Electromodulated absorption of alkyl substituted polytiophenes and polythienylenevinylenes

Electric field induced changes in the optical properties of alkyl substituted polythiophenes and polythienylenevinylenes are studied in the spectral region of the pi-pi* electronic transition. The spectral shape 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 field and its lineshape is field invariant. For the well ordered poly(3-alkylthiophene) the EA spectrum resembles the first energy derivative of the unperturbed absorption, though there are several additional features. The EA spectra of the alkyl substituted polythienylenevinylenes do not however have a characteristic (e.g. first, second or third derivative) relationship to the unperturbed absorption.