Kenichi Iwasaki

Conformational changes of poly(3-alkylthiophene)s with temperature and pressure

Abstract Thermochromism of cast films of poly(3-hexylthiophene) and poly(3-dodecylthiophene) was studied by electronic absorption and FT-IR spectra. A possible mechanism for the transition is discussed from the viewpoint of conformational changes of the methylene side chains deduced from the FT-IR spectra. Electronic absorption and vibrational spectra of poly(3-hexylthiophene) films were measured at high pressures by use of a diamond anvil cell. The absorption edge energy decreased with increasing pressure up to 3 GPa and then showed leveling off and subsequent increase. The decrease is probably due to an increased conjugation length of the thiophene main chain caused by a compact packing of methylene side chains. On the other hand, the increase in the edge energy is attributed to a distortion of a plane polymer structure caused by the steric hindrance between neighboring polymer chains. Electric conductivity of a poly(3-hexylthiophene) film showed the pressure dependence parallel to that of the absorption edge.

Photoemission study of poly(3-alkylthiophene)s: The effects of air and temperature on the electronic structures

Abstract Ultraviolet photoemission spectroscopy (UPS) was used to study the electronic structure of poly(3-alkylthiophene)s (PATs). The effects of the heat treatment and subsequent exposure to several kinds of gasses on PATs were investigated. The temperature dependence of the electronic structure was studied with respect to consistency with the thermochromic transition. The differences which arose from the synthetic method were also observed using chemically and electrochemically prepared PATs. The values of the threshold energy and the work function were determined for each measurement. The observed UPS spectra and their changes have been discussed with regard to the shortening and lengthening of the conjugation length and to the doping and dedoping of oxygen in air.