Rigid dendritic donor-acceptor ensembles: control over energy and electron transduction.
Several generations of phenylenevinylene dendrons, covalently attached to a C(60) core, have been developed as synthetic model systems with hierarchical, fine-tuned architectures. End-capping of these dendritic spacers with dibutylaniline or dodecyloxynaphthalene, as antennas/electron donors, yielded new donor-bridge-acceptor ensembles in which one, two, or four donors are allocated at the peripheral positions of the well-defined dendrons, while the electron accepting fullerene is placed at the focal point of the dendron. On the basis of our cyclic voltammetry experiments, which disclose a single anodic oxidation and several cathodic reduction processes, we rule out significant, long-range couplings between the fullerene core and the end-standing donors in their ground-state configuration. Photophysical investigations, on the other hand, show that upon photoexcitation an efficient and rapid transfer of singlet excited-state energy (6 x 10(10) to 2.5 x 10(12) s(-1)) controls the reactivity of the initially excited antenna portion. Spectroscopic and kinetic evidence suggests that yet a second contribution, that is, an intramolecular electron-transfer, exists, affording C(60)(.-) -dendron(.+) with quantum yields (Phi) as high as 0.76 and lifetimes (tau) that are on the order of hundreds of nanoseconds (220-725 ns). Variation of the energy gap modulates the interplay of these two pathways (i.e., competition or sequence between energy and electron transfer).
Radiation Laboratory, University of Notre Dame, IL 46556, USA.
Dirk M
DM
Guldi
Angela
A
Swartz
Chuping
C
Luo
Rafael
R
Gómez
José L
JL
Segura
Nazario
N
Martín