TY - JOUR A1 - Potopnyk, M. A1 - Mech-Piskorz, J. A1 - Angulo, G. A1 - Ceborska, M. A1 - Luboradzki, R. A1 - Andresen, Elina A1 - Gajek, A. A1 - Wisniewska, A. A1 - Resch-Genger, Ute T1 - Aggregation/Crystallization-Induced Emission in Naphthyridine-Based Carbazolyl-Modified Donor-Acceptor Boron Dyes Tunable by Fluorine Atoms N2 - Four donor-acceptor boron difluoride complexes based on the carbazole electron donor and the [1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridine acceptor were designed, synthesized, and systematically spectroscopically investigated in solutions, in the solid states, and dye-doped polymer films. The dyes exhibit an intense blue to red solid-state emission with photoluminescence quantum yields of up to 56% in pure dye samples and 86% in poly(methyl methacrylate) films. All boron complexes show aggregation-induced emission and reversible mechanofluorochromism. The optical properties of these dyes and their solid state luminescence can be tuned by substitution pattern, i.e., the substituents at the naphthyridine unit. Exchange of CH3- for CF3-groups does not only increase the intramolecular charge transfer character, but also provides a crystallization-induced emission enhancement. KW - Spectroscopy KW - Dye KW - Luminescence KW - Sensor KW - Fluorescence KW - Quantum yield KW - Lifetime KW - Quality assurance KW - Synthesis PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-597426 DO - https://doi.org/10.1002/chem.202400004 SN - 0947-6539 SP - 1 EP - 12 PB - Wiley VHC-Verlag AN - OPUS4-59742 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schlögl, Johanna A1 - Krappe, Alexander R. A1 - Fürstenwerth, Paul C. A1 - Brosius, Amelie L. A1 - Fasting, Carlo A1 - Hoffmann, Kurt F. A1 - Resch-Genger, Ute A1 - Eigler, Siegfried A1 - Steinhauer, Simon A1 - Riedel, Sebastian T1 - Luminescent Perhalofluoro Trityl Radicals N2 - In this proof-of-concept study, we show that polyfluorinated trityl radicals with the, to this date, highest fluorination grade can be accessed in quantitative yields in a straightforward manner starting from the perfluorinated trityl cation. The trityl skeleton is functionalized with trimethylsilyl halides to yield perhalofluoro trityl cations, which are subsequently reduced using commercial zinc powder. In this way, we prepare three perhalofluoro trityl radicals and analyze the impact of the fluorine ligands on their electro-optical properties, revealing some interesting trends. In comparison to literature-known polychlorinated trityl radicals, the new polyfluorinated derivatives exhibit substantially higher fluorescence quantum yields, longer luminescence lifetimes, and an expanded emission range that extends into the yellow spectral region. They further display enhanced photostability under light irradiation. In radical-stained polystyrene nanoparticles, an additional broad emission band in the red−NIR wavelength region is observed, which is attributed to excimer formation. Finally, the stability of the new radicals is investigated under ambient conditions, showing the slow conversion with atmospheric oxygen yielding the respective peroxides, which are characterized by single-crystal X-ray diffraction. All in all, our study extends the present scope of luminescent trityl radicals, as the functionalization of the perfluorinated cationic precursor unlocks the path toward a vast variety of polyfluorinated trityl radicals. KW - Dye KW - Fluorescence KW - Radical KW - Synthesis KW - Mechanism KW - Signal enhancement KW - Nano KW - Particle KW - Characterization KW - Quantum yield KW - Photophysics KW - Lifetime KW - Polarity KW - Polymer KW - Solvatchromism KW - Excimer PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-647973 DO - https://doi.org/10.1021/jacs.5c16418 SN - 0002-7863 VL - 147 IS - 46 SP - 1 EP - 8 PB - American Chemical Society (ACS) AN - OPUS4-64797 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Osiopova, Viktoriia A1 - Tavernaro, Isabella A1 - Ge, L. A1 - Kitzmann, W. R. A1 - Heinze, K. A1 - Reithofer, M. R. A1 - Resch-Genger, Ute T1 - Complete protection of NIR-luminescent molecular rubies from oxygen quenching in air by L-arginine-mediated silica nanoparticles N2 - The application of emerging luminophores such as near-infrared (NIR) emissive complexes based on earth-abundant chromium as central ion and triplet-triplet annihilation upconversion (TTA-UC) systems in air as optical reporters for bioimaging or photonic materials for energy conversion requires simple and efficient strategies for their complete protection from uminescence quenching by oxygen. Therefore, we explored the influence of sol–gel synthesis routes on the oxygen protection efficiency of the resulting core and core/shell silica nanoparticles (SiO2 NPs), utilizing the molecular ruby-type luminophores CrPF6 ([Cr(ddpd)2](PF6)3; ddpd = N,N'-dimethyl-N,N'-dipyridin-2-ylpyridin-2,6-diamine) and CrBF4 ([Cr(ddpd)2](BF4)3) with their oxygendependent, but polarity-, proticity-, viscosity-, and concentration-independent luminescence as optical probes for oxygen permeability. The sol–gel chemistry routes we assessed include the classical Stöber method and the underexplored Larginine approach, which relies on the controlled hydrolysis of tetraethoxysilane (TEOS) in a biphasic cyclohexane/water system with the catalyst L-arginine. As demonstrated by luminescence measurements of air- and argon-saturated dispersions of CrPF6- and CrBF4-stained SiO2 NPs of different size and particle architecture, utilizing the luminescence decay kinetics of argon-saturated solutions of CrPF6 and CrBF4 in acetonitrile (ACN) as benchmarks, only SiO2 NPs or shells synthesized by the L-arginine approach provided complete oxygen protection of the CrIII complexes under ambient conditions. We ascribe the different oxygen shielding efficiencies of the silica networks explored to differences in density and surface chemistry of the resulting nanomaterials and coatings, leading to different oxygen permeabilities. Our Larginine based silica encapsulation strategy can open the door for the efficient usage of oxygen-sensitive luminophores and TTA-UC systems as optical reporters and spectral shifters in air in the future. KW - Quality assurance KW - Fluorescence KW - Quantification KW - Advanced materials KW - Nano KW - Quantum yield KW - NIR KW - Characterization KW - Electron microscopy KW - Silica KW - Synthesis KW - Oxygen sensing KW - Surface KW - Doping KW - Lifetime KW - Cr(III) complex KW - Shielding KW - Sensing PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-638271 DO - https://doi.org/10.26599/NR.2025.94907241 SN - 1998-0000 VL - 18 IS - 3 SP - 1 EP - 13 PB - SciOpen AN - OPUS4-63827 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Soyka, J. P. A1 - Witte, J. F. A1 - Wiesner, A. A1 - Krappe, A. R. A1 - Wehner, D. A1 - Alnicola, N. A1 - Paulus, B. A1 - Resch-Genger, Ute A1 - Eigler, S. T1 - [3]Radialene Fluorophores with pH-Switchable Emission and Stable Absorption Maxima N2 - The first push–pull quino [3]radialene fluorescent dye is reported. Herein, the novel bis(dicyanomethylene)-[3]radialene electron acceptor is connected to a benzimidazole donor. With protonation, a substantial redshift of fluorescence wavelength is observed, while the absorption maximum remains stable. This process is accompanied with an increased fluorescence quantum yield to about 70%. Further, the findings are explained by a combined experimental and theoretical approach, and it is found that vibronic coupling plays a crucial role. This study highlights the yet unexplored potential of [3]radialene-based motifs for the design of environment-responsive fluorophores. KW - DADQ KW - Nanographene KW - fluorescence KW - Nano KW - Particle KW - Synthesis KW - Characterization KW - Advanced material KW - Quantum yield KW - Photophysic KW - pH KW - Probe KW - Sensor KW - Lifetime KW - Polarity PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-642147 DO - https://doi.org/10.1002/ejoc.202500669 SN - 1099-0690 SP - 1 EP - 6 PB - Wiley-VCH CY - Weinheim AN - OPUS4-64214 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hartmann, Yannic A1 - El Abbassi, Abdelouahad A1 - Mayer, Bernhard A1 - Resch-Genger, Ute A1 - Müller, Thomas J. J. T1 - Ester‐Aroyl‐S,N‐Ketene Acetals with Solid‐State Luminescence: AIEgens from Sequential Three‐Component Desymmetrization N2 - AbstractDi(hetero)aroyl dichlorides are desymmetrized upon sequential reaction with alcohols and 2‐methyl N‐benzyl thiazolium salts within the course of a one‐pot three‐component reaction yielding ester‐substituted aroyl‐S,N‐ketene acetals under mild conditions in good yields. A prerequisite for the concise one‐pot process is the different nucleophilicity of the alcohols and in situ generated S,N‐ketene acetals. The resulting compounds are merocyanines with dominant charge‐transfer absorption bands which are fluorescent in the solid state, but not in solution. In water/ethanol solvent mixtures of increasing water content, the water‐insoluble dyes display typical aggregation‐induced emission (AIE) characteristics. The water fraction inducing AIE as well as the emission color, and fluorescence quantum yield (Φf) of the aggregated dyes can be controlled by the alcohol part of the ester moiety. Encapsulation into polystyrene nanoparticles can lead to a considerable increase of the fluorescence quantum yield Φf to 30% as shown for a representatively chosen dye revealing the highest Φf of 11% within the dye series in the water/ethanol mixtures and enabling the usage of these dyes as fluorescent reporters in aqueous environments. KW - Dye KW - Fluorescence KW - Aggregation KW - Mechanism KW - Signal enhancement KW - Nano KW - Particle KW - Characterization KW - Quantum yield KW - Photophysics KW - Probe KW - Sensor KW - Lifetime KW - Polarity PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-642400 DO - https://doi.org/10.1002/chem.202502071 SN - 0947-6539 SP - 1 EP - 10 PB - Wiley-VCH CY - Weinheim AN - OPUS4-64240 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reichenauer, F. A1 - Wang, Cui A1 - Förster, C. A1 - Boden, P. A1 - Ugur, N. A1 - Báez-Cruz, R. A1 - Kalmbach, J. A1 - Carrella, L. M. A1 - Rentschler, E. A1 - Ramanan, C. A1 - Niedner-Schatteburg, G. A1 - Gerhards, M. A1 - Seitz, M. A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - Strongly Red-Emissive Molecular Ruby [Cr(bpmp)2]3+ Surpasses [Ru(bpy)3]2+ N2 - 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 spinflip 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(2-pyridylmethyl) pyridine) shifted to higher energy from ca. 780 nm observed for known highly emissive chromium(III) complexes to 709 nm. The photoluminescence quantum yields climb to 20%, and very long excited state lifetimes in the millisecond range are achieved at room temperature in acidic D2O solution. Partial ligand deuteration increases the quantum yield to 25%. The high excited state energy of [Cr(bpmp)2]3+ and its facile reduction to [Cr(bpmp)2]2+ result in a high excited state redox potential. The ligand’s methylene bridge acts as a Brønsted acid quenching the luminescence at high pH. Combined with a pH-insensitive chromium(III) emitter, ratiometric optical pH sensing is achieved with single wavelength excitation. The photophysical and Ground state properties (quantum yield, lifetime, redox potential, and acid/base) of this spin-flip complex incorporating an earth-abundant metal surpass those of the classical precious metal [Ru(α-diimine)3]2+ charge transfer complexes, which are commonly employed in optical sensing and photo(redox) catalysis, underlining the bright future of these molecular ruby analogues. KW - Fluorescence KW - Optical probe KW - Sensor KW - PH KW - Quantum yield KW - Quality assurance KW - Complex KW - Cr(III) KW - Lifetime KW - Ligand KW - Theory PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-530548 DO - https://doi.org/10.1021/jacs.1c05971 VL - 143 IS - 30 SP - 