Fluorescent Probe with Dual Energy Transfer Process for Selective Fe³⁺ Detection and Cellular Imaging

Traditional fluorescent probes often exhibit compromised response and specificity due to poor adaptability to varying polar environments. Herein, we present the development of a robust Fe³⁺-specific small-molecule sensor by linking a tetraphenylsilole derivative and rhodamine 6G hydrazide via a Schiff-base π bridge to form a fluorescent donor-acceptor system. The dispersed silole moiety serves as dark donor, while the aggregated state of silole converts into emissive donor. Upon selective binding with Fe³⁺, the molecules are found to undergo fluorescence resonance energy transfer (FRET) and dark resonance energy transfer (DRET) to rhodamine moiety in a polarity-dependent manner. Hence, fluorescence quantitation of Fe³⁺ in both high-organic (>70%) and water-rich solutions (>70%) is successfully achieved with detection limits of 0.083 μM and 0.28 μM, respectively. Further, ratiometric intracellular imaging of Fe³⁺ is demonstrated using the probe. This sensing strategy can offer a promising avenue for the development of polarity-adaptive fluorescent probes targeting other metal ions in complex biological and environmental matrices.