Fluorescent microspheres are used for biomarkers, assay substrates, chemical diagnostics, flow cytometry, and biological imaging. These applications demand the highest fluorescence intensity achievable; however, concentration quenching limits the amount of dye that can be practically incorporated in conventional fluorescent microspheres. Conjugated polymers (CPs) can be less susceptible to concentration quenching, suggesting that they can be excellent candidates for a new class of light‐emitting microspheres. Due to their long‐chain‐conjugated backbone, however, CPs can be resistant to forming smoothly curved or spherical structures. Here, strongly fluorescent CP microspheres as large as 100 µm in diameter are synthesized. Whispering gallery modes (WGMs) appear in the fluorescence spectra, and the microspheres show clear evidence of lasing above a threshold pump intensity. These conjugated polymer beads are up to 50 times larger than CP microspheres obtained by other methods, and they exceed the emission intensity of conventional fluorescent microspheres by more than an order of magnitude.

Conjugated polymers (CPs) can potentially provide an alternative to conventional fluorescent microsphere technologies; however, examples of CP microspheres encompassing an extensive range of sizes are few, and wide‐ranging spectral control, as needed for many applications, has never been demonstrated. Blended CP microspheres consisting of individual polymers are synthesized here. They are blended to have widely separated Commission Internationale de l'Éclairage (CIE) color coordinates and a compatible synthesis while at the same time forming well‐defined domain structures. By developing appropriate mixtures of selected blue, green, and red fluorescent CPs, blended CP microspheres are demonstrated to cover an extensive range of color coordinates including white. It is shown that multi‐CP microspheres with core–shell or related structures can provide optimum characteristics, while energy and/or charge transfer in finer mixtures result in microspheres without the desired emission properties. Pre‐ or postprocessing further directs consistent changes in the CP microspheres that ultimately regulate the overall spectral response. This approach can lead to a new class of bright fluorescent microparticles with applications in a wide range of disciplines that demand maximum brightness and highly specific emission spectra.

We investigate the two-photon fluorescence (TPF) of conjugated polymer (CP) microspheres with diameters up to tens of micrometers. Two polymers, emitting in either the violet or red, were first synthesized and characterized in terms of their one-photon fluorescence and three-dimensional internal microstructure. Under femtosecond infrared excitation, both types of microspheres showed a strong TPF, which was investigated by the excitation intensity dependence, emission spectroscopy, time-resolved luminescence, and photobleaching dynamics. While the violet-fluorescent microspheres performed similarly compared to dye-doped polystyrene counterparts emitting at a similar wavelength, the red-fluorescent microspheres showed a two-orders-of-magnitude stronger TPF. This excellent performance is attributed to enhanced hyperpolarizability associated with intermolecular interactions in the polymer solid, indicating a route toward designed CP microspheres that could outperform currently-available microparticles for sensing or imaging applications involving two-photon fluorescence.

This work synthesizes a green‐fluorescent conjugated polymer and performs basic photophysical characterization of this new material. Atums Green[1] is synthesized by a Suzuki cross‐coupling polymerization reaction between isostructural dibromo and diboronic acid monomers and is structurally characterized by nuclear magnetic resonance and gel permeation chromatography. The polymer consists of an alkoxy‐substituted 1,4‐bis((E)‐styryl)benzene repeating unit with molecular weight up to Mn = 50 kDa relative to polystyrene. Atums Green shows a strong green fluorescence maximized at ≈500 nm in chloroform and tetrahydrofuran solutions, with an absolute quantum efficiency as high as 98%. The photobleaching dynamics and time‐resolved photoluminescence (TRPL) are measured both in solutions and in solid films. Finally, solution‐based lasing is demonstrated in a bulk lasing cavity and in a cylindrical microcavity. Lasing emission is readily achieved in both formats, indicating that Atums Green has excellent emission characteristics, and further suggesting that it may present a viable green‐emitting conjugated polymer materials system for light emission applications.