Isolation strategy for a novel luminescent Eu3+-pyridine-2,6-dicarboxylic acid complex with high compatibility and stability for light-conversion agricultural films

Small organic conjugated molecule-based rare earth complexes are a kind of promising light-conversion material used in greenhouse films to improve the crop yield. Unfortunately, achieving a high luminescent performance of this kind of light-conversion material with a low migration rate in the film is still a big challenge. It has been predicted that increasing the interaction between the luminescent complex and polymer backbone could reduce the migration rate of the complex. Herein, we bridged two pyridine-2,6-dicarboxylic acid derivatives coordinated to Eu3+ luminescent centers using different lengths of the alkyl chain. Then, two new light-conversion agents, LDPA-4 (four carbon atoms) and LDPA-6 (six carbon atoms), were prepared. Using this strategy, we achieved a 615 nm red-light emission quantum yield (QY) of 13.16% for LDPA-6, which was much higher than that of LDPA-4 (5.28%) and the reference sample LCA-C (10.77%), respectively. In the resulting light-conversion films, rape samples treated with LDPF-6 exhibited the largest growth rate and yield of 2482.8 kg ha(-1) during the experimental plot application, which was 1.15 times higher than that of the pure PE one, demonstrating the special ligand effect of the pyridine-2,6-dicarboxylic acid and the importance of the alkyl chain length between the two luminescent centers.