Molecular Lego

Piece by piece, researchers from the UK have built Y-shaped luminescent molecules that could help in developing solar cell technology.

Gareth Williams and Kathryn Arm at the University of Durham, have developed a method for the controlled and sequential coupling of ruthenium and iridium polypyridyl complexes to make Y-shaped luminescent assemblies. Mononuclear pyridyl complexes of transition metals have interesting photophysical and electrochemical properties; the potential of these properties for use in devices is increased in polynuclear systems.

The Y-shaped molecules transfer energy efficiently and have properties that make them suitable for use in photochemical devices including information storage and converting light energy to chemical energy in solar cells. These assemblies are also important in the fundamental study of photoinduced electron and energy transfer processes.

Previous strategies to build these complexes have used bridging ligands. As well as making the control of the synthesis difficult, the properties of the component complexes are often adversely affected when attached to the ligands. Williams and Arm have used a Suzuki-type cross-coupling of complexes containing complementary functionalities to build heterometallic assemblies. Coupling is followed by bromination and then further coupling. Each complex can be seen as a building brick for the final structure.

They hope to be able to make even larger structures in the future. ’In principle there is nothing to stop further halogenation and cross-coupling. the compounds then get very large,’ says Williams, although he acknowledges that larger compounds may not be easy to work with. They would also like to immobilise the molecules onto surfaces allowing them to be used as antennae for the sensitisation of wide band-gap semiconductors.

Rebecca Lavender