Characterization of newly synthesized BODTA in Langmuir and Langmuir–Blodgett monolayers before and after UV irradiation

Polydiacetylenes (PDAs) are ordered and uniquely conjugated polymers synthesized from diacetylene monomers by UV-initiated photoreaction or thermally. The amphiphilic PDAs with controlled spacing and orientation often accomplished by Langmuir–Blodgett (LB) technique provide possible applications in the area of the photolithography, nonlinear optics and chemical sensors. In this study, we synthesized an amphiphilic of diacetylene monomer, 2,5-bis-octadeca-5,7-diynyloxy-terephthalic acid (BODTA), containing a diacetylene moiety in each of two symmetric side chains. Stable Langmuir monolayers of BODTA were constructed, and successfully transferred on the solid substrates as the monomeric form to investigate the changes of the molecular interaction, packing and orientation induced by UV-induced polymerization. In situ spectroscopic and scanning probe microscopic analyses indicate that at lower surface pressure, BODTA spontaneously forms micro-scale domains, and merges together as surface pressure increases. The molecular orientation and intermolecular interaction of BODTA were significantly altered by UV-induced polymerization. We found that two different polymerization mechanisms may be involved as the intermolecular distance and relative orientation to adjacent molecules changes by controlling the degree of compression of the monolayer at the interface.