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- ItemHole injection dynamics from two structurally related Ru-bipyridine complexes into NiOx is determined by the substitution pattern of the ligands(Cambridge : RSC Publ., 2015) Bräutigam, Maximilian; Kübel, Joachim; Schulz, Martin; Vos, Johannes G.; Dietzek, BenjaminThe dyes bis[2,2′-bipyridine][4,4′-dicarboxy-2,2′-bipyridine]ruthenium(II) dihexafluorophosphate, [Ru(bpy)2dcb](PF6)2 (Ru1), and tris[4,4′-bis(ethylcarboxy)-2,2′-bipyridine]ruthenium(II) dihexafluorophosphate, [Ru(dceb)3](PF6)2 (Ru2), attached to NiOx nanoparticle films were investigated using transient absorption and luminescence spectroscopy. In acetonitrile solution the dyes reveal very similar physical and chemical properties, i.e. both dyes exhibit comparable ground state and long-lived, broad excited state absorption. However, when immobilized onto a NiOx surface the photophysical properties of the two dyes differ significantly. For Ru1 luminescence is observed, which decays within 18 ns and ultrafast transient absorption measurements do not show qualitative differences from the photophysics of Ru1 in solution. In contrast to this the luminescence of photoexcited Ru2 on NiOx is efficiently quenched and the ultrafast transient absorption spectra reveal the formation of oxidized nickel centres overlaid by the absorption of the reduced dye Ru2 with a characteristic time-constant of 18 ps. These findings are attributed to the different localization of the initially photoexcited state in Ru1 and Ru2. Due to the inductive effect (−I) of the carboxylic groups, the lowest energy excited state in Ru1 is localized on the dicarboxy-bipyridine ligand, which is bound to the NiOx surface. In Ru2, on the other hand, the initially populated excited state is localized on the ester-substituted ligands, which are not bound to the semiconductor surface. Hence, the excess charge density that is abstracted from the Ru-ion in the metal-to-ligand charge-transfer transition is shifted away from the NiOx surface, which ultimately facilitates hole transfer into the semiconductor.
- ItemThe fate of O2 in photocatalytic CO2 reduction on TiO2 under conditions of highest purity(Cambridge : RSC Publ., 2019) Dilla, Martin; Jakubowski, Alina; Ristig, Simon; Strunk, Jennifer; Schlögl, RobertAlthough the photocatalytic reduction of CO2 to CH4 by using H2O as the oxidant presupposes the formation of O2, it is often not included in the product analysis of most of the studies dealing with photocatalytic CO2 reduction or it is reported to be not formed at all. The present study aims to clarify the absence of O2 in the photocatalytic gas phase CO2 reduction on TiO2. By modifying P25-TiO2 with IrOx co-catalysts it was possible to observe photocatalytic water splitting, i.e. the formation of gaseous O2 and H2 in almost stoichiometric amounts, without the use of sacrificial agents, while bare P25-TiO2 showed no activity in H2 and O2 formation under similar reaction conditions. Investigating the effect of improved H2O oxidation properties on the photocatalytic CO2 reduction revealed that the CH4 formation on P25 from CO2 was completely inhibited as long as the H2O splitting reaction proceeded. Furthermore, we found that a certain amount of O2 is consumed under conditions of photocatalytic water oxidation. A quantification showed it to be in the same order of magnitude as the oxygen which is missing as a byproduct from photocatalytic CO2 conversion. A detailed interpretation of the results in the context of the general understanding of the photocatalytic CO2 reduction with H2O on TiO2 allows the hypothesis that P25-TiO2 undergoes a stoichiometric reaction, meaning that the CH4 formation is not based on a true catalytic cycle and runs only as long as TiO2 can consume oxygen.
- ItemSpectroscopic evidence of 'jumping and pecking' of cholinium and H-bond enhanced cation-cation interaction in ionic liquids(Cambridge : RSC Publ., 2015) Knorr, Anne; Fumino, Koichi; Bonsa, Anne-Marie; Ludwig, RalfThe subtle energy-balance between Coulomb-interaction, hydrogen bonding and dispersion forces governs the unique properties of ionic liquids. To measure weak interactions is still a challenge. This is in particular true in the condensed phase wherein a melange of different strong and directional types of interactions is present and cannot be detected separately. For the ionic liquids (2-hydroxyethyl)-trimethylammonium (cholinium) bis(trifluoro-methylsulfonyl)amide and N,N,N-trimethyl-N-propylammonium bis(trifluoromethylsulfonyl)amide which differ only in the 2-hydroxyethyl and the propyl groups of the cations, we could directly observe distinct vibrational signatures of hydrogen bonding between the cation and the anion indicated by ‘jumping and pecking’ motions of cholinium. The assignment could be confirmed by isotopic substitution H/D at the hydroxyl group of cholinium. For the first time we could also find direct spectroscopic evidence for H-bonding between like-charged ions. The repulsive Coulomb interaction between the cations is overcome by cooperative hydrogen bonding between the 2-hydroxyethyl functional groups of cholinium. This H-bond network is reflected in the properties of protic ionic liquids (PILs) such as viscosities and conductivities.
