Leon Geerkens

University of Münster

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Jutta Kösters

University of Münster

Cristian A. Strassert

CeNTech

Stefan Buss

University of Münster

Alexander Hepp

University of Münster

María Victoria Cappellari

University of Münster

Iván Maisuls

University of Münster

Matias Ezequiel Gutierrez Suburu

University of Münster

Lukas Kletsch

University of Cologne

Michael Giese

University of Duisburg-Essen

Jens Voskuhl

University of Duisburg-Essen

Cooperative Institutions

University of Münster

CeNTech

University of Duisburg-Essen

Essen University Hospital

Consejo Nacional de Investigaciones Científicas y Técnicas

University of Cologne

Institute of Organic Chemistry

Institute of Inorganic Chemistry of the Slovak Academy of Sciences

Technische Universität Braunschweig

Fundación Ciencias Exactas y Naturales

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Tuning the Terminal N* and C^ Moieties Toward Tailored Pt(II) Complexes with Thiazole-Based N*N^C Luminophores

Organometallics (2025)

Stefan Buss Leon Geerkens Rose Jordan Lukas Kletsch Alexander Hepp

Thiazole

10.1021/acs.organomet.4c00298

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CCDC 2298210: Experimental Crystal Structure Determination

The Cambridge Structural Database (2023)

Stefan Buss Leon Geerkens María Victoria Cappellari Alexander Hepp Jutta Kösters

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

10.5517/ccdc.csd.cc2h4gty

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On the thermodynamics of aggregation toward phosphorescent metallomesogens: From electronic tuning to supramolecular design

Aggregate (2024)

Matias Ezequiel Gutierrez Suburu Meik Blanke Leon Geerkens Alexander Hepp Iván Maisuls

Abstract Two series with three Pt(II) complexes each ( PtL Ph ‐n , PtL Fpy ‐n ) bearing asymmetric tetradentate ligands as dianionic luminophores with variable alkyl chain lengths were synthesized. Hence, each ligand series is distinguished by one of its cyclometallating rings (phenyl vs. 2,6‐difluoropyrid‐3‐yl). Steady‐state and time‐resolved photoluminescence spectroscopic studies in diluted solutions at room temperature and in glassy matrices at 77 K show that the emissive state is mainly centered on the invariantly electron‐rich cyclometalated side while the second ring regulates the admixture of ligand‐centered and metal‐to‐ligand charge‐transfer character. Hence, the radiative rates can be controlled, as indicated by quantum‐mechanical calculations, which also explain the temperature‐dependent trend in the phosphorescence rate constants. Studies in condensed phases (single‐crystal X‐ray diffractometry, polarized optical microscopy, differential scanning calorimetry, steady‐state and time‐resolved photoluminescence micro(spectro)scopy) showed the development of a smectic A mesophase for the fluorinated species bearing the two longest alkyl chains. Nuclear magnetic resonance‐based studies on the thermodynamics of aggregation in solution confirm the marked enthalpic stabilization of aggregates mediated by the polar 2,6‐difluoropyrid‐3‐yl moiety (and to a lesser extent by dispersive forces between the alkyl chains). On the other hand, the negative entropy of aggregation is dominated by the restriction of degrees of freedom involving the peripheral alkyl moieties upon stacking, which becomes increasingly relevant for longer chains. All these factors control Pt···Pt coupling, a crucial interaction for the design of photofunctional mesogens based on Pt(II) complexes.

