Conjugated polymers evoke the idea of “molecular wires” having strong connection of electrons in one part of a conjugated chain to those in others: electrons, holes and excited states should move freely along the chains. Really good molecular wires might revolutionize solar energy and molecular electronics, but do they exist? Experiments in our laboratory investigate transport of electrons, holes and singlet or triplet excitons along chains to trap groups at the ends. The technique of pulse radiolysis enables rapid injection of charges into the chains with measurements by transient absorption (TA) and complementary measurements by transient microwave conductivity to examine movement of charges. The experiments seek to learn which of two competing pictures is more correct: 1) that conjugated chains are continuous “wires” or 2) that they contain defects that stop transport. Polymeric “wires” might give fast transport only in segments separated by some kind of defect, or charges or excitons might be trapped by defects. Pulse radiolysis experiments give us new insight into these questions. Pulse radiolysis also let us probe electron transfer with piecewise continuous adjustment of the free energy change. In conjugated chains we measure infrared absorption bands with extinction coefficients to 50,000 for electrons and holes.

Charge and exciton transport: Can conjugated chains be “molecular wires”

250th National Meeting (2015)

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