Iridium(III)-based charge transfer complexes are known to possess long excited-state lifetimes, high emission quantum yields, and chemically tunable emission energies. Such properties make them ideal for numerous photosensitizer applications, including photocatalytic hydrogen reduction. Towards this goal, we have synthesized a series of water-soluble iridium(III) coordination compounds incorporating peripheral sulfonate groups to promote aqueous solubility. Unexpectedly, these complexes display unique, concentration-dependent photophysics in water, while remaining molecular in organic solvents. The photoluminescence quantum yields and excited state lifetimes of these complexes markedly increase with increasing chromophore concentration until it achieves a saturation limit. The self-assembly process is clearly evident from simple bubble degassing experiments, which completely removes the chromophores from the aqueous solution in the form of photoluminescent bubbles. This unique combination of structural design elements may represent a novel way to control molecular sensitizer structures while enhancing its associated photophysical properties in aqueous media.

Unexpected photoluminescence enhancement from cyclometalated  Ir(III) complexes in water

251st National Meeting (2016)

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