412 research outputs found
Excited-State Dynamics in Borylated Arylisoquinoline Complexes in Solution and in cellulo
Two four-coordinate organoboron N,C-chelate complexes with different functional terminals on the PEG chains are studied with respect to their photophysical properties within human MCF-7â
cells. Their excited-state properties are characterized by time-resolved pump-probe spectroscopy and fluorescence lifetime microscopy. The excited-state relaxation dynamics of the two complexes are similar when studied in DMSO. Aggregation of the complexes with the carboxylate terminal group is observed in water. When studying the light-driven excited-state dynamics of both complexes in cellulo, i.âe., after being taken up into human MCF-7â
cells, both complexes show different features depending on the nature of the anchoring PEG chains. The lifetime of a characteristic intramolecular charge-transfer state is significantly shorter when studied in cellulo (360Âą170â
ps) as compared to in DMSO (âź960â
ps) at 600â
nm for the complexes with an amino group. However, the kinetics of the complexes with the carboxylate group are in line with those recorded in DMSO. On the other hand, the lifetimes of the fluorescent state are almost identical for both complexes in cellulo. These findings underline the importance to evaluate the excited-state properties of fluorophores in a complex biological environment in order to fully account for intra- and intermolecular effects governing the light-induced processes in functional dyes.This work was supported by the European Union (via the ITN
LogicLab funded under the Horizon 2020 research and
innovation program under the grant agreement No 813920).
We thank Prof. Dr. Rainer Heintzmann and Dr. Benedict Diederich
for providing BioLab facilities and supporting the image
acquisition. The ELYRA 7 (used for producing Figure 3 and S8)
was funded by the Free State of Thuringia with grant number
2019 FGI 0003 and supported by the Microverse Imaging Center
(funded by the DFG under Germany Ăs Excellence Strategy
�R EXC 2051 �R Project-ID 390713860). We further acknowledge
funding by the DFG (Project number 316213987 â SFB 1278,
INST 1757/25-1 FUGG), the Free State of Thuringia (TAB,
TMWWDG, AdvancedSTED/2018 FGI 0022; Advanced Flu-Spec/
2020 FGI 0031), BMBF (Photonics Research Germany (FKZ;
3N15713/13N15717) integrated into the Leibniz Center for
Photonics in Infection Research (LPI)) and the innovation
program by the German BMWi (ZIM; project 16KN070934 / Labon-
a-chip FCS-Easy). The Spanish Ministerio de Ciencia e
InnovaciĂłn (grants PID2020-119992GB-I00, PID2019-106358GBC21,
and PID2019-106358GB-C22), the Consejo Superior de
Investigaciones CientĂficas (grant 202080I005 for A.R.), and the
Junta de AndalucĂa/University of Huelva (grant UHU-202070) are
thanked for financial support. We thank Dr. Z. Dom Nguez for
assistance in the early stage of this project. Open Access
funding enabled and organized by Projekt DEAL
Acute upper extremity arterial thrombosis and stroke in an unresected pheochromocytoma
Pheochromocytoma is a rare cause of hypertension in the general population. Only isolated reports show an association with acute obstructive arterial thrombosis. A 50-year-old chronically noncompliant woman with a known unresected pheochromocytoma presented to the emergency department with ataxia. Imaging confirmed a right-sided ischemic stroke. During her hospital stay, the patient developed signs consistent with acute right upper extremity ischemia resulting from occlusion in the distal right subclavian, axillary, and proximal brachial arteries. Emergent open thrombectomy was successfully performed. In patients with an unresected pheochromocytoma, one must consider acute arterial thrombosis as a rare but potentially limb-threatening and even life-threatening complication
Watching Ultrafast Barrierless Excited-state Isomerization Of Pseudocyanine In Real Time
The photoinduced excited-state processes in 1,1\u27-diethyl-2,2\u27-cyanine iodine are investigated using femtosecond time-resolved pump-probe spectroscopy. Using a broad range of probe wavelengths, the relaxation of the initially prepared excited-state wavepacket can be followed down to the sink region. The data directly visualize the directed downhill motion along the torsional reaction coordinate and suggest a barrierless excited-state isomerization in the short chain cyanine dye. Additionally, ultrafast ground-state hole and excited-state hole replica broadening is observed. While the narrow excited-state wavepacket broadens during pump-probe overlap, the ground-state hole burning dynamics takes place on a significantly longer time-scale. The experiment reported can be considered as a direct monitoring of the shape and the position of the photoprepared wavepacket on the excited-state potential energy surface
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Resonance Raman Spectro-Electrochemistry to Illuminate Photo-Induced Molecular Reaction Pathways
Electron transfer reactions play a key role for artificial solar energy conversion, however, the underlying reaction mechanisms and the interplay with the molecular structure are still poorly understood due to the complexity of the reaction pathways and ultrafast timescales. In order to investigate such light-induced reaction pathways, a new spectroscopic tool has been applied, which combines UV-vis and resonance Raman spectroscopy at multiple excitation wavelengths with electrochemistry in a thin-layer electrochemical cell to study [RuII(tbtpy)2]2+ (tbtpy = tri-tert-butyl-2,2â˛:6â˛,2â˛â˛-terpyridine) as a model compound for the photo-activated electron donor in structurally related molecular and supramolecular assemblies. The new spectroscopic method substantiates previous suggestions regarding the reduction mechanism of this complex by localizing photo-electrons and identifying structural changes of metastable intermediates along the reaction cascade. This has been realized by monitoring selective enhancement of Raman-active vibrations associated with structural changes upon electronic absorption when tuning the excitation wavelength into new UV-vis absorption bands of intermediate structures. Additional interpretation of shifts in Raman band positions upon reduction with the help of quantum chemical calculations provides a consistent picture of the sequential reduction of the individual terpyridine ligands, i.e., the first reduction results in the monocation [(tbtpy)Ru(tbtpyâ˘)]+, while the second reduction generates [(tbtpyâ˘)Ru(tbtpyâ˘)]0 of triplet multiplicity. Therefore, the combination of this versatile spectro-electrochemical tool allows us to deepen the fundamental understanding of light-induced charge transfer processes in more relevant and complex systems
