We have studied structural and spectroscopic characteristics on a series of alpha,alpha'-dimethyl end-capped oligothiophenes (from two to six thiophene units) by varying temperature. Powder x-ray diffraction and infrared spectra at different temperatures between - 170 and 150 degrees C were recorded. The diffractometric study shows that the thermal expansion coefficients of these materials are highly anisotropic. The expansion in the ab plane, which is perpendicular to the chain direction, is an order of magnitude bigger than that along the chain direction. Corresponding to these structural features, the infrared spectra show interesting temperature dependence. For instance, the separation between adjacent components of the multiplets near 800 cm(-1), that are assigned to the C-II out-of-plane bending vibrations, increases with decreasing temperatures. This behavior reflects the change in the intermolecular forces caused by the thermal expansion. Furthermore, the shifts in the C=C stretching vibrations indicate that the extent of the pi-electron delocalization increases with increasing temperatures. The origin for this is briefly discussed.