Photoinduced Charge Separation in Molecular Silicon

Interest in molecular silicon semiconductors arises from the properties shared with bulk silicon like earth abundance and the unique architectures accessible from a structure distinctly different than rigid π‐conjugated organic semiconductors. We report ultrafast spectroscopic evidence for direct, photoinduced charge separation in molecular silicon semiconductors that supports the viability of molecular silicon as donor materials in optoelectronic devices. The materials in this study are σ–π hybrids, in which electron‐deficient aromatic acceptors flank a σ‐conjugated silicon chain. Transient absorption and femtosecond‐stimulated Raman spectroscopy (FSRS) techniques revealed signatures consistent with direct, optical charge transfer from the silane chain to the acceptor; these signatures were only observed by probing excited‐state structure. Our findings suggest new opportunities for controlling charge separation in molecular electronics.     

Thio- und Selenomercurate(II). K6[HgS4], K6[HgSe4], Rb6[HgS4] und Rb6[HgSe4]

Thio- and Selenomercurates(II). K₆[HgS₄], K₆[HgSe₄], Rb₆[HgS₄] and Rb₆[HgSe₄] We prepared by annealing intimate mixture of pure samples of K₂S, K₂Se, Rb₂S, and Rb₂Se with HgS or HgSe [360–380°C, 7d, Duran-glass-seal with Argon] with hexagonal Na₆ZnO₄ isotypic new mercurates: K₆[HgS₄] [bright citronic yellow a = 9.98₅, c = 7.65₂ Å], K₆[HgSe₄] [light orange yellow a = 10.3₆, c = 7.88₃ Å], Rb₆[HgS₄] [bright yellow a = 10.3₄, c = 7.94₂ Å], Rb₆[HgSe₄] [orange-red a = 10.7₂, c = 8.19₂ Å]. The crystal structure of K₆ Hgs₄ is elucidated by using diffractometer data of single crystals: P63mc, C⁴_6v, it is R = 6.6% for 304 reflexes [h k o–h k 4, anisotropic refinement MoKα]; for position and parameters see text d_rö = 2.83₅, d_pyk = 2.99 g · cm^?3. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, are calculated and discussed.     

Functionalized Porphyrin Discotic Liquid Crystals: Photoinduced Charge Separation and Trapping

Individual members of a family of highly absorptive porphyrins bearing symmetrically positioned flexible side chains form discotic liquid crystalline mesophases at modest temperature ranges. The order of this phase is preserved when a thin layer of this self-assembled material is cooled to room temperature. Exposure of such films to visible excitation, with or without an externally applied electrical field, produces photovoltaic effects and/or charge trapping. The latter effect constitutes the basis for optoelectronic information storage.     

掺Sn的纳米TiO2表面光致电荷分离及光催化活性

采用溶胶-凝胶法制备了不同掺Sn量的TiO₂纳米粒子, 主要利用表面光电压谱(SPS)和光致发光光谱(PL)对样品进行了表征, 并通过光催化降解苯酚实验来评估样品活性. 重点考察了热处理温度和掺Sn量对样品表面光生载流子的分离及光催化活性的影响, 并探讨了Sn使TiO₂纳米粒子改性的机制. 结果表明, 在适当温度处理下, 适量Sn的掺入能够有效促进TiO₂纳米粒子表面光生载流子的分离, 以至于使其光催化活性得到显著提高.     

Long‐Lived,Directional Photoinduced Charge Separation in RuII Complexes Bearing Laminate Polypyridyl Ligands

Ru^II complexes incorporating both amide‐linked bithiophene donor ancillary ligands and laminate acceptor ligands; dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz), tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h:2′′′,3′′′‐j]phenazine (tpphz), and 9,11,20,22‐tetraazatetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐l:2′′′,3′′′]‐pentacene (tatpp) exhibit long‐lived charge separated (CS) states, which have been analyzed using time‐resolved transient absorption (TA), fluorescence, and electronic absorption spectroscopy in addition to ground state electrochemical and spectroelectrochemical measurements. These complexes possess two electronically relevant ³MLCT states related to electron occupation of MOs localized predominantly on the proximal “bpy‐like” portion and central (or distal) “phenazine‐like” portion of the acceptor ligand as well as energetically similar ³LC and ³ILCT states. The unusually long excited state lifetimes (τ up to 7 μs) observed in these complexes reflect an equilibration of the ³MLCT_prox or ³MLCT_dist states with additional triplet states, including a ³LC state and a ³ILCT state that formally localizes a hole on the bithiophene moiety and an electron on the laminate acceptor ligand. Coordination of a Zn^II ion to the open coordination site of the laminate acceptor ligand is observed to significantly lower the energy of the ³MLCT_dist state by decreasing the magnitude of the excited state dipole and resulting in much shorter excited state lifetimes. The presence of the bithiophene donor group is reported to substantially extend the lifetime of these Zn adducts via formation of a ³ILCT state that can equilibrate with the ³MLCT_dist state. In tpphz complexes, Zn^II coordination can reorder the energy of the ³MLCT_prox and ³MLCT_dist states such that there is a distinct switch from one state to the other. The net result is a series of complexes that are capable of forming CS states with electron–hole spatial separation of up to 14 Å and possess exceptionally long lifetimes by equilibration with other triplet states.     

