Distinct photodynamics of κ-N and κ-C pseudoisomeric iron(ii) complexes

Two closely related FeII complexes with 2,6-bis(1-ethyl-1H-1,2,3-triazol-4yl)pyridine and 2,6-bis(1,2,3-triazol-5-ylidene)pyridine ligands are presented to gain new insights into the photophysics of bis(tridentate) iron(II) complexes. The [Fe(N^N^N)2]2+ pseudoisomer sensitizes singlet oxygen through a MC state with nanosecond lifetime after MLCT excitation, while the bis(tridentate) [Fe(C^N^C)2]2+ pseudoisomer possesses a similar 3MLCT lifetime as the tris(bidentate) [Fe(C^C)2(N^N)]2+ complexes with four mesoionic carbenes. Financial support from the Deutsche Forschungsge-meinschaft [DFG, Priority Program SPP 2102] "Light-controlled reactivity of metal complexes" (BA 4467/7-1, LO 714/11-1, …

Deuterated Molecular Ruby with Record Luminescence Quantum Yield

The recently reported luminescent chromium(III) complex 13+ ([Cr(ddpd)2]3+; ddpd=N,N’-dimethyl-N,N’-dipyridine-2-yl-pyridine-2,6-diamine) shows exceptionally strong near-IR emission at 775 nm in water under ambient conditions (F=11%) with a microsecond lifetime as the ligand design in 13+ effectively eliminates non-radiative decay pathways, such as photosubstitution, back-intersystem crossing, and trigonal twists. In the absence of energy acceptors, such as dioxygen, the remaining decay pathways are energy transfer to high energy solvent and ligand oscillators, namely OH and CH stretching vibrations. Selective deuteration of the solvents and the ddpd ligands probes the efficiency of these o…

Titelbild: Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex (Angew. Chem. 50/2019)

Deuterierter molekularer Rubin mit Rekord-Lumineszenzquantenausbeute

Der kurzlich publizierte Chrom(III)-Komplex 13+([Cr(ddpd)2]3+) zeigt in wassriger Losung unter Umgebungsbedingungen eine bemerkenswert starke Emission im nahen Infrarot-Bereich mit einer Emissionswellenlange von 775 nm. Geschicktes Ligandendesign verhindert strahlungslose Desaktivierungsprozesse wie Photosubstitution, Ruck-Intersystem-Crossing und trigonale Verzerrungen und fuhrt damit zu einer Phosphoreszenzlebensdauer im Bereich von Mikrosekunden. In Abwesenheit von Energieakzeptoren wie molekularem Sauerstoff verbleibt nur Energietransfer zu hochenergetischen Oszillatoren der Liganden und Losungsmittelmolekule wie beispielsweise OH- und CH-Streckschwingungen als Desaktivierungspfad. Sele…

A Vanadium(III) Complex with Blue and NIR-II Spin-Flip Luminescence in Solution.

Luminescence from Earth-abundant metal ions in solution at room temperature is a very challenging objective due to the intrinsically weak ligand field splitting of first-row transition metal ions, which leads to efficient nonradiative deactivation via metal-centered states. Only a handful of 3d

Strongly Red-Emissive Molecular Ruby [Cr(bpmp)2]3+ Surpasses [Ru(bpy)3]2+

Gaining chemical control over the thermodynamics and kinetics of photoexcited states is paramount to an efficient and sustainable utilization of photoactive transition metal complexes in a plethora of technologies. In contrast to energies of charge transfer states described by spatially separated orbitals, the energies of spin-flip states cannot straightforwardly be predicted as Pauli repulsion and the nephelauxetic effect play key roles. Guided by multireference quantum chemical calculations, we report a novel highly luminescent spin-flip emitter with a quantum chemically predicted blue-shifted luminescence. The spin-flip emission band of the chromium complex [Cr(bpmp)2]3+ (bpmp = 2,6-bis(…

Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex

Abstract Photoactive metal complexes employing Earth‐abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non‐innocence to tune the luminescence and photochemistry of the excited state of the [CrN6] chromophore [Cr(tpe)2]3+ with close to octahedral symmetry (tpe=1,1,1‐tris(pyrid‐2‐yl)ethane). [Cr(tpe)2]3+ exhibits the longest luminescence lifetime (τ=4500 μs) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Φ=8.2 % at room temperature in fluid solution. Furthermore, the tpe ligands in [Cr(tpe)2]3+ are redox non‐innocent, …

Ultrafast and long-time excited state kinetics of an NIR-emissive vanadium(iii) complex I: synthesis, spectroscopy and static quantum chemistry.

In spite of intense, recent research efforts, luminescent transition metal complexes with Earth-abundant metals are still very rare owing to the small ligand field splitting of 3d transition metal complexes and the resulting non-emissive low-energy metal-centered states. Low-energy excited states decay efficiently non-radiatively, so that near-infrared emissive transition metal complexes with 3d transition metals are even more challenging. We report that the heteroleptic pseudo-octahedral d2-vanadium(iii) complex VCl3(ddpd) (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-yl-pyridine-2,6-diamine) shows near-infrared singlet → triplet spin–flip phosphorescence maxima at 1102, 1219 and 1256 nm with a …

Understanding and exploiting long-lived near-infrared emission of a molecular ruby

Coordination chemistry reviews 359, 102 - 111 (2018). doi:10.1016/j.ccr.2018.01.004

Strong circularly polarized luminescence of an octahedral chromium(iii) complex

The chiral spin-flip luminophore [Cr(ddpd)2]3+ can be resolved into enantiopure material by chiral HPLC. The corresponding enantiomers show very high luminescence dissymmetry factors of up to ∣glum ∣≈ 0.093 in circularly polarized luminescence (CPL) measurements for the "ruby-like" phosphorescence transition 2E/2T1 → 4A2 in the near-IR region around λ ≈ 775 nm.

Near-IR to Near-IR Upconversion Luminescence in Molecular Chromium Ytterbium Salts

Abstract Upconversion photoluminescence in hetero‐oligonuclear metal complex architectures featuring organic ligands is an interesting but still rarely observed phenomenon, despite its great potential from a basic research and application perspective. In this context, a new photonic material consisting of molecular chromium(III) and ytterbium(III) complex ions was developed that exhibits excitation‐power density‐dependent cooperative sensitization of the chromium‐centered 2E/2T1 phosphorescence at approximately 775 nm after excitation of the ytterbium band 2F7/2→2F5/2 at approximately 980 nm in the solid state at ambient temperature. The upconversion process is insensitive to atmospheric ox…

NIR‐NIR‐Aufkonvertierung in molekularen Chrom‐Ytterbium‐Salzen

Photonen-Aufkonvertierung in hetero-oligonuklearen, Metallkomplex-Architekturen mit organischen Liganden ist ein interessantes, aber bisher selten beobachtetes Phanomen, trotz des grosen Potentials sowohl aus Sicht der Grundlagenforschung als auch aus der Anwendungsperspektive. Nun wurde ein neues photonisches Material aus molekularen Chrom(III)- und Ytterbium(III)-Komplexionen entwickelt. Dieses zeigt im Festkorper bei Raumtemperatur abhangig von der Anregungsleistungsdichte nach Anregung des 2F7/2! 2F5/2-3berganges des Ytterbiums bei ca. 980 nm eine kooperative Sensibilisierung der Chrom(III)-zentrierten 2E/2T1-Phosphoreszenz bei ca. 775 nm. Der Aufkonvertierungsprozess ist unempfindlich …

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