Piecewise Phototuning of Self-Organized Helical Superstructures

Abstract

Cholesteric liquid crystals (CLCs) exhibit selective reflection that can be tuned owing to the dynamic control of inherent self-organized helical superstructures. Although phototunable reflection is reported, these systems hitherto suffer from a limitation in that the tuning range is restricted to one narrow period and the optically addressed images have to sacrifice one color in the visible spectrum to serve as the background, resulting from the insufficient variation in helical twisting power of existing photoresponsive chiral switches that are all bistable. Here, delicate patterns of three primary red, green, and blue (RGB) colors with a black background are presented, which is realized based on piecewise reflection tuning of the CLC induced by a newly designed photoresponsive tristable chiral switch. Three stable configurations of the chiral switch endow the CLC with two continuous and adjacent tuning periods of the reflection, covering not only entire visible spectrum, but also one more wide period within near-infrared region. Therefore, the concept of piecewise tuning in CLC system demonstrates a new strategy for phototunable RGB and black reflective display.

A photoresponsive tristable chiral switch is constructed by incorporating two different azobenzenes into one chiral structure. Three stable configurations of the chiral switch endow the cholesteric liquid crystals with two tuning periods of the reflection, including the period in the visible spectrum and one more period within the near-infrared region, which provides piecewise phototuning of self-organized helical superstructures.

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