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A microsphere, assembled from a chiral π-conjugated polymer with narrow polydispersity, features a well-organized twisted-bipolar structure and exhibits highly biased circularly polarized luminescence (CPL). The CPL emitted toward the equatorial direction is 61-fold greater than that emitted along the zenith direction, which is the highest anisotropy among existing microscopic CPL emitters. [ABSTRACT FROM AUTHOR]

Lanthanide metal complexes display luminescence with narrow bandwidth. Here, we present coupling of the luminescence from europium ion (Eu3+) with whispering gallery modes (WGMs) in conjugated polymer microsphere resonators. Self‐assembly of fluorene–terpyridine alternating copolymer, coordinated by Eu3+ (F8tpy‐Eu3+), forms well‐defined microspheres with an average diameter of 3.2 μm. Upon focused laser excitation, a microsphere of F8tpy copolymer displays WGM photoluminescence (PL) at a wide spectral range from 420 to 680 nm. In contrast, F8tpy‐Eu3+ hybrid microspheres exhibit sharp WGM PL at a narrow spectral range of 615–630 nm, which is characteristic of luminescence from Eu3+. The PL behavior indicates that photoinduced energy transfer from F8tpy to Eu3+ occurs efficiently. Furthermore, the intensity of the PL peak increases nonlinearly upon strong pumping, indicating that a lasing action appears with the threshold of 1.85 mJ cm−2. These results will pave the way for developing microlasers and photonic devices from soft organic materials. [ABSTRACT FROM AUTHOR]

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Low-threshold organic microlasers are demanded for advanced optical applications such as nano/micrometer scale memory, sensing, and communication tools, and further valuable for future electrically driven laser applications. In this paper, it is demonstrated that various highly fluorescent conjugated polymers self-assemble to form single-component microspheres that exhibit, upon femtosecond pumping to a single microsphere, whispering gallery mode (WGM) lasing with blue, green, and red emission colors. In particular, the microsphere consisting of polyfluorene shows the lowest threshold fluence as low as 1.5 µJ cm−2 and high photostability against successive pumping of >105 pulse. The threshold fluence is further reduced by one fourth (0.37 µJ cm−2) by mounting the microspheres on an Ag-coated substrate, where a mirror effect of the Ag layer enhances efficiency of the photoluminescence confinement with a minor effect of plasmonic near-field. Considering the intrinsic charge injection and transport properties, π-conjugated polymer microsphere resonators will be possible materials for electrically pumped WGM luminescence. [ABSTRACT FROM AUTHOR]

Depositing minute light emitters into a regular array is a basic but essential technique in display technology. However, conventional lithographic methodologies involve multistep and energy-consuming processes. Here, we develop a facile method in which organic and polymeric fluorescent dyes spontaneously aggregate to form a patterned microarray. We find that a thin film of fluorescent π-conjugated polymer transforms into micrometer-sized aggregates when exposed to binary organic vapor at ambient temperature. The arrayed microaggregates can be formed over the whole substrate surface when using a quartz substrate that is prepatterned with regular hydrophilic boxes and hydrophobic grids. The resultant microarray is applicable to optical memories and displays when photoswitchable fluorophores are doped into the polymer matrix. [ABSTRACT FROM AUTHOR]

Self-assemblyof highly fluorescent isolated conjugated polymers (ICPs), comprisingalternating phenylene moieties with an insulating cyclic side chainand different arylene moieties, was comprehensively studied. Two outof nine ICPs were identified to form well-defined spheres of 1–6μm diameter. The degree of twisting of the main chains was foundto be an important structural factor enabling formation of spheres,for which dihedral angles >50° between the neighboring arylenemoieties were required. A single microsphere with high sphericityexhibited whispering gallery mode (WGM) photoemission upon excitationwith a focused laser. In this emission, sharp and periodic emissionlines were superimposed on a broad photoemission spectrum. The WGMspectral profiles were very sensitive to the integrity of the sphericalgeometries and surface smoothness, which depends on the self-assemblingcondition as well as the structure of the polymer backbone. Microsphericaloptical resonators consisting of such highly fluorescent conjugatedpolymers are novel. They also present advantages in that (i) thereis no need for a light waveguide and fluorescent-dye doping, (ii)its high refractive index is beneficial for light confinement, and(iii) the fabrication process is simple, not requiring sophisticated,costly microfabrication technology. [ABSTRACT FROM AUTHOR]