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The recently reported luminescent chromium(III) complex 13+ ([Cr(ddpd)2]3+; ddpd=N,N’-dimethyl-N,N’-dipyridine-2-yl-pyridine-2,6-diamine) shows exceptionally strong near-IR emission at 775 nm in water under ambient conditions (F=11%) with a microsecond lifetime as the ligand design in 13+ effectively eliminates non-radiative decay pathways, such as photosubstitution, back-intersystem crossing, and trigonal twists. In the absence of energy acceptors, such as dioxygen, the remaining decay pathways are energy transfer to high energy solvent and ligand oscillators, namely OH and CH stretching vibrations. Selective deuteration of the solvents and the ddpd ligands probes the efficiency of these oscillators in the excited state deactivation. Addressing these energytransfer pathways in the first and second coordination sphere furnishes a record 30% quantum yield and a 2.3 millisecond lifetime for a metal complex with an earth-abundant metal ion in solution at room temperature. The combined fundamental insights will pave the way for selective design strategies in the field of luminescent complexes with earth-abundant metal ions.
Two nanosensors for simultaneous optical measurements of the bioanalytically and biologically relevant analytes temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nmsized silica-coated polystyrene nanoparticles (PS-NPs) doped with a near-infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3, CrBPh4) and an inert reference dye (Nile Red, NR or 5,10,15,20tetrakis(pentafluorophenyl) porphyrin, TFPP) and are covalently labeled with pHsensitive fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal spectrally distinguishable emission bands, allowing for ratiometric intensity-based and time-resolved studies in the visible and near-infrared wavelength region. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of these nanosensors for the sensitive luminescence readout of TOP simultaneously at the same spatialposition.