Polymers Control Energy Transfer

Michael D. Wheeler

Chemists at the University of California have demonstrated a means to control energy transfer in polymer semiconductors embedded in channels of nanoporous silica. Researchers are paying close attention to such conjugated polymer chains in an attempt to make better organic optoelectronic devices.

Researchers at the University of California in Los Angeles devised a honeycomblike architecture of nanoporous silica that controls energy transfer in polymer semiconductors. Housing the polymer chains in the structure could improve the performance of organic optoelectronic devices.

The problem with the polymers is related to the photophysics of their chains. It is difficult to realize the ideal material: single, straight wires of an organic semiconductor. Instead, the polymers have coiled chains, which leads to many conjugation lengths and random interactions between the chains. These characteristics affect both charge and energy transfer, so researchers have sought to control these effects in bulk polymers by devising architectures that yield a precise ordering and separation of the chains.

The university chemists found that they could house more than 80 percent of their nanoengineered conjugated polymer chains inside the aligned pores of silica by using its host-guest chemistry. This minimized any energy transfer between the chains by separating them in the silica's hexagonal pores. Using time-resolved luminescence studies, the group demonstrated how this architecture affects energy migration along the polymer backbone, an advance that could provide insights on how to improve photoluminescence in the material and perfect its use in optoelectronics.

"What we've really done is show that we can use well-defined, nanometer-scale architecture to control the optical properties of complex polymer-based material," said Sarah H. Tolbert, a lead researcher in the group, which reported its findings in the April 28 issue of Science. The researchers plan to use this control of a polymer's geometry to tune its optical and electronic properties to specific applications, she said.

"We've been able to show that energy moves much faster between chains than along single chains, which tells us a lot about how to design optoelectronic devices based on these materials," added Benjamin J. Schwartz, the other lead researcher.