Photoinduced charge transport over branched conjugation pathways: donor-acceptor substituted 1,1-diphenylethene and 2,3-diphenylbutadiene

Photoinduced charge transport in 1,1-diphenylethene and 2,3-diphenylbutadiene functionalized with an electron donating dimethylamino group and an electron accepting cyano group is reported. UV-spectroscopy reveals that in these compounds, which incorporate a cross-conjugated spacer, a direct charge transfer transition is possible. It is shown by application of the generalized Mulliken-Hush approach that introduction of an additional branching point in the pi-electron spacer (i.e., when going from the 1,1-diphenylethene to the 2,3-diphenylbutadiene) leads to only a moderate reduction (68-92%) of the electronic coupling between the ground and the charge separated state. The sigma-electron system is however likely to be dominant in the photoinduced charge separation process.