Singlet Fission, Polaron Generation and Intersystem Crossing in Hexaphenyl Film.

The ultrafast dynamics of triplet excitons and polarons in hexaphenyl film was investigated by time-resolved fluorescence and femtosecond transient absorption techniques under various excitation photon energies. Two distinct pathways of triplet formation were clearly observed. Long-lived triplet states are populated within 4.

Growth direction dependent separate-channel charge transport in the organic weak charge-transfer co-crystal of anthracene-DTTCNQ.

Co-crystallization is an efficient way of molecular crystal engineering to tune the electronic properties of organic semiconductors. In this work, we synthesized anthracene-4,8-bis(dicyanomethylene)4,8-dihydrobenzo[1,2-:4,5-']-dithiophene (DTTCNQ) single crystals as a template to study the crystal growth direction dependent charge transport properties and attempted to elucidate the mechanism by proposing a separate-channel charge transport model. Single-crystal anthracene-DTTCNQ field-effect transistors showed that ambipolar transport properties could be observed in all crystal growth directions.

Tuning the π-π overlap and charge transport in single crystals of an organic semiconductor via solvation and polymorphism.

Polymorphism is a central phenomenon in materials science that often results in important differences of the electronic properties of organic crystals due to slight variations in intermolecular distances and positions. Although a large number of π-conjugated organic compounds can grow as polymorphs, it is necessary to have at disposal a series of several polymorphs of the same molecule to establish clear and predictive structure-property relationships. We report here on the occurrence of two solvates and three polymorphs in single crystalline form of the organic p-type semiconductor 2,2',6,6'-tetraphenyldipyranylidene (DIPO).

Single-photon upconversion in 6-pentaceneone crystal from bulk to ultrathin flakes.

Phonon-assisted single-photon upconversion, which was not previously reported in organic materials, has been demonstrated in the 6-pentaceneone crystal through the linear pumping power dependent anti-Stokes photoluminescence (ASPL), nanoseconds PL lifetime and quenched ASPL at low temperature. Furthermore, the 6-pentaceneone crystal can be mechanically exfoliated to ultrathin flakes and it exhibits thickness-dependent photoluminescence.

Trisulfide-Bond Acenes for Organic Batteries.

The molecular design of organic battery electrodes is a big challenge. Here, we synthesize two metal-free organosulfur acenes and shed insight into battery properties using first-principles calculations. A new zone-melting chemical-vapor-transport (ZM-CVT) apparatus was fabricated to provide a simple, solvent-free, and continuous synthetic protocol, and produce single crystals of tetrathiotetracene (TTT) and hexathiapentacene (HTP) at a large scale.

Preparation of 1T'-Phase ReSSe ( x = 0-1) Nanodots for Highly Efficient Electrocatalytic Hydrogen Evolution Reaction.

As a source of clean energy, a reliable hydrogen evolution reaction (HER) requires robust and highly efficient catalysts. Here, by combining chemical vapor transport and Li-intercalation, we have prepared a series of 1T'-phase ReSSe ( x = 0-1) nanodots to achieve high-performance HER in acid medium. Among them, the 1T'-phase ReSSe nanodot exhibits the highest hydrogen evolution activity, with a Tafel slope of 50.

Hole Mobility Modulation in Single-Crystal Metal Phthalocyanines by Changing the Metal-π/π-π Interactions.

Weak intermolecular interactions in organic semiconducting molecular crystals play an important role in determining molecular packing and electronic properties. Single crystals of metal-free and metal phthalocyanines were synthesized to investigate how the coordination of the central metal atom affects their molecular packing and resultant electronic properties. Single-crystal field-effect transistors were made and showed a hole mobility order of ZnPc>MnPc>FePc>CoPc>CuPc>H Pc>NiPc.

Corrigendum: Control of Radiative Exciton Recombination by Charge Transfer Induced Surface Dipoles in MoS and WS Monolayers.

This corrects the article DOI: 10.1038/srep24105.

From Linear to Angular Isomers: Achieving Tunable Charge Transport in Single-Crystal Indolocarbazoles Through Delicate Synergetic CH/NH⋅⋅⋅π Interactions.

