A Strongly Luminescent Chromium(III) Complex Acid
The synthesis, structure, reactivity, and photophysical properties of a novel acidic, luminescent chromium(III) complex [Cr(H2 tpda)2 ]3+ (23+ ) bearing the tridentate H2 tpda (2,6-bis(2-pyridylamino)pyridine) ligand are presented. Excitation of 23+ at 442 nm results in strong, long-lived NIR luminescence at 782 nm in water and in acetonitrile. X-ray diffraction analysis and IR spectroscopy reveal hydrogen-bonding interactions of the counter ions to the NH groups of 23+ in the solid state. Deprotonation of the NH groups of 23+ by using a non-nucleophilic Schwesinger base in CH3 CN switches off the luminescence. Re-protonation by using HClO4 restores the emission. In water, the pKa value of …
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…
Cover Feature: A Strongly Luminescent Chromium(III) Complex Acid (Chem. Eur. J. 48/2018)
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…
Green-Light Activation of Push-Pull Ruthenium(II) Complexes.
Abstract Synthesis, characterization, electrochemistry, and photophysics of homo‐ and heteroleptic ruthenium(II) complexes [Ru(cpmp)2]2+ (22+) and [Ru(cpmp)(ddpd)]2+ (32+) bearing the tridentate ligands 6,2’’‐carboxypyridyl‐2,2’‐methylamine‐pyridyl‐pyridine (cpmp) and N,N’‐dimethyl‐N,N’‐dipyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) are reported. The complexes possess one (32+) or two (22+) electron‐deficient dipyridyl ketone fragments as electron‐accepting sites enabling intraligand charge transfer (ILCT), ligand‐to‐ligand charge transfer (LL'CT) and low‐energy metal‐to‐ligand charge transfer (MLCT) absorptions. The latter peak around 544 nm (green light). Complex 22+ shows 3MLCT phosphorescenc…
Three‐in‐One Crystal: The Coordination Diversity of Zinc Polypyridine Complexes
The synthesis, structural and photophysical properties of two novel zinc(II) complexes bearing the tridentate ddpd (N,N' dimethyl N,N' dipyridin 2 ylpyridine 2,6 diamine) ligand are presented. Structural investigations have been carried out by single crystal X-ray diffractometry, NMR spectroscopy and Density Functional Theory calculations, revealing a diverse coordination behavior depending on the counter ion. Spectroscopic (UV-VIS and emission spectroscopy) and theoretical techniques (density functional theory and time dependent DFT calculations) have been employed to explore the photophysical properties of the complexes.
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(…
Luminescent TOP Nanosensors for Simultaneously Measuring Temperature, Oxygen, and pH at a Single Excitation Wavelength
Two nanosensors for simultaneous optical measurements of the bioanalytically and biologically relevant analytes temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nm-sized silica-coated polystyrene nanoparticles (PS-NPs) doped with a near-infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3, CrBPh4) and an inert reference dye (Nile Red, NR or 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin, TFPP) and are covalently labeled with pH-sensitive fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal spectrally distinguishable emission bands, allowing for r…
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, …
Cover Feature: Triplet–Triplet Annihilation Upconversion in a MOF with Acceptor‐Filled Channels (Chem. Eur. J. 5/2020)
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…
Triplet–Triplet Annihilation Upconversion in a MOF with Acceptor‐Filled Channels
Abstract Photon upconversion has enjoyed increased interest in the last years due to its high potential for solar‐energy harvesting and bioimaging. A challenge for triplet–triplet annihilation upconversion (TTA‐UC) processes is to realize these features in solid materials without undesired phase segregation and detrimental dye aggregation. To achieve this, we combine a palladium porphyrin sensitizer and a 9,10‐diphenylanthracene annihilator within a crystalline mesoporous metal–organic framework using an inverted design. In this modular TTA system, the framework walls constitute the fixed sensitizer, while caprylic acid coats the channels providing a solventlike environment for the mobile a…
Cover Feature: Green‐Light Activation of Push–Pull Ruthenium(II) Complexes (Chem. Eur. J. 30/2020)
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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