- ItemEnergy transfer and formation of long-lived 3MLCT states in multimetallic complexes with extended highly conjugated bis-terpyridyl ligands(Cambridge : RSC Publ., 2015) Wächtler, Maria; Kübel, Joachim; Barthelmes, Kevin; Winter, Andreas; Schmiedel, Alexander; Pascher, Torbjörn; Lambert, Christoph; Schubert, Ulrich S.; Dietzek, BenjaminMultimetallic complexes with extended and highly conjugated bis-2,2′:6′,2′′-terpyridyl bridging ligands, which present building blocks for coordination polymers, are investigated with respect to their ability to act as light-harvesting antennae. The investigated species combine Ru(II)- with Os(II)- and Fe(II)-terpyridyl chromophores, the latter acting as energy sinks. Due to the extended conjugated system the ligands are able to prolong the lifetime of the 3MLCT states compared to unsubstituted terpyridyl species by delocalization and energetic stabilization of the 3MLCT states. This concept is applied for the first time to Fe(II) terpyridyl species and results in an exceptionally long lifetime of 23 ps for the Fe(II) 3MLCT state. While partial energy (>80%) transfer is observed between the Ru(II) and Fe(II) centers with a time-constant of 15 ps, excitation energy is transferred completely from the Ru(II) to the Os(II) center within the first 200 fs after excitation.
- ItemNon-touching plasma–liquid interaction – where is aqueous nitric oxide generated?(Cambridge : RSC Publ., 2018) Jablonowski, Helena; Schmidt-Bleker, Ansgar; Weltmann, Klaus-Dieter; von Woedtke, Thomas; Wende, KristianMass transport through graphene is receiving increasing attention due to the potential for molecular sieving. Experimental studies are mostly limited to the translocation of protons, ions, and water molecules, and results for larger molecules through graphene are rare. Here, we perform controlled radical polymerization with surface-anchored self-assembled initiator monolayer in a monomer solution with single-layer graphene separating the initiator from the monomer. We demonstrate that neutral monomers are able to pass through the graphene (via native defects) and increase the graphene defects ratio (Raman ID/IG) from ca. 0.09 to 0.22. The translocations of anionic and cationic monomers through graphene are significantly slower due to chemical interactions of monomers with the graphene defects. Interestingly, if micropatterned initiator-monolayers are used, the translocations of anionic monomers apparently cut the graphene sheet into congruent microscopic structures. The varied interactions between monomers and graphene defects are further investigated by quantum molecular dynamics simulations.
- ItemTowards on-site testing of Phytophthora species(Cambridge : RSC Publ., 2014) Schwenkbier, Lydia; Pollok, Sibyll; König, Stephan; Urban, Matthias; Werres, Sabine; Cialla-May, Dana; Weber, Karina; Popp, JürgenRapid detection and accurate identification of plant pathogens in the field is an ongoing challenge. In this study, we report for the first time on the development of a helicase-dependent isothermal amplification (HDA) in combination with on-chip hybridization for the detection of selected Phytophthora species. The HDA approach allows efficient amplification of the yeast GTP-binding protein (Ypt1) target gene region at one constant temperature in a miniaturized heating device. The assay's specificity was determined by on-chip DNA hybridization and subsequent silver nanoparticle deposition. The silver deposits serve as stable endpoint signals that enable the visual as well as the electrical readout. Our promising results point to the direction of a near future on-site application of the combined techniques for a reliable detection of Phytophthora species.
- ItemCopolymerization of zinc-activated isoindigo- and naphthalene-diimide based monomers: an efficient route to low bandgap π-conjugated random copolymers with tunable properties(Cambridge : RSC Publ., 2016) Karpov, Yevhen; Maiti, Jatindranath; Tkachov, Roman; Beryozkina, Tetyana; Bakulev, Vasiliy; Liu, Wei; Komber, Hartmut; Lappan, Uwe; Al-Hussein, Mahmoud; Stamm, Manfred; Voit, Brigitte; Kiriy, AntonThe present work aims at the extension of the scope of a recently discovered polycondensation of AB-type anion-radical monomers. To this end, we investigate the polymerization of isoindigo-based monomer and its copolymerization with the naphthalenediimide-based monomer. Although polycondensations of parent naphthalenediimide- and perylenediimide-based monomers involve chain-growth mechanism, we found that the corresponding isoindigo-based monomer polymerizes in a step-growth manner under the same reaction conditions. In contrast to Stille, Suzuki and direct arylation polycondensations which require prolonged stirring at high temperatures, the polymerization approach we employed in this study proceeds fast at room temperature. It was found that near statistical copolymerization of isoindigo-based anion-radical monomers with corresponding naphtalenediimide-based monomers proceeds smoothly resulting in a library of copolymers with varying composition and properties depending on the ratio of the monomers.
