We prepared tris bipyridyl dichlororuthenium II mg

We prepared tris(2,2′-bipyridyl)dichlororuthenium(II) (0.7mg/ml) and sulfo-Cyanine5 NHS ester (0.7mg/ml) dilutions in Milli-Q ultrapure water. We spotted 2μl of dilutions onto glass, aluminum and silicon slides and left to dry for 30’, in a dry environment at atmospheric pressure. Then, we analyzed both the dried and the dissolved forms. Absorption analysis were carried out using a spectrophotometer Varian Cary50. The buy ketotifen fumarate was measured for Ru(bpy)32+ 0.7mg/ml dilution in aqueous solution, inside a cuvette (dissolved form) and over a glass slide (dried form) containing 2μl spot of solution. We chose this fluorophore concentration since the fluorescence signal is the maximum, avoiding both powder excess and optical signal saturation. For dried form absorption analysis, we collected the signal from dye spotted on glass slide fixed on solid sample holder of Cary 50. Emission analysis were carried out on the same Ru(bpy)32+ solution. Also in this case, the fluorophore was analyzed in both dissolved and dried forms. The system included: laser source (Coherent) operating at 408nm to a power of 50mW; chopper; monochromator; PMT Hamamatsu R-908; lock-in; a series of mirrors to collect the signal at the monochromator entrance slits. A computerized system for instruments management and data acquisition, through the software Labview®, completed the system. Lifetime measurements on Ru(bpy)32+ dissolved and dried forms were carried out by replacing the PMT with the Silicon Photomultiplier (SiPM) [5,14,15]. We placed the sample in front of the laser source. The laser was connected to a pulse generator to regulate the duration (10ns for measurements) and frequency (50Hz) of pulsed light. The light emitted by the sample after laser excitation reached the SiPM, located inside of a metal holed box (miniDom [16]) which also contained some electrical high-pass filters. A computer collected the SiPM detection signal, measured by a source-meter-unit (Keithley 236). Finally, an optical band-pass filter at 600±30nm was placed within the miniDom, to exclude the excitation beam. In order to study its photostability, we measured Ru(bpy)32+ absorption and emission under very unsustainable chemical-physical conditions (see Supplemental materials). Finally, transmission electron microscopy (TEM) experiments were performed using the bright field in conventional parallel beam (CTEM) mode (BF). A TEM JEOL JEM-2010 equipped with a 30mm2 window energy dispersive X-rays (EDX) spectrometer was used. Ru(bpy)32+ was examined by negative contrast according to the following protocol. A mix of 8μl of 4% uranyl acetate, used as contrast element, and 12μl of 0.7mg/ml fluorophore dilution was prepared. Subsequently, 20μl of the mix were placed on the formvar carbon coated nickel grid and the excess was removed by a filter paper. After drying for 10’ at room temperature, we examined samples inside the microscope.
Results and discussion Absorption data for Ru(bpy)32+ dissolved and dried form are shown in Fig. 1. The data obtained from the dissolved form (blue solid line) perfectly reproduce literature results [6,7]. The fluorophore exhibits two characteristic absorption peaks at 290nm and 450nm (highlighted in figure with dashed vertical lines). On the other hand, samples dried over glass slides showed a red shift of about 20nm, with electronic transition’s peaks at 310nm and 470nm, as shown in Fig. 1 (red dashed line). The absorption “red shift” is probably due either to the intensification of inter-molecular interactions or to a slight distortion of the intra-molecular bonds. Actually, drying process generates the increase of fluorophore’s molecular density and, accordingly, a structural compression and deformation. The result could be an alteration of standard intramolecular electronic transitions and absorption peaks. The data, shown in Fig. 1, clearly show a difference in the ratio between LC and MLCT transitions. The MLCT–LC ratio goes from ∼0.2 of the dissolved form to more than 0.8 of the dried form, suggesting a strong increase of the absorption efficiency, more than a factor four, of the MLCT electronic transitions with respect to the LC ones.