Multicolor Emission of Organic Microcrystals with Charge Transfer Interactions through Cocrystal Engineering

Multicolor luminescent materials offer promising optoelectronic applications, especially organic solid-state crystalline materials. Herein, we introduce a cocrystal strategy to precisely regulate the multicolor photoluminescence behaviors of microcrystals through charge transfer (CT) interactions based on two components. Thereinto, compared with the single-component CzC6Cz (1,5-di(9H-carbazol-9-yl)-pentane) microcrystals, the fluorescence emissions of sky-blue color CzC6Cz/TFIP(2,4,5,6-tetrafluoroisophthalonitrile) microcrystals, green color CzC6Cz/TFTP (2,3,5,6-tetrafluoroterephthalonitrile) microcrystals, and red color CzC6Cz/TCNB (1,2,4,5-tetracyanobenzene) microcrystals all present significant red shifts, and the degree of the red-shifted emissions is 56, 104, and 221 nm, respectively, while the fluorescence emission of CzC6Cz/FA (p-Fluoranil) microcrystals was completely quenched due to the existence of strong noncovalent intermolecular interactions between the electron donor (CzC6Cz) and acceptor (FA), which was also confirmed by the theoretical calculation. Moreover, all four cocrystals adopt ordered and layered molecular stacking patterns, in which the electron acceptors were caught in the middle of the adjacent electron donors. Therefore, this work provides a promising strategy to expand versatile solid-state crystalline materials with anticipated function and properties.