Light-Induced Charge Separation in Covalently Linked BODIPY-Quinone-Alkyne Dyads.

Visible light-induced charge separation and directional charge transfer are cornerstones for artificial photosynthesis and the generation of solar fuels. Here, we report synthetic access to a series of noble metal-free donor-acceptor dyads based on bodipy light-absorbers and redox-active quinone/anthraquinone charge storage sites. Peripheral functionalization of the quinone/anthraquinone units with alkynes primes the dyads for integration into a range of light-harvesting systems, e. g., by Cu-catalyzed cycloadditions (CLICK chemistry) or Pd-catalyzed C-C cross-coupling reactions. Initial photophysical, electrochemical and theoretical analyses reveal the principal processes during the light-induced charge separation in the reported dyads.

The three kingdoms-Photoinduced electron transfer cascades controlled by electronic couplings.

Excited states are the key species in photocatalysis, while the critical parameters that govern their applications are (i) excitation energy, (ii) accessibility, and (iii) lifetime. However, in molecular transition metal-based photosensitizers, there is a design tension between the creation of long-lived excited (triplet), e.g., metal-to-ligand charge transfer (3MLCT) states and the population of such states. Long-lived triplet states have low spin-orbit coupling (SOC) and hence their population is low. Thus, a long-lived triplet state can be populated but inefficiently. If the SOC is increased, the triplet state population efficiency is improved-coming at the cost of decreasing the lifetime. A promising strategy to isolate the triplet excited state away from the metal after intersystem crossing (ISC) involves the combination of transition metal complex and an organic donor/acceptor group. Here, we elucidate the excited state branching processes in a series of Ru(II)-terpyridyl push-pull triads by quantum chemical simulations. Scalar-relativistic time-dependent density theory simulations reveal that efficient ISC takes place along 1/3MLCT gateway states. Subsequently, competitive electron transfer (ET) pathways involving the organic chromophore, i.e., 10-methylphenothiazinyl and the terpyridyl ligands are available. The kinetics of the underlying ET processes were investigated within the semiclassical Marcus picture and along efficient internal reaction coordinates that connect the respective photoredox intermediates. The key parameter that governs the population transfer away from the metal toward the organic chromophore either by means of ligand-to-ligand (3LLCT; weakly coupled) or intra-ligand charge transfer (3ILCT; strongly coupled) states was determined to be the magnitude of the involved electronic coupling.

Tailored Charge Transfer Kinetics in Precursors for Organic Radical Batteries: A Joint Synthetic-Theoretical Approach.

Invited for this month's cover is the group of Stephan Kupfer at the Friedrich Schiller University Jena. The image shows the charge transfer from TEMPO to thiophene in organic radical batteries. The Research Article itself is available at 10.1002/cssc.202201679.

Tailored Charge Transfer Kinetics in Precursors for Organic Radical Batteries: A Joint Synthetic-Theoretical Approach.

The development of sustainable energy storage devices is crucial for the transformation of our energy management. In this scope, organic batteries attracted considerable attention. To overcome the shortcomings of typically applied materials from the classes of redox-active conjugated polymers (i. e., unstable cell voltages) and soft matter-embedded stable organic radicals (i. e., low conductivity), a novel design concept was introduced, integrating such stable radicals within a conductive polymer backbone. In the present theory-driven design approach, redox-active (2,2,6,6-tetramethylpiperidin-1-yl)oxyls (TEMPOs) were incorporated in thiophene-based polymer model systems, while structure-property relationships governing the thermodynamic properties as well as the charge transfer kinetics underlying the charging and discharging processes were investigated in a systematical approach. Thereby, the impact of the substitution pattern, the length as well as the nature of the chemical linker, and the ratio of TEMPO and thiophene units was studied using state-of-the-art quantum chemical and quantum dynamical simulations for a set of six molecular model systems. Finally, two promising candidates were synthesized and electrochemically characterized, paving the way to applications in the frame of novel organic radical batteries.

Solid-to-Liposome Conformational Transition of Phosphatidylcholine and Phosphatidylserine Probed by Atomic Force Microscopy, Infrared Spectroscopy, and Density Functional Theory Calculations.

