Two-color glowing molecule could make wind tunnel tests more accurate

Most sensors can measure only one thing 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 using two separate instruments—adding cost and complexity to the process.

Now, chemists and aerospace engineers at The University of Manchester, working with colleagues at the University of Eastern Finland, have designed a molecule that can do both simultaneously. It emits two distinct colors of light at once: one that responds to both air pressure and temperature, and one that responds only to temperature. By comparing these two signals, it's possible to get a corrected pressure reading from the molecule itself rather than using a separate temperature sensor alongside a pressure sensor.

Temperature distorts pressure readings

The molecule has been designed as an active ingredient in specialized paints that measure pressure on aircraft models in wind tunnels, addressing a major challenge in the aerospace industry. When engineers test a new aircraft design in a wind tunnel, they need to know exactly how air pressure is distributed across every surface. One of the best ways to do this is with a pressure-sensitive paint that glows in proportion to the air pressure pushing against it.

The problem is that the light these paints emit is sensitive not only to pressure but also to temperature. As a scale model heats and cools during a wind tunnel test, the glow shifts in ways that have nothing to do with pressure, introducing errors that engineers then have to correct.

Dr. Alexander Romanov, senior research fellow in the Department of Chemistry at The University of Manchester, said, "Our new Manchester material emits red light, what we call phosphorescence, which is sensitive to changes in both pressure and temperature. At the very same time, this material emits blue light as a fluorescence—responding only to temperature. By measuring blue and red light at once, we've got everything we need to separate the pressure signal from the temperature interference. That kind of built-in self-correction is simply not possible with a standard light-emitting molecule."

Gold bonds tune two light signals

The team's work, published in the journal Advanced Optical Materials, explains how the molecule is built around a gold atom bonded to a ring-shaped compound called acridine. The position of that bond within the structure determines which type of light the molecule produces.

Gold was chosen because even subtle changes to where it sits within the molecule produce reliably different light-emitting behaviors, 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, whereas a bond at a different position triggers the temperature-only blue emission.

Calculations carried out by the team's colleagues in Finland helped the researchers understand and predict these differences before the molecule was built in the laboratory. In use, the molecule is embedded in a paint applied to test models in the standard way. A camera captures both emission colors simultaneously, and the ratio between the two signals automatically corrects for temperature without a separate temperature sensor.

Making wind tunnel paints more reliable

Dr. Mark Quinn, reader in the Department of Mechanical and Aerospace Engineering at The University of Manchester, said, "In wind tunnel testing, 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 a more elegant solution, and potentially a more practical one for real test conditions, where adding extra instruments creates its own complications."