Solvatochromism and dichroism of fluorinated azoquinolin-8-ol dyes in liquid and liquid crystalline solutions

The spectroscopic properties of three new azoquinolin-8-ol derivatives (o-, m-, p-trifluoromethyl quinolin dyes) were investigated in liquid solutions as a function of the solvent type. The photo-physical behavior of the o-azoquinolin dye was examined and compared both in isotropic organic solvents and polar nematic liquid crystalline host. Analysis of absorption spectra was used to determine the azo and hydrazone forms in both isotropic and anisotropic solutions. The spectral shifts were correlated by the solvent permittivity and Kamlet-Taft parameters. The o-azoquinolin dye in the polar nematic host (C5H11-ph-ph-CN) shows an anomalous behavior. For o-azoquinolin dye, the azo form is almost entirely dominated in polar nematic host, while the compound remains dominantly in hydrazone form in dipolar aprotic solvents such as acetonitrile. The polarized absorption spectra of o-azoquinolin dye in the liquid crystalline host were measured and its degree of anisotropy was determined.