@article{60815, abstract = {{AbstractThe increasing demand for advanced sensing technologies drives the development of chemical sensors using innovative materials. In gas sensing, optical sensors are often used to detect gases such as CO, NOx, and O2. Oxygen sensors typically incorporate dyes into oxygen‐permeable matrices like polymers, silica, or zeolites. Alternatively, semiconductor surface chemistry can enable O2 detection. However, these approaches are often limited by slow response and recovery times and low selectivity, restricting their practical applications. The metal‐organic framework MOF‐76(Eu) and its yttrium‐modified variant, MOF‐76(Eu/Y) are reported to exhibit highly reversible and fast optical responses to varying O2 concentrations. Time‐resolved emission measurements are performed over short (seconds) and long (hours) timescales using N2 and synthetic air mixtures. Cross‐sensitivity to humidity is analyzed. Multichannel scaling photon‐counting experiments confirm quenching at the linker level, as the emission lifetime remains nearly constant. Yttrium significantly improves stability and performance at room temperature. Structural and optical changes induced by yttrium are investigated. Additionally, MIL‐78(Eu), another Eu‐BTC‐based MOF with a different coordination environment, is synthesized. Unlike MOF‐76(Eu), MIL‐78(Eu) exhibits distinct optical properties but lacks a reversible response to O2. These results highlight the potential of MOF‐76‐based materials for high‐performance O2 sensing.}}, author = {{Zhao, Zhenyu and Weinberger, Christian and Steube, Jakob and Bauer, Matthias and Brehm, Martin and Tiemann, Michael}}, issn = {{1616-301X}}, journal = {{Advanced Functional Materials}}, publisher = {{Wiley}}, title = {{{Fast‐Responding O2 Gas Sensor Based on Luminescent Europium Metal‐Organic Frameworks (MOF‐76)}}}, doi = {{10.1002/adfm.202511190}}, year = {{2025}}, } @article{60600, abstract = {{In the search for noble metal free photocatalytic systems, iron is the dream candidate. To increase excited state lifetimes of iron complexes, the multichromophoric approach is promising, combining organic chromophores with photoactive iron complexes, potentially enabling a reservoir effect. We present a series of chromophore-functionalized complexes based on the parental FeIII complex [Fe(ImP)2][PF6] (HImP = 1,1′-(1,3-phenylene)bis(3-methyl-1-imidazole-2-ylidene)). The four organic chromophores benzene, naphthalene, anthracene, and pyrene are attached to the ImP-ligand in para-position to the coordination site to systematically investigate the influence of the steric demand and electronic properties of the chromophore on charge transfer lifetimes as well as photodynamics. A thorough ground state characterization was conducted in addition to investigations of the excited state dynamics by transient absorption spectroscopy and streak camera emission measurements. The conclusions drawn are supported by extensive DFT calculations. The emission coefficients could be significantly improved by the addition of chromophores. After excitation of the complexes with larger chromophores, coplanarization of the backbone and complex motif occurs to stabilize the formal charge. This results in population of a superligand state that exhibits a much faster radiationless relaxation to the ground state compared to the parent complex, hindering a reservoir effect.}}, author = {{Schmitz, Lennart and Argüello Cordero, Miguel A. and Al-Marri, Mohammed J. and Schoch, Roland and Egold, Hans and Neuba, Adam and Steube, Jakob and Bracht, Bastian Johannes and Bokareva, Olga S. and Lochbrunner, Stefan and Bauer, Matthias}}, issn = {{0020-1669}}, journal = {{Inorganic Chemistry}}, keywords = {{Photo}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Chromophore Induced Effects in Iron(III) Complexes}}}, doi = {{10.1021/acs.inorgchem.5c00526}}, year = {{2025}}, } @article{58180, abstract = {{A series of CoIII complexes [Co(RImP)2][PF6], with HMeImP = 1,1′-(1,3-phenylene)bis(3-methyl-1-imidazole-2-ylidene)) and R = Me, Et, iPr, nBu, is presented in this work. The influence of the strong donor ligand on the ground and excited-state photophysical properties was investigated