Aggregation-caused quenching to crystallization-induced emission transformation: hydration-induced luminescence in crystal curcumin with tunable thermochromism for in vivo tracking

The development of solid-state materials with switchable luminescence in response to stimuli remains a challenge, especially for organic materials. While crystal water significantly impacts the absorption spectra of organic crystals, it is unclear whether the emission spectra of organic luminescent materials can be systematically manipulated by water. In this study, we successfully obtained curcumin monohydrate (Form X), a channel-type hydrate exhibiting crystallization-induced emission (CIE) at 608 nm (orange fluorescence), which contrasted with the conventional forms of aggregation-caused quenching (ACQ). Thermal treatment induced the release of hydration water, resulting in a new anhydrate (Form IV) that emitted yellow-green fluorescence with the emission peak at 575 nm. Additionally, this approach can be used to track the absorption of curcumin crystals following subcutaneous or intramuscular delivery. The hydratemediated single-crystal-to-single-crystal transition (SCSC) and its associated luminescence transition were reversible and responsive to temperature, offering a green approach for synthesizing and designing aggregation-induced-emission (AIE)-based intelligent luminescent devices for detecting air humidity or drug absorption.