2,4,6-Tri(4-pyridyl)-1,3,5-triazine: Photoinduced Charge Separation and Photochromism in the Crystalline State

2,4,6-Tri(4-pyridyl)-1,3,5-triazine (tpt) is a widely used ligand for functional coordination compounds. In this work, tpt has shown unprecedented photochromism in the crystalline state. Experimental and theoretical data has revealed that the photocoloration of tpt very likely originates from intramolecular charge separation and the formation of a triplet diradical product. This finding demonstrates a new simple, neutral photochromic molecule and endows the tpt molecule and related compounds with potential optical applications.     

Preparation,structure, and unique thermal [2+2], [4+2], and [3+2] cycloaddition reactions of 4-vinylideneoxazolidin-2-one

The terminal allene C(alpha)=C(beta) bonds of 4vinylidene-2-oxazolidinone (2) readily undergo [2+2] cycloaddition with a wide variety of terminal alkynes, alkenes, and 1,3-dienes irrespective of their electronic nature under strictly thermal activation conditions (70-100 degrees C) and provide 3substituted (Z)-methylenecyclobutenes 6, 3substituted methylenecyclobutanes 7 and 8, and 3vinylmethylenecyclobutanes 9, respectively, in good to excellent yields. Alkenes react with 2 with complete retention of configuration. The [2+2] cycloaddition is concluded to proceed via a concerted [(pi(2s)+pi(2s))(allene) + pi(2s)] Hückel transition state on the basis of experimental evidences and quantum mechanical methods. Some highly polarized enones and nitrile oxide, on the other hand, react with 2 selectively at the internal C(4)=C(alpha) double bonds and give spiro compounds 10 and 11, respectively. The bent allene bonds (173-176 degrees) and the unique reactivity associated with 2 are attributed to a low-lying LUMO (C(alpha)=C(beta)) that is substantiated by a through-space sigma*(N-SO(2))-pi*(C(alpha)=C(beta)) orbital interaction.     

Synthesis, structure, and magnetism of heterometallic carboxylate complexes [MnIII2M(II)4O2(PhCOO)10(DMF)4], M = Mn(II), Co(II), Ni(II)

Three new homo- and heterometallic hexanuclear complexes [Mn(2)M(II)(4)O(2)(PhCOO)(10)(DMF)(4)] (with M = Mn (1), Co (2) or Ni (3) and DMF = dimethylformamide) have been synthesized by redox generation of benzoate ligands from benzaldehyde in a one-pot reaction. All of the compounds are isostructural and crystallize in the I-42d space group of the tetragonal system, data for 1: a = 27.2249(8) Angstroms, c = 25.5182(5) Angstroms, R1 = 0.0681. The crystal structure contains isolated molecules. Each molecule consists of 2 x Mn(III) surrounded by four M(II) ions to form two edge-sharing OMn(2)M(2) tetrahedra giving rise to the [Mn(2)M(4)O(2)] core. The coordination sphere of each metal is completed by the bridging benzoate ligands and DMF molecules. The magnetic susceptibilities of 1-3 have been measured in the 1.8 K < T < 300 K temperature range. The magnetic susceptibilities for 1 and 2 pass through a broad maximum at low temperature which is characteristic of the diamagnetic ground state, while for 3 no maximum is detected down to 1.8 K. The magnetic data have been interpreted quantitatively for 1 and 3 on the basis of spin exchange interactions between the metallic centers (spin Hamiltonian for a pair being H(AB) = -J(AB) S(A).S(B)). Single-crystal measurements on [Mn(6)O(2)(PhCOO)(10)(CH(3)CN)(4)] (4) show that significant magnetic anisotropy develops at low temperature.     

Suppression of Charge Recombination by Auxiliary Atoms in Photoinduced Charge Separation Dynamics with Mn Oxides: A Theoretical Study

Charge separation is one of the most crucial processes in photochemical dynamics of energy conversion, widely observed ranging from water splitting in photosystem II (PSII) of plants to photoinduced oxidation reduction processes. Several basic principles, with respect to charge separation, are known, each of which suffers inherent charge recombination channels that suppress the separation efficiency. We found a charge separation mechanism in the photoinduced excited-state proton transfer dynamics from Mn oxides to organic acceptors. This mechanism is referred to as coupled proton and electron wave-packet transfer (CPEWT), which is essentially a synchronous transfer of electron wave-packets and protons through mutually different spatial channels to separated destinations passing through nonadiabatic regions, such as conical intersections, and avoided crossings. CPEWT also applies to collision-induced ground-state water splitting dynamics catalyzed by Mn₄CaO₅ cluster. For the present photoinduced charge separation dynamics by Mn oxides, we identified a dynamical mechanism of charge recombination. It takes place by passing across nonadiabatic regions, which are different from those for charge separations and lead to the excited states of the initial state before photoabsorption. This article is an overview of our work on photoinduced charge separation and associated charge recombination with an additional study. After reviewing the basic mechanisms of charge separation and recombination, we herein studied substituent effects on the suppression of such charge recombination by doping auxiliary atoms. Our illustrative systems are X–Mn(OH)₂ tied to N-methylformamidine, with X=OH, Be(OH)₃, Mg(OH)₃, Ca(OH)₃, Sr(OH)₃ along with Al(OH)₄ and Zn(OH)₃. We found that the competence of suppression of charge recombination depends significantly on the substituents. The present study should serve as a useful guiding principle in designing the relevant photocatalysts.     

