Panchromatic Ru(ii)-polypyridyl complexes as NIR emitters

Abstract

Two novel mer-Ru(II) heteroleptic complexes containing stongly donating tridendate ligands (dgpy and dgpz) were synthesised and optoelectronically characterised. These complexes exhibited quasi-reversible ligand- and metal-based redox events and panchromatic absorption with the lowest energy absorption maxima trailing up to 750 nm. These panchromatic dyes were found to be NIR emissive at λ_PL ∼ 835 nm with associated excited-state lifetimes (τ_PL) of ∼10 ns. The enhanced photophysical properties of these complexes compared to those of [Ru(tpy)₂]²⁺ (tpy = 2,2′:6′,2′′-terpyridine; λ_abs < 575 nm, λ_PL ∼ 629 nm and τ_PL ∼ 0.25 ns) are due to the larger ³MLCT–³MC energy-gap as a combined effect of larger bite angle and strong σ-donation offered by the dgpy and dgpz ligands.