Liposomes are emerging therapeutic formulations for site-specific delivery of chemotherapeutic drugs. The efficiency and selectivity of drug delivery by these carriers largely rely on their surface properties, shape, and size. There is a growing demand for analytical approaches that can be used for structural and morphological characterization of liposomes at the single-vesicle level. AFM-IR is a modern optical nanoscopic technique that combines the advantages of scanning probe microscopy and infrared spectroscopy. Our findings show that AFM-IR can be used to probe conformational changes in phospholipids that take place upon their assembly into liposomes. Such conclusions can be made based on the corresponding changes in intensities of the lipid vibrational bands as the molecules transition from a solid state into large unilamellar vesicles (LUVs). This spectroscopic analysis of LUV formation together with density functional theory calculations also reveals the extent to which the molecular conformation and local environment of the functional groups alter the AFM-IR spectra of phospholipids. Using melittin as a test protein, we also examined the extent to which LUVs can be used for protein internalization. We found that melittin enters LUVs nearly instantaneously, which protects it from possible structural modifications that are caused by a changing environment. This foundational work empowers AFM-IR analysis of liposomes and opens new avenues for determination of the molecular mechanisms of liposome-drug interactions.

Modulating the Excited-State Decay Pathways of Cu(I) 4H-Imidazolate Complexes by Excitation Wavelength and Ligand Backbone.

Cu(I) 4H-imidazolato complexes are excellent photosensitizers with broad and intense light absorption properties, based on an earth-abundant metal, and hold great promise as photosensitizers in artificial photosynthesis and for accumulation of redox equivalents. In this study, the excited-state relaxation dynamics of three novel heteroleptic Cu(I) 4H-imidazolato complexes with phenyl, tolyl, and mesityl side groups are systematically investigated by femtosecond and nanosecond time-resolved transient absorption spectroscopy and theoretical methods, complemented by steady-state absorption spectroscopy and (spectro)electrochemistry. After photoexcitation into the metal-to-ligand charge transfer (MLCT) and intraligand charge transfer absorption band, fast (0.6-1 ps) intersystem crossing occurs into the triplet MLCT manifold. The triplet-state population relaxes via the geometrical planarization of the N-aryl rings on the Cu(I) 4H-imidazolato complexes. Depending on the initial Franck-Condon state, the remaining small singlet state population relaxes into two geometrically distinct minima geometries with similar energy, S1/2,relax and S3/4,relax. Subsequent ground-state recovery from S1/2,relax and internal conversion from S3/4,relax to S1/2,relax take place on a 100 ps time scale. The internal conversion can be understood as hole transfer from a dyz-orbital to a dxz-orbital, which is accompanied with the structural reorganization of the coordination environment. Generally, the photophysical processes are determined by the steric hindrance of the side groups on the ligands. And the excited singlet-state pathways are dependent on the excitation wavelength.

Sustainable preparation of anti-inflammatory atorvastatin PLGA nanoparticles.

In the present study, the anti-inflammatory lipophilic drug atorvastatin was encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) using a sustainable method in comparison to the standard emulsion-diffusion-evaporation technique. For the sustainable method the organic solvent ethyl acetate was fully replaced by 400 g/mol poly(ethylene glycol) (PEG 400). Both techniques led to the formation of nanoparticles with comparable sizes of about 170 to 247 nm depending on the polymer type, with monomodal size distribution and negative zeta potential. All nanoparticles demonstrated a high biocompatibility in a shell-less hen's egg model and displayed an anti-inflammatory effect in human monocytes. The use of PEG 400 resulted in plasticizing effects and a lower crystallinity of the PLGA nanoparticles as determined by differential scanning calorimetry and Raman spectroscopy, which correlated with a faster drug release. Interestingly, the particles prepared by the sustainable method showed a crystallinity and drug release kinetics similar to nanoparticles made of PEG-PLGA using the standard method. Conclusively, the sustainable method is a fast and easy to perform technique suitable to prepare atorvastatin-loaded PLGA nanoparticles avoiding toxic and environmentally damaging drawbacks frequently associated with classical organic solvents.

Iron(0)-Mediated Stereoselective (3+2)-Cycloaddition of Thiochalcones via a Diradical Intermediate.

Reactions of α,ß-unsaturated aromatic thioketones 1 (thiochalcones) with Fe3 (CO)12 leading to η4 -1-thia-1,3-diene iron tricarbonyl complexes 2, [FeFe] hydrogenase mimics 3, and the thiopyrane adduct 4 are described. Obtained products have been characterized by X-ray crystallography and by computational methods. Completely regio- and diastereoselective formation of the five-membered ring system in products 3, containing four stereogenic centers, can be explained by an unprecedented, stepwise (3+2)-cycloaddition of two thiochalcone molecules mediated by Fe3 (CO)12 . Quantum chemical calculations aimed at elucidation of the reaction mechanism, suggest that the formal (3+2)-cycloaddition proceeds via sequential intramolecular radical transfer events upon homolytic cleavage of one carbon-sulfur bond leading to a diradical intermediate.