Size effects on the luminescence quenching of Tb 3+ by Ru(II) tetraammines with alkyl trans-phosphane ligands

Abstract

The luminescence quenching of ∗Tb 3+ by tetraammines of Ru(II) complexes with phosphane ligands of the type trans-[Ru(NH 3) 4(P(OR) 3) 2](PF 6) 2 with R = CH 3, C 2 H 5, i C 3 H 7, C 4 H 9, i C 4 H 9 , is studied in aqeuous solution. The results indicate that the quenching process occurs by collisional energy transfer with possible formation of a photoactive triplet ligand-field excited state of the Ru(II) complex which undergoes NH 3 photoaquation. The observed luminescence quenching rate constants are within the range 1.1 ( R = 1 C 4 H 9 ) to 3.3 (R = CH 3) × 10 6M −1s −1 depending on the type of alkyl chain in the phosphane ligand. Bulky substituents on the P ligand reduce the rate of luminescence quenching by inducing steric factors and consequently increasing the pair contact distance for collisional energy transfer. For n-alkyl phosphane ligands, this size effect on the quenching rate constant is well correlated with the ligand cone angle θ.