The photoluminescence from CdSe/ZnS core/shell quantum dots, modified to make them water-soluble by exchanging the surface ligands with dihydrolipoic acid, is partially quenched by adding the chromium(III) complex trans-Cr(cylcam)(ONO)(2)(+) (1, BF4- salt). This quenching, attributed to the formation of electrostatic assemblies due to ion pairing of 1 with the negatively charged QD surface, is accompanied by the release of NO owing to photosensitized reaction of the Cr(III) nitrito complex.