Competition between Ultrafast
Energy Flow and Electron
Transfer in a Ru(II)-Loaded Polyfluorene Light-Harvesting Polymer
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Abstract
This Letter describes the synthesis and photophysical
characterization
of a Ru(II) assembly consisting of metal polypyridyl complexes linked
together by a polyfluorene scaffold. Unlike many scaffolds incorporating
saturated linkages, the conjugated polymer in this system acts as
a functional light-harvesting component. Conformational disorder breaks
the conjugation in the polymer backbone, resulting in a chain composed
of many chromophore units, whose relative energies depend on the segment
lengths. Photoexcitation of the polyfluorene by a femtosecond laser
pulse results in the excitation of polyfluorene, which then undergoes
direct energy transfer to the pendant Ru(II) complexes, producing
Ru(II)* excited states within 500 fs after photoexcitation. Femtosecond
transient absorption data show the presence of electron transfer from
PF* to Ru(II) to form charge-separated (CS) products within 1–2
ps. The decay of the oxidized and reduced products, PF<sup>+•</sup> and Ru(I), through back electron transfer are followed using picosecond
transient absorption methods