Determination of solvatochromic solvent polarity parameters for the characterisation of some nematic liquid crystal in anisotropic and isotropic phases

Characterisation of liquid crystals (LCs) as solvents is needed, to obtain the polarity and solvatochromic polarity parameters of these media. Polarity parameters demonstrate the effects of LC media on the photo-physical behaviour of solute molecules in an anisotropic medium. The practical limitations in determining solvent polarity scale parameters for LCs can overcome the overlapping absorption band of LCs and solvent-sensitive standard compounds or their insolubility in LCs. In this work, we report Kamlet–Abboud–Taft polarity functions of some nematic LCs in different temperatures and phases, isotropic and anisotropic, with the solvatochromic method, using the Reichardt's dye and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-phenolate standard probe. In addition, a new azo and coumarin dye were used as probes to obtain some solvatochromic polarity parameters. Finally, a new polarity parameter, the LC anisotropic matrix, is introduced.