Sven Rau - Academia.edu (original) (raw)
Papers by Sven Rau
We report that the homogeneous light-driven hydrogen evolution reaction (HER) can be significantl... more We report that the homogeneous light-driven hydrogen evolution reaction (HER) can be significantly enhanced by the presence of seemingly innocent ammonium (NH4+) cations. Expermiental studies with different catalysts, photosensitizers and electron donors show this to be a general effect. Preliminary photophysical and mechanistic studies provide initial suggestions regarding the role of ammonium in the HER enhancement.
This work elaborates the effect of dynamic irradiation and enhanced mass transport on light-drive... more This work elaborates the effect of dynamic irradiation and enhanced mass transport on light-driven molecular water oxidation to counteract catalyst deactivation. It highlights the importance of overall reaction design to overcome limiting factors in artificial photosynthesis reactions. Systematic investigation of a homogenous three component ruthenium-based water oxidation system revealed significant potential to enhance the overall catalytic efficiency by synchronizing the timescales of photoreaction and mass transport in a capillary flow reactor. The overall activity could be improved by a factor of more than 10 with respect to the turnover number and a factor of 21 referring to the external energy efficiency by applying low irradiation intensities and high flow rates.
We report a catalytically active intramolecular photocatalyst, which combines a perylene photosen... more We report a catalytically active intramolecular photocatalyst, which combines a perylene photosensitizer and a Rh(III) catalyst. Spectroscopic studies reveal the formation of a charge-separated perylene radical cation-Rh(II) intermediate that results in a catalytically active species in the presence of protons.
Using a dehydrogenative chemistry on the complex approach, a new polypyridine bridging ligand tha... more Using a dehydrogenative chemistry on the complex approach, a new polypyridine bridging ligand that bridges the gap of already existing systems is synthesized. By the usage of versatile cross-coupling reactions two different coordination spheres are included in the ligand architecture. Due to the twisted geometry of the novel ditopic ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)3]2+ (bpy = 2,2´-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier molecular orbitals apparent...
Multifunctional supramolecular systems are a central research topic in light-driven solar energy ... more Multifunctional supramolecular systems are a central research topic in light-driven solar energy conversion. Here, we report a polyoxometalate (POM)-based supramolecular dyad, where two platinum-complex hydrogen evolution catalysts are covalently anchored to an Anderson polyoxomolybdate anion. Supramolecular electrostatic coupling of the system to an iridium photosensitizer enables visible light-driven hydrogen evolution. Combined theory and experiment demon-strate the multifunctionality of the POM, which acts as photosensitizer / catalyst-binding-site and facilitates light-induced charge-transfer and catalytic turnover. Chemical modification of the Pt-catalyst site leads to increased hydrogen evolution reactivity. Mechanistic studies shed light on the role of the individual components and provide a molecular understanding of the interactions which govern stability and reactivity. The system could serve as a blueprint for multifunctional polyoxometalates in energy conversion and sto...
Organic Materials
Hexaarylbenzenes (HABs) are valuable precursors for the bottom-up synthesis of (nano-)graphene st... more Hexaarylbenzenes (HABs) are valuable precursors for the bottom-up synthesis of (nano-)graphene structures. In this work the synthesis of several bis-pyrimidine substituted HABs furnished with tert-butyl groups at different sites of the four pendant phenyl rings is reported. The synthetic procedure is based on modular [4 + 2]-Diels–Alder cycloaddition reactions followed by decarbonylation. Analysis of the solid-state structures revealed that the newly synthesized HABs feature a propeller-like arrangement of the six arylic substituents around the benzene core. Here, the tilt of the aryl rings with respect to the central ring strongly depends on the intermolecular interactions between the HABs and co-crystallized solvent molecules. Interestingly, by evading the closest proximity of the central ring using an alkyne spacer, the distant pyrimidine ring is oriented in the coplanar geometry with regard to the benzene core, giving rise to a completely different UV-absorption profile.
Sustainable Energy & Fuels
The simultaneous, real time observation of oxygen evolution in the gas phase and in solution enab... more The simultaneous, real time observation of oxygen evolution in the gas phase and in solution enables advanced mechanistic studies which are critical for technologies including water electrolysis, fuel cells, oxidation catalysis and metal–air batteries.
