Self-Assembly of Conjugated Polymers at the Air/Water Interface. Structure and Properties of Langmuir and Langmuir−Blodgett Films of Amphiphilic Regioregular Polythiophenes

This paper provides the first direct structural evidence describing conjugated polymer self-assembly at the air−water interface. Grazing-incidence X-ray diffraction (GIXD) and X-ray reflectivity measurements on a number of derivatives of amphiphilic regioregular polythiophenes (e.g., poly(3‘-dodecyl-3-(2,5,8-trioxanonyl)-2‘,5-bithiophene), polymer 1) show that these conjugated polymers self-assemble as 2-dimensional polycrystalline monolayers at the air/water interface with the amphiphilic polymers preorganized into rigid boards standing edge-on on the water surface. The monolayer consists of highly ordered (∼70% crystalline) domains, with a centered rectangular unit cell having the polymer backbone along the a-axis and the thiophene π-stack along the b axis with a distance of 3.85−3.94 A depending on the applied surface pressure. These domains are connected by soft, more disordered boundaries. This is evidenced by the macroscopic compressibility of the entire LB film (Cmacro ≈ 4−7 m/N) being one order of...