Optical Spectra of Polydiacetylene (PTS, HDU, TCDU) Single Crystals Studied by Synchrotron Radiation Spectroscopy

Abstract

Polarized reflection spectra have been measured on three different kinds of polydiacetylene crystal, poly-[2,4-hexadiyne-1,6-diol-bis-(p-toluene sulfonate)] (PTS), poly-[2,4-hexadiyne-1,6-diol-bis-phenylurethane] (HDU) and poly-[5,7-decadiyne-1,12-diol-bis-phenylurethane] (TCDU), over the photon energy range of 1–25 eV by means of synchrotron radiation spectroscopy. Spectral changes, associated with topochemical transformation from monomer to polymer crystals of PTS and with the stress-induced isomeric phase-transition or TCDU crystals, were investigated. Spectral features showing characteristic polarization dependence with respect to the polymer chain axis are interpreted by an electronic band-structure model of polydiacetylene crystals. Especially, the reflection peaks located at about 2 and 7 eV are assigned to the one-dimensional excitons associated with the π–π^* transitions on the conjugated polymer chains.