Photophysical properties of sexi(3-methoxythiophene): evidence for energy migration in a conducting oligomer, based on fluorescence quenching.

The electronic absorption and fluorescence excitation and emission spectra of poly(3-methoxythiophene) (PMOT), a soluble, electroactive oligomer mainly constituted of hexamer, were investigated in dimethylsulfoxide at room temperature. The study of PMOT photophysical properties suggests the existence of important pi-electronic delocalization in the oxidized and reduced form of the oligomer. A significant fluorescence quenching of PMOT takes place in the presence of various quenchers such as dimethylterephthalate, potassium iodide and thallium acetate. Quenching mechanisms implying a quencher-induced intersystem-crossing step are proposed. Modified Stern-Volmer relationships were obtained with large quenching bimolecular rate constants (2.7 x 10(9)-6.1 x 10(11) l mol(-1) s(-1)), which suggests electronic energy migration throughout the repeat units of the PMOT hexamer.