Abstract
Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. Here we describe a simple and robust FLFL-dipeptide construct to which a meso-tetraphenylporphyrin has been appended and which self-assembles to fibrils, platelets or nanospheres depending on the solvent composition. The fibrils, functioning as quenched antennas, give intense excitonic couplets in the electronic circular dichroism spectra which are mirror imaged if the unnatural FDFD-analogue is used. By slightly increasing the solvent polarity, these light-harvesting fibres disassemble to spherical structures with silent electronic circular dichroism spectra but which fluoresce. Upon further dilution with the nonpolar solvent, the intense Cotton effects are recovered, thus proving a reversible switching. A single crystal X-ray structure shows a head-to-head arrangement of porphyrins that explains both their excitonic coupling and quenched fluorescence.
Highlights
Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state
At the simplest level, chlorosomes in green photosynthetic bacteria constitute a very large antenna formed by self-assembled BChl c, d or e, without using polypeptides or proteins to organize the chromophores in precise orientations[2,3,4]
We present a simple porphyrin decorating a self-assembling chiral system that can reversibly change its morphology via slight changes in the solvent composition from a passive state with intense excitonic couplets in the electronic circular dichroism spectra (ECD) and quenched fluorescence, to an active state with intense fluorescence but with silent ECD spectra
Summary
Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. After self-assembly, very intense and multiple Cotton effects prove that the porphyrin chromophores are excitonically coupled[40].
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