Unravelling the Quenching Mechanisms of a Luminescent Ru^II Probe for Cu^II

Abstract

We have investigated the photophysical and photochemical features of a luminescent heteroleptic Ru(II)-polypyridyl probe and of its corresponding Ru(II)-Cu(II) dinuclear complex formed upon the analyte binding through extensive density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The molecular probe contains the tailored imidazo[4,5-f]-1,10-phenanthroline (IIP) ligand for simultaneously binding the Ru(II) core and the target metal ion in aqueous solution. We have rationalized the static photoluminescence quenching observed upon the Cu(II) coordination, on the grounds of distinct excited state deactivation mechanisms which are absent in the free Ru(II) complex probe. Additionally, the emission quenching found upon increasing the solution pH has also been investigated. When coordinated IIP deprotonates, the nature of the lowest excited state of its complex changes from (3)MLCT to (3)LLCT/(3)IL. The strong base-induced emission quenching can be understood in terms of both the energy-gap law, since the (3)LLCT/(3)IL states lie at a significantly lower energy than the (3)MLCT state increasing the contribution of non-radiative mechanisms, and the expected slower radiative rates from such (3)LLCT/(3)IL states. After Cu(II) binding, the lowest triplet excited state is similar to the analyte-free probe in both energy and electronic nature. However, Cu-centered non-radiative excited states, populated after photoinduced electron transfer and intersystem crossing processes, are responsible for the population drainage of the emissive state.

Synthesis and Isomeric Analysis of RuII Complexes Bearing Pentadentate Scaffolds

“…The calculations suggest that this process will be more favorable in DCM, where the energy gap is smaller, and this might explain why the light-induced isomerization from the cis form is suppressed in this solvent but not in MeOH. Such nonadiabatic processes are common in the photoreactivity of transition-metal complexes 15 and organic molecules, 16 and involvement of a singlet/triplet crossing has been previously postulated in the photoisomerization of Ru(II) monoaquo complexes. 17 The computational results also indicate that the minor species (12−18%) detected in the NMR experiments in MeOH are the trapping products of the decoordinated intermediates.…”

Adaptive σ aromaticity in the rhenacyclopropene rings

“…All calculations involved in this work were conducted in the Gaussian 16 package. 42 All structures were optimized with the (U)B3LYP 43,44 density functional in the gas phase and its reliability is supported by various studies of reaction mechanisms [45][46][47][48] and aromaticity. [49][50][51][52][53] The 6-31G(d) basis set 54 was employed to describe C, H, N, O, P, S, and Cl atoms, whereas LanL2DZ basis set 55 was used to describe the rest of the heavy atoms.…”