Fullerene-porphyrin-based dyad

Fullerenes such as C60 are excellent electron acceptors. In a fullerene-porphyrin-based dyad, the photoexcited state of the Qo accepts an electron from the linked zinc porphyrin group to give a charge-separated state. 

A dyad is a supramolecular structure consisting of a donor and an acceptor component. In a fullerene-porphyrin-based dyad, Ceo is the acceptor component and porphyrin is the donor component. On photoirradiation of this dyad, PET process takes place in the normal region and back-electron transfer (BET) from Cgo" to Zn Por+ in the inverted region (Fig. 6.21) [23]. 

Gayathri SS, Patnaik A (2006) Electrical rectification from a fullerene[60]-dyad based metal-organic-metal junction. Chem Commun (Cambridge, UK) 1977-1979 Matino F, Arima V, Piacenza M et al (2009) Rectification in supramolecular zinc porphyrin/ fulleropyrrolidine dyads self-organized on gold(lll). Chemphyschem 10 2633-2641 Acharya S, Song H, Lee J et al (2009) An amphiphilic Cgo penta-addition derivative as a new U-type molecular rectifier. Org Electron 10 85-94... 

Figure 4. Transient states and interconversion pathways for porphyrin-futlerene dyads. The solid bars represent energies for free-base porphyrin-fullerene dyad 26, and the dashed bars represent energies for the zinc-porphyrin-fullerene dyad. Solid bars represent singlet or charge-separated states, and hollow bars stand for triplet states. The energies of the charge-separated states refer to polar solvents.

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. ... 

Another tripod-type, porphyrin-based receptor is 10. This system, characterized by flexible linkers, was readily synthesized through a one-step click reaction of an azide-functionalized porphyrin with a tertiary amine functionalized with three alkynyl groups. The resulting tripod system can capture a pyridine-functionalized fullerene with 1 1 stoichiometry. The corresponding association constant, K, was found to be 9.4 x 1(1 in o-dichlorobenzene as determined from UV-vis spectroscopic titrations. The supramolecular dyad formed via this capture event was then found capable of undergoing photoinduced ET from the zinc porphyrin to the fullerene with a charge-separated lifetime of 0.5 ns. ... 

Dyads of free base and Zn-complexed porphyrins and Cgo (8) were prepared by Gust and coworkers [109], When the porphyrin moiety in the dyads is photoexcited, there is intramolecular energy transfer from the excited porphyrin to the fullerene moiety, generating the excited singlet state of C. For the dyad consisting of Zn-complexed porphyrin, the Cjq excited singlet accepts an electron from the porphyrin, resulting in the formation of C q radical anion and porphyrin radical cation [109]. 

An interesting triad has been reported by Ito and D Souza, who have combined a covalent free base porphyrin-fullerene dyad bearing a pyridine substituent. 

As it was reported earlier in the subject literature, the NLO values of [60]fullerene-dyads calculated with the aid of the PM3 method show satisfactory agreement with the DFT results and experimental third harmonic generation values [1]. Here, we also use the PM6 method [15], The studied systems are presented in Fig.5.3. The top structure is [60]fullerene-dyad composed of fullerene and free base porphyrin linked by conjugated linear carbon spacer. In the middle structure, the free base por-... 

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