Three
ruthenium nitrosyl-
dye conjugates, namely, [((OMe)(2)bQb)Ru(NO)(Resf)] (RuNO-Resf), [((OMe)(2)bQb)Ru(NO)(Thnl)] (RuNO-Thnl), and [((OMe)(2)bQb)Ru(NO)(Seln)] (RuNO-Seln) have been synthesized using the tetradentate N4 dicarboxamido
ligand H(2)(OMe)(2)bQb. Each nitrosyl of this series is conjugated to a
phenoxazine-type heterotricyclic chromophore which has been systematically varied in a central position to test the effects of "heavy-atom" substitution (O =
Resorufin; S = Thionol; Se = Selenophore) in
photosensitization. The structure of the
chloride-bound precursor {Ru-NO}(6) nitrosyl [((OMe)(2)bQb)Ru(NO)(Cl)] (RuNO-Cl) and three nitrosyl-
dye conjugates, namely, RuNO-Resf, RuNO-Thnl and RuNO-Seln, have been determined by X-ray crystallography. All three nitrosyl-
dye conjugates exhibit sharp (1)H NMR spectra (S = 0 ground state) and nu(NO) stretches in the IR spectrum in the region 1825-1855 cm(-1), typical of {Ru-NO}(6) nitrosyls. The presence of a heavy atom in the bound
dye gives rise to a systematic red-shift in the electronic absorption spectrum, shifting from RuNO-Resf (lambda(max) = 500 nm) to RuNO-Thnl (lambda(max) = 530 nm) to RuNO-Seln (lambda(max) = 535 nm). Results of careful measurements with monochromatic light sources indicate that heavy-atom substitution in the coordinated
dye makes the resulting nitrosyl-
dye conjugates more susceptible to light of longer wavelength (lower energy). Density functional theory (DFT) calculations on RuNO-Cl, RuNO-Resf, RuNO-Thnl, and RuNO-Seln have been performed to gain insight into the electronic structure of the {
dye-Ru-NO} frame and the nature of transition(s) that sensitizes these conjugates to lights of longer wavelengths and promote NO photolability. Results of this study provide an explanation for the sensitization observed in our strategy of direct attachment of
dye molecules to {Ru-NO}(6) nitrosyls. This strategy could lead to eventual isolation of designed
metal nitrosyls that are sensitive to red- or near-infrared light and hence potential
photodynamic therapy (
PDT) agents for treatment of
malignancies with high doses of NO.