Microcrystal resonators with different orientations of thiophene/phenylene co-oligomers are prepared using a modified miniemulsion method. Strong exciton–photon coupling with Rabi splitting energy up to 1.25 eV is observed.

Herein, 5,5′‐bis(4‐biphenylyl)‐2,2′‐bithiophene (BP2T or PPTTPP) nanocrystals are prepared via a modified miniemulsion technique. X‐ray diffraction and selected area electron diffraction analyses reveal that the BP2T molecules stand almost upright against the crystal basal plane. With decreasing nanocrystal size, the peak energies of photoluminescence (PL) spectra are blue‐shifted in the photon energy range from the bulk crystal to the monomer state. Energy‐wavevector dispersion plots reproduced using the data of size‐dependent PL spectra indicate that the size dependence of optical properties cannot be explained by the conventional quantum confinement effect used in inorganic nanocrystals. The micro‐PL and time‐resolved PL measurements of the BP2T nanocrystals reveal that the size‐dependent optical properties can be attributed to a combined effect based on the surface effects as well as lattice softening, and quantum effects involving specific surface area‐dependent site shift effect and exciton confinement. Moreover, amplified spontaneous emission is observed from the nanocrystals ≈600–1000 nm in size, which is smaller than the size previously reported for organic systems.

We show the first experimental evidence that submicron particles (diameter: approximately 400 nm) using 5,5′-di(4-biphenylyl)-2,2′-bithiophene (BP2T) prepared by a miniemulsion technique are effective active media for vertical microcavities. Selected area electron diffraction patterns confirm that crystalline BP2T submicron particles are obtained. In a distributed Bragg reflector-Au microcavity with BP2T submicron particles embedded in a poly(vinyl alcohol) (PVA) matrix (thickness: ∼780 nm), gain-narrowed emissions are observed at the 0–3 emission band of BP2T above an excitation density of 107 μJ cm−2. The light amplification of 0–3 photoluminescence band obtained in the present study demonstrates that the PVA film containing the BP2T submicron particles is useful as an active medium for microcavities.

Four types of BP2T-CN crystals with different molecular orientations and crystal morphologies were obtained by changing the crystal preparation method.