Weak intermolecular interaction in organic semiconducting molecular crystals plays an important role in molecular packing and electronic properties. Here, four five-ring-fused isomers were rationally designed and synthesized to investigate the isomeric influence of linear and angular shapes in affecting their molecular packing and resultant electronic properties. Single-crystal field-effect transistors showed mobility order of 5,7-ICZ (3.

Preparation of High-Percentage 1T-Phase Transition Metal Dichalcogenide Nanodots for Electrochemical Hydrogen Evolution.

Nanostructured transition metal dichalcogenides (TMDs) are proven to be efficient and robust earth-abundant electrocatalysts to potentially replace precious platinum-based catalysts for the hydrogen evolution reaction (HER). However, the catalytic efficiency of reported TMD catalysts is still limited by their low-density active sites, low conductivity, and/or uncleaned surface. Herein, a general and facile method is reported for high-yield, large-scale production of water-dispersed, ultrasmall-sized, high-percentage 1T-phase, single-layer TMD nanodots with high-density active edge sites and clean surface, including MoS , WS , MoSe , Mo W S , and MoSSe, which exhibit much enhanced electrochemical HER performances as compared to their corresponding nanosheets.

Molecular Crystal Engineering: Tuning Organic Semiconductor from p-type to n-type by Adjusting Their Substitutional Symmetry.

Focusing on the bottleneck of molecularly engineered organic semiconductors, a breakthrough is made to tune the electronic properties of organic semiconductors from p-type to n-type by using fluorinated metal phthalocyanines as examples. The experimentally observed p-type to n-type transition characteristics of single-crystal field-effect devices result from a combination of extrinsic and intrinsic properties of materials with different fluoridation substitution.

Channels of oxygen diffusion in single crystal rubrene revealed.

Electronic devices made from organic materials have the potential to support a more ecologically friendly and affordable future. However, the ability to fabricate devices with well-defined and reproducible electrical and optical properties is hindered by the sensitivity to the presence of chemical impurities. Oxygen in particular is an impurity that can trap electrons and modify conductive properties of some organic materials.

Additive manufacturing of micrometric crystallization vessels and single crystals.

We present an all-additive manufacturing method that is performed at mild conditions, for the formation of organic single crystals at specific locations, without any photolithography prefabrication process. The method is composed of two steps; inkjet printing of a confinement frame, composed of a water soluble electrolyte. Then, an organic semiconductor solution is printed within the confinement to form a nucleus at a specific location, followed by additional printing, which led to the growth of a single crystal.

Single photon triggered dianion formation in TCNQ and F4TCNQ crystals.

Excited state dynamics in two strong organic electron acceptor systems, TCNQ and F4TCNQ single crystals, was studied. After absorption of a single photon, dianions are formed in both crystals on ultrashort timescale: TCNQ τ < 50 fs, F4TCNQ τ = 4 ps. By use of transient absorption spectroscopy, we demonstrate that the dianion formation in F4TCNQ is mediated by the radical anion precursor which is described by a two-step model.

Control of Radiative Exciton Recombination by Charge Transfer Induced Surface Dipoles in MoS2 and WS2 Monolayers.

Due to the two dimensional confinement of electrons in a monolayer of 2D materials, the properties of monolayer can be controlled by electrical field formed on the monolayer surface. F4TCNQ was evaporated on MoS2 and WS2 monolayer forming dipoles between strong acceptor, F4TCNQ, and monolayers of MoS2 or WS2. The strong acceptor attracts electrons (charge transfer) and decreases the number of the ionized excitons.

Optoelectronic properties of atomically thin ReSSe with weak interlayer coupling.

Rhenium dichalcogenides, such as ReS2 and ReSe2, have attracted a lot of interests due to the weak interlayered coupling in these materials. Studies of rhenium based dichalcogenide alloys will help us understand the differences between binary rhenium dichalcogenides. They will also extend the applications of two-dimensional (2D) materials through alloying.

Preparation of Single-Layer MoS(2x)Se2(1-x) and Mo(x)W(1-x)S2 Nanosheets with High-Concentration Metallic 1T Phase.

