Photothermal beam deflection spectroscopy in the near IR on poly[3-alkylthiophene]s

Photothermal beam deflection spectra of non-oxidized polythiophenes with different lengths of alkyl side chains have been taken in the near IR, which is the interesting spectral regime for nonlinear optical waveguide applications. Two kinds of films could be fabricated for all polythiophene derivatives which differ in the optical density and the strength of vibrational bands. For films of low absorption the intensity of the symmetric and antisymmetric CH2/CH3-stretching vibrations increase more than linearly with increasing side chain length. In a partly fluorinated polythiophene these modes disappear. An electronic absorption band in the shoulder of the main absorption of the conjugated main chain was found in derivatives which have regio regular substituted side chains and impurities of iron trichloride. (C) 1998 Elsevier Science B.V.