TEMPERATURE EVOLUTION OF THE ELECTRONIC BAND-STRUCTURE OF THE UNDOPEDAND DOPED REGIOREGULAR ANALOG OF POLY(3-ALKYLTHIOPHENES) - A SPECTROSCOPIC AND THEORETICAL-STUDY

The undoped and ferric chloride p-doped ''head-to-head'' ''tail to tai l'' analog of poly(3-decylthiophene) obtained from substituted bithiop henes, i.e., poly(4,4'didecyl-2,2'bithiophene)-PDDBT has been investig ated. The samples were studied by means of ultraviolet photoelectron s pectroscopy, optical absorption measurements, and polymer bands struct ure calculations. Experiments were carried out at different temperatur es 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, howev er, lowering of the temperature results in an increase of the system p lanarity that modifies the electronic band structure. This effect has been shown to be fully reversible with temperature.