in the context of different alkyl substituents at the imidazole nitrogen. X-ray diffraction revealed no significant alterations of the structures and all differences in the series emerge from the electronic structures. These were probed via cyclic voltammetry and UV–vis spectroscopy, detailing the influence of the different alkyl substituents on the ground-state properties. All complexes are emissive at 77 K from a 3MC state, which exhibits lifetimes in the range of 1–5 ns at room temperature, depending on the alkyl substituent. Therefore, it is clearly shown that even small differences in the electronic structure have a large impact on the details of the excited state landscape. The observed behavior was rationalized by a detailed DFT analysis, which shows that the minimum-energy crossing point to the ground-state is located only slightly above the MC energy: Consequently, nonradiative decay to the ground state at room temperature is enabled, while at 77 K this path is prohibited, leading to low-temperature 3MC emission.}}, author = {{Krishna, Athul and Fritsch, Lorena and Steube, Jakob and Argüello Cordero, Miguel A. and Schoch, Roland and Neuba, Adam and Lochbrunner, Stefan and Bauer, Matthias}}, issn = {{0020-1669}}, journal = {{Inorganic Chemistry}}, keywords = {{Photo}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Low Temperature Emissive Cyclometalated Cobalt(III) Complexes}}}, doi = {{10.1021/acs.inorgchem.4c04479}}, year = {{2025}}, } @article{62816, abstract = {{The increasing demand for advanced sensing technologies drives the development of chemical sensors using innovative materials. In gas sensing, optical sensors are often used to detect gases such as CO, NOx, and O2. Oxygen sensors typically incorporate dyes into oxygen-permeable matrices like polymers, silica, or zeolites. Alternatively, semiconductor surface chemistry can enable O2 detection. However, these approaches are often limited by slow response and recovery times and low selectivity, restricting their practical applications. The metal-organic framework MOF-76(Eu) and its yttrium-modified variant, MOF-76(Eu/Y) are reported to exhibit highly reversible and fast optical responses to varying O2 concentrations. Time-resolved emission measurements are performed over short (seconds) and long (hours) timescales using N2 and synthetic air mixtures. Cross-sensitivity to humidity is analyzed. Multichannel scaling photon-counting experiments confirm quenching at the linker level, as the emission lifetime remains nearly constant. Yttrium significantly improves stability and performance at room temperature. Structural and optical changes induced by yttrium are investigated. Additionally, MIL-78(Eu), another Eu-BTC-based MOF with a different coordination environment, is synthesized. Unlike MOF-76(Eu), MIL-78(Eu) exhibits distinct optical properties but lacks a reversible response to O2. These results highlight the potential of MOF-76-based materials for high-performance O2 sensing.}}, author = {{Zhao, Zhenyu and Weinberger, Christian and Steube, Jakob and Bauer, Matthias and Brehm, Martin and Tiemann, Michael}}, issn = {{1616-301X}}, journal = {{Advanced Functional Materials}}, publisher = {{Wiley}}, title = {{{Fast‐Responding O2 Gas Sensor Based on Luminescent Europium Metal‐Organic Frameworks (MOF‐76)}}}, doi = {{10.1002/adfm.202511190}}, year = {{2025}}, } @article{56075, abstract = {{An isostructural series of FeII, FeIII, and Fe(IV)complexes [Fe(ImP)2]0/+/2+ utilizing the ImP 1,1′-(1,3-phenylene)-bis(3-methyl-1-imidazol-2-ylidene) ligand, combining N-heterocy-clic carbenes and cyclometalating functions, is presented. The strong donor motif stabilizes the high-valent Fe(IV) oxidation state yet keeps the FeII oxidation state accessible from the parent Fe(III)compound. Chemical oxidation of [Fe(ImP)2]+ yields stable [FeIV(ImP)2]2+. In contrast, [FeII(ImP)2]0, obtained by reduction,is highly sensitive toward oxygen. Exhaustive ground state characterization by single-crystal X-ray diffraction, 1H NMR,Mössbauer spectroscopy, temperature-dependent magnetic measurements, a combination of X-ray absorption near edge structureand valence-to-core, as well as core-to-core X-ray emission spectroscopy, complemented by detailed density functional theory (DFT) analysis, reveals that the three complexes[Fe(ImP)2]0/+/2+ can be unequivocally attributed to low-spin d6, d5, and d4 complexes. The excited state landscape of the Fe(II) and Fe(IV) complexes is characterized by short-lived 3MLCT and 3LMCT states, with lifetimes of 5.1 and 1.4 ps, respectively. In the FeII-compound, an energetically low-lying MC state leads to fast deactivation of the MLCT state. The distorted square-pyramidal state, where one carbene is dissociated, can not only relax into the ground state, but also into a singlet dissociated state. Its formation was investigated with time-dependent optical spectroscopy, while insights into its structure were gained by NMR spectroscopy.}}, author = {{Steube, Jakob and Fritsch, Lorena and Kruse, Ayla and Bokareva, Olga S. and Demeshko, Serhiy and Elgabarty, Hossam and Schoch, Roland and Alaraby, Mohammad and Egold, Hans and Bracht, Bastian Johannes and Schmitz, Lennart and Hohloch, Stephan and Kühne, Thomas D. and Meyer, Franc and Kühn, Oliver and Lochbrunner, Stefan and Bauer, Matthias}}, issn = {{0020-1669}}, journal = {{Inorganic Chemistry}}, keywords = {{Photo}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Isostructural Series of a Cyclometalated Iron Complex in Three Oxidation States}}}, doi = {{10.1021/acs.inorgchem.4c02576}}, year = {{2024}}, } @article{46481, abstract = {{AbstractAlthough iron is a dream candidate to substitute noble metals in photoactive complexes, realization of emissive and photoactive iron compounds is demanding due to the fast deactivation of their charge-transfer states. Emissive iron compounds are scarce and dual emission has not been observed before. Here we report the FeIII complex [Fe(ImP)2][PF6] (HImP = 1,1′-(1,3-phenylene)bis(3-methyl-1-imidazol-2-ylidene)), showing a Janus-type dual emission from ligand-to-metal charge transfer (LMCT)- and metal-to-ligand charge transfer (MLCT)-dominated states. This behaviour is achieved by a ligand design that combines four N-heterocyclic carbenes with two cyclometalating aryl units. The low-lying π* levels of the cyclometalating units lead to energetically accessible MLCT states that cannot evolve into LMCT states. With a lifetime of 4.6 ns, the strongly reducing and oxidizing MLCT-dominated state can initiate electron transfer reactions, which could constitute a basis for future applications of iron in photoredox catalysis.}}, author = {{Steube, Jakob and Kruse, Ayla and Bokareva, Olga S. and Reuter, Thomas and Demeshko, Serhiy and Schoch, Roland and Argüello Cordero, Miguel A. and Krishna, Athul and Hohloch, Stephan and Meyer, Franc and Heinze, Katja and Kühn, Oliver and Lochbrunner, Stefan and Bauer, Matthias}}, issn = {{1755-4330}}, journal = {{Nature Chemistry}}, keywords = {{General Chemical Engineering, General Chemistry}}, number = {{4}}, pages = {{468--474}}, publisher = {{Springer Science and Business Media LLC}}, title = {{{Janus-type emission from a cyclometalated iron(iii) complex}}}, doi = {{10.1038/s41557-023-01137-w}}, volume = {{15}}, year = {{2023}}, } @article{46548, abstract = {{The use of iron as a replacement for noble metals in photochemical and photophysical applications is challenging due to the typically fast deactivation of short-lived catalytically active states. Recent success of a cyclometalated iron(III) complex utilizing a bis-tridentate ligand motif inspired the use of phenyl-1H-pyrazole as a bidentate ligand. Five complexes using the tris(1-phenylpyrazolato-N,C2)iron(III) complex scaffold are presented. In addition to the parent complex, four derivatives with functionalization in the meta-position of the phenyl ring are thoroughly investigated by single crystal diffractometry, UV-Vis-spectroscopy, and cyclic voltammetry. Advanced X-ray spectroscopy in the form of X-ray absorption and emission spectroscopy allows unique insights into the electronic structure as well as DFT calculations. The ligand design leads to overlapping MLCT and LMCT absorption bands, and emissive behavior is suppressed by low-lying MC states.