Different mechanisms for lanthanide(III) sensitization and Yb-field-induced singlemolecule magnet behaviour in a series of pentagonal bipyramidal and octahedral lanthanide complexes with axial phosphine oxide ligands Hadjer, Allia Rodríguez Expósito, Ana Palacios López, María de los Ángeles Jiménez Gallego, Juan Ramón Carneiro Neto, Albano Moura, Renaldo Piccinelli, Fabio Navarro, Amparo Quesada Moreno, María del Mar Colacio Rodríguez, Enrique Financial support from Consejería de Universidad, Investigación e Innovación and ERDF Andalusia Program 2021-2027 (projects C-EXP-140-UGR23 and M.1.B.B TA_000722), Ministerio de Ciencia e Innovación (Project PID2022-138090NB-C21 funded by MCIN/AEI/10.13039/501100011033/FEDER,UE), Junta de Andalucía (FQM-195 and FQM-337), the University of Granada and University of Jaén is grateful acknowledged. The authors acknowledge the Centro de Servicios de Informática y Redes de Comunicaciones (CSIRC) for computational time and facilities. J. R. J. and M. M. Q. M. thank Ministerio de Ciencia e Innovación for their Ramón y Cajal contracts (RYC2022-037255-I and RYC2021-034288-I, respectively, funded both by MCIN/AEI/10.13039/501100011033 and by FSE+ and the European Union “NextGenerationEU”/PRTR”, respectively). RTMJr thanks the Brazilian National Council for Scientific and Technological Development – CNPq, Grant numbers 406483/2023-0, 310988/2023-3, and 404742/2024-6. F.P. acknowledge the Italian Ministry of University and Research for the received funds [PRIN (Progetti di Ricerca di Rilevante Interesse Nazionale, Bando 2022 PNRR) project “TheCURA”, Grant No. P20222TPZS]. Seven mononuclear lanthanide complexes have been isolated and structurally characterised. Four of them are cationic, whose charges are balanced by chloride counteranions, and exhibit pentagonal bipyramidal coordination geometry, whereas the rest of them are neutral and display octahedral coordination environment. In all cases, the coordination sphere of the LnIII ions consists of two di(1-adamantyl)benzylphosphine oxide ligands in axial positions, whereas in the equatorial plane the former contains a chloride and four water molecules and the latter a solvent molecule and three chloride ligands. We report a detailed photophysical investigation, including time-dependent density functional theory (TD-DFT) calculations and intramolecular energy transfer (IET) analysis, which reveals two distinct lanthanide sensitization mechanisms. Compound-specific energy transfer pathways occur through either the S1 or T1 states, as supported by calculated IET rates and resonance with lanthanide acceptor transitions. In addition, dc and ac magnetic properties were measured on complexes 1 and 2, showing that compound 1 behaves as a bi-functional compound, exhibiting field-induced single molecule magnet behaviour together with YbIII-centred NIR luminescence. The relaxation of the magnetization in this pentagonal bipyramidal complex takes place through Raman and direct processes, as supported by ab initio calculations. 2025-06-26T07:13:09Z 2025-06-26T07:13:09Z 2025-04-25 journal article Allia, H., Rodríguez-Expósito, A., Palacios, M. A., Jiménez, J.-R., Carneiro Neto, A. N., Moura, R. T., Jr, Piccinelli, F., Navarro, A., Quesada-Moreno, M. M., & Colacio, E. (2025). Different mechanisms for lanthanide(III) sensitization and Yb-field-induced single-molecule magnet behaviour in a series of pentagonal bipyramidal and octahedral lanthanide complexes with axial phosphine oxide ligands. Physical Chemistry Chemical Physics: PCCP, 27(25), 13266–13279. [DOI: 10.1039/d4cp04862h] https://hdl.handle.net/10481/104860 10.1039/d4cp04862h eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional Royal Society of Chemistry