Influence of inter-ring bridge on the optical properties of thiophene-based oligomers

Four tetramers, based on thiophene and phenylene residues in which the torsion angles between thiophene rings are blocked by a chemical bridge, are characterized with X-ray diffraction analysis and optical spectroscopy by comparison with quaterthiophene. Structural determinations show different packing arrangements for substituted and unsubstituted oligomers, resulting in different π-overlap among adjacent molecules. While in solution, the locked molecules display red-shifted absorptions and decreased Stokes-shifts, in the solid state, their optical properties strongly depend on the packing arrangements.