Color–Tunable Triple–State "Smart" Window. Issue 10 (5th August 2021) - Timmermans, Gilles H.
Abstract : Materials that rapidly change their optical properties in response to external stimuli are crucial for displays and "smart" window applications. Herein, a fluorescent red dye modified with liquid crystal (LC) side chains is described to be interactive with a LC host, resulting in a color‐tunable triple‐state smart window. The dye solubilizes in the LC matrix with increasing temperature, resulting in a red‐colored, absorbing state, recovering transparency again by reaggregation of the dye within minutes upon cooling. This dye is used to fabricate a device that can be electrically switched from a red‐colored, absorbing state to an intermediate scattering state and at greater electrical fields, a transparent state. Using a second dichroic fluorescent dye, heating the device transitions the window's color from yellow/green to red. The multiresponsive optical changes could find applications in many fields, including displays, smart windows, electricity generation, and signage. Abstract : A color‐tunable triple‐state "smart" window is fabricated that is responsive to both temperature changes and electrical fields. Cyano‐biphenyl groups are attached to a perylene dye to enhance the interaction with the liquid crystal host. At low temperatures, the dye is aggregated and at higher temperatures, it dissolves. The system can find applications as "smart" windows but also in rewritable signage.