Synthesis and applications of rhodium porphyrin complexes.

Organotransition metal complexes capable of forming metalloradicals have been an intriguing subject of study for the past fifty years. Of these, rhodium porphyrin complexes have proven particularly interesting due to their straightforward synthesis and unique reactivity; indeed, these complexes are responsible for some highly influential transformations of organic compounds, including rare C-H and C-C bond activations. The complexity and selectivity of rhodium porphyrins has been attractive for catalytic transformations, with specific interest in their usage for selective carbon monoxide reduction for fuel cell applications. This review will highlight historical and modern syntheses of rhodium porphyrins, as well as their respective reactions with small molecules and applications therein. The discussion will be limited to rhodium porphyrins consisting of four pyrrolic rings bridged with four methine units.

Monoanionic bis(carbene) pincer complexes featuring cobalt(I-III) oxidation states.

The synthesis and characterization of a series of cobalt complexes featuring a pincer bis(carbene) ligand of the meta-phenylene-bridged bis-N-heterocyclic carbene ((Ar)CCC, Ar = 2,6-diispropylphenyl or mesityl) are reported. Cleavage of the aryl C-H bond of the ligand was achieved in a one-pot metalation procedure using Co(N(SiMe3)2)2(py)2, an equivalent of exogenous base, and trityl chloride to form the ((DIPP)CCC)CoCl2py complex. This species could be reduced to the Co(ii) and Co(i)-N2 molecules with the appropriate equivalents of reductant. Subsequent generation of ((Mes)CCC)Co(I-III) derivatives with the mesityl ligand proceeded in good yields. A suite of characterization techniques and the interconversion between all three oxidation states of the cobalt complexes is described.

Distance and plasmon wavelength dependent fluorescence of molecules bound to silica-coated gold nanorods.

Plasmonic nanoparticles can strongly interact with adjacent fluorophores, resulting in plasmon-enhanced fluorescence or fluorescence quenching. This dipolar coupling is dependent upon nanoparticle composition, distance between the fluorophore and the plasmonic surface, the transition dipole orientation, and the degree of spectral overlap between the fluorophore's absorbance/emission and the surface plasmon band of the nanoparticles. In this work, we examine the distance and plasmon wavelength dependent fluorescence of an infrared dye ("IRDye") bound to silica-coated gold nanorods. Nanorods with plasmon band maxima ranging from 530 to 850 nm are synthesized and then coated with mesoporous silica shells 11-26 nm thick. IRDye is covalently attached to the nanoparticle surface via a click reaction. Steady-state fluorescence measurements demonstrate plasmon wavelength and silica shell thickness dependent fluorescence emission. Maximum fluorescence intensity, with approximately 10-fold enhancement, is observed with 17 nm shells when the nanorod plasmon maximum is resonant with IRDye absorption. Time-resolved photoluminescence reveals multiexponential decay and a sharp reduction in fluorescence lifetime with decreasing silica shell thickness and when the plasmon maximum is closer to IRDye absorption/emission. Control experiments are carried out to confirm that the observed changes in fluorescence are due to plasmonic interactions, is simply surface attachment. There is no change in fluorescence intensity or lifetime when IRDye is bound to mesoporous silica nanoparticles. In addition, IRDye loading is limited to maintain a distance between dye molecules on the surface to more than 9 nm, well above the Förster radius. This assures minimal dye-dye interactions on the surface of the nanoparticles.