The optical properties of substituted and unsubstituted oligothiophenes are analysed with respect to their supramolecular organization in the solid state. The spectra typical of the isolated molecules are obtained by reducing the intermolecular interactions by both lateral chain substitution and by inclusion in a host organic crystal. The photophysical properties of the weakly interacting oligothiophenes are strongly influenced by their backbone conformation and conformational mobility. Oligomers included in the channels of a guest crystal show fast torsional relaxation processes during the photoexcitation. Powders of β-substituted oligomers display optical properties dependent on the conformation of their particular chain packing arrangement.