Structural control of the optical properties of thin films of oligothiophenes

Absorption and photoluminescence properties of thin films of sexithiophene are largely determined by the molecular organization in the film, which can be controlled by chemical modification of the oligomers. The optical properties (absorption and emission) of sexithiophene and substituted sexithiophenes, in the β and in α-ω terminal positions by linear alkyl groups, have been characterized in solution, in the isolated molecule and in thin films. The solid film characteristics are discussed in terms of the structural organization of these molecular materials analysed by X rays. Results show that the optical properties are largely determined by the mesoscopic organization of the oligothiophene molecules in the film, which can be in turn controlled by the type of chemical substitution performed on the oligomer.