1) and the dominant peak in the near-ultraviolet region around 39,000 cm(-1) can thus be assigned to transitions with a high degree of sigma-sigma* character. The situation is slightly more complicated in the case of DPTTP because sterically induced twisting of the phenyl groups leads to mixing of pi and sigma orbitals.
authors.affiliation: Department of Life Sciences and Chemistry, Roskilde University, Denmark. spanget@ruc.dk
authors.forename: Jens
authors.initials: J
authors.lastname: Spanget-Larsen
mesh_terms: D003517:Cyclopentanes / Q000138:chemical synthesis / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods; D007700:Kinetics; D008745:Methylation; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols; D013053:Spectrophotometry / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: C472952:1,6,6a lambda4-trithiapentalene; C472954:2,5-dimethyl-trithiapentalene; C472953:2,5-diphenyl-trithiapentalene; D003517:Cyclopentanes; D010636:Phenols; D013438:Sulfhydryl Compounds