Protonation of the ground states of ruthenium(II) photosensitizers

摘要

Ru(II) complexes that possess 2,2'-bipyrazine, 2,2'-bipyrimidine, and 2-(2'-pyridyl)pyrimidine ligands in combination with 2,2'-bipyridine undergo protonation at the basic nitrogen heteroatoms on the periphery of the aromatic rings as the solution is made more acidic, resulting in changes in the absorption spectra. In this study, the acidity of the solution was controlled with concentrated H2SO4; titration curves for the first protonations were obtained from plots of absorbance versus acidity, from which the pK(a1) values for the monoprotonated species were extracted. As has been observed before for the acid-base properties of the excited states and the one-electron reduced forms of the complexes, the pK(a1) values of the protonated forms of the ground states (- 1.6 to - 5.0) correlate with the reduction potentials, and demonstrate site selectivity of the protonation process. (C) 1998 Elsevier Science S.A. All rights reserved. [References: 18]