Abstract
Plexcitonic antenna complexes, inspired by photosynthetic light-harvesting complexes, are formed by attachment of chlorophylls (Chl) to poly(cysteine methacrylate) (PCysMA) scaffolds grown by atom-transfer radical polymerisation from gold nanostructure arrays. In these pigment–polymer antenna complexes, localised surface plasmon resonances on gold nanostructures are strongly coupled to Chl excitons, yielding hybrid light–matter states (plexcitons) that are manifested in splitting of the plasmon band. Modelling of the extinction spectra of these systems using a simple coupled oscillator model indicates that their coupling energies are up to twice as large as those measured for LHCs from plants and bacteria. Coupling energies are correlated with the exciton density in the grafted polymer layer, consistent with the collective nature of strong plasmon–exciton coupling. Steric hindrance in fully-dense PCysMA brushes limits binding of bulky chlorophylls, but the chlorophyll concentration can be increased to ∼2 M, exceeding that in biological light-harvesting complexes, by controlling the grafting density and polymerisation time. Moreover, synthetic plexcitonic antenna complexes display pH- and temperature-responsiveness, facilitating active control of plasmon–exciton coupling. Because of the wide range of compatible polymer chemistries and the mild reaction conditions, plexcitonic antenna complexes may offer a versatile route to programmable molecular photonic materials.
Highlights
The absorption of light by molecules leads to the formation of excitons
We showed that antenna complexes from bacteria[64] and plants[65] are strongly coupled to Localised surface plasmon resonances (LSPRs) on arrays of gold nanostructures, and showed that the coupling energy could be manipulated via control of the protein structure and pigment complement
We describe the synthesis of pigment–polymer antenna complexes, in which surface-gra ed poly(amino acid methacrylate) scaffolds replace the polypeptides in light-harvesting antenna complexes (LHCs) (Fig. 1b)
Summary
The absorption of light by molecules leads to the formation of excitons (electron–hole pairs). By gra ing these pigment–polymer complexes to gold nanostructures, we form plexcitonic complexes via strong coupling of localised surface plasmon resonances to the ensemble of excitons arrayed on the polymer scaffolds (Fig. 1c).
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