Date of this Version
The electronic spectra of polydiacetylene crystals have often been typified by poly-2, 4-hexadiyne-1, 6-diol-bis-(p-toluene sulfonate) (PTS). The spectra of crystals of this polydiacetylene have been unique in that they have displayed a pronounced “doubling” of the 300 K spectral bands at temperature below 170 K. The reflection bands are also observed to undergo a continuous red shift with continued decrease of temperature. The reflection band observed at lowest energy at 300 K is resolved at 77 K into two clearly separated bands at 15,700 cm-1 (Ib) and 16,050 cm-1(IIb). A recent study by modulated piezoreflection spectroscopy on PTS crystals demonstrated that this “doubling” persists to 300 K. The phenomenon is best explained by recent x-ray crystallographic studies which show that at 170 K the unit cell of the PTS doubles along the c axis.