Zur Kenntnis der Oxocobaltate(II) Na4[CoO3], ein Nesocobaltat(II)

On the Knowledge of Oxocobaltates(II). Na₄[CoO₃], the First Nesocobaltate(II) Newly prepared transparent, blood red single crystals of Na₄[CoO₃] (Na₂O/?CoO’? Na:Co = 4.4:1, cobalt tube, 550°C, 20d, dry argon), crystallize triclinically, P1, a = 8.14₄, b = 6.22₀, c = 5.75₈ Å; α = 117.5, β = 89.9, γ = 111.2 (diffractometer data), Z = 2. There are carbonate-like, isolated [CoO₃] groups, respectively parameters and distances see text. 2358 symmetry independent reflections (automatical four cycle diffractometer PW 1100, Mo–Kα, graphite monochromator, 4° ? Θ ? 36°), R = 0.0597. The Madelung Part of the Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN and Mean Fictive Ionic Radii, MEFIR are calculated and discussed.     

The Driving Force of Photoinduced Charge Separation in Metal‐Cluster‐Encapsulated Triphenylamine‐[80]fullerenes

Understanding photoinduced charge separation in fullerene‐based dye‐sensitized solar cells is crucial for the development of photovoltaic devices. We investigate here how the driving force of the charge separation process in conjugates of M@C₈₀ (M=Sc₃N, Sc₃CH, Sc₃NC, Sc₄O₂, and Sc₄O₃) with triphenylamine (TPA) depends on the nature of the metal cluster. Both singlet and triplet excited‐state electron‐transfer reactions are considered. These results based on TD‐DFT calculations demonstrate that the driving force of charge separation in TPA‐M@C₈₀ can be tuned well by varying the structure of the metal cluster encapsulated inside the fullerene cage.     

Synthesis of Functionalized [3], [4], [5] and [6]Dendralenes through Palladium-Catalyzed Cross-Couplings of Substituted Allenoates

A mild method for the synthesis of highly functionalized [3]–[6]dendralenes is reported, representing a general strategy to diversely substituted higher homologues of the dendralenes. The methodology utilizes allenoates bearing various substitution patterns, along with a wide range of boron and alkenyl nucleophiles that couple under palladium catalysis leading to sp-, sp²-, and sp³-substituted arrays. Regioselective transformations of the newly formed unsymmetrical dendralene derivatives are demonstrated. The use of micellar catalysis, where water is the global reaction medium, and room temperature reaction conditions, highlights the green nature of this technology.     

Noncovalent Functionalization of Few-Layered Antimonene with Fullerene Clusters and Photoinduced Charge Separation in the Composite

Few-layered antimonene (FLSb) nanosheets were noncovalently functionalized with fullerene C₆₀ clusters by quick addition of a poor solvent (i.e., acetonitrile) into a mixed dispersion of FLSb and C₆₀ in a good solvent (i.e., toluene). In a flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurement, the FLSb-C₆₀ composite, (FLSb+C₆₀)_m, showed a rapid rise in transient conductivity, whereas no conductivity signal was observed in the single components, FLSb and C₆₀. This demonstrated the occurrence of photoinduced charge separation between FLSb and C₆₀ in (FLSb+C₆₀)_m. Furthermore, a photoelectrochemical device with an electrophoretically deposited (FLSb+C₆₀)_m film exhibited an enhanced efficiency of photocurrent generation, compared to those of the single-components, FLSb and C₆₀, due to the photoinduced charge separation between FLSb and C₆₀. This work provides a promising approach for fabrication of antimonene–organic molecule composites and paves the way for their application in optoelectronics.     

Zur Magnetochemie der Fluoroargentate(II): Messungen an Ba[AgF4], Sr[AgF4], Ba2AgF6 sowie K[AgF3] und Cs[AgF3]

Magnetochemistry of Fluoroargentates(II): Investigation of Ba[AgF₄], Sr[AgF₄], Ba₂AgF₆, K[AgF₃], and Cs[AgF₃] Ba[AgF₄] (Θ = -4 K, μ = 1.9₂ μ_B), isostructural with K[BrF₄] with planar [AgF₄] groups, fullfil the Curie-Weiss-law, also Ba₂AgF₆ (Θ = 4 K, Θ = 1.8₅ μ_B) which is related with the structure of Ba₂CuF₆. The variante of perovskite-type K[AgF₃] (orthorhombic) and Cs[AgF₃] (tetragonal perovscite) show collective magnetic interactions (T_N = 80 K, KAgF₃, and 50 K, CsAgF₃) and show a behaviour like AgF₂ (T_N160 K) correspondingly to the magnetic dilution. Above T_N paramagnetism is nearly independend of tempearture.