Reaction of the β-diketone ligand, 2-cyano-1,3-phenyl-1,3-propandione (LH), with hydrated EuCl3 in the presence of 1,10-phenanthroline (Phen), results in the crystallisation of a one-dimensional Eu3+ coordination polymer of formulation [Eu(Phen)(L)3]∞, formed by coordination of the nitrile group of an O,O′-bound ligand to a neighbouring metal centre. An investigation of the metal-centred emission of the polymer, both in the solid state and solution, revealed red emission characterised by relatively long-lived excited state lifetimes and high intrinsic quantum yields. However, analysis of the overall quantum yield and sensitisation efficiency reveals that ultrafast processes in the ligand potentially inhibit Eu3+ sensitisation. Further investigations into these processes using transient absorption spectroscopy suggest that substitution at the α-C position may significantly decrease sensitisation via the antenna effect.