{"database":"biostudies-literature","file_versions":[],"scores":null,"additional":{"submitter":["Ogawa T"],"funding":["Swiss National Science Foundation","Fonds National de la Recherche Luxembourg","Staatssekretariat f?r Bildung, Forschung und Innovation","Japan Society for the Promotion of Science"],"pagination":["21948-21960"],"full_dataset_link":["https://www.ebi.ac.uk/biostudies/studies/S-EPMC9732883"],"repository":["biostudies-literature"],"omics_type":["Unknown"],"volume":["144(48)"],"pubmed_abstract":["Square-planar Ni<sup>II</sup> complexes and their electronically excited states play key roles in cross-coupling catalysis and could offer new opportunities to complement well-known isoelectronic Pt<sup>II</sup> luminophores. Metal-to-ligand charge transfer (MLCT) excited states and their deactivation pathways are particularly relevant in these contexts. We sought to extend the lifetimes of <sup>3</sup>MLCT states in square-planar Ni<sup>II</sup> complexes by creating coordination environments that seemed particularly well adapted to the 3d<sup>8</sup> valence electron configuration. Using a rigid tridentate chelate ligand, in which a central cyclometalated phenyl unit is flanked by two coordinating N-heterocyclic carbenes, along with a monodentate isocyanide ligand, a very strong ligand field is created. Bulky substituents at the isocyanide backbone furthermore protect the Ni<sup>II</sup> center from nucleophilic attack in the axial directions. UV-Vis transient absorption spectroscopies reveal that upon excitation into <sup>1</sup>MLCT absorption bands and ultrafast intersystem crossing to the <sup>3</sup>MLCT excited state, the latter relaxes onward into a metal-centered triplet state (<sup>3</sup>MC). A torsional motion of the tridentate ligand and a Ni<sup>II</sup>-carbon bond elongation facilitate <sup>3</sup>MLCT relaxation to the <sup>3</sup>MC state. The <sup>3</sup>MLCT lifetime gets longer with increasing ligand field strength and improved steric protection, thereby revealing clear design guidelines for square-planar Ni<sup>II</sup> complexes with enhanced photophysical properties. The longest <sup>3</sup>MLCT lifetime reached in solution at room temperature is 48 ps, which is longer by a factor of 5-10 compared to previously investigated square-planar Ni<sup>II</sup> complexes. Our study contributes to making first-row transition metal complexes with partially filled d-orbitals more amenable to applications in photophysics and photochemistry."],"journal":["Journal of the American Chemical Society"],"pubmed_title":["Molecular Design Principles to Elongate the Metal-to-Ligand Charge Transfer Excited-State Lifetimes of Square-Planar Nickel(II) Complexes."],"pmcid":["PMC9732883"],"funding_grant_id":["200020","2020.0027","202160473","200021_207329","14583224"],"pubmed_authors":["Pfund B","Prescimone A","Ogawa T","Wenger OS","Sinha N"],"additional_accession":[]},"is_claimable":false,"name":"Molecular Design Principles to Elongate the Metal-to-Ligand Charge Transfer Excited-State Lifetimes of Square-Planar Nickel(II) Complexes.","description":"Square-planar Ni<sup>II</sup> complexes and their electronically excited states play key roles in cross-coupling catalysis and could offer new opportunities to complement well-known isoelectronic Pt<sup>II</sup> luminophores. Metal-to-ligand charge transfer (MLCT) excited states and their deactivation pathways are particularly relevant in these contexts. We sought to extend the lifetimes of <sup>3</sup>MLCT states in square-planar Ni<sup>II</sup> complexes by creating coordination environments that seemed particularly well adapted to the 3d<sup>8</sup> valence electron configuration. Using a rigid tridentate chelate ligand, in which a central cyclometalated phenyl unit is flanked by two coordinating N-heterocyclic carbenes, along with a monodentate isocyanide ligand, a very strong ligand field is created. Bulky substituents at the isocyanide backbone furthermore protect the Ni<sup>II</sup> center from nucleophilic attack in the axial directions. UV-Vis transient absorption spectroscopies reveal that upon excitation into <sup>1</sup>MLCT absorption bands and ultrafast intersystem crossing to the <sup>3</sup>MLCT excited state, the latter relaxes onward into a metal-centered triplet state (<sup>3</sup>MC). A torsional motion of the tridentate ligand and a Ni<sup>II</sup>-carbon bond elongation facilitate <sup>3</sup>MLCT relaxation to the <sup>3</sup>MC state. The <sup>3</sup>MLCT lifetime gets longer with increasing ligand field strength and improved steric protection, thereby revealing clear design guidelines for square-planar Ni<sup>II</sup> complexes with enhanced photophysical properties. The longest <sup>3</sup>MLCT lifetime reached in solution at room temperature is 48 ps, which is longer by a factor of 5-10 compared to previously investigated square-planar Ni<sup>II</sup> complexes. Our study contributes to making first-row transition metal complexes with partially filled d-orbitals more amenable to applications in photophysics and photochemistry.","dates":{"release":"2022-01-01T00:00:00Z","publication":"2022 Dec","modification":"2025-04-20T03:34:23.247Z","creation":"2025-04-20T03:34:23.247Z"},"accession":"S-EPMC9732883","cross_references":{"pubmed":["36417782"],"doi":["10.1021/jacs.2c08838"]}}