High resolution spectra and luminescent lifetimes of 6 europium(III)-cinnamic acid complex ([Eu2L6(DMF) (H2O)]center dot nDMF center dot H2O}, (L = cinnamic acid I, 4-methyl-cinnamic acid II, 4-chloro-cinnamic acid III, 4-methoxy-cinnamic acid IV, 4-hydroxy-cinnamic acid V, 4-nitro-cinnamic acid VI; DMF = N, N-dimethylformamide, C3H7NO) were recorded from 8 K to room temperature. The energy levels of Eu3+ in these 6 complexes are obtained from the spectra analysis. It is found that the energy levels of the central Eu3+ ions are influenced by the nephelauxetic effect, while the triplet state of ligand is lowered by the p-pi conjugation effect of the para-substituted functional groups. The best energy matching between the ligand triplet state and the central ion excited state is found in complex L While the other complexes show poorer matching because the gap of D-5(0) and triplet state contracts. (C) 2016 Elsevier B.V. All rights reserved.