Universität zu Köln

Kletsch, Lukas ORCID: 0000-0001-9970-6967, Jordan, Rose ORCID: 0000-0003-0764-1639, Koecher, Alicia S., Buss, Stefan, Strassert, Cristian A. and Klein, Axel ORCID: 0000-0003-0093-9619 (2021). Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me(2)dpb)Cl] Obtained from C-H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me(2)dpbH). Molecules, 26 (16). BASEL: MDPI. ISSN 1420-3049

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Abstract

The three complexes [M(Me(2)dpb)Cl] (M = Ni, Pd, Pt) containing the tridentate N,C,N-cyclometalating 3,5-dimethyl-1,5-dipyridyl-phenide ligand (Me(2)dpb(-)) were synthesised using a base-assisted C-H activation method. Oxidation potentials from cyclic voltammetry increased along the series Pt < Ni < Pd from 0.15 to 0.74 V. DFT calculations confirmed the essentially ligand-centred pi*-type character of the lowest unoccupied molecular orbital (LUMO) for all three complexes in agreement with the invariant reduction processes. For the highest occupied molecular orbitals (HOMO), contributions from metal d(yz), phenyl C4, C2, C1, and C6, and Cl p(z) orbitals were found. As expected, the d(z)(2) (HOMO-1 for Ni) is stabilised for the Pd and Pt derivatives, while the antibonding d(x)(-y)(2)(2) orbital is de-stabilised for Pt and Pd compared with Ni. The long-wavelength UV-vis absorption band energies increase along the series Ni < Pt < Pd. The lowest-energy TD-DFT-calculated state for the Ni complex has a pronounced d(z)(2)-type contribution to the overall metal-to-ligand charge transfer (MLCT) character. For Pt and Pd, the d(z)(2) orbital is energetically not available and a strongly mixed Cl-to-pi*/phenyl-to-pi*/M(d(yz))-to-pi* (XLCT/ILCT/MLCT) character is found. The complex [Pd(Me(2)dpb)Cl] showed a structured emission band in a frozen glassy matrix at 77 K, peaking at 468 nm with a quantum yield of almost unity as observed for the previously reported Pt derivative. No emission was observed from the Ni complex at 77 or 298 K. The TD-DFT-calculated states using the TPSSh functional were in excellent agreement with the observed absorption energies and also clearly assessed the nature of the so-called dark, i.e., d-d*, excited configurations to lie low for the Ni complex (>= 3.18 eV), promoting rapid radiationless relaxation. For the Pd(II) and Pt(II) derivatives, the dark states are markedly higher in energy with >= 4.41 eV (Pd) and >= 4.86 eV (Pt), which is in perfect agreement with the similar photophysical behaviour of the two complexes at low temperatures.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Kletsch, Lukas UNSPECIFIED orcid.org/0000-0001-9970-6967 UNSPECIFIED Jordan, Rose UNSPECIFIED orcid.org/0000-0003-0764-1639 UNSPECIFIED Koecher, Alicia S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Buss, Stefan UNSPECIFIED UNSPECIFIED UNSPECIFIED Strassert, Cristian A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Klein, Axel UNSPECIFIED orcid.org/0000-0003-0093-9619 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-572550
DOI:	10.3390/molecules26165051
Journal or Publication Title:	Molecules
Volume:	26
Number:	16
Date:	2021
Publisher:	MDPI
Place of Publication:	BASEL
ISSN:	1420-3049
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language PLATINUM(II) COMPLEXES; PHOTOPHYSICAL PROPERTIES; PALLADIUM(II) COMPLEXES; CATALYTIC-ACTIVITY; CRYSTAL-STRUCTURES; METAL-COMPLEXES; EXCHANGE-ENERGY; PT-II; EMISSION; NI Multiple languages Biochemistry & Molecular Biology; Chemistry, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/57255