ELECTROMODULATED ABSORPTION OF ALKYL SUBSTITUTED POLYTHIOPHENES AND POLYTHIENYLENEVINYLENES

Electric field induced changes in the optical properties of alkyl subs tituted polythiophenes and polythienylenevinylenes are studied in the spectral region of the pi-pi electronic transition. The spectral shap e and the magnitude of the electroabsorption (EA) signal are compared for mono- and di-alkyl substituted polythienylenevinylenes as well as for a well ordered poly(3-alkylthiophene). For all these polymers the induced absorption scales quadratically with the applied electric fiel d and its lineshape is field invariant. For the well ordered poly(3-al kylthiophene) the EA spectrum resembles the first energy derivative of the unperturbed absorption, though there are several additional featu res. The EA spectra of the alkyl substituted polythienylenevinylenes d o not however have a characteristic (e.g. first, second or third deriv ative) relationship to the unperturbed absorption.