}}, author = {{Hirschhausen, Tanja and Fritsch, Lorena and Lux, Franziska and Steube, Jakob and Schoch, Roland and Neuba, Adam and Egold, Hans and Bauer, Matthias}}, issn = {{2304-6740}}, journal = {{Inorganics}}, keywords = {{Photo}}, number = {{7}}, publisher = {{MDPI AG}}, title = {{{Iron(III)-Complexes with N-Phenylpyrazole-Based Ligands}}}, doi = {{10.3390/inorganics11070282}}, volume = {{11}}, year = {{2023}}, } @unpublished{40994, abstract = {{Photoactive compounds are essential for photocatalytic and luminescent applications, such as photoredox catalysis or light emitting diodes. However, the substitution of noble metals, which are almost exclusively used, by base metals remains a major challenge on the way to a more sustainable world.1 Iron is a dream candidate for this ambitious aim.2 But compared to noble metal complexes that show long-lived metal-to-ligand charge-transfer (MLCT) states, realization of emissive and photoactive iron complexes is demanding, due to the fast deactivation of charge transfer states into non-emissive inactive states. No MLCT emission has been observed for monometallic iron complexes before. Consequently, dual emission could also not yet be realized with iron complexes, as it is a very rare property even of noble metal compounds. Here we report the FeIII complex [Fe(ImP)2][PF6] (HImP = 1,1’-(1,3-phenylene)bis(3-methyl-1-imidazol-2-ylidene)), showing Janus-type dual emission by combining LMCT (ligand-to-metal charge transfer) with MLCT luminescence. The respective excited states are characterized by a record lifetime of τMLCT = 4.2 ns, and a moderate τLMCT = 0.2 ns. Only two emissive FeIII compounds are known so far and they show LMCT luminescence only.3,4 The unique properties of the presented complex are caused by the specific ligand design combining four N-heterocyclic carbenes with two cyclometalating groups, using the σ-donor strength of six carbon atoms and the acceptor capabilities of the central phenyl rings. Spectroscopically, doublet manifolds could be identified in the deactivation process, while (TD)DFT analysis revealed the presence of quartets as well. With three key advancements of realizing the first iron complex showing dual luminescence, a MLCT luminescence and a world record MLCT lifetime, the results constitute a basis for future application of iron complexes as white light emitters and new photocatalytic reactions making use of the Janus-type properties of the developed complex.}}, author = {{Bauer, Matthias and Steube, Jakob and Päpcke, Ayla and Bokareva, Olga and Reuter, Thomas and Demeshko, Serhiy and Schoch, Roland and Hohloch, Stephan and Meyer, Franc and Heinze, Katja and Kühn, Oliver and Lochbrunner, Stefan}}, publisher = {{Research Square Platform LLC}}, title = {{{Janus-type dual emission of a Cyclometalated Iron(III) complex}}}, year = {{2020}}, } @article{16312, author = {{Steube, Jakob and Burkhardt, Lukas and Päpcke, Ayla and Moll, Johannes and Zimmer, Peter and Schoch, Roland and Wölper, Christoph and Heinze, Katja and Lochbrunner, Stefan and Bauer, Matthias}}, issn = {{0947-6539}}, journal = {{Chemistry – A European Journal}}, pages = {{11826--11830}}, title = {{{Excited‐State Kinetics of an Air‐Stable Cyclometalated Iron(II) Complex}}}, doi = {{10.1002/chem.201902488}}, year = {{2019}}, } @article{16317, author = {{Zimmer, Peter and Burkhardt, Lukas and Friedrich, Aleksej and Steube, Jakob and Neuba, Adam and Schepper, Rahel and Müller, Patrick and Flörke, Ulrich and Huber, Marina and Lochbrunner, Stefan and Bauer, Matthias}}, issn = {{0020-1669}}, journal = {{Inorganic Chemistry}}, pages = {{360--373}}, title = {{{The Connection between NHC Ligand Count and Photophysical Properties in Fe(II) Photosensitizers: An Experimental Study}}}, doi = {{10.1021/acs.inorgchem.7b02624}}, year = {{2017}}, } @article{16319, author = {{Zimmer, Peter and Müller, Patrick and Burkhardt, Lukas and Schepper, Rahel and Neuba, Adam and Steube, Jakob and Dietrich, Fabian and Flörke, Ulrich and Mangold, Stefan and Gerhards, Markus and Bauer, Matthias}}, issn = {{1434-1948}}, journal = {{European Journal of Inorganic Chemistry}}, pages = {{1504--1509}}, title = {{{N-Heterocyclic Carbene Complexes of Iron as Photosensitizers for Light-Induced Water Reduction}}}, doi = {{10.1002/ejic.201700064}}, year = {{2017}}, }