Researchers at University of Tsukuba have discovered that a vortex-like molecular orientation forms on the surfaces of microspheres composed of chiral π-conjugated polymers (light-emitting molecules with alternating single and double carbon-carbon bonds). Furthermore, the microspheres can emit laser light in a ring-like pattern reminiscent of Saturn's rings.

Tsukuba, Japan—Controlling light within microscopic spaces is crucial for next-generation optical devices such as photonic integrated circuits and localized sensors. Microspheres formed of luminescent π-conjugated polymers act as optical resonators that confine and amplify light via whispering gallery modes (WGMs), and they are promising candidates for microscale organic lasers and photonic applications. However, conventional microsphere resonators are geometrically isotropic and emit isotropic light, making directional control of emissions challenging.

In this study, the researchers show that microspheres formed through the self-assembly of chiral π-conjugated polymers possess a characteristic twisted-bipolar molecular configuration, thereby enabling angle-selective optical resonance and laser oscillation with distinct azimuthal directionality. Using polarization-dependent photoluminescence imaging, the research team directly visualized a vortex-like (swirling) arrangement formed by the polymer main chains on the spherical surface.

Furthermore, this vortex-like surface molecular orientation induces an azimuth-dependent refractive-index distribution along the light propagation path, resulting in angle-dependent WGM resonance wavelengths and spatially localized emission. Consequently, the microspheres exhibit directional laser oscillation, preferentially emitting the amplified light along a specific azimuthal direction. The resulting emission pattern is analogous to Saturn's rings.

This work presents the first demonstration of controlled light-emission directionality in a spherical resonator achieved by exploiting topological molecular ordering on the microsphere surface.

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This work was supported by JST CREST (JPMJCR20T4, JPMJCR19T1), ACT-X (JPMJAX23D8), JSPS KAKENHI (JP19J20398, JP24H00470, JP24H01693, JP24K17742, JP26H01697), and DAAD-Tsukuba partnership program and DFG (SFB 1375 NOA, Project No.: 398816777 & IRTG 2675 Meta Active, Project No.: 437527638).

Original Paper

Title of original paper:

Angle-Selective Optical Resonance and Circular Radial Lasing from a Chiral Polymeric Microsphere

Journal:

Journal of the American Chemical Society

DOI:

10.1021/jacs.6c01819

Correspondence

Professor YAMAMOTO Yohei
Assistant Professor OKI Osamu
Institute of Pure and Applied Sciences, University of Tsukuba

Professor IWAMOTO Satoshi
Research Center for Advanced Science and Technology, University of Tokyo

Assistant Professor Wenbo Lin
Institute of Integrated Research, Institute of Science Tokyo

Related Link

Institute of Pure and Applied Sciences