Fullerene Electron-donor Systems

Williams R M, Zwier J M and Verhoeven J W 1995 Photoinduced intramolecular electron transfer in a bridged Cgg (acceptor)-aniline (donor) system. Photophysical properties of the first active fullerene diad J. Am. Chem. See. 117 4093-9... 

The bis-dienes 13-15 form ladder-type bis-fullerene adducts. Cycloadditions proceed in good yields also with electron-deficient dienes such as 21-23. Porphyrin donor systems such as 25 or 30 or quinoidal acceptor systems such as 19 and 20 were introduced to study the properties of the charge transfer in Cjq donor-acceptor systems. 

Once the synthetic methodologies were developed, the research efforts were focused on the preparation of photoactive systems where fullerenes had already shown potential applicability, such as organic photovoltaic materials. In these molecular-scale engineered systems, a fullerene electron acceptor contained in one submolecular fragment is coupled with an electron donor contained in the opposite component. Zinc porphyrins were thus coupled to in many different architectures such as, for instance, in that shown in Scheme 9.11, where the ZnP was appended to... 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

Similarly, the pyridyl fullerenes 30 and 31 also axially bind to ZnNcCBu)4 (28) to form supramolecular triads in which the zinc(II) naphthalocyanine acts as an electron donor, the pyridyl fullerenes act as primary electron acceptors, and either the ferrocene (Fc) or iV,iV-dimethylaminophenyl (DMA) moiety serves as a second electron donor [43], Fig. 2 shows the optimized structures of the resulting triads calculated by density functional theory (DFT), showing that the three components are arranged in a linear fashion. The binding constants of these systems (7.4 x 104M 1 for [ZnNc( Bu)4] 30 and 10.2 x 104M 1 for [ZnNc( Bu)4] 31 in o-dichlorobenzene) determined by UV-Vis spectroscopy are comparable with... 

The significant effect of metal ions to stabilize the CS state described above can also make it possible to use fullerene as an electron donor rather than an electron acceptor (see below). Fullerene normally was used only as an electron acceptor in electron donor-acceptor linked systems, because the ET... 

There continues to be an enormous amount of activity in the area of PET, much of it directed towards the development of systems capable of delivering artificial photosynthesis. Many of these systems involve porphyrin units as electron-donors and thus it is appropriate to consider them in this section of the review. A number of new fullerene-porphyrin dyads have been reported. A pyrazolinofullerene (155) has been constructed which facilitates efficient PET when strong donors such as iV,Ar-diethylaniline or ferrocene are linked to the pyrazoline ring. A photosynthetic multi-step ET model (156) based on a triad consisting of a meso,meso- inked porphyrin dimer connected to ferrocene and Ceo as electron-donor and electron-acceptor, respectively, has been synthesized and its ET dynamics (Scheme 38) have been investigated using time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. ... 

Langa et al. [38] described the first synthesis of D-A dyads (30a-c) based on C o and used ruthenocene as the electron-donor fragment (Scheme 21.12). Synthesis of these pyrrolidine)60]fullerene systems was achieved by 1,3-dipolar cycloaddition of ruthenocenecarboxaldehyde (28), N-methylglycine, and C o in toluene under the action of microwave irradiation in a focused microwave oven. The adducts 30a-c were obtained in moderate yields (26-31%). 

Zeng and coworkers [39] described the synthesis, under microwave irradiation, of several donor-acceptor systems based on amino-pyrrolidino[60]fullerene in which the Cgo (electron acceptor) and amino group (electron donor) were covalently bonded with a short linker (Scheme 21.13). 

Photophysical studies on a nanosecond time scale provided clear evidence of in-termolecular PET from TTF, an excellent electron donor, to the pyrazolino)60]-fullerene systems (58a,b). 

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