Optical properties of poly[(3-pentyl-5-oxyazobenzene)thiophene].

The extensive spectroscopical characterization here reporteù indicates tlat the prese,nce ofthe azobenzene chromophore in the side chain is not substantially affecting the optical properties of the conjugated backbone. The long lived photoexcited species leading to the photoinduced absorption spectial features are intrinsic to the thiophene backbone, even when tle azobe,nzene chromophore is photoexcited by W light. Ifpe increase of photoconductivity [2] is a general feature of polyalkylthiophene containing azíbenzene ohromophores in the side chain, our results bring oovel data for understanding the mechanism of the enhanoement of photoconduotivity. Two different mechanisms may explain this enhancement : an increase of mobility due to azobenzenes actitrg as hopping sites for the thiophene photocarriers[2]; or the prese,lroe of azoberzene may favour ttre formation of charge photocarriers of the thiophene backbone. In the second case, like in polyhexylthiophene-C6g composites [13], an increase oft]e photoinduced activity ofthe thiophene backbone should be expected. Our data bring support to île increase of charge mobility as the inorease ofthe photoinduced signal is not detected.