My watch list


Inverted Fluorescence

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

© Wiley-VCH

23-Dec-2020: 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.

Original publication:
Naoyuki Harada et al.; "Discovery of Key TIPS‐Naphthalene for Efficient Visible‐to‐UV Photon Upconversion under Sunlight and Room Light"; Angewandte Chemie International Edition; 2020

Facts, background information, dossiers

More about Kyushu University

More about Angewandte Chemie

  • News

    Degradable sugar-based polymers may store and release useful molecular freight

    Degradable, bio-based polymers offer options for chemical recycling, and they can be a tool to store and release useful molecules. Scientists have developed a class of sugar-based polymers that are degradable through acid hydrolysis. The researchers also integrated “cargo” molecules in the ... more

    Useful “Fake” Peptides

    Some useful drugs consist of peptides acting on their protein targets. To make them more efficient and stable, scientists have found a way to replace crucial segments of the peptides with ureido units. These oligoureas, which are composed of urea-based units, fold into a structure similar t ... more

    Combination Therapy against Cancer

    In their quest to destroy cancer cells, researchers are turning to combinational therapies more and more. Scientists from Germany and China have now combined a chemotherapeutic and photodynamic approach. All agents are encapsulated in nanocapsules with a protein shell to be delivered to the ... 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:


Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE