Dyads, porphyrin-based

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. 

Intramolecular Photoinduced Electron Transfer in Porphyrin-Based Systems Dyads... 

The first covalently linked porphyrin-based systems for mimicry of photosynthetic electron transfer were reported in the late 1970s. These were porphyrin-quinone dyad molecules 6 and 7 [45-47]. Subsequent to these reports, a very large number of porphyrin-quinone dyads have been studied, and still work in this field continues. Connolly and Bolton reviewed the work in the 1970s and 1980s [48]. Since that... 

More useful mechanistic information is obtained from intramolecular electron-transfer reactions if the kinetics for the electron-transfer step can be isolated from the effects of diffusion. The main stimulus for making such studies is the urge to design systems that mimic some of the essential features of the photosynthetic reaction centre complex and much attention has focussed on the study of porphyrin-based photoactive dyads. Thus, a series of N-alkylporphyrins linked to a quinolinium cation has been synthesized and found to display a rich variety of photoreactions. The singlet excited state of the quinolinium cation operates in both intramolecular energy- and electron-transfer reactions while the excited singlet state of the porphyrin transfers an electron to the appended quinolinium cation. Several new porphyrin-quinone dyads have been studied,including cyclophane-derived systems where the reactants are held in a face-to-face orienta-... 

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. ... 

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... 

The efficient on/off switching of fluorescence from substituted zinc porphyrin-ferrocene dyads 16a and 16b is achieved through redox control of the excited-state electron transfer quenching.26 This redox fluorescence switch is based on the switching of the excited-state electron transfer from the ferrocene to the zinc porphyrin through the use of the ferrocene/ferrocenium (Fc/Fc +) redox couple. 

One of the first reported Ceo-based donor-acceptor systems is also the H2P-C60 and the analog ZnP-Cso dyad (20), in which H2P denotes the metal-free base tetraphenyl porphyrin and ZnP is the corresponding zinc tetraphenylporphyrin... 

Work from a different laboratory focuses on the synthesis and photophysical properties of Ceo-based porphyrin dyads with a variety of linkers [367-371], These include new types of flexible polyether linkers (30) [367, 368], rigid steroid linkers [370] as well as novel doubly linked porphyrins [369, 371], which provide the means for a parachute-shaped dyad (e.g., ZnP-Ceo (29) and H2P-C60 (28)). In both para-... 

The photophysical properties of a Ceo-linked phytochlorin (31) [344, 373], a porphyrin analog, are quite different from those of conventional Cgo-linked porphyrins. The phytochlorin-Cfio exciplex is formed in both toluene and benzonitrile via either the singlet excited states of the phytochlorin or the Ceo- The exciplex relaxes directly to the ground state in toluene, whereas it undergoes a conversion to the charge-separated state, followed by the decay to the ground state in benzonitrile. A similar proposal for the exciplex formation has been forwarded by the report on a free-base porphyrin Ceo dyad [374, 375]. 

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