The high-yield and scalable production of single-layer ternary transition metal dichalcogenide nanosheets with ≈66% of metallic 1T phase, including MoS(2x)Se2(1-x) and Mo(x)W(1-x)S2 is achieved via electrochemical Li-intercalation and the exfoliation method. Thin film MoS(2x)Se2(1- x) nanosheets drop-cast on a fluorine-doped tin oxide substrate are used as an efficient electrocatalyst on the counter electrode for the tri-iodide reduction in a dye-sensitized solar cell.

Correlation of Local Structure and Diffusion Pathways in the Modulated Anisotropic Oxide Ion Conductor CeNbO(4.25).

CeNbO4.25 is reported to exhibit fast oxygen ion diffusion at moderate temperatures, making this the prototype of a new class of ion conductor with applications in a range of energy generation and storage devices. To date, the mechanism by which this ion transport is achieved has remained obscure, in part due to the long-range commensurately modulated structural motif.

Weak Van der Waals Stacking, Wide-Range Band Gap, and Raman Study on Ultrathin Layers of Metal Phosphorus Trichalcogenides.

2D semiconducting metal phosphorus trichalcogenides, particularly the bulk crystals of MPS3 (M = Fe, Mn, Ni, Cd and Zn) sulfides and MPSe3 (M = Fe and Mn) selenides, have been synthesized, crystallized and exfoliated into monolayers. The Raman spectra of monolayer FePS3 and 3-layer FePSe3 show the strong intralayer vibrations and structural stability of the atomically thin layers under ambient condition. The band gaps can be adjusted by element choices in the range of 1.

Plasma-enhanced microwave solid-state synthesis of cadmium sulfide: reaction mechanism and optical properties.

CdS synthesis by plasma-enhanced microwave physical vapor transport (PMPVT) has been developed in this work. The photoluminescence (PL), absorbance, Raman spectra and the mechanism of CdS crystal growth have been investigated. Furthermore, plasma-enhanced microwave chemical vapour transport (PMCVT) synthesis of CdS with additional chemical transport agents has been explored.

Fluorination of metal phthalocyanines: single-crystal growth, efficient N-channel organic field-effect transistors, and structure-property relationships.

The fluorination of p-type metal phthalocyanines produces n-type semiconductors, allowing the design of organic electronic circuits that contain inexpensive heterojunctions made from chemically and thermally stable p- and n-type organic semiconductors. For the evaluation of close to intrinsic transport properties, high-quality centimeter-sized single crystals of F16CuPc, F16CoPc and F16ZnPc have been grown. New crystal structures of F16CuPc, F16CoPc and F16ZnPc have been determined.

Excited-state dynamics in an α-perylene single crystal: two-photon- and consecutive two-quantum-induced singlet fission.

Excited-state dynamics in α-perylene single crystals is studied by time-resolved fluorescence and transient absorption techniques under different excitation conditions. The ultrafast lifetimes of the "hot" excimer (Y) state were resolved. Three competing excited-states decay channels are observed: excimer formation, dimer cation generation, and singlet fission.

Origin of indirect optical transitions in few-layer MoS2, WS2, and WSe2.

It has been well-established that single layer MX2 (M = Mo, W and X = S, Se) are direct gap semiconductors with band edges coinciding at the K point in contrast to their indirect gap multilayer counterparts. In few-layer MX2, there are two valleys along the Γ-K line with similar energy. There is little understanding on which of the two valleys forms the conduction band minimum (CBM) in this thickness regime.

Lattice dynamics in mono- and few-layer sheets of WS2 and WSe2.

Thickness is one of the fundamental parameters that define the electronic, optical, and thermal properties of two-dimensional (2D) crystals. Phonons in molybdenum disulfide (MoS2) were recently found to exhibit unique thickness dependence due to the interplay between short and long range interactions. Here we report Raman spectra of atomically thin sheets of WS2 and WSe2, isoelectronic compounds of MoS2, in the mono- to few-layer thickness regime.

Two-photon-induced singlet fission in rubrene single crystal.

The two-photon-induced singlet fission was observed in rubrene single crystal and studied by use of femtosecond pump-probe spectroscopy. The location of two-photon excited states was obtained from the nondegenerate two-photon absorption (TPA) spectrum. Time evolution of the two-photon-induced transient absorption spectra reveals the direct singlet fission from the two-photon excited states.