Variable circularly polarized light reflector combining circularly polarized light-reflection by insect exoskeletons with a conductive polymer

Tsukuba, Japan—Some beetles, such as Anomala albopilosa, strongly reflect left circularly polarized light (electromagnetic waves that oscillate leftward relative to the direction of light reception). This property originates from the formation of a cholesteric liquid crystal phase with an optically active, helical structure during chrysalis during exoskeleton formation and the solidification of this phase into a rigid skeleton while retaining its helical structure. The conductive polymer polyaniline does not reflect circularly polarized light; however, electrical or chemical oxidation of the polymer changes its coloration, thereby changing its light transmittance. In this research, the researchers have created a device capable of variable circularly polarized light reflection by combining the circularly polarized light-reflecting properties of the insect exoskeletons with the properties of polyaniline.

First, the researchers examined the circularly polarized light reflectance of the exoskeleton of Anomala albopilosa. They confirmed that the green reflection of the exoskeleton is not caused by dyes, etc., but is a structural color (i.e., its coloration results from the reflection of light from the surface microstructure). They also confirmed that the exoskeleton strongly reflects left circularly polarized light. Next, they coated the exoskeleton with polyaniline and created a polymer element with a two-layered structure comprising a conductive polymer and a sheath spring. For this coating, they measured the circularly polarized reflectance spectra of polyaniline in the oxidized state by doping it with ammonia and in the reduced state by dedoping. They found that no circularly polarized light was reflected in the oxidized state. However, in the reduced state, left circularly polarized light was reflected. This research realizes a new bio/synthetic photofunctional material that combines the excellent optical properties of insects and the external field responsiveness of conductive polymers.

_{Original Paper}

Title of original paper:
Circularly polarized reflection spectra of a photonic beetle and preparation of tunable circularly polarized light reflecting device consisting of conductive polymer/beetle exoskeleton

Journal:
Next Materials (Elsevier)

DOI:
10.1016/j.nxmate.2025.100516

_{Correspondence}

Associate Professor GOTO, Hiromasa
Institute of Pure and Applied Sciences, University of Tsukuba

_{Related Link}

Institute of Pure and Applied Sciences