The observation of electron motion along individual polydiacetylene chains in solution: The molecular wire

A unique experiment using pulsed photoconductivity techniques demonstrates that photocarriers may be created, move along a polymer chain in solution, and be detected as a current in an external circuit, provided that the polymer is in a chain extended conformation. For a random coil no signal is detected. Using the 3 and 4BCMU polydiacetylene urethane derivatives it is possible, it has been argued, to go from a random coil to rigid rod conformation, this phase change being signalled by a colour change. Because an external circuit detecting charge motion is only sensitive to the real space distance travelled by the photocharge in the field direction, it is to be expected that currents will only be detected in the chain extended conformation, as observed. Further, it is seen that modifying the theory of one dimensional Onsager geminate recombination to account for the case of finite chain lengths causes the probability of avoiding geminate recombination to be drastically reduced.