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Photophysical Study on the Rigid Pt(II) Complex [Pt(naphen)(Cl)] (Hnaphen = Naphtho[1,2- b ][1,10]Phenanthroline and Derivatives

Affiliation
University of Cologne, Faculty of Mathematics and Natural Sciences, Department of Chemistry, Institute for Inorganic Chemistry, Greinstrasse 6, 50939 Köln, Germany
Krause, Maren;
Affiliation
Westfälische Wilhelms-Universität Münster, Institut für Anorganische und Analytische Chemie, CeNTech, CiMIC, SoN, Heisenbergstr. 11, 48149 Münster, Germany
Maisuls, Iván;
ORCID
0000-0002-0199-8832
Affiliation
Westfälische Wilhelms-Universität Münster, Institut für Anorganische und Analytische Chemie, CeNTech, CiMIC, SoN, Heisenbergstr. 11, 48149 Münster, Germany
Buss, Stefan;
Affiliation
Westfälische Wilhelms-Universität Münster, Institut für Anorganische und Analytische Chemie, CeNTech, CiMIC, SoN, Heisenbergstr. 11, 48149 Münster, Germany
Strassert, Cristian A.;
ORCID
0000-0003-0757-8721
Affiliation
Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstr. 10, 07743 Jena, Germany
Winter, Andreas;
Affiliation
Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstr. 10, 07743 Jena, Germany
Schubert, Ulrich S.;
Affiliation
Institute for Physical Chemistry (IPC), Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany
Nair, Shruthi S.;
Affiliation
Institute for Physical Chemistry (IPC), Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany
Dietzek-Ivanšić, Benjamin;
ORCID
0000-0003-0093-9619
Affiliation
University of Cologne, Faculty of Mathematics and Natural Sciences, Department of Chemistry, Institute for Inorganic Chemistry, Greinstrasse 6, 50939 Köln, Germany
Klein, Axel

The electrochemistry and photophysics of the Pt(II) complexes [Pt(naphen)(X)] (Hnaphen = naphtho[1,2- b ][1,10]phenanthroline, X = Cl or C≡CPh) containing the rigid tridentate C^N^N -coordinating pericyclic naphen ligand was studied alongside the complexes of the tetrahydro-derivative [Pt(thnaphen)(X)] (Hthnaphen = 5,6,8,9-tetrahydro-naphtho[1,2- b ][1,10]phenanthroline) and the N^C^N -coordinated complex [Pt(bdq)(Cl)] (Hbdq = benzo[1,2- h :5,4- h ’]diquinoline. The cyclic voltammetry showed reversible reductions for the C^N^N complexes, with markedly fewer negative potentials (around −1.6 V vs. ferrocene) for the complexes containing the naphen ligand compared with the thnaphen derivatives (around −1.9 V). With irreversible oxidations at around +0.3 V for all of the complexes, the naphen made a difference in the electrochemical gap of about 0.3 eV (1.9 vs. 2.2 eV) compared with thnaphen. The bdq complex was completely different, with an irreversible reduction at around −2 V caused by the N^C^N coordination pattern, which lacked a good electron acceptor such as the phenanthroline unit in the C^N^N ligand naphen. Long-wavelength UV-Vis absorption bands were found around 520 to 530 nm for the C^N^N complexes with the C≡CPh coligand and were red-shifted when compared with the Cl derivatives. The N^C^N -coordinated bdq complex was markedly blue-shifted (493 nm). The steady-state photoluminescence spectra showed poorly structured emission bands peaking at around 630 nm for the two naphen complexes and 570 nm for the thnaphen derivatives. The bdq complex showed a pronounced vibrational structure and an emission maximum at 586 nm. Assuming mixed 3 LC/ 3 MLCT excited states, the vibronic progression for the N^C^N bdq complex indicated a higher LC character than assumed for the C^N^N -coordinated naphen and thnaphen complexes. The blue-shift was a result of the different N^C^N vs. C^N^N coordination. The photoluminescence lifetimes and quantum yields Φ L massively increased from solutions at 298 K (0.06 to 0.24) to glassy frozen matrices at 77 K (0.80 to 0.95). The nanosecond time-resolved study on [Pt(naphen)(Cl)] showed a phosphorescence emission signal originating from the mixed 3 LC/ 3 MLCT with an emission lifetime of around 3 µs.

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