Intramolecular charge transfer alternating donor-acceptor

For example, the excessive addition of sensitizer can result in crystallization of the sensitizer. Some sensitizers, even when present in low concentrations can result in over-sensitization of the composition, in that the photocurrent generated upon exposure will persist comparatively long after the illumination ceases. As an alternative to the sensitization by additives, intramolecular charge transfer complexes have been proposed, where the electron donor and electron acceptor functions are located along a common vinyl backbone. Examples are nitrated vinyl polymers of poly-(acenaphthylene), poly(9-vinylcarbazole) and poly(l-vinylnaphthalene), copolymers from 3,6-diphenyl-vinylcarbazoleand 3,6-dinitro-9-vinylcarb-azole. ° and copolymers from NVK and iV-vinylphthahntide. ... 

Zhang, Q.X., Tour, J.M., 1998. Alternating donor/acceptor repeat units in polythiophenes, intramolecular charge transfer for reducing band gaps in fully substituted conjugated polymers. J. Am. Chem. Soc. 120, 5355-5362. 

The diamines are isoelectronic with hydroquinone (an eiectron donor) while the diimines are isoelectronic with p-benzoquinone (an electron acceptor). It was recently proposed that this built-in redox couple, which is pH-sensitive, is the source of charge carriers in the form of semiquinone radical cations which are generated upon protonation of the quinonediimine, whose accepting power is expected to increase on protonation. A subsequent perusal of the literature indicates that a similar idea was proposed many years ago. A key issue yet to be resolved is whether electron transfer from diamine to diimine is an inter- or intramolecular process. An alternative mechanism of carrier generation which involves spin unpairing of diimines (creating a pair of radical cations) has recently been proposed." Carrier transport is believed to occur via intermolecular redox reactions between radical cations and diamine and/or diimine units. 

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