Ultra-Solvatochromic Probe Based on Binaphthofuran for Visual Detection of Early Trace Oil Leakage in Oil Reservoir Capsules

The long-term reliability of converter transformers hinges on the integrity of oil reservoir capsules, whose early-stage oil leakage detection remains challenging. We present Probe (R)-1, a novel D–π–A solvatochromic fluorescent probe synthesized via a binaphthofuran donor–π-bridge scaffold functionalized with a p-trifluoromethylbenzoyl acceptor, designed for rapid, visual, on-site identification of trace oil leaks. The probe exhibits a pronounced positive solvatochromic shift of 138 nm across solvent polarity gradients, enabling unambiguous, naked-eye discrimination of structurally similar organic liquids through distinct fluorescence color transitions. In ethanol solutions, the probe achieves an exceptionally low detection limit of 5.88 μL/mL for insulating oil, surpassing industry sensitivity requirements. On real-world oil capsule surfaces, the probe produces a stark fluorescence contrast between the oil stains and the capsule background, permitting clear visualization of micro-volume droplets under a 365 nm handheld UV lamp. This method eliminates reliance on complex instrumentation, offering a rapid, cost-effective, and field-deployable solution for proactive maintenance in power grid infrastructure.