Room temperature phosphorescence has been observed in a synthetically facile Pt(II) complex, Pt(dbbpy)(CtriplebondC-pyrene)(2) (dbbpy = 4,4'-di(tert-butyl)-2,2'-bipyridine; CtriplebondC-pyrene = 1-ethynylpyrene), in fluid solution. The static and time-resolved absorption and luminescence data are consistent with phosphorescence emerging from the appended CtriplebondC-pyrenyl units following excitation into the low energy dpi Pt --> pi* dbbpy metal-to-ligand charge transfer absorption bands.

We describe the synthesis, electrochemical, and photophysical properties of two new luminescent Ru(II) diimine complexes covalently attached to one and three 4-piperidinyl-1,8-naphthalimide (PNI) chromophores, [Ru(bpy)(2)(PNI-phen)](PF(6))(2) and [Ru(PNI-phen)(3)](PF(6))(2), respectively. These compounds represent a new class of visible light-harvesting Ru(II) chromophores that exhibit greatly enhanced room-temperature metal-to-ligand charge transfer (MLCT) emission lifetimes as a result of intervening intraligand triplet states ((3)IL) present on the pendant naphthalimide chromophore(s). In both Ru(II) complexes, the intense singlet fluorescence of the pendant PNI chromophore(s) is nearly quantitatively quenched and was found to sensitize the MLCT-based photoluminescence. Excitation into either the (1)IL or (1)MLCT absorption bands results in the formation of both (3)MLCT and (3)IL excited states, conveniently monitored by transient absorption and fluorescence spectroscopy. The relative energy ordering of these triplet states was determined using time-resolved emission spectra at 77 K in an EtOH/MeOH glass where dual emission from both Ru(II) complexes was observed. Here, the shorter-lived higher energy emission has a spectral profile consistent with that typically observed from (3)MLCT excited states, whereas the millisecond lifetime lower energy band was attributed to (3)IL phosphorescence of the PNI chromophore. At room temperature the data are consistent with an excited-state equilibrium between the higher energy (3)MLCT states and the lower energy (3)PNI states. Both complexes display MLCT-based emission with room-temperature lifetimes that range from 16 to 115 micros depending upon solvent and the number of PNI chromophores present. At 77 K it is apparent that the two triplet states are no longer in thermal equilibrium and independently decay to the ground state.

We discuss SECM tip voltammetry, where a UME tip is held above a conductive substrate within about a tip radius and a tip voltammogram is recorded as its potential is slowly scanned while the substrate is held at a fixed potential. When the potential of the substrate is changed, the series of steady-state tip voltammograms provide information about the reactants and products. When the potential of the substrate, ES, is set so that the reaction at the substrate is opposite to that at the tip (the usual SECM conditions), a total positive feedback (tpf) tip voltammogram is recorded. When the substrate potential is set to values where the reaction at the substrate is the same as that occurring on the tip, the tip is shielded from the species in the bulk solution. Depending upon the substrate potential, this can cause total shielding (ts) or a voltammogram that is the result of partial feedback/partial shielding (pf-ps). The result is a series of tip voltammograms that are characterized by tpf, pf-ps, or ts, depending upon ES. Experimental tip voltammograms resulting from the reversible reduction of TCNQ and oxidation of ferrocene in MeCN are reported. These are compared with those from simulations and approximate equations developed to describe the features of the tip voltammograms generated under tpf, ts, or pf-ps conditions. The effect of the diffusion coefficient ratio on the ability of the UME tip to reach a true steady state is also addressed and possible applications, e.g., obtaining information about the reversibility of an electrochemical reaction, the product of an electrochemical reaction, the stability of that product, or the diffusion coefficients of the electroactive species, are discussed.