Time-Dependent Solvent-Driven Solid-State Fluorescence-based Numeric Coding

Controllable solid-state transformations can provide a basis for novel functional materials. Herein, we report a series of solid-state systems that can be readily transformed between amorphous, co-crystalline, and mixed crystalline states via grinding or exposure to solvent vapors. The present solid materials were constructed using an all-hydrocarbon macrocycle, cyclo[8](1,3-(4,6-dimethyl)benzene) (-CDMB-8) (host), and neutral aggregation-caused quenching dyes (guests), including 9,10-dibromoanthracene (1), 1,8-naphtholactam (2), diisobutyl perylene-3,9-dicarboxylate (3), 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (4), 4,7-di(2-thienyl)-benzo[2,1,3]thiadiazole (5), and 4-imino-3-(pyridin-2-yl)-4H-quinolizine-1-carbonitrile (6). Seven co-crystals and six amorphous materials were obtained via host-guest complexation. Most of these materials displayed turn-on fluorescence emission (up to 20-fold enhancement relative to the corresponding solid-state guests). The interconversion between amorphous, co-crystalline states, and crystalline mixtures could be induced by exposure to solvent vapors or by subjecting to grinding. The transformations could be monitored readily by means of single-crystal and powder X-ray diffraction analyses, as well as solid-state fluorescent emission spectroscopy. The externally induced structural interconversions resulted in time-dependent fluorescence changes. This allowed sets of privileged number array codes to be generated.