The effect of molecular structure on the quenching of the charge-transfer luminescence of ruthenium(II) complexes

Abstract

The effect of molecular structure on the quenching of the luminescent charge-transfer state of Ru(bpy)32+ and Ru(bpic)32+ has been studied with eight geometric ß-diketonate isomers of Co(III) and Cr(III). The isomers have identical electronic spectra, but differ in their molecular structure. The Co(III) isomers quench at essentially a diffusion-controlled limit, whereas the Cr(III) isomers quench at an order of magnitude less than the theoretical limit. The cis and trans isomers of the Co(III) complexes yield identical Stern-Volmer constants suggesting little or no discrimination during the quenching encounter. A similar lack of discrimination is found with the phenyl substituted Cr(III) complex, Cr(bzac)3. With the trifluoro-substituted analogue, however, cis-Cr(tfac)3 is ca. 40% more efficient in quenching than trans-Cr(tfac)3.