Moiety

10.1002/agt2.473

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The Effect of Monodentate Co-Ligands on the Properties of Pt(II) Complexes Bearing a Tridentate C^N*N-Luminophore

Molecules (2023)

Stefan Buss Leon Geerkens María Victoria Cappellari Alexander Hepp Jutta Kösters

In this study, the insertion of different monodentate co-ligands on Pt(II) complexes bearing a monoanionic C^N*N luminophore as a tridentate chelator was achieved beyond the previously reported chlorido- ([PtCl(L)]) and cyanido-decorated ([PtCN(L)]) analogues. To investigate the impact of the auxiliary ligand on the photophysical properties, we introduced a neutral carbonyl-ligand and observed a lower photoluminescence quantum yield (ΦL) than with a cyanido moiety. However, the direct substitution of the chlorido co-ligand by a NO-related derivative was not successful. Interestingly, the attempted reduction of the successfully inserted nitrito-N-ligand in [PtNO2(L)] resulted in the oxidation of the Pt(II)-center to Pt(IV), as demonstrated by X-ray diffractometry. For comparison, the trifluoroacetato Pt(II) and chlorido Pt(IV) complexes ([PtTFA(L)] and [PtCl3(L)], respectively) were also synthesized. The photophysical characterization revealed similar photoluminescence profiles for all complexes, indicating a weak effect of the co-ligand on the excited state; in fact, all complexes display emission from metal-perturbed ligand-centered states (even the Pt(IV) species). Nonetheless, longer excited state lifetimes (τav) suggest a reduced thermally-activated radiationless deactivation via metal-centered states upon exchange of the chlorido units for other monodentate entities, yet without significantly improving the overall ΦL at room temperature. The irreversible oxidation waves (measured via cyclic voltammetry) mostly stem from the Pt(II)-center; the co-ligand-related drop of these potentials correlates with the increasing σ-donating capacities of the ancillary ligand. In summary, an enhanced π-acceptor capacity does not necessarily improve the ΦL and can even impair radiative rates by compromising the perturbative participation of the metal center on the emissive triplet state; in addition, strong σ-donor abilities improve the phosphorescence efficiencies by hampering the thermal population of dissociative electronic configurations related to the participation of antibonding d*-orbitals at the metal center.

Luminophore

Moiety

Quantum yield

10.3390/molecules28237834

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CCDC 2298209: Experimental Crystal Structure Determination

The Cambridge Structural Database (2023)

Stefan Buss Leon Geerkens María Victoria Cappellari Alexander Hepp Jutta Kösters

10.5517/ccdc.csd.cc2h4gsx

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CCDC 2298208: Experimental Crystal Structure Determination

The Cambridge Structural Database (2023)

Stefan Buss Leon Geerkens María Victoria Cappellari Alexander Hepp Jutta Kösters

10.5517/ccdc.csd.cc2h4grw

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CCDC 2298207: Experimental Crystal Structure Determination

The Cambridge Structural Database (2023)

Stefan Buss Leon Geerkens María Victoria Cappellari Alexander Hepp Jutta Kösters

10.5517/ccdc.csd.cc2h4gqv

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Toward Highly Planar d⁸-Configured Metal Complexes with Tunable Phosphorescence, ¹O₂ Photogeneration, and Glass-Forming Abilities

Organometallics (2024)

Stefan Buss Leon Geerkens Iván Maisuls Jutta Kösters Nils Bäumer

The synthesis, characterization, and photophysical properties of 16 d8-configured metal complexes featuring Pt(II) or Pd(II) centers with N*N∧C-coordinated ligands is presented. Key findings include the discovery that distortion of the coordination plane improves solubility, as observed for compounds with a pyridine-N-donor instead of a thiazole unit. In addition, we found that substitution of the chlorido coligand by a monodentate cyanido unit enhances the emitters' performance by decreasing the nonradiative decay rate. The switch from Pt(II) to Pd(II) resulted in weaker ligand field splitting and reduced spin–orbit coupling, leading to longer average lifetimes without luminescence at room temperature. Interestingly, complexes with a cyclometalated thiophenyl moiety exhibited a red-shifted luminescence and dual emission. Finally, we observed that the photoinduced generation of singlet dioxygen (1O2), a highly reactive oxygen species, is critically influenced by the chelated metal centers and by the monodentate coligands, as they control the 1O2 photoproduction quantum yields. These results have significant implications for photocatalysis, optoelectronics, and biomedical applications.

Moiety

10.1021/acs.organomet.3c00540

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Citations (2)