Application of Raman spectroscopy and quantum chemistry for featuring the structure of positively charged species in macrocyclic π-conjugated diacetylene-bridged oligothiophenes

Different types of stable positively charged defects compatible with the electronic and molecular structure of a series of macrocyclic molecular materials containing symmetrically butylated terthienyl or quinquethienyl segments connected through diacetylenic bridges were studied by means of Raman spectroscopy. In all cases iodine was used as the oxidant, whereas for the largest macrocycle in situ spectroelectrochemistry was also employed. Comparison of the Raman spectra obtained either electrochemically or on treatment with iodine indicates that iodine behaves as a moderate oxidant giving rise to fairly stable positive charged defects. The comparison of the Raman spectra obtained upon iodine doping for two series of homologous molecules, namely open-chain diacetylene-bridged and non-bridged oligothiophenes, with those of the macrocyclic compounds suggests that each terthienyl or quinquethienyl building block is able to accommodate one positive charge in the form of a polaron. Density functional theory quantum chemical calculations were performed, at the DFT//B3LYP/3-21G* level, for two model systems to assess useful information about the evolution of the molecular structure and charge distribution upon oxidative doping of the compounds. Copyright (C) 2004 John Wiley Sons, Ltd.