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- ItemBlock Copolymers Featuring Highly Photostable Photoacids Based on Vinylnaphthol: Synthesis and Self-Assembly(Weinheim : Wiley-VCH, 2020) Wendler, Felix; Tom, Jessica C.; Sittig, Maria; Biehl, Philip; Dietzek, Benjamin; Schacher, Felix H.The synthesis of a photoresponsive amphiphilic diblock quarterpolymer containing 5-vinyl-1-naphthol (VN) as a photostable photoacidic comonomer is presented. The preparation is realized via a sequential reversible addition fragmentation chain transfer (RAFT) polymerization starting from a nona(ethylene glycol) methyl ether methacrylate (MEO9MA/“O”) hydrophilic block, which is then used as a macro-RAFT agent in the terpolymerization of styrene (S), 2-vinylpyridine (2VP), and TBS-protected VN (tVN). The terpolymerization proceeds in a controlled fashion and two diblock quarterpolymers, P(Om)-b-P(Sx-co-2VPy-co-VNz), with varying functional comonomer compositions are prepared. These diblock quarterpolymers form spherical core-corona micelles in aqueous media according to dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM). Upon irradiation, the photoacids within the micellar core experience a drastic increase in acidity causing a proton transfer from the photoacid to neighboring 2VP units. As a result, the hydrophilic/hydrophobic balance of the entire assembly is shifted, and the encapsulated cargo is released. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemPhotodoping and Fast Charge Extraction in Ionic Carbon Nitride Photoanodes(Weinheim : Wiley-VCH, 2021) Adler, Christiane; Selim, Shababa; Krivtsov, Igor; Li, Chunyu; Mitoraj, Dariusz; Dietzek, Benjamin; Durrant, James R.; Beranek, RadimIonic carbon nitrides based on poly(heptazine imides) (PHI) represent a vigorously studied class of materials with possible applications in photocatalysis and energy storage. Herein, for the first time, the photogenerated charge dynamics in highly stable and binder-free PHI photoanodes using in operando transient photocurrents and spectroelectrochemical photoinduced absorption measurements is studied. It is discovered that light-induced accumulation of long-lived trapped electrons within the PHI film leads to effective photodoping of the PHI film, resulting in a significant improvement of photocurrent response due to more efficient electron transport. While photodoping is previously reported for various semiconductors, it has not been shown before for carbon nitride materials. Furthermore, it is found that the extraction kinetics of untrapped electrons are remarkably fast in these PHI photoanodes, with electron extraction times (ms) comparable to those measured for commonly employed metal oxide semiconductors. These results shed light on the excellent performance of PHI photoanodes in alcohol photoreforming, including very negative photocurrent onset, outstanding fill factor, and the possibility to operate under zero-bias conditions. More generally, the here reported photodoping effect and fast electron extraction in PHI photoanodes establish a strong rationale for the use of PHI films in various applications, such as bias-free photoelectrochemistry or photobatteries. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- Item1,7,9,10-Tetrasubstituted PMIs Accessible through Decarboxylative Bromination: Synthesis, Characterization, Photophysical Studies, and Hydrogen Evolution Catalysis(Weinheim : Wiley-VCH, 2020) Costabel, Daniel; Skabeev, Artem; Nabiyan, Afshin; Luo, Yusen; Max, Johannes B.; Rajagopal, Ashwene; Kowalczyk, Daniel; Dietzek, Benjamin; Wächtler, Maria; Görls, Helmar; Ziegenbalg, Dirk; Zagranyarski, Yulian; Streb, Carsten; Schacher, Felix H.; Peneva, KalinaIn this work, we present a new synthetic strategy for fourfold-substituted perylene monoimides via tetrabrominated perylene monoanhydrides. X-ray diffraction analysis unveiled the intramolecular stacking orientation between the substituents and semicircular packing behavior. We observed the remarkable influence of the substituent on the longevity and nature of the excited state upon visible light excitation. In the presence of poly(dehydroalanine)-graft-poly(ethylene glycol) graft copolymers as solubilizing template, the chromophores are capable of sensitizing [Mo3S13]2− clusters in aqueous solution for stable visible light driven hydrogen evolution over three days. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
- ItemIt Takes Three to Tango - the length of the oligothiophene determines the nature of the long-lived excited state and the resulting photocytotoxicity of a Ru(II) photodrug(Weinheim : Wiley-VCH, 2021) Chettri, Avinash; Roque, John A.; Schneider, Kilian R.A.; Cole, Houston D.; Cameron, Colin G.; McFarland, Sherri A.; Dietzek, BenjaminTLD1433 is the first Ru(II) complex to be tested as a photodynamic therapy agent in a clinical trial. In this contribution we study TLD1433 in the context of structurally-related Ru(II)-imidozo[4,5-f][1,10]phenanthroline (ip) complexes appended with thiophene rings to decipher the unique photophysical properties which are associated with increasing oligothiophene chain length. Substitution of the ip ligand with ter- or quaterthiophene changes the nature of the long-lived triplet state from metal-to-ligand charge-transfer to 3ππ* character. The addition of the third thiophene thus presents a critical juncture which not only determines the photophysics of the complex but most importantly its capacity for 1O2 generation and hence the potential of the complex to be used as a photocytotoxic agent.
