Scientists Use Computer Calculations, Not Trial and Error, to Design Molecules That Glow When Clumped

Researchers led by Associate Professor Gen-ichi Konishi at the Institute of Science Tokyo in Japan have found a way to predict, through computer calculations, which molecules will glow brightly when clumped together rather than when dissolved — a property called aggregation-induced emission (AIE).

Most light-emitting molecules behave the opposite way: they glow in solution but go dark once they aggregate into a solid. AIE molecules, known as AIEgens, do the reverse, staying dim in dilute solution and lighting up once aggregated. This makes them useful for organic light-emitting diodes (OLEDs), biological imaging, sensors, and light-based cancer therapy. Until now, most AIEgens were found by trial and error, because the underlying chemistry was too complex to calculate easily.

The team proposed that AIE depends on how easily an excited molecule can reach a conical intersection (CI), a point in its energy landscape where it can lose energy quietly as heat instead of as light. In solution this energy-losing path is easy to reach; in the solid state it is blocked, so light is emitted instead. Using quantum chemical calculations on 30 versions of bridged stilbenes, a well-studied family of light-responsive molecules, the team identified a small number of measurable properties that predict how easily a molecule can reach a CI.

The calculations showed that adding electron-donor and electron-acceptor chemical groups, and choosing where on the molecule they sit, changes how easily the excited molecule reaches the CI. Based on these predictions, the researchers designed and built four bridged stilbene molecules, and their light-emitting behavior, measured with ultrafast laser spectroscopy, matched what the calculations had predicted.

The findings, published in the journal Advanced Science, point toward designing AIE materials by calculation rather than trial and error. Konishi said the framework is expected to contribute to the development of high-efficiency OLED materials, fluorescent probes for bioimaging, and sensing materials.