A Key Strategy for the Rational Incorporation of Long-lived NIR Emissive Cr(III) Chromophores into Polymetallic Architectures

The CrIIIN6 chromophores are particularly appealing for low energy sensitization via energy transfer processes since they show extremely long excited state lifetime reaching millisecond range in the technologically crucial near-infrared domain. However, their properties were barely harnessed in multimetalic structures because of the lack of both monitoring methods and accessible synthetic pathways. We herein report a remedy to monitor and control the formation of CrIII-containing assemblies in solution via the design of a CrIIIN6 inert “complex-as-ligand” that can be included into polymetalic architectures. As a proof of concept, these CrN6 building blocks were reacted in solution with ZnII or FeII to give extended trinuclear linear Cr-M-Cr assemblies, the structure of which could be addressed by NMR spectroscopy despite the presence of two slow relaxing CrIII paramagnetic centers. In addition to long CrIII excited state lifetimes and weak sensitivity to oxygen quenching, these polymetallic assemblies display controlled CrIII
to MII energy transfers, which pave the way for use of the “complex-as-ligand” strategy for introducing photophysically active CrIII probes into light-converting polymetalic devices.