Solvent and distance dependent charge separation in rigid trichromophoric systems

Transient absorption and time-resolved microwave studies have been carried out on a series of D(onor)2−[bridge]−D(onor)1−[bridge]−A(cceptor) compounds, in which a dimethoxynaphthalene (DMN) primary donor (D1) and a dicyanovinyl (DCV) acceptor are separated by a rigid norbornylogous bridge eight σ-bonds in length and an N,N-dimethylaniline secondary donor (D2) is separated from D1 by a norbornylogous bridge of variable length (four, six, or eight σ-bonds). The identity of the charge-separated state populated upon photoexcitation, i.e., from D1 to A or from D2 to A, depends on the solvent polarity and the length of the bridge separating both donor chromophores. It was found that the final charge-separated state is formed on a (sub)nanosecond time scale, whereas charge recombination shows strong solvent dependence, due to “inverted region” behavior.