Published under the paper title “Stacked nanocarbon photosensitizer for efficient blue light excited Eu(III) emission” in the Communications Chemistry journal, the findings could lead to more efficient photosensitizers with a wide variety of applications, including the manufacture of molecular light-emitting devices.
Photosensitizers are molecules that become excited when they absorb light and then transfer this excited energy to another molecule. They are used in photochemical reactions, energy conversion systems, and in photodynamic therapy, which uses light to kill some kinds of early-stage cancer.
The design of currently available photosensitizers often leads to inevitable energy loss, and so they are not as efficient in light absorption and energy transfer as scientists would like. It also requires high energy light such as UV for excitation.
The new photosensitizer concept is based on extending the lifetime of a molecular energy state called the triplet excited state and reducing gaps between energy levels within the photosensitizer molecule, aiming to more efficiently use the photons by reducing energy losses.
The researchers designed a nanocarbon “antenna” made of coronene, a polycyclic aromatic hydrocarbon containing six benzene rings, before stacking two such antennas one on top of the other, connecting them on either side to the rare Earth metal europium. Extra connectors were added to strengthen the bonds between the nanocarbon antennas and europium. When the nanocarbon antennas absorb light, they transfer this energy to europium, causing the complex to emit red light.
Experiments showed the complex best absorbed light at wavelengths around 450nm. When a blue LED (light-emitting diode) light was shone on the complex, it glowed more than five times brighter than the europium complex which until now had the strongest reported emission under blue light. The researchers also demonstrated that the new complex can withstand high temperatures above 300ºC thanks to its rigid structure.
Hokkaido University –www.icredd.hokudai.ac.jp