Thin films of an axially chiral bibenzo[c]phenanthrene diol and its enantiomers: Film structure, optical property, and photoelectrochemical response

Abstract

A helically distorted and polycondensed bisphenol [1,1′-bibenzo[c]phenanthrene]-2,2′-diol (HEBPOL) and its separated optically pure enantiomers were used to prepare thin films and to explore their optoelectronic properties. Due to both hydrophobic aromatic rings and hydrophilic −OH groups the compound possessed amphiphilic characters, which helps to form a stable layer at the air-water interface. The stable film from the air-water interface was then transferred to different types of solid substrates by Langmuir-Blodgett (LB) technique. In the atomic force microscopic (AFM) images, circular-shaped islands were observed for the films of racemic mixture and their enantiomers deposited at different surface pressures. Thin films of different thickness were also prepared by spin coating (SP) method. The information about thickness, roughness, and electron density of layers or films was determined through X-ray reflectivity (XR) experiments. The multilayer formation was observed in the LB film, which was suggested by the height of islands in AFM images and the thickness determined by the XR experiments. The generation of photocurrent was measured by a conventional three-electrode system with a light source of the Xenon lamp. The photocurrent generation was speculated higher for the films having a higher thickness and experimentally found above 0.4μA/cm2 for 100Å. The compound is axially chiral and both the enantiomers respond to circularly polarized light irradiation in solution as well as in LB and SP films.