An Europium (III) Luminophore with Pressure‐Sensing Units: Effective Back Energy Transfer in Coordination Polymers with Hexadentate Porous Stable Networks

Abstract

A luminescent EuIII coordination polymer with O2‐sensing units under air, EuIII‐hcpt (hcpt: 2,3,6,7,10,11‐hexakis(4‐carboxy‐phenyl)triphenylene), is reported. The hexadentate carboxylic acids in hcpt ligands play an important role in the formation of tight‐packed three‐dimensional networks in EuIII‐hcpt, giving hyper thermo‐stable structures (decomposition temperature=420 °C). The three‐dimensional porous network promotes bright luminescence (4f–4f emission quantum yield=70 %). The emission lifetime of EuIII‐hcpt under vacuum (0.86 ms) was twice as large as that under O2 (0.48 ms, 1 atom:101.3 kPa). The Arrhenius analysis of the emission decay profile indicates that the back energy transfer (BEnT) from the emitting level of the europium(III) ion to the excited T1 state of the hcpt ligand should be activated at room temperature. The gradual decrease of emission lifetime is caused by the BEnT process in EuIII‐hcpt. Finally, an advanced pressure‐sensitive luminophore is demonstrated.

Drastic Enhancement of Photosensitized Energy Transfer Efficiency of a Eu(III) Complex Driven by Arsenic

“…For lanthanide complexes, components of nonradiative processes in the energy transfer process may include thermal deactivation, ISC (Path E3), and changes in the coordination geometry due to structural relaxation. Furthermore, nonradiative deactivation through singlet oxygen ( 1 O 2 ) generation (Path E4) and ligand-to-metal charge transfer (LMCT, Path E5) is known as the parameter that dictates the reduction of Φ tot . , In the present case, only the replacement of heteroatoms in the antenna ligands led to an increase in η sens , even under ambient conditions. We thus explored the reason for the enhancement of η sens by the introduction of arsenic.…”

“…Generally, when the energy gap between the excited state of Eu 3+ and the T 1 energy level of the antenna ligands is small, the probability increases that 1 O 2 quenches the T 1 state of ligands generated (Path E4) by energy back transfer from T 1 of antenna ligands to Eu 3+ excited state (Path E7). This would decrease the photosensitized energy transfer efficiency . Thus, the relationship between the T 1 energy level of the ligand and the excited state of Eu 3+ is very important.…”

Emission Properties of Eu(III) Complexes Containing Arsine and Phosphine Ligands with Annulated Structures

“…In the mechanism of Eu 3+ -center emission through photosensitized energy transfer, ISC and structural relaxation are included as non-radiative processes. In addition, non-radiative deactivation through singlet oxygen ( 1 O 2 ) generation and ligand-to-metal charge transfer (LMCT) decreases Φ tot . , It is necessary to examine these non-radiative processes to understand the difference in η sens between Eu 3+ complexes.…”

“…These meant that the large lowering of the T 1 energy level for 3-b and 4-b was induced to the intramolecular interaction between two π-conjugated planes of antenna ligands ( 3 and 4 ). The singlet oxygen ( 1 O 2 ) generation could quench the T 1 of the antenna ligands generated by the back-energy transfer from the Eu 3+ -center to the antenna ligands . Thus, we measured the emission properties of the Eu 3+ complexes under air and argon atmospheres to investigate the effect of air on the emission properties (Table S17).…”

Bright red emission with high color purity from Eu(iii) complexes with π-conjugated polycyclic aromatic ligands and their sensing applications

“…7c ). 53 The small energy gap between excited T 1 and emitting levels ( 5 D 0 ) is 1650 cm −1 for the effective back energy transfer is a key point for the lifetime-based oxygen sensor using the excited state equilibrium.…”