Measurement of interfacial dielectric polarization for the investigation of the orientational structure of monolayers comprised of banana-shaped molecules at an air–water interface

Chirality and orientational structure of monolayers comprised of 1-butyl-2,6-bis-[2-(4-dibutylaminophenyl)-vinyl]-pyridiniumiodide (M53) banana-shaped achiral molecules at an air–water interface were studied by Maxwell displacement current (MDC) and optical second harmonic generation (SHG) measurements. In the MDC–SHG measurements, the chirality originating from the assembly of achiral molecules, however, was not detected from M53 monolayers during monolayer compression. It was found that M53 monolayers could not form chiral structures due to the geometrical constraint imposed on orientation of the molecules at the air–water interface (interfacial binding effect). To further investigate the properties of the interfacial binding effect, theoretical analysis was carried out in association with molecular ordering. The result of the MDC–SHG measurements and that of the molecular theoretical analysis demonstrated that the interfacial binding effect plays an important role in the formation of chiral structures as well as orientational structures on monolayers comprised of banana-shaped achiral molecules.