ANALYSIS OF COLOR TRANSITIONS AND CHANGES ON LANGMUIR-BLODGETT-FILMS OF A POLYDIACETYLENE DERIVATIVE

Color transitions and color changes of polymerized Langmuir-Blodgett (LB) films of a diacetylene derivative (10,12-pentacosadiynoic acid, PDA) with annealing has been investigated by measuring UV and visible spectra, differential scanning calorimeter (DSC) curves, and IR spectra. Reversibility of the color transitions of the polymerized PDA LB films held during heating from 23 (room temperature, RT) to 50-degrees-C, but not above 70-degrees-C. On the other hand, on a DSC curve of the PDA LB film, an endothermal peak appeared at 67-degrees-C, and on that of the polymerized PDA LB film, two peaks appeared at about 70 and 190-degrees-C. The temperatures (about 60-degrees-C) at which a drastic color change appeared were close to those of the endothermal peak (67-degrees-C) on the PDA LB film and the first endothermal peak (62-degrees-C) on the polymerized PDA LB film. This indicates that the color transitions (means reversible absorption peak shift between about 650 and about 540 nm caused by heating or cooling) of the PDA polymer at temperatures below 50-degrees-C is caused by a fluctuation of side chain groups linked to the polymer backbone chain (polydiacetylenic bond). The color change (means irreversible absorption peak shift from about 650 to about 540 nm caused by heating or cooling) at temperatures between 70 and 170-degrees-C is caused by a structural disorder of the side chain groups.