The effects of ligand substitution and deuteriation on the spectroscopic and photophysical properties of [Ru(LL)(CN)4]2− complexes

The spectroscopic characterisation of a series of [Ru(LL)(CN)4]2− complexes, where LL = 1,10-phenanthroline (phen) and its methyl- and phenyl-substituted derivatives and several deuteriated isotopologues are reported. The optical and vibrational properties of these complexes are compared with that of the series of 2,2'-bipyridine (bipy) derivatives and analogous [Ru(LL)3]2+ complexes. It has been demonstrated that substitution at the 4,4' positions of bipy and 4,7-positions of phen by electron donating (CH3) and withdrawing (C6H5, COO−) groups induces a pronounced blue and red shift, respectively, in the lowest energy 1MLCT absorption band of [Ru(LL)(CN)4]2−. The energy of the emission originating from the 3MLCT excited state is found to be dependant on the nature of the vibrational modes of the aromatic rings and the electron donating and/or withdrawing properties of the substituents. Single-mode Franck–Condon analysis indicates that methyl substitution leads to a significant increase in the Huang–Rhys factor (SM), while phenyl substitution results in a decrease in SM for both series (bipy and phen) of complexes. The rate of non-radiative (knr) and radiative decay (kph) to the ground state and the parameters of thermally activated deactivation pathways (A4th, ΔE4th and Add, ΔEdd) were estimated from the temperature dependence of luminescence quantum yields and lifetimes. It has been demonstrated that the non-radiative decay rate and the temperature dependent decay processes are more efficient for bipy complexes than for phen derivatives due to the rigidity of the latter ligand.