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.
Researchers at the University of Tsukuba have coated the surface of its exoskeleton with an electrically conductive polymer, polyaniline. The polymer does not reflect circularly polarized light; however, electrical or chemical oxidation of the polymer changes its coloration, thereby changing its light transmittance.
By combining the color change caused by the oxidation and reduction of polyaniline with the exoskeleton’s properties of reflecting circularly polarized light, the researchers have crafted a new polymer element that can modulate the reflection intensity of the circularly polarized light. The work is published in the journal Next Materials.
First, the researchers examined the circularly polarized light reflectance of the exoskeleton. 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.
More information: Hiromasa Goto et al, Circularly polarized reflection spectra of a photonic beetle and preparation of tunable circularly polarized light reflecting device consisting of conductive polymer/beetle exoskeleton, Next Materials (2025). DOI: 10.1016/j.nxmate.2025.100516
Provided by University of Tsukuba