Dual-Emitting Gold Molecule Promises Sharper Wind Tunnel Pressure Maps

Wind tunnel testing is one of the most demanding arenas in modern engineering. When a new aircraft design is placed inside a wind tunnel, engineers need to know precisely how air pressure is distributed across every square centimetre of its surface, because those pressure patterns determine lift, drag, and ultimately whether the aircraft will fly as intended. One of the most powerful tools for capturing this information is pressure-sensitive paint, a specialist coating that glows in proportion to the air pressure pushing against it. But these paints have long carried a stubborn flaw: their glow responds not only to pressure but also to temperature, and as a scale model heats up and cools down during a test run, the light output shifts in ways that have nothing to do with aerodynamics. Now a team at The University of Manchester, working with colleagues at the University of Eastern Finland, has designed a single molecule that could dissolve this problem at its root.

The breakthrough, published in the journal Advanced Optical Materials, centres on a molecule capable of measuring both air pressure and temperature at the same time, from the same spot on a surface. Most sensors can only measure one property at a time, like a thermometer for temperature or a pressure gauge for pressure. Measuring two properties accurately from the same surface at the same moment usually means deploying two separate instruments, which adds cost and complexity to an already intricate testing process. The new molecule sidesteps that requirement entirely by emitting two distinct colours of light simultaneously: one signal that responds to both air pressure and temperature, and another that responds only to temperature. By comparing the two, the molecule itself provides a corrected pressure reading without any external temperature sensor.

Dr Alexander Romanov, Senior Research Fellow in the Department of Chemistry at The University of Manchester, explained the dual nature of the emission. The Manchester material emits red light, a form of phosphorescence, which is sensitive to changes in both pressure and temperature. At the very same time, it emits blue light as fluorescence, responding only to temperature. By measuring blue and red light at once, researchers obtain everything needed to separate the pressure signal from the temperature interference. According to Romanov, that kind of built-in self-correction is simply not possible with a standard light-emitting molecule, which is precisely why the achievement matters for the aerospace industry.

The chemistry behind the molecule is as elegant as the concept. The structure is built around a gold atom bonded to a ring-shaped compound called acridine, and remarkably, the position of that bond within the molecule determines which type of light it produces. Gold was chosen because even subtle changes to where it sits within the structure produce reliably different light-emitting behaviours, giving chemists precise control over the sensing properties. When the gold atom bonds to one position on the molecule, it triggers the pressure-sensitive red emission; a bond at a different position triggers the temperature-only blue emission. This positional sensitivity turns a single molecular scaffold into a two-channel sensor, with each channel carrying distinct physical information about its environment.

Theoretical work played a crucial role before any molecule was made. Calculations carried out by collaborators at the University of Eastern Finland helped the Manchester team understand and predict the differences in emission behaviour before the compound was built in the laboratory. That predictive step is significant because designing dual-emitting molecules is notoriously difficult: the two emission pathways must coexist in the same structure without quenching each other, and their responses to external conditions must be cleanly separable. With the computational groundwork in place, the team could proceed to synthesis with a clear target, confident that the gold-acridine framework would deliver the two independent optical signals the concept required.

In practical use, the molecule is embedded in a paint applied to test models in the standard way for pressure-sensitive paint measurements. A camera captures both emission colours at the same time, and the ratio between the two signals automatically corrects for temperature, without any separate temperature sensor being mounted on or near the model. This ratio-based approach is the key to the self-correction. Because temperature affects both emissions while pressure affects only one, the blue signal acts as a continuous internal reference. Dividing one signal by the other cancels out the thermal contribution mathematically, leaving a clean pressure measurement even as the surface temperature of the model drifts during a run.

The implications for wind tunnel testing are considerable. Dr Mark Quinn, Reader in the Department of Mechanical and Aerospace Engineering at The University of Manchester, noted that temperature correction is currently one of the main challenges to making pressure-sensitive paints reliable. Having both pressure and temperature measurements come from the same molecule simultaneously is, in his view, a more elegant solution, and potentially a more practical one for real test conditions, where adding extra instruments creates its own complications. Traditional temperature correction often relies on infrared cameras, embedded thermocouples, or separate temperature-sensitive paints, each of which adds expense, calibration burden, and potential sources of error to a test campaign.

Pressure-sensitive paint technology itself deserves a closer look, because it represents a fundamental shift in how aerodynamicists gather data. Before such paints existed, mapping surface pressure required drilling hundreds of tiny pressure taps into a model and connecting each one to a transducer, a slow and expensive process that provided data only at discrete points. Pressure-sensitive paint turns the entire surface into a continuous sensor: illuminate the coating, photograph its glow, and the brightness map becomes a pressure map across the whole model. The catch has always been that the luminous molecules in these paints are also thermally active, so a wing that warms under the tunnel lights or cools in the airflow produces glow variations that masquerade as pressure changes. The new dual-emitting molecule attacks that vulnerability directly within the paint itself.

The work sits within a broader programme of research at Manchester into improving pressure-sensitive paint for aerospace applications. A related study, recently published in ACS Applied Engineering Materials, addresses the temperature problem from a different direction, by designing a platinum-based paint with inherently low temperature sensitivity. Together, the two studies represent complementary approaches to one of the industry’s most persistent challenges. One strategy minimises the temperature response at the level of the emitting molecule; the other, embodied in the new gold-acridine complex, accepts the temperature response but measures it simultaneously so it can be subtracted. Having both tools available gives engineers flexibility to choose the approach best suited to a given test, or potentially to combine them for even greater robustness.

The research, published under the full title Temperature Correction in a Single Luminophore Pressure-Sensitive Paint Using a Dual-Emitting Gold Acridine Complex, points toward a future in which wind tunnel data is cleaner, faster to process, and less dependent on elaborate correction procedures. For an industry in which a single wind tunnel campaign can cost millions and every improvement in measurement fidelity translates directly into better aircraft, a molecule that carries its own thermometer is more than a laboratory curiosity. It is a candidate to become a standard ingredient in the paints that coat the next generation of wings, fuselages, and rotor blades, turning two colours of light into a single, trustworthy picture of the forces that keep aircraft aloft.

Subject of Research: A dual-emitting gold-acridine molecule for temperature-corrected pressure-sensitive paint in wind tunnel testing

Article Title: Two-color glowing molecule could make wind tunnel tests more accurate[

Article References: Two-color glowing molecule could make wind tunnel tests more accurate[. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: pressure-sensitive paint, wind tunnel testing, aerospace engineering, gold acridine complex, phosphorescence, fluorescence, temperature correction, molecular sensors, University of Manchester, Advanced Optical Materials, luminophore, aircraft testing