Synthesis and Atropisomerism of Cascaded Tetraphenylporphyrin–[60]Fullerene Hybrids

Abstract

Flexible, linked dendritic tetraphenylporphyrin (TPP)-fullerene hybrids were synthesized. They were designed to gain insight into and mimic the primary events in the natural photosynthetic reaction center. These multiporphyrin moieties are based on a light-harvesting concept. Moreover, they incorporate multiple redox components aligned along a redox gradient. Newkome-type dendrons were added to these TPP-fullerene hybrids. In principle they can mediate pH-dependent water solubility, which, however, could not be observed in this case. A protecting-group strategy using tert-butyldiphenylsilyl groups allows convergent synthesis of the dendritic compounds. The dendritic multiporphyrins were synthesized separately and can be used as individual building blocks. Atropisomerism was observed in the dendritic compounds, and single atropisomers could be assigned to the corresponding peaks of a characteristic pattern in the NMR spectra. Deprotection of the Newkome-type dendrons was shown to be feasible under mild conditions that leave the redox gradient intact.

Rigid, Branched Porphyrin Antennas: Control over Cascades of Unidirectional Energy Funneling and Charge Transfer

“…21−25 Next to apolar examples of electron donor−acceptor systems, also watersoluble 26−30 and dendritic systems are reported. 31,32 Key for the design of electron donor−acceptor systems featuring more than just a single porphyrin and fullereneis to create energy and redox gradients and to control the unidirectional flow of excited-state energies and charges. Linear-shaped representatives of a multicomponent system featuring several different porphyrins and a fullerene have been reported: ZnP−H 2 P−C 60 , Fc−ZnP−H 2 P−C 60 , etc.…”

“…A unidirectional energy transfer and a fast charge separation afforded, nevertheless, (ZnP) − charge-separated state. 32 In light of the structural flexibility, charge separation and charge recombination proceed exclusively through-space rather than through-bond. Through-space interactions are difficult to control.…”

“…Of particular relevance is the fact that a fast charge separation is typically combined with a slow charge recombination. In most porphyrin/fullerene electron donor–acceptor systems, kinetically long-lived and energetically high-lying charge-separated states are formed in high quantum yields. − It is typically the first singlet excited state of the porphyrin from which charge separation evolves, while only a few examples are known in which the second singlet excited states powers the charge separation. − Next to apolar examples of electron donor–acceptor systems, also water-soluble − and dendritic systems are reported. , …”

A Convenient Synthesis of Pentaporphyrins and Supramolecular Complexes with a Fulleropyrrolidine

“…In fact, architectures consisting of porphyrin derivatives (donors) and fullerenes (acceptors) are of particular interest, either as models for natural photosynthesis or for the conversion of light into electricity. Because of the unique three-dimensional structure of fullerenes, their low reduction potentials and small reorganization energy, providing the formation of long-lived charge separated states [47], porphyrin–fullerene photoactive systems have provided promising materials for photovoltaic applications [48,49,50,51,52,53,54]. In many cases, the photoactive system is a supramolecular complex formed by a multiporphyrin receptor and a fullerene guest [55,56,57,58,59,60,61,62,63].…”

Synthesis of Metal Complexes with an Open‐Cage Fullerene as the Ligand

“…[3] Amongt hem, fullerened erivatives with attachedp orphyrins have been wells tudied. [4] Interaction between the fullerene cage and the porphyrin metal centerc an be tuned by the length and nature of the linker covalently bonded to the fullerenec age. [5] Recently, an iridium pyrrolidinofullerenec omplex was prepared [3e] and was shown to act as an effective hydrogen-transfer catalyst.…”