Electronic structure change at a phase transition in a polydiacetylene crystal

Abstract

A Raman spectral study is reported for a polydiacetylene crystal with substituent group (CH2)4OCONHC6H5. At low temperatures (<100 K) or high pressures (≳1.5 kbar) a phase change occurs accompanied by changes in the electronic structure of the polymer backbone. The Raman evidence suggests that the high temperature phase is best described with a butatriene bonding sequence [‐RC=C=C=CR‐n] while the low temperature (or high pressure) phase is best described with an acetylene bonding sequence [‐RC–C≡C–CR‐n].