N‐Heterocyclic Carbene Ligands: Coordination Chemistry, Reactivity, and Applications Steṕhane Bellemin-Laponnaz*,†,‡ and Samuel Dagorne* †IPCMS (Institut de Physique et Chimie des Mateŕiaux de Strasbourg), CNRS-Universite ́ de Strasbourg, 23 rue du Loess BP 43, F-67034 Strasbourg, France ‡University of Strasbourg Institute for Advanced Study (USIAS), 5 alleé du Geńeŕal Rouvillois, F-67083 Strasbourg, France Institut de Chimie de Strasbourg, CNRS-Universite ́ de Strasbourg, 1 rue Blaise Pascal, F-67000 Strasbourg, France

Group 1 and 2 and Early Transition Metal Complexes Bearing N-Heterocyclic Carbene Ligands: Coordination Chemistry, Reactivity, and Applications

Gates-Cambridge Trust, Winton Programme for the Physics of Sustainability, Freie Universitat Berlin within the Excellence Initiative of the German Research Foundation, Engineering and Physical Sciences Research Council (Grant ID: EP/G060738/1)

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Strongly exchange-coupled triplet pairs in an organic semiconductor

A long-lived triplet excited state of the well-known fluorophore boron dipyrromethene (Bodipy) was observed for the first time via efficient radical-enhanced intersystem crossing (EISC). The triplet state has been obtained in two dyads in which the Bodipy unit is linked to a nitroxide radical, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), with two different length spacers. The photophysical properties were studied with steady-state and time-resolved transient optical spectroscopies and electron spin resonance (cw-ESR and TR-ESR). The fluorescence of Bodipy units is significantly quenched in the dyads, and the spin-polarized TEMPO signals were observed with TR-ESR, generated by a radical triplet pair mechanism. Efficient EISC (ΦT = 80%) was observed for the dyad with a shorter linker, and the triplet state lifetime of the Bodipy chromophore is exceptionally long (62 μs). The EISC takes 250 ps. Poor ISC was observed for the dyad with a longer linker. The efficient ISC and long-lived triplet excited state i...

Radical-Enhanced Intersystem Crossing in New Bodipy Derivatives and Application for Efficient Triplet-Triplet Annihilation Upconversion.

Since azaacenes have electron-deficient backbones and lone-pair electrons on nitrogen centers, they can efficiently detect the target molecules or ions through supramolecular interactions such as anion–π attractions and coordinate bonding. These special features make azaacenes very designable for various sensors, which can be further used in the bio field. In this review, we will summarize the recent progress in the applications of azaacenes in sensing and bio fields. We believe that a rapid development in the research of sensors and bio applications based on azaacenes will be witnessed in the coming years due to their tuneable structures, optical properties and binding abilities.

Azaacenes as active elements for sensing and bio applications

Multidentate N-heterocyclic carbene complexes of the 3d metals: Synthesis, structure, reactivity and catalysis

The synthesis and characterization of a series of manganese nitrides in a tripodal chelating tris(carbene) ligand framework is described. Photolysis of [(TIMENxyl)Mn(N3)]+ (where TIMENxyl = tris[2-(3-xylylimidazol-2-ylidene)ethyl]amine) yields the isolable molecular MnIV nitride, [(TIMENxyl)Mn(N)]+. Spectroscopic and DFT studies indicate that this MnIV d3 complex has a doublet electronic ground state. The metal-centered one-electron oxidation of this MnIV species results in formation of the pentavalent MnV nitride, [(TIMENxyl)Mn(N)]2+. Unlike previously reported, tetragonal MnV nitrides with a d2, nonmagnetic S = 0 ground state, this trigonal bipyramidal complex has a triplet ground state S = 1. One-electron reduction of [(TIMENxyl)Mn(N)]+ produces the neutral, nonmagnetic trivalent [(TIMENxyl)Mn(N)] species with a d4 low-spin, S = 0, ground state.

Manganese nitride complexes in oxidation states III, IV, and V: synthesis and electronic structure.

Understanding the fundamental spin dynamics of photoexcited pentacene derivatives is important in order to maximize their potential for optoelectronic applications. Herein, we report on the synthesis of two pentacene derivatives that are functionalized with the [(2,2,6,6-tetramethylpiperidin-1-yl)oxy] (TEMPO) stable free radical. The presence of TEMPO does not quench the pentacene singlet excited state, but does quench the photoexcited triplet excited state as a function of TEMPO-to-pentacene distance. Time-resolved electron paramagnetic resonance experiments confirm that triplet quenching is accompanied by electron spin polarization transfer from the pentacene excited state to the TEMPO doublet state in the weak coupling regime.

Pentacene appended to a TEMPO stable free radical: the effect of magnetic exchange coupling on photoexcited pentacene.

This work illustrates that manganese(V) nitrido complexes are able to undergo a coordination-induced spin-state change by altering the ligand field from trigonal to tetragonal symmetry. For the reversible coordination of acetonitrile to trigonal [(TIMENxyl)Mn(N)]2+ (1; high-spin S = 1; with TIMENxyl = tris[2-(3-xylylimidazol-2-ylidene)ethyl]-amine), a temperature-dependent coordination-induced spin-state switch is established. Starting from the manganese(V) nitrido complex 1, the synthesis and characterization of a series of octahedral, low-spin (S = 0) manganese(V) nitrido complexes of the type [(TIMENxyl)Mn(N)(L)]n+ (L = MeCN (2), tBuNC (3), CN– (4), NCS– (5), F– (6), μ-{Ag(CN)2}− (7), with n = 1, 2) is described. These represent the first examples of d2 transition metal complexes showing a coordination-induced spin-state change. Spectroscopic, as well as ligand-field theory and density functional theory studies suggest a transition from a 2 + 2 + 1 orbital splitting in the trigonal case to a 1 + 2 + 1 ...

Henning Kropp

Papers

Manganese nitride complexes in oxidation states III, IV, and V: synthesis and electronic structure.

Pentacene appended to a TEMPO stable free radical: the effect of magnetic exchange coupling on photoexcited pentacene.

Coordination-induced spin-state change in manganese(V) complexes: the electronic structure of manganese(V) nitrides.