High Carrier Mobility in a Series of New Semiconducting PPV-Type Polymers

The synthesis and characterization of a series of semiconducting polymers of the polyphenylenevinylene (PPV) type is presented. These new polymers have every second phenylene ring substituted by two alkyl groups of equal length which are hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl. The polymers were synthesized from the corresponding dialkyldialdehydes by a Horner−Wadsworth−Emmons condensation reaction with 1,4-bis(diethylphosphonomethyl)benzene in a high boiling solvent mixture. The purified polymers were found to have charge carrier mobilities in the range 0.01−0.1 cm2 V-1 s-1 and carrier lifetimes of the order of 0.1−5 ms measured by the PR−TRMC technique. A possible explanation for the unexpectedly large magnitudes of both the charge carrier mobility and lifetimes was arrived at by powder X-ray diffraction studies which provided a putative structural model. Finally the electronic structure was studied by ultraviolet photoelectron spectroscopy and the photodegradative properties of thin films of the polymers characterized by illumination through a suitable photopositive mask allowing for subsequent doping giving highly anisotropic conducting patterns.