Effect of substituent groups with two types on benzene ring on photoluminescence property of complexes of benzoic acid—Functionalized polystyrene with Eu(III) Ion

Abstract

Abstract Two benzoic acid derivatives, methoxybenzoic acid (MOBA) and formylbenzoic acid (FBA), on whose benzene ring, an electron-donating substituent group (methoxy group) and an electron-withdrawing substituent group (formyl group) exist, respectively, were bonded onto the side chains of polystyrene (PS) through polymer reactions, obtaining two benzoic acid derivative-functionalized PSs, PS-MOBA and PS-FBA. The two macromolecule ligands were made to coordinate to Eu 3+ ion, preparing two binary polymer-rare earth complexes, PS-(MOBA) 3 -Eu(III) and PS-(FBA) 3 -Eu(III) as well as two ternary complexes with phenanthroline (Phen) as the second small-molecule ligand. The luminescence property of theses complexes was mainly examined, and the effect of the two types of substituent groups on the benzene ring of the bonded benzoic acid on the photo physical behavior of these complexes was investigated in depth. The experimental results show that both the two types of substituent groups on the benzene ring of the bonded benzoic acid can effectively strengthen their fluorescence emission intensities, but the mechanisms are different. For MOBA series complexes, through p-π conjugation effect between methoxy group and the π orbit of the bonded ligand MOBA, the triplet state level of the bonded ligand MOBA can be remarkably decline, so the energy level matching degree between the triplet state level of the bonded ligand MOBA and the resonant energy level of Eu(III) ion is greatly enhanced, resulting in a drastically enhancing of the luminescence intensities of the MOBA series complexes. For FBA series complexes, through n–π* transition between the formyl group and π* orbit of the bonded ligand FBA and the accompanying intraligand charge transfer, the triplet state energy of the bonded ligand FBA can also be reduced, and the energy level matching degree can also be improved, leading to an obvious enhancement of luminescence intensities of the complexes.