Photodynamic therapy (PDT) is a photochemistry-based modality useful in the treatment of localized disease and tumors.  The treatment utilizes a photoactive drug that is nontoxic in the dark and becomes highly cytotoxic upon irradiation. For the success of PDT, molecules that absorb light at longer wavelengths are advantageous, as irradiation at lower energy results in deeper penetration and greater treatment efficacy. Recently, metal complexes have been investigated as new drugs for use in PDT as photo-activated analogs to cisplatin. These complexes are only activated by irradiation at certain wavelengths of light to localize toxicity within a given treatment area. In this way, control of activation and toxicity is a direct consequence of the photochemistry of transition metal complex. The photosubstitution of several ruthenium(II) complexes has been extensively reported as photoactivated drug candidates. However, a major drawback for their success in vivo continues to be appreciable activation within the PDT window (600 � 800 nm). Recently, the oxygen-nitrogen chelating ligand 8-hydroxyquinoline has shown promise for red-shifting absorbance and photoreactivity in tris-chelated ruthenium (II) complexes. Here, we report the synthesis, structural characterization and photophysical properties of a series of ruthenium (II) complexes using para-substituted derivatives of 8-hydroxyquinoline (R=H, NO2, Cl, CH3, SO3) aimed at tuning absorbance and photoreactivity.  Within this series, weakening of the electron donating ability of the oxygen atom was observed with increasing electron withdrawing ability of the substituted quinolate ligand by TD-DFT calculations.  In addition, a red shift in the lowest energy transition for complexes with electron withdrawing substitutes was observed and was found to be a result of increasing mixed metal-ligand HOMO character.

Synthesis of ruthenium(II) complexes with N,O-chelates: An investigation of the effect of ligand s-donation on oxidation state, spectroscopy, and photochemistry

248th National Meeting (2014)

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