OPTICAL, CALORIMETRIC, AND MASS SPECTROSCOPIC STUDY OF NONTHERMOCHROMIC CRYSTALLINE FORMS OF THE POLYDIACETYLENE BIS(ETHYLURETHANE)-5,7-DODECADIYNE-1,12-DIOL (ETCD)

Exposure of single crystals of the thermochromic polydiacetylene bis(ethylurethane)-5,7-dodecadiyne-1,12-diol (ETCD) to boiling chlorobenzene leads to nonthermochromic crystalline materials whose structures are similar to that of pristine ETCD. X-ray powder diffraction, differential scanning calorimetry (DSC), and room-temperature specular reflection and absorption spectra are reported for two nonthermochromic forms of ETCD. In addition, electron impact and fast atom bombardment mass spectrometric measurements were performed on the chlorobenzene extracts to determine substances removed by the boiling chlorobenzene along with a calorimetric study to correlate the loss of thermochromism with time of extraction. The mass spectrometry data indicate that ETCD monomer and possibly ETCD oligomer are removed during the extraction process. The crystallographic and optical data show that extraction with boiling chlorobenzene not only removes the interactions responsible for observable thermochromic behavior but also implies that both forms' electronic and lattice structure is significantly altered. The anisotropic reflection and corresponding absorption spectra show a dramatic blue-shift of the most intense spectral transitions by approximately 3500 cm-1 along the long axis, while spectra along the short axis remain essentially featureless. The X-ray data of both forms indicate an expansion of the lattice in the direction of the urethane side groups that significantly reduces the restriction to motion of the side groups and allows for a concomitant relaxation of the backbone. Results are also presented indicating the presence of residual thermochromic ETCD in the two nonthermochromic forms.