No abstract

Polymer materials able to change reflective properties due to mechanical deformation fundamentally challenge the theory of soft materials and are important for a number of emerging applications. The most promising of those are chiral lasers. In this communication, we report novel cholesteric materials that display large color change from far red to blue and a shift of the position of the selective reflection band under uniaxial strain from near infrared to ultraviolet. Optical pumping of these materials which are doped with laser dyes, leads to lasing at the wavelengths controlled by strain within the emission interval of laser dyes of 80 nm.

Chiral composition is designed for highly viscous lasing microemitters. The composition forms cholesteric liquid crystal and after doping with pyrromethene 597 was used as an active lasing media in stretchable aluminized silicone cavities. Optical pumping of the system led to lasing at the wavelengths defined by a degree of cavity deformation. Lasing thresholds were lower in aluminized cavity than in transparent cavity. A simple model allowing to predict the shift of lasing wavelength as a function of deformation is developed.

Large shifts of the selective reflection band and colour changes are achieved in highly viscous mixtures of cholesteric polymers and low molar mass liquid crystals subject to mechanical deformation. The liquid crystal mixture was sandwiched between two silicone strips and stretched. The colour of the material changed instantaneously during stretching, and the time for the colour to be completely restored increased with the viscosity of the polymer mixture. A quantitative model considering the material as an incompressible viscoelastic fluid is proposed. The model accurately describes colour changes (shift of the selective reflection band) and its relaxation back to the original spectral location.

No abstract