Orientational changes of supported chiral 2,2′-dihydroxy-1,1′binaphthyl molecules

Abstract

Well defined thin molecular films of 2,2′-dihydroxy-1,1′binaphthyl (binol) molecules at coverages between 5 × 10¹⁵ molecules per cm² and 10¹⁷ molecules per cm² on thin glass (BK7) substrates were investigated under ultra-high-vacuum (UHV) conditions. Second-Harmonic-Generation Optical-Rotatory-Dispersion measurements (SHG-ORD) were performed using a dedicated spectroscopic setup which allows for the determination of the rotation angle of the SH-signal of two enantiomers. Rotation angles of up to 38 degrees were measured. The chirality of the two enantiomers has been studied at 674 nm (337 nm resonance wavelength) in the transmission mode. Coverage dependent orientation evolution of binol molecular films was revealed by precise monitoring of the surface coverage while performing SHG-ORD experiments. We show that the molecules reach their final orientation at a surface coverage of 5 × 10¹⁶ molecules per cm². From the obtained experimental data the ratio of chiral and achiral susceptibility components could be calculated and was observed to change with coverage.