Molecular ruby used as optical pressure sensor

Chemists have developed a molecular system capable of very precise optical pressure measurements.

The team at Johannes Gutenberg University Mainz and at the Université de Montréal created a ‘molecular ruby’ that can measure pressure both in the solid and in solution thanks to its solubility. Like the gemstone ruby, the molecule contains the element chromium giving it a red colour.

The principle of optical pressure measurements using chromium based materials is not new. However, up to now, all the materials usedare completely insoluble. Pressure measurements with a single type of dissolved molecular species reporting pressure changes directly in solution has been difficult to develop.

"However, our molecular ruby can do the trick," said Professor Katja Heinze. "We hope that our findings will pave the way for completely different applications beyond the classical ones and we are currently working in this direction."

Measuring the pressure with the molecular ruby is, the team say, very straightforward. The relevant site is irradiated with blue light which is absorbed by the molecular ruby, which then emits infrared radiation. Depending on the pressure, the energy of the emitted light varies in a very sensitive manner. The actual pressure can then be read from the luminescence energy. The team say the system has potential applications in the fields of materials sciences, homogeneous and heterogeneous catalysis, and all fields where pressure changes need to be monitored.

Sophisticated pressure-dependent luminescence measurements up to 45,000 bar have been performed by Sven Otto, a doctoral candidate in Heinze's team, in the laboratories of the Reber group at the Université de Montréal. He said: "The successful proof of concept was just fantastic. The highest pressures employed in a so-called diamond anvil cell are roughly 45 times higher than that experienced at the deepest known spot in the ocean", explained Otto.

The research findings have recently been published in Angewandte Chemie International Edition.