Direct Screening of Colloidal Sol Crystallinity by π-π Stacking-Regulated Fluorescence

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