Fabrication and Characterization of Molecular Films of 11-Oxa[9]helicene and 9-Diethyleneglycoxy-11-oxa[9]helicene

Abstract

A highly π-conjugated helical compound, 11-oxa [9]helicene (O9H), and its derivative 9-diethyleneglycoxy-11-oxa[9]helicene (2EO9H) were used to prepare thin films by the Langmuir technique, and their structures and photoelectrochemical properties were evaluated. Brewster angle microscopic (BAM) observation implied that 2EO9H molecules formed a homogeneous, flat monolayer but O9H molecules three-dimensionally aggregated at the air-water interface. The same morphological features were also observed for films deposited on silicon wafers using atomic force microscopy (AFM). The film structures on solid supports were estimated by X-ray reflectivity (XR) measurements. The XR fitting analysis and theoretical calculation suggested that in the 2EO9H monolayer the hydrophobic aromatic planes of helicene moiety oriented perpendicularly to the monolayer plane and the hydrophilic diethyleneglycoxy group (DEG) was bended/twisted. It was also indicated that optical band gaps estimated from UV-visible spectra are not much changed due to introduction of DEG chain to the O9H moiety, but the 2EO9H monolayer showed larger photocurrent densities.