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

Buss, S.; Geerkens, L.; Cappellari ,M. V.; Hepp, A.; Kösters, J.; Strassert, C.A.

Forschungsartikel (Zeitschrift) | Peer reviewed

Zusammenfassung

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.

Details zur Publikation

FachzeitschriftMolecules
Jahrgang / Bandnr. / Volume28
Ausgabe / Heftnr. / Issue23
StatusVeröffentlicht
Veröffentlichungsjahr2023
Sprache, in der die Publikation verfasst istEnglisch
DOI10.3390/molecules28237834
Link zum Volltexthttps://api.elsevier.com/content/abstract/scopus_id/85179370717
Stichwörterco-ligand exchange; photophysics; soluble triplet emitters; structural characterization; synthesis of Pt(II) complexes; time-resolved photoluminescence spectroscopy

Autor*innen der Universität Münster

Hepp, Alexander
Professur für Anorganische Chemie (Prof. Hahn)
Strassert, Cristian
Professur für Coordination Chemistry and Functional Imaging (Prof. Strassert)