Angewandte Chemie
Understanding photodriven multielectron reaction pathwaysrequires the identification and spectros... more Understanding photodriven multielectron reaction pathwaysrequires the identification and spectroscopic characterization of intermediates and their excited-state dynamics, which is very challenging due to their short lifetimes.Tothe best of our knowledge,this manuscript reports for the first time on in situ spectroelectrochemistry as an alternative approach to study the excited-state properties of reactive intermediates of photocatalytic cycles.U V/Vis,r esonance-Raman, and transient-absorption spectroscopyhave been employed to characterizet he catalytically competent intermediate [(tbbpy) 2 Ru II-(tpphz)Rh I Cp*] of [(tbbpy) 2 Ru(tpphz)Rh(Cp*)Cl]Cl(PF 6) 2 (Ru(tpphz)RhCp*), ap hotocatalyst for the hydrogenation of nicotinamide (NAD-analogue) and proton reduction, generated by electrochemical and chemical reduction. Electronic transitions shifting electron density from the activated catalytic center to the bridging tpphz ligand significantly reduce the catalytic activity upon visible-light irradiation.
![Research paper thumbnail of Product Selectivity in Homogeneous Artificial Photosynthesis Using [(bpy)Rh(Cp*)X]n+-Based Catalysts](https://attachments.academia-assets.com/82438682/thumbnails/1.jpg)
](Inorganics
Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bond... more Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bonds using artificial photosynthesis has been under intensive investigation within the last decades. As the understanding of the underlying working principle of these complex systems continuously grows, more focus will be placed on a catalyst design for highly selective product formation. Recent reports have shown that multifunctional photocatalysts can operate with high chemoselectivity, forming different catalysis products under appropriate reaction conditions. Within this context [(bpy)Rh(Cp*)X]n+-based catalysts are highly relevant examples for a detailed understanding of product selectivity in artificial photosynthesis since the identification of a number of possible reaction intermediates has already been achieved.
Journal of the American Chemical Society, Jan 15, 2017
Organelle-targeted photosensitization represents a promising approach in photodynamic therapy whe... more Organelle-targeted photosensitization represents a promising approach in photodynamic therapy where the design of the active photosensitizer (PS) is very crucial. In this work, we developed a macromolecular PS with multiple copies of mitochondria-targeting groups and ruthenium complexes that displays highest phototoxicity toward several cancerous cell lines. In particular, enhanced anticancer activity was demonstrated in acute myeloid leukemia cell lines, where significant impairment of proliferation and clonogenicity occurs. Finally, attractive two-photon absorbing properties further underlined the great significance of this PS for mitochondria targeted PDT applications in deep tissue cancer therapy.
Dalton Trans., 2016
Electrostatic repulsion between gold(iii) coordination spheres exceeds π-stacking for the first t... more Electrostatic repulsion between gold(iii) coordination spheres exceeds π-stacking for the first time in a tpphz-bridged dinuclear PMD model complex.
Zeitschrift für Naturforschung B, 2010
The results of a detailed investigation of the influence of substituents in a variety of rutheniu... more The results of a detailed investigation of the influence of substituents in a variety of ruthenium biimidazole-type complexes [Ru(R-bpy)
Dalton transactions (Cambridge, England : 2003), Jan 28, 2014
Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging... more Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging ligands have been prepared and structurally and photophysically characterised. The identity of the NHC-unit of the bridging ligand was established unambiguously by means of X-ray structural analysis of a heterodinuclear ruthenium-silver complex. The photophysical data indicate ultrafast intersystem crossing into an emissive and a non-emissive triplet excited state after excitation of the ruthenium centre. Exceptionally high luminescence quantum yields of up to 39% and long lifetimes of up to 2 μs are some of the triplet excited state characteristics. Preliminary studies into the visible light driven photocatalytic hydrogen formation show no induction phase and constant turnover frequencies that are independent on the concentration of the photocatalyst. In conclusion this supports the notion of a stable assembly under photocatalytic conditions.
Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
The synthesis and characterisation of an asymmetric potential bridging ligand bmptpphz (bmptpphz ... more The synthesis and characterisation of an asymmetric potential bridging ligand bmptpphz (bmptpphz = 2,17-bis(4-methoxyphenyl)tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine) is presented. This ligand contains a 1,10-phenanthroline (phen) and a 2,9-disubstituted phen sphere and possesses a strong absorbance in the visible. Facile coordination of the phen sphere to a Ru(tbbpy) 2 core leads to Ru(bmptpphz) ([(tbbpy) 2 Ru(bmptpphz)](PF 6) 2 ; tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine). UV-vis, emission, resonance Raman and theoretical investigations show that this complex possesses all properties associated with a Ru(tpphz) ([(tbbpy) 2 Ru(tpphz)](PF 6) 2 ; tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine) moiety and that the ligand based absorbances in the vis-part also populate an MLCT like state. The coordination of a Pd-core in the new 2,9-disubstituted phen sphere is possible, leading to a cyclometallation. The tridentate complexation leads to changes in the UV-vis and emission behaviour. Furthermore, the stability of the Pd-coordination is significantly enhanced if compared to the unsubstituted Ru(tpphz). Ru(bmptpphz)PdCl proved to be an active photocatalyst for H 2 evolution, albeit with lower activity than the mother compound Ru(tpphz)PdCl 2. † Electronic supplementary information (ESI) available. See
Dalton Transactions, 2014
Supramolecular activation of an intramolecular ruthenium palladium hydrogen evolving photocatalys... more Supramolecular activation of an intramolecular ruthenium palladium hydrogen evolving photocatalyst using polyaromatic compounds.
Dalton Trans., 2014
The photophysical properties of Ruthenium-bipyridine complexes bearing a bibenzimidazole ligand w... more The photophysical properties of Ruthenium-bipyridine complexes bearing a bibenzimidazole ligand were investigated. The nitrogens on the bibenzimidazole-ligand were protected, by adding either a phenylene group or a 1,2-ethandiyl group, to remove the photophysical dependence of the complex on the protonation state of the bibenzimidazole ligand. This protection results in the bibenzimidazole ligand contributing to the MLCT transition, which is experimentally evidenced by (resonance) Raman scattering in concert with DFT calculations for a detailed mode assignment in the (resonance) Raman spectra. † Electronic supplementary information (ESI) available: Experimental details and instrumentation, resonance Raman spectra recorded at excitation wavelengths of 458 and 488 nm, emission data. See
Zeitschrift für Naturforschung B, 2012
A synthesis of novel hexacyclic bis-benzimidazoles 6 starting from 2,3-diarylamino-quinoxalines v... more A synthesis of novel hexacyclic bis-benzimidazoles 6 starting from 2,3-diarylamino-quinoxalines via an oxidative cyclization cascade is described. These very stable and high-melting derivatives are featured by their strong fluorescence in the blue region of the visible spectrum. The cyclization reaction between 2,3-dichloroquinoxaline and 1,2-phenylenediamine did not lead to derivatives of type 6. In this case, only fluoflavine 7 was isolated quantitatively.
We report that the homogeneous light-driven hydrogen evolution reaction (HER) can be significantl... more We report that the homogeneous light-driven hydrogen evolution reaction (HER) can be significantly enhanced by the presence of seemingly innocent ammonium (NH4+) cations. Expermiental studies with different catalysts, photosensitizers and electron donors show this to be a general effect. Preliminary photophysical and mechanistic studies provide initial suggestions regarding the role of ammonium in the HER enhancement.
This work elaborates the effect of dynamic irradiation and enhanced mass transport on light-drive... more This work elaborates the effect of dynamic irradiation and enhanced mass transport on light-driven molecular water oxidation to counteract catalyst deactivation. It highlights the importance of overall reaction design to overcome limiting factors in artificial photosynthesis reactions. Systematic investigation of a homogenous three component ruthenium-based water oxidation system revealed significant potential to enhance the overall catalytic efficiency by synchronizing the timescales of photoreaction and mass transport in a capillary flow reactor. The overall activity could be improved by a factor of more than 10 with respect to the turnover number and a factor of 21 referring to the external energy efficiency by applying low irradiation intensities and high flow rates.
We report a catalytically active intramolecular photocatalyst, which combines a perylene photosen... more We report a catalytically active intramolecular photocatalyst, which combines a perylene photosensitizer and a Rh(III) catalyst. Spectroscopic studies reveal the formation of a charge-separated perylene radical cation-Rh(II) intermediate that results in a catalytically active species in the presence of protons.
Using a dehydrogenative chemistry on the complex approach, a new polypyridine bridging ligand tha... more Using a dehydrogenative chemistry on the complex approach, a new polypyridine bridging ligand that bridges the gap of already existing systems is synthesized. By the usage of versatile cross-coupling reactions two different coordination spheres are included in the ligand architecture. Due to the twisted geometry of the novel ditopic ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)3]2+ (bpy = 2,2´-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier molecular orbitals apparent...
