We have synthesised a neutral, water-soluble, PtII complex able to aggregate more efficiently in aqueous solutions than in organic solvents. The aggregates are luminescent and are not quenched by molecular oxygen. Further, we have prepared phosphorescent hydrogels utilising host–guest interactions between cyclodextrins and the tetraethylene glycol tails of the PtII complex. The soft assemblies feature host-dependent emission properties.