A switchable self-assembling and disassembling chiral system based on a porphyrin-substituted phenylalanine-phenylalanine motif

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.Funding Agencies|European Commission [229927]; University of Crete; PHOTOPEPMAT, ARISTEIA II Action, action Education and Lifelong Learning [3941]; European Union (the European Social Fund); AngioMatTrain, Marie Curie Industry Initial Training Network (ITN), call FP7-PEOPLE ITN [317304]; SERC (Swedish e-Science Research Center); DFG-Center for Functional Nanostructures (CFN); Helmholtz STN programme; FP7 Future and Emerging Technologies for Energy Efficiency project PEPDIODE [256672]; CNRS; Aix-Marseille University through the A*MIDEX project EtNA; Region Provence-Alpes Cote dAzur through project NanoMosaique; Region Provence-Alpes Cote dAzur through project CaliGraph