Multifunctional supramolecular systems are a central research topic in light-driven solar energy ... more Multifunctional supramolecular systems are a central research topic in light-driven solar energy conversion. Here, we report a polyoxometalate (POM)-based supramolecular dyad, where two platinum-complex hydrogen evolution catalysts are covalently anchored to an Anderson polyoxomolybdate anion. Supramolecular electrostatic coupling of the system to an iridium photosensitizer enables visible light-driven hydrogen evolution. Combined theory and experiment demon-strate the multifunctionality of the POM, which acts as photosensitizer / catalyst-binding-site and facilitates light-induced charge-transfer and catalytic turnover. Chemical modification of the Pt-catalyst site leads to increased hydrogen evolution reactivity. Mechanistic studies shed light on the role of the individual components and provide a molecular understanding of the interactions which govern stability and reactivity. The system could serve as a blueprint for multifunctional polyoxometalates in energy conversion and sto...
Organic Materials
Hexaarylbenzenes (HABs) are valuable precursors for the bottom-up synthesis of (nano-)graphene st... more Hexaarylbenzenes (HABs) are valuable precursors for the bottom-up synthesis of (nano-)graphene structures. In this work the synthesis of several bis-pyrimidine substituted HABs furnished with tert-butyl groups at different sites of the four pendant phenyl rings is reported. The synthetic procedure is based on modular [4 + 2]-Diels–Alder cycloaddition reactions followed by decarbonylation. Analysis of the solid-state structures revealed that the newly synthesized HABs feature a propeller-like arrangement of the six arylic substituents around the benzene core. Here, the tilt of the aryl rings with respect to the central ring strongly depends on the intermolecular interactions between the HABs and co-crystallized solvent molecules. Interestingly, by evading the closest proximity of the central ring using an alkyne spacer, the distant pyrimidine ring is oriented in the coplanar geometry with regard to the benzene core, giving rise to a completely different UV-absorption profile.
Sustainable Energy & Fuels
The simultaneous, real time observation of oxygen evolution in the gas phase and in solution enab... more The simultaneous, real time observation of oxygen evolution in the gas phase and in solution enables advanced mechanistic studies which are critical for technologies including water electrolysis, fuel cells, oxidation catalysis and metal–air batteries.
Angewandte Chemie
Understanding photodriven multielectron reaction pathwaysrequires the identification and spectros... more Understanding photodriven multielectron reaction pathwaysrequires the identification and spectroscopic characterization of intermediates and their excited-state dynamics, which is very challenging due to their short lifetimes.Tothe best of our knowledge,this manuscript reports for the first time on in situ spectroelectrochemistry as an alternative approach to study the excited-state properties of reactive intermediates of photocatalytic cycles.U V/Vis,r esonance-Raman, and transient-absorption spectroscopyhave been employed to characterizet he catalytically competent intermediate [(tbbpy) 2 Ru II-(tpphz)Rh I Cp*] of [(tbbpy) 2 Ru(tpphz)Rh(Cp*)Cl]Cl(PF 6) 2 (Ru(tpphz)RhCp*), ap hotocatalyst for the hydrogenation of nicotinamide (NAD-analogue) and proton reduction, generated by electrochemical and chemical reduction. Electronic transitions shifting electron density from the activated catalytic center to the bridging tpphz ligand significantly reduce the catalytic activity upon visible-light irradiation.
Inorganics
Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bond... more Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bonds using artificial photosynthesis has been under intensive investigation within the last decades. As the understanding of the underlying working principle of these complex systems continuously grows, more focus will be placed on a catalyst design for highly selective product formation. Recent reports have shown that multifunctional photocatalysts can operate with high chemoselectivity, forming different catalysis products under appropriate reaction conditions. Within this context [(bpy)Rh(Cp*)X]n+-based catalysts are highly relevant examples for a detailed understanding of product selectivity in artificial photosynthesis since the identification of a number of possible reaction intermediates has already been achieved.
Journal of the American Chemical Society, Jan 15, 2017
Organelle-targeted photosensitization represents a promising approach in photodynamic therapy whe... more Organelle-targeted photosensitization represents a promising approach in photodynamic therapy where the design of the active photosensitizer (PS) is very crucial. In this work, we developed a macromolecular PS with multiple copies of mitochondria-targeting groups and ruthenium complexes that displays highest phototoxicity toward several cancerous cell lines. In particular, enhanced anticancer activity was demonstrated in acute myeloid leukemia cell lines, where significant impairment of proliferation and clonogenicity occurs. Finally, attractive two-photon absorbing properties further underlined the great significance of this PS for mitochondria targeted PDT applications in deep tissue cancer therapy.
