Strain dependence of the dominant electronic excitation of a conjugated polymer crystal

The strain dependence of the reflection spectrum of a 0.62 mu thick single crystal of toluene sulphonate diacetylene polymer has been measured to an elastic strain of 3.3%. The peak of the reflection spectrum near 2 eV shifted to higher energy at a rate of 0.037+or-0.002 eV/%. This result is shown to be in good agreement with the prediction of a molecular orbital calculation.