Direct Screening\nof Colloidal Sol Crystallinity by\nπ–π Stacking-Regulated Fluorescence

The properties and applications of colloidal sol nanomaterials\nare largely affected by their crystallinity, making the rapid screening\nof colloidal sol crystallinity important to explore diverse advanced\nnanomaterials. Yet, the rational design of a novel technique for colloidal\nsol crystallinity analysis remains a great challenge. In this study,\nwe synthesized an imidazole-anchored naphthalene diamine (IANA) fluorophore\nwith a planar naphthalene motif. Using IANA as the fluorescence probe,\nwe demonstrated the rapid and direct screening of colloidal sol crystallinity\nin model layered materials (cadmium–aluminum layered double\nhydroxides, CdAl-LDHs). The crystallinity-promoted fluorescence quenching\nis attributed to the crystallinity-enhanced ordered arrangement of\nIANA by Cd-imidazole coordination, which benefits its face-to-face\nπ–π stacking and inhibits the absorption of ultraviolet\nlight. Without drying treatment, this technique directly reveals the\ncrystallinity information of colloidal sol CdAl-LDHs. In addition,\nthe practical application of the proposed fluorescence technique is\nverified by accurate colloidal sol crystallinity determination of\nthe CdAl-LDHs sample with unknown crystallinity. This work has opened\na new avenue for exploring an alternative to X-ray diffraction for\nthe rapid screening of the colloidal sol crystallinity of layered\nmaterials and even organic crystals through π–π\nstacking-regulated fluorescence.