Langmuir films from tailor-made semi-amphiphilic alternating (AB) heterocyclic copolymers

Alkyl-substituted polyheterocycles (cf. poly(3-alkylthiophene) and poly(N-alkylpyrrole)) do not form true monomolecular films at the air–water interface, due to lack of the required hydrophobic–hydrophilic balance. We designed and synthesized two new semi-amphiphilic alternating (AB) heterocyclic copolymers via a Stille coupling route, in order to study their film forming properties at the air–water interface, as inferred through surface pressure–area isotherms and Brewster angle microscopy. The copolymers I and II possess a N-alkylpyrrole unit, alternated with phenylene and benzothiadiazole units, respectively. While copolymer-I formed a stable multilayer stack, copolymer-II was found to form a monomolecular monolayer, at the air–water interface. The Langmuir film of copolymer-II could also be transferred layer-by-layer onto a substrate by vertical dipping method.