11843 EP - 11855 PB - ACS Publications AN - OPUS4-53054 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wang, Cui A1 - Kitzmann, W.R. A1 - Weigert, Florian A1 - Förster, Ch. A1 - Wang, X. A1 - Heintze, K. A1 - Resch-Genger, Ute T1 - Matrix Effects on Photoluminescence and Oxygen Sensitivity of a Molecular Ruby N2 - The molecular ruby analogue [Cr(ddpd)2]3+ (ddpd=N,N’-dimethyl-N,N’-dipyridine-2-ylpyridine-2,6-diamine) exhibits near infrared (NIR) emission with a high photoluminescence (PL) quantum yield ΦPL of 11 % and a lifetime of 898 μs in deaerated water at room temperature. While ligand-based control of the photophysical properties has received much attention, influences of the counter anions and microenvironment are still underexplored. In this study, the luminescence properties of the molecular ruby were systematically examined for the counter anions Cl−, Br−, [BF4]−, [PF6]−, [BPh4]−, and [BArF24]− in acetonitrile (MeCN) solution, in crystals, and embedded into polystyrene nanoparticles (PSNP). Stern-Volmer analyses of the oxygen quenching studies in the intensity and lifetime domain showed the highest oxygen sensitivity of the complexes with the counter anions of [BF4]− and [BArF24]−, which also revealed the longest luminescence lifetimes. Embedding [Cr(ddpd)2][PF6]3 in PSNPs and shielding with poly(vinyl alcohol) yields a strongly NIR-emissive oxygen-insensitive material with a record ΦPL of 15.2 % under ambient conditions. KW - Fluorescence KW - Sensor KW - Oxygen KW - Quantum yield KW - Quality assurance KW - Complex KW - Cr(III) KW - Lifetime KW - Ligand KW - Solid state KW - X-Ray analysis KW - Structure-property relationship KW - Nano KW - Polymer KW - Particle PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-546057 DO - https://doi.org/10.1002/cptc.202100296 SN - 2367-0932 VL - 6 IS - 6 SP - 1 EP - 9 PB - Wiley-VCH CY - Weinheim AN - OPUS4-54605 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sun, C. A1 - Schäferling, Michael A1 - Resch-Genger, Ute A1 - Gradzielski, M. T1 - Solvothermal Synthesis of Lanthanide-doped NaYF4 Upconversion N2 - Lanthanide-doped NaYF4 upconversion nano- and microcrystals were synthesized via a facile solvothermal approach. Thereby, the influence of volume ratios of ethylene glycol (EG)/H2O, molar ratios of NH4F/RE3+ (RE3+ represents the total amount of Y3+ and rare-earth dopant ions), Gd3+ ion contents, types of activator dopant ions, and different organic co-solvents on the crystal phase, size, and morphology of the resulting particles were studied systematically. A possible formation mechanism for the growth of crystals of different morphology is discussed. Our results show that the transition from the α- to the β-phase mainly depends on the volume ratio of EG/H2O and the molar ratio of NH4F/RE3+, while the morphology and size could be controlled by the type of organic co-solvent and Gd3+ dopant ions. Furthermore, the reaction time has to be long enough to convert α-NaYF4 into β-NaYF4 during the growth process to optimize the upconversion luminescence. The formation of larger β-NaYF4 crystals, which possess a higher upconversion luminescence than smaller particles, proceeds via intermediates of smaller crystals of cubic structure. In summary, our synthetic approach presents a facile route to tailor the size, Crystal phase, morphology, and luminescence features of upconversion materials. