Pressure dependence of the 2 eV electronic transition of a polydiacetylene

Abstract

Optical absorption and reflection spectroscopy has been used to determine the pressure dependence of the 2 eV electronic transition of single crystals of toluene sulphonate diacetylene polymer up to 3 GPa. In an optical cell, which used argon as the pressure-transmitting medium up to 0.5 GPa, it was found that the peak in the absorption spectrum shifted to lower energy at a constant rate of 70+or-3 meV GPa^-1 over the whole range. Detailed study of the 0.03-0.09 GPa range gave no evidence for a structural phase transition previously reported. The higher-pressure range was investigated using an opposed anvil press with light introduced into the sample volume by means of optical fibres passed through the sealing gasket. The peaks in the absorption and reflection spectra continued to shift to lower energy but at an ever-decreasing rate. This departure from linearity arose primarily from pressure-induced changes of shape in the polymer backbone.