The role of the bridge in photoinduced electron transfer in donor-bridge-acceptor systems

The work in this thesis presents results and analysis of the influence of the bridge in covalently linked organic donor-bridge-acceptor (D-B-A) systems. These systems were designed and synthesized for the purpose of studying photoinduced electron transfer from the donor to the acceptor through transient absorption spectroscopy and time resolved electron paramagnetic resonance (TREPR). Each series uses the same donor and acceptor moieties, allowing for a comparison of the bridges. While D-B-A systems are not new, there is little research that uses the same donor and acceptor with varying bridges. The donor used in these systems is 3,5-dimethyl-4-(9-anthracenyl)-julolidine (DMJ-An) and the acceptor is naphthalene-1,8:4,5-bis(dicarboximide) (NI).;The first series of D-B-A molecules explores a fluorenone bridge where the energetic properties are favorable such that direct participation of the bridge in electron transfer was observed. The fluorenone radical anion has a spectroscopic signature that conclusively shows the electron residing on the bridge in the femtosecond transient absorption experiment.;The second and third series of D-B-A molecules look at how the structural dynamics of the bridge affect the rates of electron transfer. One series uses a p-phenylethynylene bridge while the other directly compares two related bridges, p-phenylene and [n]phenacene, specifically designed to determine how conformational flexibility affects electron transfer.;The last series explores varying types of conjugated bridges, specifically cross-conjugated, linearly conjugated, and saturated bridges. The following bridges were utilized in the study: (1) 1,1-diphenylethene, (2) trans -stilbene, (3) diphenylmethane, and (4) xanthone. These bridges compare and contrast the consequences of linear and cross-conjugation in D-B-A systems. In addition, calculations of the electron transport properties of the bridges bound to metallic electrodes are shown to correlate well with the results obtained from synthetic systems. This shows that a qualitative understanding of electron transfer rates can be gained through electron transport calculations.