TY - JOUR

T1 - Photophysics and Excited State Dynamics of Cyclometalated [M(Phbpy)(CN)] (M = Ni, Pd, Pt) Complexes

T2 - A Theoretical and Experimental Study

AU - Eskelinen, Toni

AU - Buss, Stefan

AU - Petrovskii, Stanislav K.

AU - Grachova, Elena V.

AU - Krause, Maren

AU - Kletsch, Lukas

AU - Klein, Axel

AU - Strassert, Cristian A.

AU - Koshevoy, Igor O.

AU - Hirva, Pipsa

N1 - Publisher Copyright: © Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/6/21

Y1 - 2021/6/21

N2 - Cyclometalated complexes [M(Phbpy)(CN)] (HPhbpy = 6-phenyl-2,2′-bipyridine) of the group 10 metals (Ni, Pd, and Pt) bearing a carbanionic -C∧N∧N pincer ligand were synthesized and studied in a combined experimental and computational DFT approach. All three complexes were crystallographically characterized showing closely packed dimers with head-to-tail stacking and short metal-metal contacts in the solid state. The computational models for geometries, excited states, and electronic transitions addressed both monomeric (Ni-mono, Pd-mono, and Pt-mono) and dimeric (Ni-dim, Pd-dim, and Pt-dim) entities. Photophysical properties and excited state dynamics of all title complexes were investigated in solution and in the solid at 298 and 77 K. [Ni(Phbpy)(CN)] and [Pd(Phbpy)(CN)] are virtually nonemissive in solution at 298 K, whereas [Pt(Phbpy)(CN)] shows phosphorescence in CH2Cl2 (DCM) solution (λem = 562 nm) stemming from a mixed 3MLCT/ILCT (metal-to-ligand charge transfer/intraligand charge transfer) state. At 77 K in a glassy frozen DCM:MeOH matrix, [Pd(Phbpy)(CN)] shows a remarkable emission (λem = 571 nm) with a photoluminescence quantum yield reaching almost unity, whereas [Ni(Phbpy)(CN)] is again nonemissive. Calculations on the monomeric models M-mono show that low-lying metal-centered states (MC, i.e., d-d∗ configuration) with dissociative character quench the photoluminescence. In the solid state, the complexes [M(Phbpy)(CN)] show defined photoluminescence bands (λem = 561 nm for Pd and 701 nm for Pt). Calculations on the dimeric models M-dim shows that the axial M···M interactions alter the photophysical properties of Pd-dim and Pt-dim toward MMLCT (metal-metal-to-ligand charge transfer) excited states with Pd-dim showing temperature-dependent emission lifetimes, suggesting thermally activated delayed fluorescence, whereas Pt-dim displayed phosphorescence with excimeric character. The metal-metal interactions were analyzed in detail with the quantum theory of atoms in molecules approach.

AB - Cyclometalated complexes [M(Phbpy)(CN)] (HPhbpy = 6-phenyl-2,2′-bipyridine) of the group 10 metals (Ni, Pd, and Pt) bearing a carbanionic -C∧N∧N pincer ligand were synthesized and studied in a combined experimental and computational DFT approach. All three complexes were crystallographically characterized showing closely packed dimers with head-to-tail stacking and short metal-metal contacts in the solid state. The computational models for geometries, excited states, and electronic transitions addressed both monomeric (Ni-mono, Pd-mono, and Pt-mono) and dimeric (Ni-dim, Pd-dim, and Pt-dim) entities. Photophysical properties and excited state dynamics of all title complexes were investigated in solution and in the solid at 298 and 77 K. [Ni(Phbpy)(CN)] and [Pd(Phbpy)(CN)] are virtually nonemissive in solution at 298 K, whereas [Pt(Phbpy)(CN)] shows phosphorescence in CH2Cl2 (DCM) solution (λem = 562 nm) stemming from a mixed 3MLCT/ILCT (metal-to-ligand charge transfer/intraligand charge transfer) state. At 77 K in a glassy frozen DCM:MeOH matrix, [Pd(Phbpy)(CN)] shows a remarkable emission (λem = 571 nm) with a photoluminescence quantum yield reaching almost unity, whereas [Ni(Phbpy)(CN)] is again nonemissive. Calculations on the monomeric models M-mono show that low-lying metal-centered states (MC, i.e., d-d∗ configuration) with dissociative character quench the photoluminescence. In the solid state, the complexes [M(Phbpy)(CN)] show defined photoluminescence bands (λem = 561 nm for Pd and 701 nm for Pt). Calculations on the dimeric models M-dim shows that the axial M···M interactions alter the photophysical properties of Pd-dim and Pt-dim toward MMLCT (metal-metal-to-ligand charge transfer) excited states with Pd-dim showing temperature-dependent emission lifetimes, suggesting thermally activated delayed fluorescence, whereas Pt-dim displayed phosphorescence with excimeric character. The metal-metal interactions were analyzed in detail with the quantum theory of atoms in molecules approach.

KW - METAL-COMPLEXES

KW - MOLECULES

KW - ENERGIES

KW - SPECTRA

KW - PT(II)

KW - DFT

KW - PHOSPHORESCENCE

KW - LUMINESCENCE

KW - SIMULATION

UR - http://www.scopus.com/inward/record.url?scp=85108536854&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/de39e417-ce4e-3857-a34b-4e5f19dec195/

U2 - 10.1021/acs.inorgchem.1c00680

DO - 10.1021/acs.inorgchem.1c00680

M3 - Article

C2 - 34097403

AN - SCOPUS:85108536854

VL - 60

SP - 8777

EP - 8789

JO - Inorganic Chemistry

JF - Inorganic Chemistry

SN - 0020-1669

IS - 12

ER -