The complex [Ru(NH3)4dppz]2+ shows a metal to ligand charge transfer (MLCT) transition at ∼544 nm but does not show any photoluminescence. The complex does not exhibit any solvent-dependent MLCT changes, unlike its bpy and phen counterparts. The complex showed intercalative binding to calf thymus DNA that was weaker than [Ru(phen)2dppz]2+.

The complex [Ru(phen)(2)dppz](2+) is not photoluminescent in water but does emit in nonaqueous solvents (alcohols, acetonitrile) and in the presence of hydrated polymers such as DNA. Here we examine the steady-state and time-resolved photoluminescence spectra of [Ru(phen)(2)dppz](2+) in a series of nonaqueous solvents. We find that solvent polarity, as defined by the E(T) scale, is the single most important parameter in predicting luminescence lifetime and intensity in nonaqueous systems. These results are compared to the data for DNA, and the sequence-dependent microenvironment of the complex bound to DNA also follows the trends observed herein. The addition of high concentrations of water to solutions of [Ru(phen)(2)dppz](2+) dissolved in nonaqueous solvents leads to decreases in emission intensity that follow the Perrin sphere of quenching model. The nonradiative rate constants for luminescence decay increase as the solvent polarity increases, while the radiative rate constants are relatively unaffected by the local environment.

We have characterized the fluorescence spectral properties of rhodamine 800 (Rh800) in plasma and blood in order to test the possibility of making clinical fluorescence measurements in whole blood without separation steps. Rh800 was used because of its absorption at red/near-infrared wavelengths away from the absorption bands of hemoglobin. We utilized the front-face illumination and detection to minimize the effects of absorption and/or scatter during measurements. The presence of Rh800 was detected in plasma and blood using steady-state fluorescence measurements. Absorption due to hemoglobin reduced the Rh800 intensity from the blood. Fluorescence lifetime measurements in plasma and blood showed that it is possible to recover lifetime parameters of Rh800 in these media. We obtained mean lifetimes of 1.90 and 1.86 ns for Rh800 in plasma and blood, respectively. Using the recently described modulation sensing method, we quantified the concentrations of Rh800 in plasma and blood. Rh800 was detected at a concentration of as low as 2 microM in both media. High anisotropy values were obtained for Rh800 in plasma and blood using steady-state and anisotropy decay measurements, implying the tight binding of this probe to the contents of these media. This binding can be exploited to monitor the concentrations of different blood components using already existing or new red-emitting probes that will be specially designed to bind to these components with high specificity. To test this possibility of direct measurements in blood, we used Rh800 to monitor albumin in the presence of red blood cells. Increase in the polarization of Rh800 as the concentration of albumin was increased in the presence of the red cells showed the feasibility of such measurements.

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