Excitation‐Energy Migration in Self‐Assembled Cyclic Zinc(II)–Porphyrin Arrays: A Close Mimicry of a Natural Light‐Harvesting System

Abstract

The excitation-energy-hopping (EEH) times within two-dimensional cyclic zinc(II)-porphyrin arrays 5 and 6, which were prepared by intermolecular coordination and ring-closing metathesis reaction of olefins, were deduced by modeling the EEH process based on the anisotropy depolarization as well as the exciton-exciton annihilation dynamics. Assuming the number of energy-hopping sites N = 5 and 6, the two different experimental observables, that is, anisotropy depolarization and exciton-excition annihilation times, consistently give the EEH times of 8.0 +/- 0.5 and 5.3 +/- 0.6 ps through the 1,3-phenylene linkages of 5 and 6, respectively. Accordingly, the self-assembled cyclic porphyrin arrays have proven to be well-defined two-dimensional models for natural light-harvesting complexes.

Construction of Giant Porphyrin Macrorings Self‐Assembled from Thiophenylene‐Linked Bisporphyrins for Light‐Harvesting Antennae

“…already been observed [47,51,60] and measurements of the EEH rates for a series of systematic ring variations of this study may extend this tendency. Further studies are ongoing.…”

“…This observation was supported by a gradual increase of the coupling interactions of porphyrin transition dipoles. [47,51] Experimental Section General: Analytical GPC was performed on a Hewlett-Packard HP1100 series instrument using a JAIGEL 3H-A column (Japan Analytical Industry, polystyrene gel, diameter = 8 mm, length = 50 cm, exclusion limit = 70 000 Da, eluent: CHCl 3 /0.05 % Et 3 N) or a Shimadzu LC workstation M10 equipped with an SPD-M10 AVP photodiode array detector using a Tosoh TSK-GEL G3000H HR column (polystyrene gel, exclusion limit = 60 000 Da). Recycling GPC was carried out on a recycling GPC-HPLC system (Japan Analytical Industry, LC-908) connected with two series columns (JAIGEL 3HA, diameter = 20 mm, length = 60 cm 2, polystyrene, exclusion limit = 70 000 Da, eluent: CHCl 3 /0.05 % Et 3 N), or two series columns of Tosoh TSK-GEL G3000H HR (polystyrene gel, exclusion limit = 60 000 Da, eluent: pyridine).…”

“…Even in strongly coordinating solvents, such as pyridine, covalently linked macrorings retain their cyclic structures. [46,47,51,53] The peak maxima of the split Soret bands at longer wavelengths were gradually redshifted in the order 7-< 8-< 9-< 10-mer (insets of Figure 6). …”

“…A similar tendency was observed for pentagonal and hexagonal macrocyclic porphyrins. [47,51,60] In the present case, a more generalized treatment may be required by including interactions among not only the neighboring porphyrins, but also with other component porphyrins in the macrorings.…”

“…[45,46] Interestingly, the hexagonal macrorings showed faster excitation energy hopping (EEH) rates than the pentagonal structures. [47] The result suggested the importance of the orientation factor of linker-separated chromophore components in determining the EEH rates and encouraged us to prepare larger macrorings.…”