The Lowest Excited State of Heptacenes Is Dark.

Understanding the electronic structure of polycyclic aromatic compounds is of fundamental importance for their potential applications. The optoelectronic properties of shorter acenes such as tetracene and pentacene have been extensively studied with regard to excitation, emission, and nonlinear effects such as singlet fission. The longer homologues present a unique challenge due to their low stability both in the solid state and in solution.

Mechanically Robust Supercrystals from Antisolvent-Induced Assembly of Perovskite Nanocrystals.

Ordered arrays of nanocrystals, called supercrystals, have attracted significant attention owing to the collective quantum effects arising from the coupling between neighboring nanocrystals. In particular, lead halide perovskite nanocrystals are widely used because of the combination of the optical properties and faceted cubic shape, which enables the formation of highly ordered supercrystals. The most frequently used method for the fabrication of perovskite supercrystals is based on the self-assembly of nanocrystals from solution via slow evaporation of the solvent.

Rearrangement Cascade Initiated by Nucleophilic Benzyne Attack on 3,6-Di(2-pyridyl)-1,2-diazines.

Aryne intermediates in synthetic organic chemistry offer versatile routes to complex heterocyclic structures that are valuable in pharmaceuticals and materials science. We present a one-step aryne-mediated reaction to synthesize pyrido[1,2-]indoles interconnected through vinylene or 1,2-phenylene linkers to pyridotriazoles using 2-pyridyl-substituted pyridazines and phthalazines as confirmed via single-crystal X-ray crystallography and NMR spectroscopy. This unexpected rearrangement proceeds under mild conditions.

The family of tetranuclear NbOI clusters ( = 0, 1, 2): from the molecular NbOI cluster to extended chains and layers.

Unconventional reduction reactions in the Nb-O-I system have produced a number of niobium oxyiodides containing the oxygen-centered [NbO] cluster. Crystalline NbOI and two modifications of NbOI were structurally characterized by means of single-crystal X-ray diffraction studies. The new compounds can be classified as members of the NbOI family, together with the already known NbOI.

Spectroelectrochemistry with hydrogen-doped indium oxide electrodes monitors electron and hole injection into PbS quantum dots.

We combine potential-modulated absorption spectroscopy with working electrodes made of hydrogen-doped indium oxide on glass to study the electrochemically induced changes to the infrared absorption of ethanedithiol-crosslinked PbS quantum dot thin films. We demonstrate an electrochemical window of -1.5 V to 1 V ferrocene/ferrocenium as well as a spectral window of 800 nm - 1900 nm, and we show how these ranges can be fine-tuned by tailoring the composition of the working electrode.

Ultrafast Hot Carrier Cooling Enabled van der Waals Photodetectors at Telecom Wavelengths.

Two-dimensional (2D) materials with high carrier mobility and picosecond intrinsic response times exhibit large potential for fast optoelectronics operating at telecom wavelengths. However, due to the inefficient utilization of hot carriers, 2D photodetectors for the telecom C-band have rarely been realized. Here, we report a high-performance and waveguide-free WS/graphene photodetector operating at 1560 nm enabled by hot carrier injection and long-lived charge separation.

Reactivatable stimulated emission depletion microscopy using fluorescence-recoverable nanographene.

Stimulated emission depletion (STED) microscopy, a key optical super-resolution imaging method, has extended our ability to view details to resolution levels of tens of nanometers. Its resolution depends on fluorophore de-excitation efficiency, and increases with depletion laser power. However, high-power irradiation permanently turns off the fluorescence due to photo-bleaching of the fluorophores.

Fluorescence lifetime imaging unravels the pathway of glioma cell death upon hypericin-induced photodynamic therapy.

Malignant primary brain tumors are a group of highly aggressive and often infiltrating tumors that lack adequate therapeutic treatments to achieve long time survival. Complete tumor removal is one precondition to reach this goal. A promising approach to optimize resection margins and eliminate remaining infiltrative so-called guerilla cells is photodynamic therapy (PDT) using organic photosensitizers that can pass the disrupted blood-brain-barrier and selectively accumulate in tumor tissue.

TaSBr: A Cluster Mott Insulator with a Corrugated, Van der Waals Layered Structure.

The compound TaSBr was prepared by a comproportionation reaction of tantalum bromide with tantalum and elemental sulfur. The crystal structure, as refined by single-crystal X-ray diffraction, is composed of clusters with TaS cores, arranged in corrugated van der Waals layers. Individual layers appear to be displaced relative to each other along one direction.

