The undoped and ferric chloride p-doped "head-to-head" "tail to tail" analog of poly(3-decylthiophene) obtained from substituted bithiophenes, i.e., poly(4,4’didecyl-2,2’bithiophene)-PDDBT has been investigated. The samples were studied by means of ultraviolet photoelectron spectroscopy, optical absorption measurements, and polymer bands structure calculations. Experiments were carried out at different temperatures between 100 degrees C and -180 degrees C. The results indicate that PDDBT is nonplanar in the undoped state. No temperature effects have been observed in the pi-electron properties. In the doped state, however, lowering of the temperature results in an increase of the system planarity that modifies the electronic band structure. This effect has been shown to be fully reversible with temperature.