Learning from plants: visible light energy harvesting

Jun 23, 2011

How do they do it? Plants make use of only the energy of sunlight for their requirements. Many researchers are trying to mimic the process to harness the vast energy of the sun. In the article published recently in Angew. Chem. Int. Ed.,[1] Jianzhang Zhao et al. of the Dalian University of Technology (China) showed that long-lived triplet excited states are tremendously important for applications in light harvesting. Now they report in the European Journal of Inorganic Chemistry significantly long room-temperature triplet excited state lifetimes for cyclometallated, coumarin-containing IrIII complexes with strong absorption in the visible range.

Coumarin, which is known for its intense , is a suitable "antenna" to enhance the absorption of complexes to be used as sensitizers. Light-harvesting RuII–coumarin dyads have been designed previously; however, their absorption is in the UV region. The excitation wavelengths of typical cyclometalated IrIII complexes are in the UV or blue region, and their absorption is weak in the . The addition of a coumarin group to the diimine ligand in a cyclometallated iridium(III) complex increased its absorption in the visible region tremendously. Zhao et al. report a light-harvesting cyclometalated IrIII molecular array with intense absorption in the visible region and a triplet excited state with a lifetime over 25 times longer than those of analogous ruthenium compounds.

Although the dyads are weakly phosphorescent (ΦP = 0.6%), the authors prove that the triplet excited states of the IrIII complexes are efficiently populated upon photoexcitation, by using the complexes as triplet sensitizers for triplet–triplet annihilation upconversion. Upconversion quantum yields (ΦUC) of up to 23.4% were observed. With these results, the authors also question the classical understanding of triplet–triplet annihilation upconversion, which stipulates that quenching of the phosphorescence of the sensitizer should accompany upconverted fluorescence. Upconversion from a weakly phosphorescent excited state opens the way to a completely new approach to the design of light-harvesting complexes.

[1] S. Ji, W. Wu, W. Wu, H. Guo, J. Zhao, Angew. Chem. Int. Ed. 2011, 50, 1626–1629

Explore further: Structure of sodium channels different than previously believed

More information: Jianzhang Zhao et al, Visible-Light Harvesting with Cyclometalated Iridium(III) Complexes Having Long-Lived 3IL Excited States and Their Application in Triplet–Triplet-Annihilation Based Upconversion, European Journal of Inorganic Chemistry, dx.doi.org/10.1002/ejic.201100501

add to favorites email to friend print save as pdf

Related Stories

Theorists make discovery in odd triplet pairing

Dec 14, 2007

In a paper which will shortly appear in Physical Review Letters, School of Physics and Astronomy Professor Oriol Valls along with lead author Klaus Halterman (China Lake, Naval Warfare Center) and co-author Paul Barsic (Unive ...

New NIST reference material reinforces fragile-x screens

Feb 25, 2005

A new Standard Reference Material from the National Institute of Standards and Technology (NIST) will help clinical genetics labs improve the accuracy of their diagnostic tests for the most common cause of hereditary mental ...

Recommended for you

Breakthrough points to new drugs from nature

Apr 16, 2014

Researchers at Griffith University's Eskitis Institute have developed a new technique for discovering natural compounds which could form the basis of novel therapeutic drugs.

World's first successful visualisation of key coenzyme

Apr 16, 2014

Japanese researchers have successfully developed the world's first imaging method for visualising the behaviour of nicotine-adenine dinucleotide derivative (NAD(P)H), a key coenzyme, inside cells. This feat ...

User comments : 0

More news stories

Continents may be a key feature of Super-Earths

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Under some LED bulbs whites aren't 'whiter than white'

For years, companies have been adding whiteners to laundry detergent, paints, plastics, paper and fabrics to make whites look "whiter than white," but now, with a switch away from incandescent and fluorescent lighting, different ...