The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

A colorimetric and fluorescent probe ER-ClO was presented in this work to detect cellular hypochlorite with high selectivity and sensitivity. With an organelle targeting unit, ER-ClO was successfully applied in the bio-imaging of exogenous and endogenous hypochlorite in the endoplasmic reticulum in a ratiometric manner.

A highly “reactive” probe showed a ratiometric fluorescence response to HSO₃⁻ with fast response and low detection limit (3.0 nM).

Organic compounds with bright solid-state emission are emerging as versatile materials in many fields. However, traditional fluorescent dyes generally show high-emissive fluorescence in solution but faint or quenched emission in the solid state. Therefore, it remains a great challenge to develop bright solid-state emissive materials based on traditional fluorescent dyes. Herein, we report several solid-state emissive meso-substituted BODIPYs (PhMe₃-BODIPY, PhMe-BODIPY, Ph-BODIPY and Me-BODIPY) obtained by using a simple two-step synthesis. Interestingly, these BODIPYs exhibit bright dual-state emission (DSE) with green fluorescence (512–520 nm, fluorescence quantum yield Φ_F is up to 85%) in THF and solid-state red emission (601–632 nm, Φ_F is up to 32.2%) in the crystalline state. The highly emissive fluorescence in the crystalline state is demonstrated to be due to the formation of J-aggregation. More importantly, the single crystals of the meso-aryl-substituted BODIPYs exhibit an unusual high-contrast mechanochromic property, which displays remarkable fluorescence color changes from red to yellow upon gentle grinding due to the transition from single crystals to microcrystals. Furthermore, strong grinding completely destroys the J-aggregation and leads to the transformation from microcrystals to a free state, hence the fluorescence color becomes green after strong grinding.