A simple 230 MHz photodetector based on exfoliated WSe multilayers.

We demonstrate 230 MHz photodetection and a switching energy of merely 27 fJ using WSe multilayers and a very simple device architecture. This improvement over previous, slower WSe devices is enabled by systematically reducing the RC constant of devices through decreasing the photoresistance and capacitance. In contrast to MoS, reducing the WSe thickness toward a monolayer only weakly decreases the response time, highlighting that ultrafast photodetection is also possible with atomically thin WSe.

Synthesis of Thiourea and Thioamide -Oxides via SO Transfer from a Thiirane -Oxide onto -Heterocyclic Carbenes.

Thiourea -oxides are labile compounds that suffer from a quick overoxidation when directly prepared from thioureas. Therefore, we have developed an alternative route on the basis of the SO transfer from a thiirane -oxide onto sterically encumbered -heterocyclic carbenes, including imidazole- and imidazoline-ylidenes, and a cyclic alkyl amino carbene. Reaction conditions and DFT computations suggest a concerted SO transfer mechanism.

Dual polarization-enabled ultrafast bulk photovoltaic response in van der Waals heterostructures.

The bulk photovoltaic effect (BPVE) originating from spontaneous charge polarizations can reach high conversion efficiency exceeding the Shockley-Queisser limit. Emerging van der Waals (vdW) heterostructures provide the ideal platform for BPVE due to interfacial interactions naturally breaking the crystal symmetries of the individual constituents and thus inducing charge polarizations. Here, we show an approach to obtain ultrafast BPVE by taking advantage of dual interfacial polarizations in vdW heterostructures.

Toward Gigahertz Photodetection with Transition Metal Dichalcogenides.

ConspectusTransition metal dichalcogenides (TMDCs) exhibit favorable properties for optical communication in the gigahertz (GHz) regime, such as large mobilities, high extinction coefficients, cheap fabrication, and silicon compatibility. While impressive improvements in their sensitivity have been realized over the past decade, the bandwidths of these devices have been mostly limited to a few megahertz. We argue that this shortcoming originates in the relatively large RC constants of TMDC-based photodetectors, which suffer from high surface defect densities, inefficient charge carrier injection at the electrode/TMDC interface, and long charging times.

Colloidal 2D MoWS nanosheets: an atomic- to ensemble-level spectroscopic study.

Composition dependent tuning of electronic and optical properties in semiconducting two-dimensional (2D) transition metal dichalcogenide (TMDC) alloys is promising for tailoring the materials for optoelectronics. Here, we report a solution-based synthesis suitable to obtain predominantly monolayered 2D semiconducting MoWS nanosheets (NSs) with controlled composition as substrate-free colloidal inks. Atomic-level structural analysis by high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectroscopy (EDXS) depicts the distribution of individual atoms within the MoWS NSs and reveals the tendency for domain formation, especially at low molar tungsten fractions.

Electronic structure and transport in the potential Luttinger liquids CsNbBrS and RbNbBrS.

The crystal structures of ANbBrS (A = Rb and Cs) have been refined by single crystal X-ray diffraction, and are found to form highly anisotropic materials based on chains of the triangular Nb cluster core. The Nb cluster core contains seven valence electrons, six of them being assigned to Nb-Nb bonds within the Nb triangle and one unpaired d electron. The presence of this surplus electron gives rise to the formation of correlated electronic states.

Direct laser induced writing of high precision gold nanosphere SERS patterns.

The high sensitivity and molecular fingerprint capability of Surface-Enhanced Raman Spectroscopy (SERS) have lead to a wide variety of applications ranging from classical physics, chemistry over biology to medicine. Equally, there are numerous methods to fabricate samples owing to the desired properties and to create the localized surface plasmon resonances (LSPRS). However, for many applications the LSPRs must be specifically localized on micrometer sized areas and multiple steps of lithography are needed to achieve the desired substrates.

Stabilization of Colloidal Germanium Nanoparticles: From the Study to the Prospects of the Application in Thin-Film Technology.

We present the stabilization of halide-terminated Ge nanoparticles prepared via a disproportionation reaction of metastable Ge(I)X solutions with well-defined size distribution. Further tailoring of the stability of the Ge nanoparticles was achieved using variations in the substituent. Ge nanoparticles obtained in this way are readily dispersed in organic solvents, long-term colloidally stable, and are perfect prerequisites for thin-film preparation.

