Probing Co-Assembly of Supramolecular Photocatalysts and Polyelectrolytes Using Isothermal Titration Calorimetry

The creation of renewable fuels to replace dwindling fossil energy resources is one of the greatest challenges facing the scientific community. Generating H₂ fuel from water is a carbon-neutral strategy that demonstrates great promise. Photocatalysts of the molecular architecture [{(TL)₂Ru(BL)}₂RhX₂]⁵⁺ (BL = bridging ligand, TL = terminal ligand, X = halide) catalyze the formation of H₂ in deoxygenated organic solvents but are limited by poor performance in air-saturated aqueous solutions. Addition of the water-soluble polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) was recently shown as being a promising new strategy to increase efficiency and stability of H₂ evolving photocatalysts in air-saturated aqueous solutions. Herein we investigate intermolecular interactions between Ru,Rh,Ru photocatalysts and water-soluble polyelectrolytes using isothermal titration calorimetry (ITC). ITC studies provide insight into the thermodynamic forces that drive assembly of PSS-photocatalyst aggregates and give new evidence for the intermolecular forces that lead to increased photocatalytic efficiency.