Chiro-optical signals from chiral molecules/structures are inherently weak. In particular, enhancing the circular-dichroism (CD) effect (different absorption of left or right circularly polarized light) in the non-linear optical (NLO) signal from chiral molecular materials is challenging and imperative since it is advantageous in various areas, from biomedical sciences to miniaturized photonic devices. Here we suggest and realize for the first time an approach to enhance the CD effect taking advantage of the NLO effects resonantly enhanced in the nonlinear chiral organic micro-resonators. These R- and S-type resonators in the form of micro-spheres are prepared by the self-assembly technique from the corresponding axially chiral enantiomeric molecules, namely R- and S-4-[2,2′-diethoxy-6′-(4-formylphenyl)-[1,1′-binaphthalen]-6-yl]benzaldehyde in CHCl₃/MeOH mixtures. Each enantiomeric micro-sphere, upon optical pumping, acts as a whispering gallery mode (WGM) resonator as the photo-luminescence (PL) is excited in a single- or in a two-photon regime. We show that the NLO-CD effect and the two-photon absorption (TPA) in the case of micro-spheres are at least twice as high as compared to a continuous film of the same effective thickness. This is due to pronounced field localization effects in micro-spheres with high Q-factor, which increases the photon residence time (τ_P) in a chiral medium and thus strengthens the light–matter interaction. Finite-difference time-domain (FDTD) numerical calculations confirm a strong light localization near the boundary of the micro-spheres.

Two chiral π‐conjugated polymers with optical nonlinearity (NLO), abbreviated as R‐ and S‐BP, are prepared by copolymerization of R‐ and S‐6,6'‐dibromo‐2,2'‐diethoxy‐1,1'‐binaphthyl with 1,4‐diethynyl‐2,5‐bis(octyloxy)benzene by Sonogashira coupling. The R‐ and S‐BP copolymers self‐assemble in a tetrahydrofuran/H₂O/ethanol mixture producing microspherical particles. Remarkably, the obtained polymer microspheres support excitation of whispering gallery mode resonances (500–720 nm) in one‐ and two‐photon excited luminescence or two‐photon luminescence (TPL) with a quality factor (Q) of up to ≈700. As a result of a high Q value, a single (R‐ or S‐BP) microsphere displays a circular dichroism (CD) effect in the TPL signal. At high laser pump‐power (≥10 mW), the TPL spectral features of microspheres change significantly, suggesting alterations of the polymer packing. Similar spectral variations are observed for microspheres heated thermally or with high power continuous‐wave laser. Photoluminescence lifetime imaging microscopy down to the single microsphere level corroborate transformations of polymer packing from a J type to a mixture of J, H, and H‐like (with disordered side chains) types. This work demonstrates the tremendous potential of tailor‐made chiral polymer microspheres exhibiting multifunctional properties, such as i) light‐confinement, ii) NLO‐CD, and iii) laser‐driven optical emission shifts, useful for many optoelectronic and photonic device applications.