MOLECULAR IMAGING OF THERMOCHROMIC CARBOHYDRATE-MODIFIED POLYDIACETYLENE THIN-FILMS

Polymerized thin films based on polydiacetylenes (PDAs) undergo distin ct color transitions that lend themselves to applications in biosensin g, surface modification, nonlinear optics, and molecular electronics. The mechanism of the thermochromic blue to red color transition of PDA thin films was investigated at the molecular level using atomic force microscopy and at the macroscopic level with visible absorption and F ourier transform infrared spectroscopy. The thermochromic transition t emperature is found to be between 70 and 90 degrees C. At the molecula r level, the ordering of the film increases at the thermochromic trans ition and remains ordered up to temperatures well above the transition (e.g., 130 degrees C). No evidence for previously suggested entanglem ent or disordering of the alkyl side chains is observed. The pendant s ide chains rearrange from a partially disordered configuration charact eristic of the blue film, to a well-ordered close-packed hexagonal arr angement in the red form. The rearrangment of the pendant side chains is linked to the formation of the red phase PDA.