Linking semiconductor nanocrystals into gel networks through all-inorganic bridges

For colloidal semiconductor nanocrystals (NCs), replacement of insulating organic capping ligands with chemically diverse inorganic clusters enables the development of functional solids in which adjacent NCs are strongly coupled. Yet controlled assembly methods are lacking to direct the arrangement of charged, inorganic cluster-capped NCs into open networks. Herein, we introduce coordination bonds between the clusters capping the NCs thus linking the NCs into highly open gel networks. As linking cations (Pt²⁺) are added to dilute (under 1 vol %) chalcogenidometallate-capped CdSe NC dispersions, the NCs first form clusters, then gels with viscoelastic properties. The phase behavior of the gels for variable [Pt²⁺] suggests they may represent nanoscale analogues of bridged particle gels, which have been observed to form in certain polymer colloidal suspensions. To cap it all: Capping inorganic nanocrystals (NCs) with chalcogenidometallate clusters allows the chalcogenidometallate clusters to act as anchors for coordinating metal ions. Pt²⁺ ions can bind to the clusters and act as linkers by forming coordination bonds. Depending on Pt²⁺ ion concentration the linked chalcogenidometallate-capped NCs can form all-inorganic gel networks.