Spherical resonators from π-conjugated polymers

Abstract

Optical resonators have an important role in optical devices; they confine, sharpen and amplify light. Self-assembled polymer resonators are advantageous for their simple fabrication processes with low cost and low energy consumption. In this focus review, we show recent advances in the self-assembly of π-conjugated polymers to form microspheres that act as optical resonators. The key factors in sphere assembly are low crystallinity of the polymers and slow diffusion of polar nonsolvent during the assembling process. Focused laser irradiation of a single isolated microsphere excites whispering gallery modes (WGMs), in which sharp and periodic lines are observed in the photoluminescence (PL) spectrum; these are characterized as transverse electric and magnetic modes. Efficient intrasphere energy transfer occurs in the case of microspheres composed of energy-donating and -accepting polymer blends. Furthermore, WGM-mediated long-range intersphere PL propagation and subsequent color conversion were observed in the case of linearly coupled microspheres. Conjugated polymer microspheres are beneficial as optical resonators in terms of their high refractive indices, high absorptivity and high PL efficiency, which are achieved by using simple fabrication processes. Various conjugated polymers self-assemble to form well-defined microspheres that act as optical resonators. Upon focused laser irradiation, the single isolated microspheres exhibit whispering gallery mode photoluminescence (PL), where sharp and periodic emission lines appear in the PL spectra. Efficient and long-range intersphere light energy transfer is demonstrated using coupled microspheres. Conjugated polymer microspheres are advantageous as optical resonators in terms of their high refractive index, photoabsorptivity, and PL efficiency, as well as simple and low-energy fabrication processes, beneficial for the practical application.