Shining a light on Co(terpyridine)2 complexes: Unravelling the impact of ligand substitution at the 4’-position on optical and electrochemical properties through experimental and theoretical investigations

The present work involves synthesis, characterisation and study of absorption, emission and electrochemical properties of cobalt(III) bis-terpyridine complexes with varying substituent at the 4’-position of the central pyridine ring of terpyridine moiety. The work clearly demonstrates the modulation of the light harvesting window with changing the substituent viz. phenyl, naphthalenyl and thienyltriphenylamine. The naphthalenylterpyridine based cobalt complex shows considerable room temperature luminescence. Cyclic voltammetry data of the complexes reveal a reversible Co^III/II based redox feature. DFT based structure optimisations for all the complexes were performed at the B3LYP level using 6-31G (d,p) and LANL2DZ basis sets. TD-DFT based theoretical calculations were performed with the optimised structures to simulate the experimental absorption spectrum for all the complexes and hence the electronic transitions for the observed absorption peaks were assigned.