Structure of diethylâphosphonic acid anchoring group affects the chargeâseparated state on an iridium(III) complex functionalized NiO surface
Abstract Cyclometalated Iridium(III) complexes, i.âe . [Ir(CâN) 2 (dppz)][PF 6 ], bearing either two or four âCH 2 PO(OH) 2 anchoring groups ( IrP 2 dppz or IrP 4 dppz ) are explored as photosensitizers for pâtype 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 longâlived charge separated state (CSS) at the NiO|IrP x dppz interface is of a different nature comparing the two complexes. For IrP 2 dppz and IrP 4 dppz the electron density of the CSS dominantly resides on the dppz and the CâN ligand, respectively. The stability of the CSS can be correlated to the solar cell performance in NiOâbased pâDSSCs, which yield conversion efficiencies which are among the highest in the class of iridium(III) complexes developed for pâDSSCs
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Structure of Diethyl-Phosphonic Acid Anchoring Group Affects the Charge-Separated State on an Iridium(III) Complex Functionalized NiO Surface
Cyclometalated 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. Š 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
Reductive Activation of Aryl Chlorides by Tuning the Radical Cation Properties of N âPhenylphenothiazines as Organophotoredox Catalysts
Aryl chlorides as substrates for arylations present a particular challenge for photoredox catalytic activation due to their strong C(sp)âCl bond and their strong reduction potential. Electron-rich N-phenylphenothiazines, as organophotoredox catalysts, are capable of cleaving aryl chlorides simply by photoinduced electron transfer without the need for an additional electrochemical activation setup or any other advanced photocatalysis technique. Due to the extremely strong reduction potential in the excited state of the N-phenylphenothiazines the substrate scope is high and includes aryl chlorides both with electron-withdrawing and electron-donating substituents. We evidence this reactivity for photocatalytic borylations and phosphonylations. Advanced time-resolved transient absorption spectroscopy in combination with electrochemistry was the key to elucidating and comparing the unusual photophysical properties not only of the N-phenylphenothiazines, but also of their cation radicals as the central intermediates in the photocatalytic cycle. The revealed photophysics allowed the excited-state and radical-cation properties to be fine-tuned by the molecular design of the N-phenylphenothiazines; this improved the photocatalytic activity
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Polymeric Photoacids Based on NaphtholsâDesign Criteria, Photostability, and Light-Mediated Release
The implementation of photoswitches within polymers offers an exciting toolbox in the design of light-responsive materials as irradiation can be controlled both spatially and temporally. Herein, we introduce a range of water-soluble copolymers featuring naphthol-based chromophores as photoacids in the side chain. With that, the resulting materials experience a drastic increase in acidity upon stimulation with UV light and we systematically studied how structure and distance of the photoacid from the copolymer backbone determines polymerizability, photo-response, and photostability. Briefly, we used RAFT (reversible additionâfragmentation chain transfer) polymerization to prepare copolymers consisting of nona(ethylene glycol) methyl ether methacrylate (MEO9MA) as water-soluble comonomer in combination with six different 1-naphthol-based (âNâ) monomers. Thereby, we distinguish between methacrylates (NMA, NOeMA), methacrylamides (NMAm, NOeMAm), vinyl naphthol (VN), and post-polymerization modification based on [(1-hydroxynaphthalen-2-amido)ethyl]amine (NOeMAm, NAmeMAm). These P(MEO9MAx-co-âNây) copolymers typically feature a 4:1 MEO9MA to âNâ ratio and molar masses in the range of 10 kg molâ1. After synthesis and characterization by using NMR spectroscopy and size exclusion chromatography (SEC), we investigated how potential photo-cleavage or photo-degradation during irradiation depends on the type and distance of the linker to the copolymeric backbone and whether reversible excited state proton transfer (ESPT) occurs under these conditions. In our opinion, such materials will be strong assets as light-mediated proton sources in nanostructured environments, for example, for the site-specific creation of proton gradients. We therefore exemplarily incorporated NMA into an amphiphilic block copolymer and could demonstrate the light-mediated release of Nile red from micelles formed in water as selective solvent. Š 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
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Monitoring excited-state relaxation in a molecular marker in live cellsâa case study on astaxanthin
Small molecules are frequently used as dyes, labels and markers to visualize and probe biophysical processes within cells. However, very little is generally known about the light-driven excited-state reactivity of such systems when placed in cells. Here an experimental approach to study ps time-resolved excited state dynamics of a benchmark molecular marker, astaxanthin, in live human cells is introduced. Š The Royal Society of Chemistry 2021
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Quinoline Photobasicity: Investigation within Water-Soluble Light-Responsive Copolymers
Quinoline 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. Š 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb
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