RESUMO
This work reports a series of five-acetate triruthenium clusters [Ru3O(OAc)5(L)(py)2]PF6, where L = dppn (benzo[i]dipyrido[3,2-a:2',3'-c]phenazine, 1); dppz (dipyrido[3,2-a:2',3'-c]phenazine, 2); CH3-dppz (7-methyldipyrido [3,2-a:2',3'-c] phenazine, 3); Cl-dppz (7-chlorodipyrido [3,2-a:2',3'-c] phenazine, 4); and phen (1,10-phenanthroline, 5). The EPR spectra collected at 10 K displayed one isotropic signal without a hyperfine structure and with g values of â¼2.0, which showed that the five-acetate triruthenium clusters are paramagnetic, and that their electronic delocalization resembled the electronic delocalization of the parent hexa-acetate complexes. 1H NMR analysis showed that the orthometalated phenazines lowered the symmetry of the compounds significantly. Inductive effects from the carbanion and ring current effects outweighed the effect of paramagnetic anisotropy and dominated the spectra. This resulted in a lack of typical correlations with ligand parameters such as pKa that are observed for the parent hexa-acetate compounds. DFT calculations allowed for a discussion of those parameters in terms of the optimized geometry of compound 2. Natural bond orbital (NBO) results, in turn, aided the rationalization of the orthometalation reaction. The intra-cluster transitions (IC) at â¼690 nm consistently shifted to higher energies, and the redox pair [Ru3O]0/+1 also shifted to more positive E1/2 values. Again, the shifts were small and produced poor correlations with phenazine basicity. Overall, the substitution of one acetate bridge caused poor π-interactions between the delocalized [Ru3O] unit and the phenazine electron cloud. fsTA experiments, performed for the first time for such systems, showed that an 2IC excited state decayed very fast on the picosecond timescale.
RESUMO
This work presents a new procedure to synthesize ruthenium-phthalocyanine complexes and uses diverse spectroscopic techniques to characterize trans-[RuCl(Pc)DMSO] (I) (Pc = phthalocyanine) and trans-[Ru(Pc)(4-ampy)2] (II) (4-ampy = 4-aminopyridine). The triplet excited-state lifetimes of (I) measured by nanosecond transient absorption showed that two processes occurred, one around 15 ns and the other around 3.8 µs. Axial ligands seemed to affect the singlet oxygen quantum yield. Yields of 0.62 and 0.14 were achieved for (I) and (II), respectively. The lower value obtained for (II) probably resulted from secondary reactions of singlet oxygen in the presence of the ruthenium complex. We also investigate how axial ligands in the ruthenium-phthalocyanine complexes affect their photo-bioactivity in B16F10 murine melanoma cells. In the case of (I) at 1 µmol/L, photosensitization with 5.95 J/cm2 provided B16F10 cell viability of 6%, showing that (I) was more active than (II) at the same concentration. Furthermore, (II) was detected intracellularly in B16F10 cell extracts. The behavior of the evaluated ruthenium-phthalocyanine complexes point to the potential use of (I) as a metal-based drug in clinical therapy. Changes in axial ligands can modulate the photosensitizer activity of the ruthenium phthalocyanine complexes.