Tunable Emission Color and Morphology of Organic Microcrystals by a Cocrystal Approach

Organic cocrystals formed with two or more different molecules through intermolecular noncovalent interactions, such as pi-pi 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 (k(r)) 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.