Bioinspiration from Photosynthetic Light-Harvesting Protein Complexes

Proteins execute their programmed functions in a finely regulated way with extraordinary efficiency, despite ample environmental disorder and densely crowded, heterogeneous environments. These capabilities serve as a useful source of inspiration for polymer design. The way in which photosynthetic light-harvesting proteins establish robustness to conformational disorder is particularly meaningful for conjugated polymers where such disorder gives rise to spatial localization of excitons and the formation of electronic traps, whereby exciton lifetimes and charge diffusion lengths are significantly reduced. In photosynthetic light-harvesting proteins, these limitations are largely overcome by the binding of chromophores in dense arrangements, allowing the formation of molecular excitons that are coherently shared across a number of neighboring chromophores. Having a significantly reduced susceptibility to structural disorder, these spatially delocalized excitations offer various functional benefits such as faster energy transport and less trapping and ensuing loss of excitation energy. These functions are often enhanced by mixing of the excitons with charge-transfer states. In the first part of the presentation, I will discuss molecular design strategies of conjugated polymers with enhanced robustness to static disorder. I will also show how subunit aggregation types can be quantified, using as an example the application of three computational methods to the experimental absorption and photoluminescence spectra of a benzodithiophene-isoindigo copolymer. In the second part of the presentation, I will discuss how the photosystem organization of cyanobacteria serves as inspiration for the design of conjugated terpolymers whereby the use of one donor and two acceptor units mimics the design of one main type of light-harvesting complex channeling excitation energy to two different types of photosystems.