- ItemCovalent Linkage of BODIPY-Photosensitizers to Anderson-Type Polyoxometalates Using CLICK Chemistry(Weinheim : Wiley-VCH, 2021) Cetindere, Seda; Clausing, Simon T.; Anjass, Montaha; Luo, Yusen; Kupfer, Stephan; Dietzek, Benjamin; Streb, CarstenThe covalent attachment of molecular photosensitizers (PS) to polyoxometalates (POMs) opens new pathways to PS-POM dyads for light-driven charge-transfer and charge-storage. Here, we report a synthetic route for the covalent linkage of BODIPY-dyes to Anderson-type polyoxomolybdates by using CLICK chemistry (i. e. copper-catalyzed azide-alkyne cycloaddition, CuAAC). Photophysical properties of the dyad were investigated by combined experimental and theoretical methods and highlight the role of both sub-components for the charge-separation properties. The study demonstrates how CLICK chemistry can be used for the versatile linkage of organic functional units to molecular metal oxide clusters. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
- ItemQuinoline Photobasicity: Investigation within Water-Soluble Light-Responsive Copolymers(Weinheim : Wiley-VCH, 2021) Sittig, Maria; Tom, Jessica C.; Elter, Johanna K.; Schacher, Felix H.; Dietzek, BenjaminQuinoline photobases exhibit a distinctly higher pKa in their electronically excited state than in the ground state, thereby enabling light-controlled proton transfer reactions, for example, in molecular catalysis. The absorption of UV light translates to a pKa jump of approximately 10 units, as established for small-molecule photobases. This contribution presents the first synthesis of quinoline-based polymeric photobases prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization. The integration of quinolines as photobase chromophores within copolymers offers new possibilities for light-triggered proton transfer in nanostructured materials, that is, in nanoparticles, at surfaces, membranes and interfaces. To exploit the light-triggered reactivity of photobases within such materials, we first investigated how the ground- and excited-state properties of the quinoline unit changes upon polymer integration. To address this matter, we combined absorption and emission spectroscopy with time-resolved transient-absorption studies to reveal photoinduced proton-transfer dynamics in various solvents. The results yield important insights into the thermodynamic and kinetic properties of these polymeric quinoline photobases. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
- ItemIntracellular Photophysics of an Osmium Complex bearing an Oligothiophene Extended Ligand(Weinheim : Wiley-VCH, 2020) Schneider, Kilian R.A.; Chettri, Avinash; Cole, Houston D.; Reglinski, Katharina; Breckmann, Jannik; Roque, John A. III; Stumper, Anne; Nauroozi, Djawed; Schmid, Sylvia; Lagerholm, Christoffer B.; Rau, Sven; Bäuerle, Peter; Eggeling, Christian; Cameron, Colin G.; McFarland, Sherri A.; Dietzek, BenjaminThis contribution describes the excited-state properties of an Osmium-complex when taken up into human cells. The complex 1 [Os(bpy)2(IP-4T)](PF6)2 with bpy=2,2′-bipyridine and IP-4T=2-{5′-[3′,4′-diethyl-(2,2′-bithien-5-yl)]-3,4-diethyl-2,2′-bithiophene}imidazo[4,5-f][1,10]phenanthroline) can be discussed as a candidate for photodynamic therapy in the biological red/NIR window. The complex is taken up by MCF7 cells and localizes rather homogeneously within in the cytoplasm. To detail the sub-ns photophysics of 1, comparative transient absorption measurements were carried out in different solvents to derive a model of the photoinduced processes. Key to rationalize the excited-state relaxation is a long-lived 3ILCT state associated with the oligothiophene chain. This model was then tested with the complex internalized into MCF7 cells, since the intracellular environment has long been suspected to take big influence on the excited state properties. In our study of 1 in cells, we were able to show that, though the overall model remained the same, the excited-state dynamics are affected strongly by the intracellular environment. Our study represents the first in depth correlation towards ex-vivo and in vivo ultrafast spectroscopy for a possible photodrug. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemStructure of Diethyl-Phosphonic Acid Anchoring Group Affects the Charge-Separated State on an Iridium(III) Complex Functionalized NiO Surface(Weinheim : Wiley-VCH, 2020) Wahyuono, Ruri Agung; Amthor, Sebastian; Müller, Carolin; Rau, Sven; Dietzek, BenjaminCyclometalated Iridium(III) complexes, i. e. [Ir(C N)2(dppz)][PF6], bearing either two or four -CH2PO(OH)2 anchoring groups (IrP2dppz or IrP4dppz) are explored as photosensitizers for p-type dye sensitized solar cell (DSSC). The synthetic route is described and the iridium(III) complexes are characterized with respect to their electrochemical and photophysical properties. The modified anchoring ligand geometry exploited in this work not only alters the electronic nature of the complex (that is by destabilizing the LUMO energetically) but more importantly improves the grafting ability of the complex towards the NiO surface. The photoinduced long-lived charge separated state (CSS) at the NiO|IrPxdppz interface is of a different nature comparing the two complexes. For IrP2dppz and IrP4dppz the electron density of the CSS dominantly resides on the dppz and the C N ligand, respectively. The stability of the CSS can be correlated to the solar cell performance in NiO-based p-DSSCs, which yield conversion efficiencies which are among the highest in the class of iridium(III) complexes developed for p-DSSCs. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemYield—not only Lifetime—of the Photoinduced Charge-Separated State in Iridium Complex–Polyoxometalate Dyads Impact Their Hydrogen Evolution Reactivity(Weinheim : Wiley-VCH, 2020) Luo, Yusen; Maloul, Salam; Schönweiz, Stefanie; Wächtler, Maria; Streb, Carsten; Dietzek, BenjaminCovalently linked photosensitizer–polyoxometalate (PS-POM) dyads are promising molecular systems for light-induced energy conversion processes, such as “solar” hydrogen generation. To date, very little is known of their fundamental photophysical properties which affect the catalytic reactivity and stability of the systems. PS-POM dyads often feature short-lived photoinduced charge-separated states, and the lifetimes of these states are considered crucial for the function of PS-POM dyads in molecular photocatalysis. Hence, strategies have been developed to extend the lifetimes of the photoinduced charge-separated states, either by tuning the PS photophysics or by tuning the POM redox properties. Recently, some of us reported PS-POM dyads based on cyclometalated IrIII complexes covalently linked to Anderson-type polyoxometalate. Distinct hydrogen evolution reactivity (HER) of the dyads was observed, which was tuned by varying the central metal ion M of the POMM (M=Mn3+, Co3+, Fe3+). In this manuscript, the photoinduced electron-transfer processes in the three Ir-POMM dyads are investigated to rationalize the underlying reasons for the differences in HER activity observed. We report that upon excitation of the IrIII complex, ultrafast (sub-ps) charge separation occurs, leading to different amounts of the charge-separated states (Ir.+-POMM.−) generated in the different dyads. However, in all dyads studied, the resulting Ir.+-POMM.− species are short-lived (sub-ns) when compared to reference electron acceptors (e.g. porphyrins or fullerenes) reported in the literature. The reductive quenching of Ir.+-POMM.− by a sacrificial donor, triethyl amine (1 m), to generate the intermediate Ir-POMM.− is estimated to be very efficient (70–80 %) for all dyads studied. Based on this analyses, we conclude that the yield instead of the lifetime of the Ir.+-POMM.− charge-separated state determines the catalytic capacity of the dyads investigated. This new feature in the PS-POM photophysics could lead to new design criteria for the development of novel PS-POM dyads. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.