Spectra, energy levels, and energy transition of lanthanide complexes with cinnamic acid and its derivatives

• The splitting of 5D0–7F0 caused by coordination environments was observed.
• The fine energy levels of Eu3 + are obtained by high resolution spectra.
• The electric states of Eu3 + are influenced by the nephelauxetic effect.
• The triplet state of ligands is lowered due to the p–π conjugation effect.

High resolution spectra and luminescent lifetimes of 6 europium(III)–cinnamic acid complex {[Eu2L6(DMF)(H2O)]·nDMF·H2O}m (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–π 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 I. While the other complexes show poorer matching because the gap of 5D0 and triplet state contracts.

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