The degree of pi conjugation in a novel series of molecular materials containing a central oligothiophene moiety of variable length, with its end alpha positions capped by phenyl groups (PnTP; n=1-4) is closely inspected by means of Fourier-transform infrared and Fourier-transform Raman spectroscopies in the neutral state as solids. Density functional theory quantum chemical calculations were performed for each co-oligomer, at the B3LYP/6-31G** level, to obtain the optimized molecular geometry and force field. The thermal stability of these oligothiophenes has been also investigated, at the molecular level, by recording infrared and Raman spectra at different temperatures between -170 degreesC and 160 degreesC.