Photoinduced electron transfer within linear and stacked aromatic systems

Photoinduced electron transport is studied in a series of organic donor-acceptor compounds arranged in an end-to-end (linear) fashion or vertically stacked. The first system studied is a covalently linked donor-bridge-acceptor system in which one excitation pulse creates an ion-pair that lives for 700 ns. A second pump pulse excites the bridging chromophore during maximum ion-pair population creating a secondary recombination pathway that is 7000 fold faster.; A second linear donor-bridge-acceptor system studies triplet state excitation. One photon sensitizes a triplet state on the bridge via the donor. A second photon excites the bridge triplet state which triplet energy transfers to the donor rather than electron transfer to the acceptor.; The third linear system studies electron transfer from the S₂ state of a zinc porphyrin to pyromellitimide through a meso- or β-carbon of porphyrin. Imide attachment to the porphyrin core increases the S ₂ → S₁ internal conversion rate, which greatly reduces S₂ electron transfer efficiency. The internal conversion rate recovers by inserting a phenyl bridge between donor and acceptor. A bridged system shows efficient S₂ electron transfer in 2-methyltetrahydrofuran.; Aggregation of a zinc-porphyrin-tetrakis(perylene-3,4:9,10-diimide) occurs via van der Waals attraction by the perylenediimides. These nanostructures persist in the gas, liquid, and solid phases. Transient absorption experiments determine that an electron migrates through the face-to-face stacked perylene-diimides.; The stacked base pairs of DNA modulate electron or hole transfer in DNA hairpins capped by organic chromophores. Six results are reported. In the first project, equilibrium constants are determined for hole transport between G (guanine) and GG and between G and GGG sequences. In the second project, the dynamics of forward and return hole transport from G to 7-deazaguanine establish that 7-deazaguanine is a much deeper hole trap than GG or GGG. The third project analyzes intrastrand hole transport. The fourth project investigates electron injection from stilbenediether onto the DNA strand. The fifth project provides the first characterization of the radical anion and radical cation products of photoinduced electron transfer in triplex DNA. The sixth and final project describes how contact radical ion-pair formation and recombination depend on the identity of the adjacent nucleobase in DNA.