Spectroscopic Characteristics and Intermolecular Interactions of Thiophene/Phenylene Co-Oligomers in Solutions

Thiophene/phenylene co-oligomers that include the thiophenes and phenylenes with various arrangements in the molecule were investigated spectroscopically in solutions and compared with oligothiophenes and oligophenylenes. The electronic spectra are influenced by both the molecular size and the difference in the thiophene/phenylene arrangements. In the dilute regime (∼10-5 M) monomeric emissions prevail. Quantum efficiencies of the fluorescence emissions of the co-oligomers are estimated in this regime. High quantum efficiencies of 0.79 and 0.74 were recorded for 4,4‘-bis(2-thienyl)biphenyl (T2P) and 1,4-bis(5-phenylthiophene-2-yl)benzene (AC5), respectively. The experimental data in the dilute regime are compared with the results of the quantum chemical calculations at semiempirical levels. Intermolecular interactions increasingly play a role for higher concentrations. The spectroscopic characteristics in this regime are closely inspected using 2,5-diphenylthiophene (P1T), 5,5‘-diphenyl-2,2‘-bithiophene (...