3 research outputs found
Mechanism and Dynamics of Electron Injection and Charge Recombination in DNA. Dependence on Neighboring Pyrimidines
The
mechanism and dynamics of photoinduced electron injection and charge
recombination have been investigated for several series of DNA hairpins.
The hairpins possess a stilbenediether linker, which serves as an
electron donor and base pair stems that possess different pyrimidine
bases adjacent to the linker. Hairpins with adjacent thymine-adenine
(T-A) base pairs undergo fast electron injection and relatively slow
charge recombination with rate constants that are not strongly dependent
upon the following base pair. Hairpins with adjacent cytosine-guanine
(C-G) base pairs undergo reversible electron injection and much faster
charge recombination than those with adjacent T-A base pairs. Hairpins
with 5-fluorouracil or other halogenated pyrimidines in their first
and second base pair undergo fast electron injection and multiexponential
charge recombination. The difference in kinetic behavior for the different
series of hairpins and its implications for the formation of long-lived
charge-separated states are discussed and compared to results reported
previously for other electron-donor chromophores
Different Mechanisms for Hole and Electron Transfer along Identical Molecular Bridges: The Importance of the Initial State Delocalization
We
report measurements of hole and electron transfer along identical
oligo-<i>p</i>-phenylene molecular bridges of increasing
length. Although the injection barriers for hole and electron transfer
are similar, we observed striking differences in the distance dependence
and absolute magnitude of the rates of these two processes. Electron
transfer is characterized by an almost distance-independent, fast
charge-transfer rate. Hole transfer presents a much slower rate that
decreases significantly with the length of the bridge. Time-dependent
density functional calculations show that the observed differences
can be explained by the delocalization of the respective initial excitation.
The evaluation of the initial state is therefore essential when comparing
charge-transfer rates between different donor–bridge–acceptor
systems
Synthesis and Photophysical Properties of Conjugated and Nonconjugated Phthalocyanine–Perylenediimide Systems
The synthesis and
characterization of different conjugated phthalocyanine–perylenemonoimidebenzimidazole
[ZnPc-PBIm(OR)<sub>4</sub>] and nonconjugated phthalocyanine–perylenediimide
[ZnPc-PDI(OR)<sub>4</sub>] dyads are carried out. UV–vis, <sup>1</sup>H NMR, and electrochemistry measurements reveal the interaction
between perylene and phthalocyanine moieties in the ground state in
the conjugated hybrid and the lack of interaction in the nonconjugated
one. Ultrafast transient absorption measurements show that a state
with substantial charge-transfer character is formed in both compounds,
but the rates for the formation and recombination from this state
are much faster for the conjugated compound