Fluorene Molecular Wires

In Sect. 8.1.2 we have already introduced o/igo-fluorenes (oFLs) as molecular wires implemented into dumbbell architectures (i.e. Cso oFL -C6o)- h has been 

To probe the charge-transfer characteristics of these conjugates, we have carried out an extensive photophysical study and a number of quantum chemical calculation. Details on the synthesis and the electrochemical investigation are described elsewhere [15]. 

When compared to C ,o- 4 L and Cgo-oFL -C6o, drastic changes of the emission properties are observed upon inspecting the fullerene fluorescence 

a strong solvent dependence emerges. When varying the solvent polarity from, for example, toluene to benzonitrile, the C l0 emission quenching increases (Fig. 9.44). In summary, such observations imply charge-transfer interactions between the Ceo electron acceptor and exTTF electron donor. Obviously, the charge transfer pathway passes the transiently formed C,l0 singlet excited state. 

To prove these hypotheses, time-resolved measurements were employed. Transient absorption measurements on the femto- and nanosecond time-scale, i.e. 

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Thus, addressing DONOR-(oFL) -C,5o ensembles utilizing strong electron donor groups advanced as a promising task to probe the role of >//go(fluorene) molecular wires into donor-acceptor couples. The corresponding results will be presented further in this thesis. 

We have demonstrated that the donor-acceptor conjugates 18a,b exhibit efficient charge-transfer processes upon photoexcitation over distances of more than 24 A. The charge-transport mechanisms are comparable to those established for the corresponding exTTF-oPPV -C6o and exTI -oPP, systems. In view of the molecular-wire behavior of the oFLs, we have shown that in fluorene-based oligomers the ability to conduct charges lies between that of oPPVs and that of... 

In the context of oligo-fluorene (oFL) molecular wires, we will conclude with an outlook that focuses on donor-acceptor conjugates bearing Ceo electron-accepting units and zinc porphyrin (ZnP) or ferrocene (Fc) electron-donating moieties, respectively. Both, the donor and acceptor are covalently connected by oFL bridges of variable length. 

Carmen Atienza-Castellanos, Mateusz Wielopolski, Dirk M. Guldi, Cornelia van der Pol, Martin R. Bryce, Salvatore Filippone, Nazario Martin. Determination of the Attenuation Factor in Fluorene-Based Molecular Wires. Chem. Commun. 2007, 48, 5164. 

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