Cyclic Tetramers of Zinc Chlorophylls as a Coupled Light‐Harvesting Antenna–Charge‐Separation System

Abstract

A coupled light-harvesting antenna-charge-separation system, consisting of self-assembled zinc chlorophyll derivatives that incorporate an electron-accepting unit, is reported. The cyclic tetramers that incorporated an electron acceptor were constructed by the co-assembly of a pyridine-appended zinc chlorophyll derivative, ZnPy, and a zinc chlorophyll derivative further decorated with a fullerene unit, ZnPyC60 . Comprehensive steady-state and time-resolved spectroscopic studies were conducted for the individual tetramers of ZnPy and ZnPyC60 as well as their co-tetramers. Intra-assembly singlet energy transfer was confirmed by singlet-singlet annihilation in the ZnPy tetramer. Electron transfer from the singlet chlorin unit to the fullerene unit was clearly demonstrated by the transient absorption of the fullerene radical anion in the ZnPyC60 tetramer. Finally, with the co-tetramer, a coupled light-harvesting and charge-separation system with practically 100 % quantum efficiency was demonstrated.

A Light‐Harvesting/Charge‐Separation Model with Energy Gradient Made of Assemblies of meta‐Pyridyl Zinc Porphyrins

“…We have previously reportedalight-harvesting antenna/charge-separation system, which resulted from statistical assembly of af luorescentc hlorophyll derivative and an onfluorescent chlorophyll-fullerenec onjugate. [26] As the fullereneu nit oxidatively quenches the fluorescence, the presents ystem is complementary,i nt he sense that the porphyrin fluorescence is reductively quenched.…”

“…[24] Formation of supramolecular squares by means of a para-pyridyl unit was also appliedt oc hlorophyll derivatives to prepare square-shaped chlorophyll assemblies. [25][26][27][28] Much less is known about the assembly behavior of zinc meso-(meta-pyridyl)porphyrins. Aida et al investigated assemblies of porphyrins with a meta-pyridyl substituent at one of the meso positions.…”

Supramolecular strategies in artificial photosynthesis

“…Supramolecular assemblies have been thoroughly studied for the purpose of PET and CS, 45 such as self-assembled dimers of porphyrins and fullerenes as well as trimers and porphyrin squares. 46 Another strategy is to use a rigid pyridine functionalized template to organize porphyrins in close proximity, resulting in rapid energy transfer among the chromophores. 47 In addition to axial binding, functionalization of porphyrin macrocycles with specific binding motifs can result in supramolecular organization of chromophore arrays using metal–ligand, hydrogen bonding, ion-dipole and π–π stacking interactions.…”

Synthetically Important Ring-Opening Acylations of Alkoxybenzenes

“…The product 5-oxopentanoic acid was converted into fullerene alcohol in five steps (Scheme 32). 45 The fullerene system was installed by the decomposition of in situ generated tosyl-hydrazone ester in the presence of C 60 . The initially obtained [5,6] isomers in the mixture were completely converted into the [6,6] isomer by refluxing in o-dichlorobenzene.…”