23-Dec-2020 - Kyushu University

Inverted Fluorescence

Discovery of chromophores that emit light in the ultraviolet region when excited with visible light

Fluorescence usually entails the conversion of light at shorter wavelengths to light at longer wavelengths. Scientists have now discovered a chromophore system that goes the other way around. When excited by visible light, the fluorescent dyes emit light in the ultraviolet region. According to the study published in the journal Angewandte Chemie, such light upconversion systems could boost the light-dependent reactions for which efficiency is important, such as solar-powered water splitting.

Fluorescent dyes absorb light at shorter wavelengths (high energy, e.g. blue light) and emit light at longer wavelengths (low energy, e.g. red light). Upconversion of light is much more difficult to achieve. Upconversion means that a fluorescent dye is excited with radiation in the visible range but emits in the ultraviolet. Such dyes could be used to run high-energy catalytic reactions such as solar-powered water splitting just using normal daylight as an energy source. Such dyes would expand the range of available excitation energy.

Nobuhiro Yanai and colleagues at Kyushu University, Japan, are exploring multi-chromophore systems for their ability to upconvert fluorescence light. Yanai explains how upconversion works: “Fluorescence upconversion occurs when two chromophore molecules, which have been excited in the triplet state by a sensitizer, collide. This collision annihilates the sensitized energy and lifts the chromophores to a higher energy level. From there, they emit the energy as radiation.”

In practice, however, it is difficult to achieve effective upconverting chromophore designs—existing systems need high-intensity radiation and still do not achieve more than ten percent efficiency. “The main reason for the low efficiency is that the sensitizer chromophore molecules also absorb much of the upconverted light, which is then lost,” Yanai says.

In contrast, the donor–acceptor chromophore pair developed by Yanai and colleagues exhibits energy levels that are so finely adjusted that it achieved a record-high 20 percent upconversion efficiency. Almost no back-absorption and low nonradiative loss occurred. The novel chromophore pair consisted of an iridium-based donor, which was an established sensitizer, and a naphthalene-derived acceptor, which was a novel compound.

Low back-absorption and few radiative losses mean that the intensity of the exciting radiation can be low. The researchers reported that solar irradiance was sufficient to achieve high upconversion efficiency. Even indoor applications were possible using artificial light. The authors held an LED lamp above an ampoule filled with the chromophore solution and measured the intensity of the emitted UV light.

Facts, background information, dossiers

More about Kyushu University

More about Angewandte Chemie

  • News

    New Tools Against Hospital Infections?

    Antibiotic-resistant hospital pathogens are not to be underestimated as a health risk. A research team has now introduced a new approach for treating multiple-drug resistant Staphylococcus in the journal Angewandte Chemie. It is based on a synthetic peptide that reduces the virulence of the ... more

    Firefly Luminescence Reveals Pesticides

    A luminescence reaction modeled on fireflies can detect contamination with organophosphates with high sensitivity, ease, and low cost. At the center of this technology is a new enzymatic method for the synthesis of analogues of luciferin, the substance that makes fireflies glow. As reported ... more

    Strong and elastic, yet degradable: protein-based bioplastics

    More than eight million tons of plastic end up in the oceans every year—a serious danger for the environment and health. Biodegradable bioplastics could provide an alternative. In the journal Angewandte Chemie, a research team has now introduced a new method for the production of protein-ba ... more

q&more – the networking platform for quality excellence in lab and process

The q&more concept is to increase the visibility of recent research and innovative solutions, and support the exchange of knowledge. In the broad spectrum of subjects covered, the focus is on achieving maximum quality in highly innovative sectors. As a modern knowledge platform, q&more offers market participants one-of-a-kind networking opportunities. Cutting-edge research is presented by authors of international repute. Attractively presented in a high-quality context, and published in German and English, the original articles introduce new concepts and highlight unconventional solution strategies.

> more about q&more

q&more is supported by: