Jürgen Hauer

Efficient harvesting, storage, and on‐demand release of solar energy are essential for overcoming the intermittency of sunlight and enabling continuous solar energy‐driven processes, yet achieving storage of photogenerated charge remains challenging. Here, we report a Ti‐based bipyridine MOF, COK47‐bpy, and its ReCl(CO) ₃ ‐functionalized analogue, ReCl47‐bpy , as photochargeable materials for time‐decoupled solar energy utilization. Re incorporation introduces localized photosensitizing and “electron sink” sites while preserving the parent framework structure, enabling visible‐light response, faster charge accumulation, and improved charge retention. In colloidal suspension, ReCl47‐bpy reaches an electron storage capacity of 19.5 C g ⁻¹ _MOF under simulated solar irradiation and retains about 70% of the stored charge after 2.5 months. The stored electrons can be released on demand for dark hydrogen (H ₂ ) evolution with electron‐to‐H ₂ efficiencies exceeding 90%. Beyond colloids, when fabricated as robust FTO‐supported layers, ReCl47‐bpy |FTO photoelectrodes deliver capacities of up to ∼7.0 mAh g ⁻¹ _MOF upon photocharging under 1 Sun irradiation. Overall, this work establishes Re‐functionalized Ti‐MOFs as versatile platforms for solar‐driven charge storage, dark photocatalysis, and MOF‐based photoelectrodes, toward the development of next‐generation MOF‐based energy devices.

Peridinin is a light-harvesting apocarotenoid whose excited-state relaxation is often described by population transfer among 1Bu, 2Ag, and intramolecular charge-transfer states. Here broadband-detected transient fluorescence reveals a simpler picture for peridinin in ethylene glycol. Following optical excitation, we observe instantaneous blue-green emission from the bright 1Bu state that depopulates with a 150 fs time constant and directly gives rise to weak red emission from the lowest 2Ag state, which decays in 12 ps. The presence of an isosbestic point and the absence of additional fluorescence components indicate direct internal conversion without a resolvable hot S1 or a separate equilibration process involving a charge-transfer state. XMS-RASPT2 and DFT/MRCI calculations reproduce this behavior by showing strong displacement of the 1Bu and 2Ag minima from the Franck–Condon region and weak oscillator strength at the relaxed 2Ag minimum. The results identify peridinin as an emitter from its 1Bu and 2Ag states and revise the interpretation of its charge-transfer-like signatures.

Benzaldehydes carrying an alkenyloxy substituent in the 3-position undergo a photocycloaddition reaction, in which the olefin adds intramolecularly to the carbonyl carbon atom and to the carbon atom C2 of the benzene core forming a cyclopentane ring. The reaction was shown to proceed upon AlBr3 catalysis (10 mol %) by irradiation with visible light (λ = 435 nm). A total of 30 tricyclic products (44–94% yields) were obtained with high simple and facial diastereoselectivity. Transient absorption spectroscopy and mechanistic experiments suggested that both the uncatalyzed reaction at λ = 280–340 nm and the Lewis acid-catalyzed reaction occur from the triplet state.

Optoelectronic performance, defect density, and thin-film morphology of solution-processable lead halide perovskites are highly dependent on nucleation and growth conditions during processing. Additionally, Cs+ incorporation into the lattice can have benign effects on the thin films, which is challenging for scalable, deposition-friendly solvents such as 2-methoxyethanol or acetonitrile due to their highly limited solubility of Cs-containing salts. To address both issues, we present an interface-engineering approach that utilizes CsPbI3 nanocubes as seed crystals for slot-die coating of FAPbI3. The seeds improve growth-control at the bottom interface and enhance Cs+ incorporation into the active layer lattice. Incidence angle varied grazing-incidence wide-angle X-ray scattering enables depth-resolved structural probing of thin films, revealing increased Cs+ incorporation with increasing film depth. Additionally, morphological parameters, such as thin-film “face-on” orientation and crystallographic texture, are significantly improved in the seeded film. Accordingly, the seeded films exhibit reduced defect density and enhanced charge-carrier separation due to increased structural ordering and Cs+ alloy-induced bandgap tuning across the active layer thickness. Resulting p-i-n photovoltaic devices exhibit superior mean values as well as a narrower spread across short-circuit current density, fill factor, and power conversion efficiency, highlighting the beneficial effects of nanocrystal seeding on active-layer quality and reproducibility.

Methylorubrum species are prominent members of the plant phyllosphere, where they are exposed to fluctuating environmental conditions, including intense ultraviolet (UV) radiation. To mitigate such stressors, these bacteria commonly synthesise carotenoids as an oxidative protection. In this study, we investigated the carotenoid production of two closely related methylotrophic strai ns, Methylorubrum extorquens PA1 and AM1 (short PA1 & AM1), with a particular focus on the influence of iron availability. We identified and comprehensively structurally characterised the main carotenoid produced by both strains by using ultraviolet–visible (UV– Vis ) spectroscopy, high-performance liquid chromatography (HPLC), high-resolution mass spectrometry (HRMS) with collision-induced dissociation (CID), ion mobility–mass spectrometry (IM–MS), nuclear magnetic resonance (NMR) spectroscopy, and ultrafast transient absorption (TA) spectroscopy. We show that both strains produce, unaffected by the iron availability, the same carotenoid, identified as 4-[2-O-11Z-octadecenoyl-β-D-glucopyranosyl]-4,4′-diapo-Ψ,Ψ-carotene-4,4′-dioate. However, the iron availability strongly influenced the carotenoid production making it a tuneable parameter for boosting bacterial carotenogenis in biotechnological settings.

Methylobacterium species are prominent members of the plant phyllosphere, where they are exposed to fluctuating environmental conditions, including intense ultraviolet (UV) radiation. To mitigate such stressors, these bacteria commonly synthesise carotenoids as an oxidative protection. In this study, we investigated the carotenoid production of two closely related methylotrophic strains, Methylobacterium extorquens PA1 and AM1 (short PA1 & AM1), with a particular focus on the influence of iron availability. We identified and comprehensively structurally characterised the main carotenoid produced by both strains by using ultraviolet-visible (UV-Vis) spectroscopy, high-performance liquid chromatography (HPLC), high-resolution mass spectrometry (HRMS) with collision-induced dissociation (CID), ion mobility-mass spectrometry (IM-MS), nuclear magnetic resonance (NMR) spectroscopy, and ultrafast transient absorption (TA) spectroscopy. We show that both strains produce, unaffected by the iron availability, the same carotenoid, identified as 4-[2-O-11Zoctadecenoyl-β-D-glucopyranosyl]-4,4′-diapo-Ψ,Ψ-carotene-4,4′-dioate. However, the iron availability strongly influenced the carotenoid production making it an potentially interesting factor for boosting bacterial carotenogenis in biotechnological settings.

Transient absorption (TA) is the most prominent method to observe relaxation dynamics in the toolbox of ultrafast spectroscopy. Within the framework of time-dependent perturbation theory, TA is a third-order technique as it relies on two interactions with the pump and one with the probe field. Since the advent of ultrafast TA, researchers have struggled to limit or better quantify the contributions of higher orders, such as the fifth order, as they will emerge along the same phase matching direction as the desired third order. Intensity cycling is a recently demonstrated experimental approach to isolate third from higher order signals. It requires transient absorption spectra at a minimum of three different intensities. This is experimentally challenging as the conditions for these three experiments need to be as similar as possible for a meaningful comparison. We present a solution to this problem based on a Sagnac-interferometer. Our design allows for shot-to-shot variations of pump pulse intensities. An entire intensity cycling dataset with 290 delay times for three different pump excitation densities is recorded within 30 min. We demonstrate the feasibility of our setup on a cyanine dye in solution.

Coordination polymers (CPs) represent an innovative class of materials with proven potential for multiphoton absorption applications. However, understanding the structure‐property relationships that govern their nonlinear optical behavior remains challenging. This study presents an in‐depth investigation of the effects of intermolecular interactions on multiphoton absorption by focusing on the synthesis and characterization of 1,6,7,12‐tetrachloroperylenediimide‐N,N'‐di‐(acetic acid) ( H ₂ tpda ) and its coordination with zinc to form [Zn ₂ tpda(DMA) ₂ (DMF) _0.3 ] ( Zntpda ). How the packing of tpda linkers within the coordination framework influences their optical properties is revealed. The analysis demonstrates that Zntpda exhibits a broadened UV–vis absorption spectrum with no emission indicative of H‐type aggregation with additional evidence of a photo‐induced electron transfer. Z‐scan measurements show enhanced two‐photon absorption (2PA) cross‐sections of Zntpda compared to H ₂ tpda and even three‐photon absorption (3PA). This is explained by intermolecular interactions, electronic coupling, and spatial confinement effects within the polymer. The findings underscore the critical role of chromophore orientation and packing in optimizing nonlinear optical performance, offering insights for designing advanced functional CP materials tailored for photonic applications.

Metal–organic frameworks (MOFs) are emerging as promising materials for multiphoton absorption (MPA), a nonlinear optical phenomenon relevant for applications, such as bioimaging, phototherapy, and photonic devices. However, the structural features that govern their exceptional MPA activity remain poorly understood. To address this, a family of pyrene‐based MOFs (NU‐1000, NU‐901, SrTBAPy, and BaTBAPy), that vary in topology and secondary building units (SBUs), is systematically investigated. Significant differences are observed in the two‐photon absorption (2PA) cross‐section σ ⁽²⁾ , with BaTBAPy exhibiting the highest activity (8.2 × 10 ⁴ GM). Quantum mechanical calculations reveal that intermolecular chromophore interactions and SBU‐induced effects contribute strongly to enhanced σ ⁽²⁾ values, particularly in NU‐901 and BaTBAPy. The findings demonstrate that both framework topology and metal coordination environments are critical to modulating MPA behavior. These insights into the structure–property relationships of MOFs pave the way for rational design of next‐generation nonlinear optical materials.

Two-dimensional fluorescence excitation spectroscopy (2D-FLEX) was introduced recently as a novel ultrafast spectroscopic technique focusing on excited state dynamics. 2D-FLEX is an extension of broadband-detected time-gated fluorescence experiments, upgraded by double pulse excitation. A Fourier transformation over the pulse-pair delay retrieves the excitation frequency dependence of the fluorescence signal. This is especially advantageous for studying ultrafast excited state relaxation and reorganization processes in excitonically coupled systems. This work describes two experimental implementations of 2D-FLEX using fluorescence upconversion and non-collinear optical parametric amplifier (NOPA) technology. We compare and discuss both approaches, outlining their advantages and limitations. We present first results from two-photon excitation spectroscopy measurement conducted with 10 fs pulses. Graphical abstract