- ItemPolyethenetetrathiolate or polytetrathiooxalate? Improved synthesis, a comparative analysis of a prominent thermoelectric polymer and implications to the charge transport mechanism(Cambridge : RSC Publ., 2018) Tkachov, Roman; Stepien, Lukas; Grafe, Robert; Guskova, Olga; Kiriy, Anton; Simon, Frank; Reith, Heiko; Nielsch, Kornelius; Schierning, Gabi; Kasinathan, Deepa; Leyens, Christoph1,1,2,2-Ethenetetrathiolate (ett4-) coordination polymers, such as poly[Kx(Ni-ett)], have been known for decades for their excellent thermoelectric properties. However in reality, ett4- is neither a "true" comonomer which participates in the polymerization, nor represents a "true" repeat unit of the target polymer. Indeed, poly[K2(Ni-ett)], which is formally the product of Ni-induced polymerization of ett4-, has a poor conductivity and needs to be oxidized to show attractive thermoelectric characteristics. The polymerization and oxidation processes are poorly controllable which causes irreproducibility of the polymer properties. To improve the synthesis reproducibility, we studied polymerization of potassium tetrathiooxalate (K2tto), the convenient synthesis of which was developed in our recent work. Because K2tto is the "true monomer", and not its precursor, a high quality product is reproducibly formed simply by mixing K2tto with NiCl2 at room temperature. The procedure does not require additional components (bases), or special conditions (prolonged heating), which are usually needed for the preparation of this polymer from the monomer precursor 1,3,4,6-tetrathiapentalene-2,5-dione (TPD). Furthermore, as tto2- is formally the product of two-electron oxidation of ett4-, the poorly controllable oxidation process is avoided and poly[Ni-tto] almost free from K is directly formed upon the complexation of Ni2+ and tto2-. Thus-obtained poly[Ni-tto] possesses conductivity in the range of 27-47 S cm-1 and a Seebeck coefficient in the range of -38 to -55 μV K-1, which are superior thermoelectric properties compared to poly[Kx(Ni-ett)] samples obtained by the previously reported methods. Redox and structural properties of poly[Ni-tto] were compared with those of poly[Kx(Ni-ett)] obtained by the reported methods. Furthermore, DFT calculations were performed to shed more light on generally promising properties of this class of materials. Particularly, possible packing models have been predicted for polymers, and the molecular dynamics simulations have been used to simulate the molecular arrangements under ambient conditions.
- ItemOn the impact of competing intra- and intermolecular triplet-state quenching on photobleaching and photoswitching kinetics of organic fluorophores(Cambridge : RSC Publ., 2019) Smit, Jochem H.; van der Velde, Jasper H. M.; Huang, Jingyi; Trauschke, Vanessa; Henrikus, Sarah S.; Chen, Si; Eleftheriadis, Nikolaos; Warszawik, Eliza M.; Herrmann, Andreas; Cordes, ThorbenWhile buffer cocktails remain the most commonly used method for photostabilization and photoswitching of fluorescent markers, intramolecular triplet-state quenchers emerge as an alternative strategy to impart fluorophores with ‘self-healing’ or even functional properties such as photoswitching. In this contribution, we evaluated combinations of both approaches and show that inter- and intramolecular triplet-state quenching processes compete with each other. We find that although the rate of triplet-state quenching is additive, the photostability is limited by the faster pathway. Often intramolecular processes dominate the photophysical situation for combinations of covalently-linked and solution-based photostabilizers and photoswitching agents. Furthermore we show that intramolecular photostabilizers can protect fluorophores from reversible off-switching events caused by solution-additives, which was previously misinterpreted as photobleaching. Our studies also provide practical guidance for usage of photostabilizer–dye conjugates for STORM-type super-resolution microscopy permitting the exploitation of their improved photophysics for increased spatio-temporal resolution. Finally, we provide evidence that the biochemical environment, e.g., proximity of aromatic amino-acids such as tryptophan, reduces the photostabilization efficiency of commonly used buffer cocktails. Not only have our results important implications for a deeper mechanistic understanding of self-healing dyes, but they will provide a general framework to select label positions for optimal and reproducible photostability or photoswitching kinetics in different biochemical environments.
- ItemEndohedral metal-nitride cluster ordering in metallofullerene-NiII(OEP) complexes and crystals : A theoretical study(Cambridge : RSC Publ., 2019) Dubrovin, Vasilii; Gan, Li-Hua; Büchner, Bernd; Popov, Alexey A.; Avdoshenko, Stanislav M.The ordering of endohedral clusterfullerenes Sc3N@C80 and YSc2N@C80 co-crystallized with Ni(OEP) and isolated complexes with Ni(OEP) have been investigated theoretically. Having used multiple orientations of M3N clusters inside the cages with Fibonacci sampling, we describe the effect of intermolecular interactions on the orientation of the endohedral cluster. © the Owner Societies.