Charge transport in solid polymer matrixes with redox centers

Abstract

Charge transport in solid polymer matrixes with redox centers in their ground and photoexcited states was reviewed. Charge transport in the ground state can be investigated mainly by electrochemical methods, which provides information about integrated charge propagation in the polymer matrix. Charge transport in a photoexcited state can be investigated by photochemical methods providing information on one single charge transfer step at an excited state. In the ground state, charges are transported by molecular diffusion, charge hopping between molecules, or a combination of the former and the latter. Methods to study the mechanism were described, and typical examples for each mechanism are given. An important factor to determine the mechanism was concluded to be the interaction between the redox molecule and the polymer matrix. Typical examples of charge transport distance are presented. This is near 1.3 nm without mediator (molecule's center-to-center), and 40–100% longer in the presence of a mediator molecule. Electrocatalysis by a polymer–redox molecule coated electrode and examples of its analysis are also mentioned. Charge transport in the photoexcited state can be investigated by photochemical methods such as laser flash photolysis and luminescence quenching. The mechanism here is both dynamic and static; the former taking place by diffusion and collision of the molecules and the latter taking place without diffusion. Various models are presented to analyze the mechanism and the charge transfer distance by luminescence quenching. In solid polymer matrixes, charge transport in the excited state takes place mainly by a static mechanism, and the charge transport distance is similar to that in the ground state; around 1.3 nm without mediator and nearly twice with a mediator molecule. Combined systems of charge transport in the ground and excited states are also briefly reviewed, and some approaches to more photoelectric devices are introduced.