Photoinduced infrared spectra of oligomers and polymers of thiophene h
ave been recorded and systematically studied. The interpretation of th
e data is based on the ECC theory1.The experimental results and the th
eory provide the way to measure the effective delocalization lenght in
the materials studied and give information about their intra and inte
rmolecular structure. Temperature, power density and excitation wavele
ngth dependencies are discussed.