UC Santa Cruz

Conjugated polyelectrolytes (CPEs) absorb light, are soluble in aqueous media, and are amenable to forming higher-order architectures via non-covalent interactions. CPEs provide rapid coherent intra-chain exciton transfer due to delocalization of excited states and have pendant ionic sidechains that make them soluble in aqueous media and enable complexation with oppositely charged CPEs to form conjugated polyelectrolyte complexes (CPECs). CPECs as building blocks for multi-component light-harvesting systems approach panchromaticity and participate in rapid intra-chain and inter-chain electronic energy transfer (EET) for directionally guiding excited states towards a reaction center.To increase the density of and proximity between CPE chains in solution, high ionic strength conditions induce liquid-liquid phase separation, which form CPE rich and CPE poor phases. The CPE rich phase containing exciton donor-acceptor pairs will form the basis of a multicomponent light-harvesting fluid, which offers the ability to host components that would perform specific tasks such as chemical reactions or charge separation. Fluidity is necessary for diffusion of reactants in and out of the light harvesting scaffold. To this end, progress has been made forming complex light- harvesting fluids with fully conjugated CPECs, albeit the phase of the system tends toward being more rigid than fluid. To combat the rigidity of the desired complex light-harvesting fluid, a brush-like polyfluorene-based exciton-donor CPE series was designed and synthesized to increase the polar-character of the CPEC. This copolymeric series has one monomer that contains pendant ionic sidechains and another monomer that is functionalized with oligoethylene glycol (oEG) sidechains with 3, 6, 9 , or 12 ethylene glycol (EG) units. The brush-like PFNGX series is highly water-soluble and remarkably stable at high ionic strength. To answer whether beyond a certain length of oEG sidechain, complexation and EET will be hindered, CPECs were formed using the synthesized exciton-donor PFNGX (3, 6, 9) series and a polythiophene-based exciton acceptor, and then interrogated with a combination of photoluminescence (PL) quenching experiments and photoluminescence excitation experiments. Complexation and EET between exciton donor-acceptor CPE pairs was found to be independent of oEG chain length, and led to a postulated CPEC structure which rationalize these findings.