Ion-Specific Freezing-Induced NIR Phosphorescence: Interfacial Synergy Enables Imaging of "Invisible Ice"

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• Icing poses significant risks to aviation, power transmission, and wind energy systems.
• Detecting concealed or transparent ice remains a major challenge.

Purpose of the Study:

• To develop a novel imaging strategy for detecting "invisible ice" using freezing-induced near-infrared (NIR) phosphorescence (FIP).
• To investigate the mechanism behind FIP and its dependence on counterions for enhanced ice detection.

Main Methods:

• Utilized aryl-substituted pyrrolo[3,2-b]pyrrole probes (PP4P-X) for FIP imaging.
• Investigated counterion dependence (F-, Br-, I-, NO3-, SCN-) on phosphorescence.
• Conducted mechanistic studies on interfacial adsorption and molecular aggregation at the ice-water interface.
• Performed wind-tunnel tests for aircraft icing detection.

Main Results:

• Developed a FIP imaging strategy enabling deep-penetration, low-background detection of ice.
• Demonstrated strong FIP turn-on for PP4P-F and PP4P-Br probes, with significant signal-to-background ratio (SBR) increase.
• Mechanistic studies revealed interfacial adsorption of F-/Br- promotes aggregation and enhances phosphorescence.
• Successfully mapped ice onset, thickness, and propagation on aircraft wings in wind-tunnel tests.

Conclusions:

• Established a noncontact, in situ, and quantitative method for "invisible ice" detection.
• Provided a framework for utilizing NIR phosphorescent probes in frozen-phase monitoring.
• The FIP strategy offers a promising solution for enhancing safety in various critical infrastructure systems.