Media release

From: Queensland University of Technology (QUT)

An international team led by QUT researchers continues to challenge a long-held assumption in photochemistry with potential applications in fields ranging from medicine to manufacturing.

Published in the Journal of the American Chemical Society, the research introduces a theory explaining that the effectiveness of light in triggering chemical reactions is not solely determined by how strongly a molecule absorbs it.

The research team led by principle investigator Distinguished Professor Christopher Barner-Kowollik and lead authors Dr Joshua Carroll and Fred Pashely-Johnson, from the QUT Soft Matter Materials Group, has identified a new mechanism involving molecular microenvironments that can dramatically influence how molecules respond to light.

“Since light consists of a spectrum of colours, it has been expected for many years that the colour that is absorbed the most by a molecule will be the most efficient at triggering any photoreactions,” Dr Carroll said.

“Our experiments confirmed that the microenvironment around each individual absorbing molecule can lead to vastly different properties.”

The QUT team found that these effects can lead to longer excited-state lifetimes, making certain molecules more reactive under lower-energy, red-shifted light.

The behaviour was linked to a known phenomenon in fluorescence science called the ‘red-edge effect’ and its influence on photochemical reactivity was confirmed through advanced experimental techniques including fluorescence spectroscopy and photochemical action plots.

Fluorescence spectroscopy is a technique used to study the fluorescent properties of substances – that is how they absorb light at one wavelength and then emit light at a longer wavelength. Photochemical action plots show how effective different wavelengths of light are at driving a specific photochemical reaction.

The QUT research team also comprised Dr Maciej Klein and Associate Professor Ajay Pandey as well as Professor Andreas Unterreiner and Theresa Stephan from the Karlsruhe Institute of Technology (KIT) and Dr Michael Walter from the University of Freiburg in Germany.

The potential impact of the observed and rationalised effect will enable researchers to develop more sophisticated photochemical technologies in fields such as photodynamic therapy, 3D printing, organic chemistry, solar energy and many more.

“The implications are enormous,” Professor Barner-Kowollik said.

“By controlling microenvironments, through solvent choice or molecular design, we can tune how light affects molecules, allowing for more precision in photochemical drug delivery, polymer engineering and light harvesting.”

The research was supported by the Australian Research Council and the German Research Foundation.

Read the full study, Microenvironments as an Explanation for the Mismatch between Photochemical Absorptivity and Reactivity, published in the Journal of the American Chemical Society online.