Organic cocrystals formed with two or more different molecules through intermolecular noncovalent interactions, such as π–π interaction and hydrogen/halogen bonds, have received increasing attention due to their promising applications in organic optoelectronics. For organic photonics and electronics, the growth morphology of organic micro/nanocrystals coupled with their shape and emission color is of great importance. In this study, using a “cocrystal” approach, the organic microcrystals can be modulated from the yellow‐emissive polyhedral microcrystals of 1,4‐bis (4‐cyanostyryl) benzene (p‐BCB) to the sky‐blue‐emissive microwires of p‐BCB:1,4‐diiodo tetrafluorobenzene (p‐BCB:DIFB), which are self‐assembled in solution at room temperature. Additionally, with the formation of the cocrystals, the radiative decay (kr) rate of these organic microcrystals is enhanced from 0.04 to 0.12 ns−1, which is attributed to the absence of excimers in the organic cocrystals. Therefore, this “cocrystal” approach can simultaneously tune the emission color, morphology, and molecular packing mode of these as‐prepared organic microcrystals, which can contribute to the development of organic integrated optoelectronic devices.

Organic semiconductor micro-/nanocrystals with regular shapes have been demonstrated for many applications, such as organic field-effect transistors, organic waveguide devices, organic solid-state lasers, and therefore are inherently ideal building blocks for the key circuits in the next generation of miniaturized optoelectronics. In the study, blue-emissive organic molecules of 1,4-bis(2-methylstyryl)benzene (o-MSB) can assemble into rectangular microcrystals at a large scale via the room-temperature solution-exchange method. Because of the Förster resonance energy transfer, the energy of the absorbed photons by the host matrix organic molecules of o-MSB can directly transfer to the dopant organic molecules of tetracene or 1,2:8,9-dibenzopentacene (DBP), which then emit visible photons in different colors from blue to green, and to yellow. More impressively, by modulating the doping molar ratios of DBP to o-MSB, bright white-emissive organic microcrystals with well-preserved rectangular morphology can be successfully achieved with a low doping ratio of 1.5%. These self-assembled organic semiconductor microcrystals with multicolor emissions can be the white-light sources for the integrated optical circuits at micro-/nanoscale.