A comprehensive study of the spectral and photophysical properties of arylthiophenes

A series of conjugated oligomers with rigid (fused-ring) structure, consisting in different polycyclic aromatic hydrocarbons (PAHs) possessing a single thiophene unit, here designated as arylthiophenes, were investigated in solution. For presentation clarity, the compounds were organized in two different groups. The first group includes the compounds where one, two, three and four benzene rings are added to a thiophene unit (a compound with two dibenzothiophene units was also investigated) and the second group includes those compounds where a single thiophene ring is located at different positions in a skeletal-type polyaromatic hydrocarbon (in the present case phenanthrene). The study includes a complete spectroscopic evaluation (including singlet–singlet and triplet–triplet absorption, fluorescence and phosphorescence spectra) as well as a photophysical evaluation (fluorescence, phosphorescence and triplet lifetimes together with fluorescence and triplet occupation quantum yields. With all the above, a complete set of deactivation rate constants (kF, kIC and kISC) was determined. From the fluorescence and phosphorescence spectra the energy of the lowest lying singlet and triplet states (S1 and T1) and the energy of splitting between the two states (ΔES1–T1)(ΔES1–T1) was obtained. Semi-empirical ZINDO/S-CI calculations were performed and corroborated the nature and state order experimentally obtained.