A Complex Comprising a Cyanine Dye Rotaxane and a Porphyrin Nanoring as a Model Light-Harvesting System.

Jiratheep Pruchyathamkorn,Andrew T Frawley,Harry L Anderson,William J Kendrick,Susana F Huelga,Andrea Mattioni,Felipe Caycedo-Soler,Martin B Plenio

doi:10.1002/anie.202006644

Jiratheep Pruchyathamkorn, Andrew T Frawley + Show 6 more

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https://doi.org/10.1002/anie.202006644

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Abstract

A nanoring‐rotaxane supramolecular assembly with a Cy7 cyanine dye (hexamethylindotricarbocyanine) threaded along the axis of the nanoring was synthesized as a model for the energy transfer between the light‐harvesting complex LH1 and the reaction center in purple bacteria photosynthesis. The complex displays efficient energy transfer from the central cyanine dye to the surrounding zinc porphyrin nanoring. We present a theoretical model that reproduces the absorption spectrum of the nanoring and quantifies the excitonic coupling between the nanoring and the central dye, thereby explaining the efficient energy transfer and demonstrating similarity with structurally related natural light‐harvesting systems.

Highlights

Living organisms achieve photosynthesis using a wide diversity of supramolecular chlorophyll arrays to absorb sunlight and channel energy to a reaction center (RC), where it is converted into chemical potential.[1]
Systems have been synthesized as models of the light-harvesting complex 1 (LH1)/RC supercomplex to investigate energy transfer between a ring of chromophores and a central acceptor/donor chromophore.[3,6]
In order to model the LH1/RC supercomplex, a chromophore must be positioned at the center of the porphyrin nanoring to mimic the RC. a-CD is an ideal scaffold for achieving this spatial arrangement: its six primary OH groups can be functionalized with 4-pyridyl substituents to form a template (T6*) for a six-porphyrin nanoring (c-P6), while its hydrophobic cavity can be used to encapsulate guest molecules, such as the hexamethylindotricarbocyanine dye (HITC, Cy7), via rotaxane formation.[11]

Summary

Introduction

Living organisms achieve photosynthesis using a wide diversity of supramolecular chlorophyll arrays to absorb sunlight and channel energy to a reaction center (RC), where it is converted into chemical potential.[1]. A-CD is an ideal scaffold for achieving this spatial arrangement: its six primary OH groups can be functionalized with 4-pyridyl substituents to form a template (T6*) for a six-porphyrin nanoring (c-P6), while its hydrophobic cavity can be used to encapsulate guest molecules, such as the hexamethylindotricarbocyanine dye (HITC, Cy7), via rotaxane formation.[11] This concept led us to target the structure Cy7&c-P6·T6* (Figure 1 and Scheme 1): the cP6 and Cy7 units mimic the LH1 and RC respectively, and the a-CD fixes the spatial arrangement of the chromophores.

Results

Conclusion