Substituent effects on the electronic properties of complexes with dipyridophenazine and triazole ligands: Electronically connected and disconnected ligands

•We review substituent effects in complexes with dppz and triazole ligands.•Modulation of dppz properties is associated with the phenazine or phenanthroline MOs.•Dppz with donor groups give ligand-centred charge-transfer optical transitions.•For triazoles optical properties do not alter with substituent.•Excited state properties of triazole complexes give a muted response to substituent.

Substituent effects may tune and alter the optical and electronic properties of ligands and the complexes which they comprise. We review the effect of electron-withdrawing and -donating groups on the dipyridophenazine (dppz) framework. The observation of selected modulation of the properties associated with the phenazine or phenanthroline MOs is observed and reflected in the electrochemical and optical properties. The effect of donor groups that can give rise to ligand-centred charge-transfer optical transitions is also discussed. The effect of substituents on complexes with triazole ligands is examined; in stark contrast to the findings for dppz systems, and virtually regardless of the type of triazole ligand, substituents have only a muted effect on optical and electrochemical properties.