Fluorescence switch in red-phase polydiacetylene films and vesicles upon thermal cycles.

The switch phenomena of thermochromism of red-phase polymerized PCDA (10,12-pentacosadiynoic acid) Langmuir-Schaefer (LS) films and vesicles were investigated in situ during repeated heating and cooling processes between 25 degrees C and 70 degrees C. During repeated thermal cycles, the solid-supported LS films exhibited switch phenomena in both the visible and fluorescent spectra, that is, the colorimetric response (CR) of the PCDA LS films was ca. 80% at 70 degrees C but is ca. 50-60% at 25 degrees C with an increase of fluorescent intensity in the cooling process and a decrease in the heating process. On the other hand, the PCDA vesicles exhibited such phenomenon only in the fluorescent spectra, that is, the CR of the PCDA vesicles was constant as ca. 100% after being stable red form with the same trend in the fluorescent intensity. The changes in molecular configuration revealed by in situ Fourier transform infrared (FTIR) were in good agreement with the trend of fluorescence emission upon repeated thermal stimuli rather than that of visible absorption.