A fluorescent switch that can be made to turn on and off merely by changing the voltage across it has been prepared by a collaboration between French and South Korean scientists. The switch could have potential for optical display panels, said the researchers.

The switch relies on a polymer-based electrolyte containing chloromethoxytetrazine. Under ultraviolet light the neutral molecule is fluorescent, but the anion is colourless. By adjusting the voltage across an electrolyte containing the tetrazine, Pierre Audebert, from the Ecole Normale Supérieure in Cachan, and Eunkyoung Kim from Yonsei University, Seoul, were able to make the cell switch between the fluorescent and non-fluorescent states.

Since the anion was found to be too reactive to use in conventional solutions, the researchers sandwiched a thin layer of the tetrazine-containing electrolyte between two transparent electrodes, one of which was coated in an inert polymer electrolyte. When the current was switched on, the conversion between the two forms of the molecule was fast enough to avoid any decomposition. What's more, the contrast between these two states remained the same even after 120 switching cycles, said Audebert.

According to Knut Rurack, an expert in fluorescence probes at the Federal Institute for Materials Research and Testing in Berlin, Germany, Audebrt and Kim have 'combined in a unique way the advantages of fluorescence and redox chemistry'.

Koji Araki from the University of Tokyo, Japan, was also enthusiastic about the research, saying that it 'will open the way for development of novel displays or electro-optical switches'. He pointed out, though, that in order to achieve this, the cell response time and the durability of the device will be important - work which Audebert said is now in progress.

David Barden