| Over the last fifteen years, the library of luminescent Ir(III) complexes has expanded significantly. Spontaneous cyclometalation of the iridium center produces molecules with large ligand-field stabilization energies and thereby enhanced photochemical stability and emission tunability. However, the limited aqueous solubility of these complexes imposes restrictions on their utility in water-based applications, particularly solar fuels photochemistry.;To address this issue, a series of bis-cyclometalated diimine Ir(III) complexes incorporating sulfonated ancillary ligands were synthesized to promote aqueous solubility; the excited state properties of the resulting molecule can be adjusted through modification of the cyclometalating ligands. Unexpectedly, this structural motif encourages self-assembly in water, producing soapy solutions where the chromophores can be completely removed in the form of photoluminescent bubbles via slow nitrogen sparging. These Ir(III) complexes display concentration-induced aggregation in water, which blue shifts their photoluminescence emission energies and increases excited state lifetimes and quantum yields up to a factor of five.;Through a combination of spectroscopy, particle characterization techniques, and the study of model complexes, we have investigated the self-assembly phenomenon in these Ir(III) chromophores. Our data suggests the formation of small, heterogeneous aggregate structures, with the sulfonated diimine ancillary ligand acting as a pro-aggregating unit.;Such chromophores are uniquely suited for aqueous-based photocatalysis, where increased photosensitizer concentration renders the composition more reactive than its molecular counterpart. We demonstrate impressive activity from these Ir(III) chromophores in photocatalytic proton reduction experiments. |
