Photo-switching behaviour in liquid crystalline materials incorporating a non-planar dithienylcyclopentene core and their birefringence properties

Reversible photochromic phase transition of non-planar dithienylcyclopentene-containing liquid crystalline molecules has been studied in this work. All materials showed the smectic A and nematic phases in the cooling process and had reversible and high interconversion yield >90% between colourless-open/blue-closed isomers in the liquid crystalline state as well as in solution by UV- and visible light-irradiation alternatively, as confirmed by nuclear magnetic resonance spectroscopy, polarised optical microscopy, differential scanning calorimetry, powder X-ray diffraction and UV-visible spectroscopy. The thermal stability of both isomers also ensures that they can maintain liquid crystalline phases during ring-open and ring-closure reactions. Their birefringence is between 0.1 and 0.2, which is comparable to that of standard liquid crystalline materials used in optical applications.