A Saddle-Shaped Expanded Porphyrinoid Fitting C.

We present the synthesis of a new type of an expanded porphyrinoid macrocycle with a saddle-shaped morphology and its complexation of C guest molecules. The new macrocycle contains four carbazole and four triazole moieties and can be readily synthesized via a copper-catalyzed click reaction. It shows specific photo-physical properties including fluorescence with a high quantum yield of 60 %.

Edge contacts accelerate the response of MoS photodetectors.

We use a facile plasma etching process to define contacts with an embedded edge geometry for multilayer MoS photodetectors. Compared to the conventional top contact geometry, the detector response time is accelerated by more than an order of magnitude by this action. We attribute this improvement to the higher in-plane mobility and direct contacting of the individual MoS layers in the edge geometry.

Zwitterionic Carbazole Ligands Enhance the Stability and Performance of Perovskite Nanocrystals in Light-Emitting Diodes.

We introduce a new carbazole-based zwitterionic ligand (DCzGPC) synthesized via Yamaguchi esterification which enhances the efficiency of lead halide perovskite (LHP) nanocrystals (NCs) in light-emitting diodes (LED). A facile ligand exchange of the native ligand shell, monitored by nuclear magnetic resonance (NMR), ultraviolet-visible (UV-vis), and photoluminescence (PL) spectroscopy, enables more stable and efficient LHP NCs. The improved stability is demonstrated in solution and solid-state LEDs, where the NCs exhibit prolonged luminescence lifetimes and improved luminance, respectively.

Heading toward Miniature Sensors: Electrical Conductance of Linearly Assembled Gold Nanorods.

Metal nanoparticles are increasingly used as key elements in the fabrication and processing of advanced electronic systems and devices. For future device integration, their charge transport properties are essential. This has been exploited, e.

Nanometer Sized Direct Laser-Induced Gold Printing for Precise 2D-Electronic Device Fabrication.

Flexible electronics manufacturing technologies are essential and highly favored for future integrated photonic and electronic devices. Direct laser induced writing (DIW) of metals has shown potential as a fast and highly variable method in adaptable electronics. However, most of the DIW procedures use silver structures, which tend to oxidize and are limited to the micrometer regime.

Electronic Structure of Colloidal 2H-MoS Mono and Bilayers Determined by Spectroelectrochemistry.

The electronic structure of mono and bilayers of colloidal 2H-MoS nanosheets synthesized by wet-chemistry using potential-modulated absorption spectroscopy (EMAS), differential pulse voltammetry, and electrochemical gating measurements is investigated. The energetic positions of the conduction and valence band edges of the direct and indirect bandgap are reported and observe strong bandgap renormalization effects, charge screening of the exciton, as well as intrinsic n-doping of the as-synthesized material. Two distinct transitions in the spectral regime associated with the C exciton are found, which overlap into a broad signal upon filling the conduction band.

Preparation, photoluminescence and excited state properties of the homoleptic cluster cation [(WI)(CHCN)].

Solvated tungsten iodide cluster compounds are presented with the homoleptic cluster cation [(WI)(CHCN)] and the heteroleptic [(WI)I(CHCN)], synthesized from WI in acetonitrile. Crystal structures were solved and refined on deep red single-crystals of [(WI)(CHCN)](I)(BF)·HO, [(WI)I(CHCN)](I)(BF), and on a yellow single-crystal of [WI(CHCN)](BF)·2(CHCN) on the basis of X-ray diffraction data. The structure of the homoleptic [(WI)(CHCN)] cluster is based on the octahedral [WI] tungsten iodide cluster core, coordinated by six apical acetonitrile ligands.

Untangling the intertwined: metallic to semiconducting phase transition of colloidal MoS nanoplatelets and nanosheets.

2D semiconducting transition metal dichalcogenides (TMDCs) are highly promising materials for future spin- and valleytronic applications and exhibit an ultrafast response to external (optical) stimuli which is essential for optoelectronics. Colloidal nanochemistry on the other hand is an emerging alternative for the synthesis of 2D TMDC nanosheet (NS) ensembles, allowing for the control of the reaction tunable precursor and ligand chemistry. Up to now, wet-chemical colloidal syntheses yielded intertwined/agglomerated NSs with a large lateral size.