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Photoluminescence KW - Lanthanide KW - Quantum yield KW - Photophysics KW - Lifetime KW - Surface chemistry KW - Single particle KW - Brightness KW - NIR KW - Synthesis PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-520307 DO - https://doi.org/10.1002/cnma.202000564 VL - 7 IS - 2 SP - 174 EP - 183 PB - Wiley AN - OPUS4-52030 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bastos, V. A1 - Oskoei, P. A1 - Andresen, Elina A1 - Saleh, Maysoon I. A1 - Rühle, Bastian A1 - Resch-Genger, Ute A1 - Oliveira, H. T1 - Stability, dissolution, and cytotoxicity of NaYF4‑upconversion nanoparticles with different coatings N2 - Upconversion nanoparticles (UCNPs) have attracted considerable attention owing to their unique photophysical properties. Their utilization in biomedical applications depends on the understanding of their transformations under physiological conditions and their potential toxicity. In this study, NaYF4: Yb,Er UCNPs, widely used for luminescence and photophysical studies, were modified with a set of four different coordinatively bound surface ligands, i.e., citrate, alendronate (AA), ethylendiamine tetra(methylene phosphonate) (EDTMP), and poly(maleic anhydride-alt-1-octadecene) (PMAO), as well as silica coatings with two different thicknesses. Subsequently, the aging-induced release of fluoride ions in water and cell culture media and their cytotoxic profile to human keratinocytes were assessed in parallel to the cytotoxic evaluation of the ligands, sodium fluoride and the lanthanide ions. The cytotoxicity studies of UCNPs with different surface modifications demonstrated the good biocompatibility of EDTMP-UCNPs and PMAO-UCNPs, which is in line with the low amount of fluoride ions released from these samples. An efficient prevention of UCNP dissolution and release of cytotoxic ions, as well as low cytotoxicity was also observed for UCNPs with a sufficiently thick silica shell. Overall, our results provide new insights into the understanding of the contribution of surface chemistry to the stability, dissolution behavior, and cytotoxicity of UCNPs. Altogether, the results obtained are highly important for future applications of UCNPs in the life sciences and bioimaging studies. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Excitation power density KW - Surface chemistry KW - Coating PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-544681 DO - https://doi.org/10.1038/s41598-022-07630-5 SN - 2045-2322 VL - 12 SP - 1 EP - 13 PB - Springer Nature CY - London AN - OPUS4-54468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Witte, F. A1 - Rietsch, P. A1 - Nirmalananthan-Budau, Nithiya A1 - Weigert, Florian A1 - Götze, J. P. A1 - Resch-Genger, Ute A1 - Eigler, S. A1 - Paulus, B. T1 - Aggregation-induced emission leading to two distinct emissive species in the solid-state structure of high-dipole organic chromophores N2 - The concept of aggregation-induced emission represents a means to rationalise photoluminescence of usually nonfluorescent excimers in solid-state materials. In this publication, we study the photophysical properties of selected diaminodicyanoquinone (DADQ) derivatives in the solid state using a combined approach of experiment and theory. DADQs are a class of high-dipole organic chromophores promising for applications in non-linear optics and light-harvesting devices. Among the compounds investigated, we find both aggregation-induced emission and aggregation-caused quenching effects rationalised by calculated energy transfer rates. Analysis of fluorescence spectra and lifetime measurements provide the interesting result that (at least) two emissive species seem to contribute to the photophysical properties of DADQs. The main emission peak is notably broadened in the long-wavelength limit and exhibits a blue-shifted shoulder. We employ high-level quantum-chemical methods to validate a molecular approach to a solid-state problem and show that the complex emission features of DADQs can be attributed to a combination of H-type aggregates, monomers, and crystal structure defects. KW - Fluorescence KW - Optical probe KW - Dye KW - Photophysics KW - Theory KW - Quantum yield KW - Mechanism KW - Quantum chemistry KW - Modelling KW - Aggregation KW - Lifetime KW - Single particle KW - Microscopy KW - Solid KW - Crystal PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-531138 DO - https://doi.org/10.1039/d1cp02534a SP - 1 EP - 9 PB - Royal Society of Chemistry AN - OPUS4-53113 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -