EFFECTS OF MOLECULAR AREA ON THE POLYMERIZATION AND THERMOCHROMISM OFLANGMUIR-BLODGETT-FILMS OF CD2-DIACETYLENES STUDIED USING UV-VISIBLE SPECTROSCOPY( SALTS OF 5,7)

The first study of the polymerization and thermochromism in Langmuir-B lodgett films of the Cd2+ salts of 5,7-docosadiynoic acid (DCDA) and 5 ,7-tretracosadiynoic acid (TTCDA) formed at molecular areas of 22 and 26 Angstrom(2)/molecule is reported. The polymerization behavior and:s ubsequent thermochromism of the resulting polymers was followed using visible spectroscopy. The high-density (low molecular area) polymerize d films resulted in visible absorption spectra which were distinctly d ifferent from the spectra resulting from the low-density (high molecul ar area) polymerized films. The temperature dependence of the visible absorption spectra of the two densities of films was distinctly differ ent as well. In addition, the temperature dependence of the visible ab sorption spectra of the polymerized films could be qualitatively accou nted for by a two-reaction scheme in which the blue (B) form of the po lymer forms an intermediate purple (P) form in a reversible reaction. The purple form of the polymer is transformed to the red (R) form in a n irreversible reaction. (B reversible arrow P, P --> R). Estimated ac tivation barriers for the forward reaction B --> P were obtained from the temperature dependence of the visible absorption spectra using a n ormal preexponential factor of 10(12) s(-1). For LB films of DCDA thes e were E = 22.4 and 21.7 kcal/mol for the low- and high-density films, respectively. For LB films of TTCDA these were E = 23 and 21 kcal/mol for the low- and high-density films, respectively.