Dalton Trans., 2016
Electrostatic repulsion between gold(iii) coordination spheres exceeds π-stacking for the first t... more Electrostatic repulsion between gold(iii) coordination spheres exceeds π-stacking for the first time in a tpphz-bridged dinuclear PMD model complex.
Zeitschrift für Naturforschung B, 2010
The results of a detailed investigation of the influence of substituents in a variety of rutheniu... more The results of a detailed investigation of the influence of substituents in a variety of ruthenium biimidazole-type complexes [Ru(R-bpy)
Dalton transactions (Cambridge, England : 2003), Jan 28, 2014
Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging... more Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging ligands have been prepared and structurally and photophysically characterised. The identity of the NHC-unit of the bridging ligand was established unambiguously by means of X-ray structural analysis of a heterodinuclear ruthenium-silver complex. The photophysical data indicate ultrafast intersystem crossing into an emissive and a non-emissive triplet excited state after excitation of the ruthenium centre. Exceptionally high luminescence quantum yields of up to 39% and long lifetimes of up to 2 μs are some of the triplet excited state characteristics. Preliminary studies into the visible light driven photocatalytic hydrogen formation show no induction phase and constant turnover frequencies that are independent on the concentration of the photocatalyst. In conclusion this supports the notion of a stable assembly under photocatalytic conditions.
Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
The synthesis and characterisation of an asymmetric potential bridging ligand bmptpphz (bmptpphz ... more The synthesis and characterisation of an asymmetric potential bridging ligand bmptpphz (bmptpphz = 2,17-bis(4-methoxyphenyl)tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine) is presented. This ligand contains a 1,10-phenanthroline (phen) and a 2,9-disubstituted phen sphere and possesses a strong absorbance in the visible. Facile coordination of the phen sphere to a Ru(tbbpy) 2 core leads to Ru(bmptpphz) ([(tbbpy) 2 Ru(bmptpphz)](PF 6) 2 ; tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine). UV-vis, emission, resonance Raman and theoretical investigations show that this complex possesses all properties associated with a Ru(tpphz) ([(tbbpy) 2 Ru(tpphz)](PF 6) 2 ; tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine) moiety and that the ligand based absorbances in the vis-part also populate an MLCT like state. The coordination of a Pd-core in the new 2,9-disubstituted phen sphere is possible, leading to a cyclometallation. The tridentate complexation leads to changes in the UV-vis and emission behaviour. Furthermore, the stability of the Pd-coordination is significantly enhanced if compared to the unsubstituted Ru(tpphz). Ru(bmptpphz)PdCl proved to be an active photocatalyst for H 2 evolution, albeit with lower activity than the mother compound Ru(tpphz)PdCl 2. † Electronic supplementary information (ESI) available. See
Dalton Transactions, 2014
Supramolecular activation of an intramolecular ruthenium palladium hydrogen evolving photocatalys... more Supramolecular activation of an intramolecular ruthenium palladium hydrogen evolving photocatalyst using polyaromatic compounds.
Dalton Trans., 2014
The photophysical properties of Ruthenium-bipyridine complexes bearing a bibenzimidazole ligand w... more The photophysical properties of Ruthenium-bipyridine complexes bearing a bibenzimidazole ligand were investigated. The nitrogens on the bibenzimidazole-ligand were protected, by adding either a phenylene group or a 1,2-ethandiyl group, to remove the photophysical dependence of the complex on the protonation state of the bibenzimidazole ligand. This protection results in the bibenzimidazole ligand contributing to the MLCT transition, which is experimentally evidenced by (resonance) Raman scattering in concert with DFT calculations for a detailed mode assignment in the (resonance) Raman spectra. † Electronic supplementary information (ESI) available: Experimental details and instrumentation, resonance Raman spectra recorded at excitation wavelengths of 458 and 488 nm, emission data. See
Zeitschrift für Naturforschung B, 2012
A synthesis of novel hexacyclic bis-benzimidazoles 6 starting from 2,3-diarylamino-quinoxalines v... more A synthesis of novel hexacyclic bis-benzimidazoles 6 starting from 2,3-diarylamino-quinoxalines via an oxidative cyclization cascade is described. These very stable and high-melting derivatives are featured by their strong fluorescence in the blue region of the visible spectrum. The cyclization reaction between 2,3-dichloroquinoxaline and 1,2-phenylenediamine did not lead to derivatives of type 6. In this case, only fluoflavine 7 was isolated quantitatively.