Effect of Position of Butadiyne Moiety in Amphiphilic Diacetylenes on the Polymerization in the Langmuir−Blodgett Films

We synthesized a series of amphiphilic diacetylenes with the same total length of the alkyl chains but with the butadiyne moiety at different positions in the molecules. These molecules formed monolayers, which were transferred on solid substrates to fabricate Langmuir−Blodgett (LB) films. UV−vis absorption spectra of the LB films changed on polymerization by the irradiation with UV light. The LB films were categorized into blue-red, red, and yellow phases on the basis of the spectral change. These different behaviors on polymerization were explained in terms of the tilt angle of the butadiyne moiety and the distance between the adjacent molecules. Surface pressure−area isotherms showed that the intermolecular distance was ca. 5 Å for all the LB films. This value was almost the same with the typical one for polymerizable diacetylenes in crystals. The tilt angle of the butadiyne moiety was estimated using IR spectroscopy, XRD, and the CPK model. The value for blue-red phase was similar to the typical one for polymerizable diacetylenes in crystals. The tilt angle for the red phase was larger than that for the blue-red phase, while the butadiyne moiety in the yellow phase was almost perpendicular to the film surface.