An international team of researchers has stumbled across some unique coil-shaped nanostructures when investigating photoresponsive functional assemblies. 

Shiki Yagai, at Chiba University, Japan, and colleagues mixed an azobenzene photoswitching dye with a perylene bisimide light-harvesting dye. Because the dyes have complementary hydrogen-bonding sites, the team expected the dyes to form 1:1 complexes. 'However, the complexation of these two building blocks proved very complicated due to an unconventional multiple-hydrogen bonding network,' says Yagai. 'We decided to chase this complex system.' 

After careful spectroscopic and atomic force microscopy studies, the team found that the dyes formed helical nanostructures with twice as much of the azobenzene dye as the perylene bisimide. The helices have a slipped stacking arrangement of the light-harvesting dye, explains Yagai, which is seen in naturally occurring light-harvesting systems of photosynthetic organisms. 

'Growing demands on the miniaturisation of electronic and photonic devices are motivating chemists to create complicated functional nanostructures,' Yagai comments. 'Specific arrangements of functional building blocks within nanostructures are crucial. Our system is very attractive because it fulfils these requirements.' 

The team are now developing smart nanostructures with morphologies and light-harvesting functions that can be controlled by light pulses. 

Joanne Thomson