"Jumpy" chromophores could enable molecular electronics
10/01/2006
Researchers at the U. of Pennsylvania and St. Josephs U. are touting their work on chromophores, which when linked together enable transfer of electrical charges that exceed mobility in organic semiconductors by up to a factor of three, and hold promise for applications in displays and solar cells.
Chemically speaking, a chromophore is a molecule or part of one that is responsible for its color-light hitting the chromophore excites an electron, which then emits light of a particular color. In their research, the scientists have linked several chromophores (porphyrins) in oligomers via a carbon-carbon triple bond (acetylene), and constructed arrays of them through a series of sequential reactions (Pd-catalyzed cross-coupling reactions). Introducing a charge to a chain array of the chromophores, by using an electrode or appropriate chemical reagent serving as an oxidant, enables electrons to "quickly hop from one chromophore to the next," said Michael Therien, a professor in Penn’s Department of Chemistry and lead project researcher.
Key to achieving extensive charge delocalization and high charge mobilities is building polymeric structures with long chromophores and short links, which leads to small structural changes where holes and electrons are introduced-a previously unaddressed factor in designing conducting and semiconducting organic materials, explained Therien.
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In the current construction (see figure), the positions and nature of the nitrogen and carbon atoms cannot be altered, or the material will lose its designed charge delocalization properties, according to Therien. Zinc was used as a central metal ion in the original constructs "to make the synthesis as straightforward as possible," he said, although researchers are looking at different types of central metal ions to engineer oligomers and polymers with improved charge mobilities.
The scientists say they’ve already built chromophore circuits that could serve as functional elements in plastic electronics, RFID tags, drivers in active-matrix LCDs, organic LEDs, and lightweight solar cells. Results suggest that molecular conductive elements can be produced on a 10nm length scale, Therien said. -J.J.M.