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The regioselective methylation of a ruthenium polypyridyl complex bearing both a 1,2,4-triazolato and a pyrazine moiety is reported. In contrast to previous studies in which methylation of the 1,2,4-triazolato ring was observed, in the present system methylation takes place exclusively at the non-coordinated nitrogen of the pyrazine ring. The monomethylation is confirmed by (1)H NMR spectroscopy and ESI-MS and the electronic properties of the methylated complexes are studied by UV/vis absorption, emission, surface enhanced, resonance and transient resonance Raman spectroscopy. Ligand deuteriation is used to simplify the (1)H NMR spectra and to assign definitively the Raman spectra. Acid-base studies show that the triazolato ring of the N-methylated complexes can be protonated at low pH and that at high pH the N-methyl group can be deprotonated reversibly. Furthermore it is shown that under conditions where the methyl group is deprotonated, demethylation occurs to recover the initial complex.

Two series of ruthenium(II) polypyridyl complexes [Ru(bipy)(2)(phpytr)](+) and [Ru(bipy)(2)(phpztr)](+) (where Hphpytr = 2-(5-phenyl-1H-[1,2,4]triazol-3-yl)-pyridine and Hphpztr = 2-(5-phenyl-1H-[1,2,4]triazol-3-yl)-pyrazine) are examined by electrochemistry, UV/Vis, emission, resonance Raman, transient resonance Raman and transient absorption spectroscopy, in order to obtain a more comprehensive understanding of their excited state electronic properties. The interpretation of the results obtained is facilitated by the availability of several isotopologues of each of the complexes examined. For the pyridine-1,2,4-triazolato based complex the lowest emissive excited state is exclusively bipy based, however, for the pyrazine based complexes excited state localisation on particular ligands shows considerable solvent and pH dependency.

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 (CH(3)) and withdrawing (C(6)H(5), COO(-)) groups induces a pronounced blue and red shift, respectively, in the lowest energy (1)MLCT absorption band of [Ru(LL)(CN)(4)](2-). The energy of the emission originating from the (3)MLCT 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 (S(M)), while phenyl substitution results in a decrease in S(M) for both series (bipy and phen) of complexes. The rate of non-radiative (k(nr)) and radiative decay (k(ph)) to the ground state and the parameters of thermally activated deactivation pathways (A(4th), DeltaE(4th) and A(dd), DeltaE(dd)) 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.

Rational design of supramolecular systems for application in photonic devices requires a clear understanding of both the mechanism of energy and electron transfer processes and how these processes can be manipulated. Central to achieving these goals is a detailed picture of their electronic structure and of the interaction between the constituent components. We review several approaches that have been taken towards gaining such understanding, with particular focus on the physical techniques employed. In the discussion, case studies are introduced to illustrate the key issues under consideration.