KINETICS OF THE REVERSIBLE THERMOCHROMISM IN LANGMUIR-BLODGETT-FILMS OF CD2-VIS SPECTROSCOPY( SALTS OF POLYDIACETYLENES STUDIED USING UV)

The first quantitative model for the partially reversible thermochromi sm in Langmuir-Blodgett films of the polymerized Cd2+ salts of 10,12-t ricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCDA) is pr esented. The visible spectrum as a function of temperature provides ev idence for two parallel processes, one of which is reversible. The fol lowing kinetic model is proposed which qualitatively and quantitativel y accounts for the observed reversible thermochromism: B reversible R (k(f), k(r)); P --> R (k2). B and P stand for two distinct forms of th e blue polymer, and R stands for the red form of the polymer. Activati on barriers of E(f) = 22.5 kcal/mol, E(r) = 21.4 kcal/mol, and E2 = 23 .0 kcal/mol are obtained from the TCDA spectra as a function of temper ature using a ''normal'' preexponential factor of 10(12) s-1 and E(f) and E(r) as adjustable parameters. The same model can be fit to films of PCDA and gives activation barriers of E(f) = 21.5 kcal/mol, E(r) = 21.0 kcal/mol, and E2 = 22.5 kcal/mol.