Mixture of cholesteric copolymer with dithienylethene photochromic dopant: a new material combining optical properties of cholesterics with photochromism

The phase behaviour and optical properties of the mixture based on cholesteric copolymer with 6 wt% of a photochromic dithienylethene dopant was studied. It was shown that planarly-oriented films of the mixture possess a selective light reflection in the visible region of the spectrum (lambda (max) similar to 600 nm). UV irradiation of the mixture film leads to the appearance of an intense absorbance peak in the spectral range coinciding with the selective reflection band. This process is associated with the photocyclization of dopant and the "degeneration" of the selective light reflection. The photoinduced coloured form of dopant is thermally stable, but subsequent irradiation of the film by visible light (633 nm) induces a back decoloration process. For the first time the influence of temperature on the rates of forward and back photoprocesses in such polymeric liquid crystalline films was studied. The potential for the use of such a type of material for reversible data recording and storage was demonstrated.