The optical properties of thin films of α,ω-dihexyl-quaterthiophene grown by organic molecular beam deposition on different substrates are illustrated. Vibronic transitions in both the absorption and the emission spectra are observed, which originate from the coupling between vibronic states in the solid, similarly as in unsubstituted quaterthiophene films. Nevertheless, the alkyl chains in α,ω-dihexyl-quaterthiophene are responsible for a shift in both the absorption and emission peaks with respect to unsubstituted quaterthiophene and for an increased mesoscopic disorder.