Boron chemistry lights the way: optical properties of molecular and polymeric systems

Electrooptical and electronic materials are the subject of much research interest, whereby the focus has often been on electron-rich organic molecules. In the past years, new routes to electron-deficient systems have been developed that take advantage of the fact that three-coordinate boron is isoelectronic and isostructural with a positively charged carbocation, which allows neutral, p-type materials to be synthesized directly. This minireview summarizes recent work on compounds with 3- and 4-coordinate boron as well as boron clusters, placing it in the context of prior studies by the research groups of Williams and Glowgowski, Kaim, Lequan, and Marder.     

A re-evaluation of the photophysical properties of 1,4-bis(phenylethynyl)benzene: a model for poly(phenyleneethynylene)

Photophysical measurements, recorded in aerated cyclohexane at 283 K, indicate that 1,4-bis(phenylethynyl)benzene behaves in a conventional manner, undergoing emission from the lowest vibrational level of the first excited singlet state; there is no evidence for aggregation of this material in cyclohexane solution in the concentration range (1-250) x 10(-6) mol dm(-3). However, in highly viscous, low-temperature glasses, the material does exhibit inhomogeneous fluorescence behavior, and wavelength-dependent excitation and emission spectra, indicative of a slow rate of relaxation of conformers of the excited states compared to the rate of fluorescence.     

Tris(2‐methylphenyl)phosphonium tetrachloroborate

The title compound, C₂₁H₂₂P⁺·BCl₄^?, is the first structurally characterized example of the [HP(o‐tolyl)₃]⁺ cation, presented here with BCl₄^? as the counter‐ion. The cation has a near‐tetrahedral P atom and the BCl₄^? anion is near‐tetrahedral at boron. There are no unusually short cation–anion contacts.     

Stoichiometric and Catalytic Aryl−Cl Activation and Borylation using NHC-stabilized Nickel(0) Complexes

NHC-nickel (NHC=N-heterocyclic carbene) complexes are efficient catalysts for the C−Cl bond borylation of aryl chlorides using NaOAc as a base and B₂pin₂ (pin=pinacolato) as the boron source. The catalysts [Ni₂(ICy)₄(μ-(η²:η²)-COD)] ( 1 , ICy=1,3-dicyclohexylimidazolin-2-ylidene; COD=1,5-cyclooctadiene), [Ni(ICy)₂(η²-C₂H₄)] ( 2 ), and [Ni(ICy)₂(η²-COE)] ( 3 , COE=cyclooctene) compare well with other nickel catalysts reported previously for aryl-chloride borylation with the advantage that no further ligands had to be added to the reaction. Borylation also proceeded with B₂neop₂ (neop=neopentylglycolato) as the boron source. Stoichiometric oxidative addition of different aryl chlorides to complex 1 was highly selective affording trans-[Ni(ICy)₂(Cl)(Ar)] (Ar=4-(F₃C)C₆H₄, 11 ; 4-(MeO)C₆H₄, 12 ; C₆H₅, 13 ; 3,5-F₂C₆H₃, 14 ).     

Surface Functionalization of Black Phosphorus with a Highly Reducing Organoruthenium Complex: Interface Properties and Enhanced Photoresponsivity of Photodetectors

In this work, a heterostructure obtained by vacuum evaporation of a strong molecular n-dopant, [RuCp*(mes)]₂, onto black phosphorus (BP) is reported, along with the systematic investigation of the interfacial structure and properties by various in situ characterization techniques. Ultraviolet photoelectron spectra (UPS) showed a large decrease in the work function of BP and a new peak within the bandgap, which is attributed to electron transfer from dopants to the underlying BP. The electrons trapped at the interface act as hole traps and induce photogating effect so that a photodetector based on BP–organoruthenium complex heterostructure demonstrates a photoresponsivity of 5.5 mA W⁻¹ and an EQE of 1.3 % at 515 nm, a tenfold improvement compared to the pristine BP device.     

Reductive Coupling of Diynes at Rhodium Gives Fluorescent Rhodacyclopentadienes or Phosphorescent Rhodium 2,2’‐Biphenyl Complexes

Reactions of [Rh(κ²‐O,O‐acac)(PMe₃)₂] (acac=acetylacetonato) and α,ω‐bis(arylbutadiynyl)alkanes afford two isomeric types of MC₄ metallacycles with very different photophysical properties. As a result of a [2+2] reductive coupling at Rh, 2,5‐bis(arylethynyl)rhodacyclopentadienes ( A ) are formed, which display intense fluorescence (Φ=0.07–0.54, τ=0.2–2.5 ns) despite the presence of the heavy metal atom. Rhodium biphenyl complexes ( B ), which show exceptionally long‐lived (hundreds of μs) phosphorescence (Φ=0.01–0.33) at room temperature in solution, have been isolated as a second isomer originating from an unusual [4+2] cycloaddition reaction and a subsequent β‐H‐shift. We attribute the different photophysical properties of isomers A and B to a higher excited state density and a less stabilized T₁ state in the biphenyl complexes B , allowing for more efficient intersystem crossing S₁→T_n and T₁→S₀. Control of the isomer distribution is achieved by modification of the bis‐ (diyne) linker length, providing a fundamentally new route to access photoactive metal biphenyl compounds.     

The Series of Rare Earth Complexes [Ln2Cl6(μ‐4,4′‐bipy)(py)6], Ln=Y,Pr, Nd,Sm‐Yb: A Molecular Model System for Luminescence Properties in MOFs Based on LnCl3 and 4,4′‐Bipyridine

A series of 12 dinuclear complexes [Ln₂Cl₆(μ‐4,4′‐bipy)(py)₆], Ln=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, ( 1 – 12 , respectively) was synthesized by an anhydrous solvothermal reaction in pyridine. The complexes contain a 4,4′‐bipyridine bridge and exhibit a coordination sphere closely related to luminescent lanthanide MOFs based on LnCl₃ and 4,4‐bipyridine. The dinuclear complexes therefore function as a molecular model system to provide a better understanding of the luminescence mechanisms in the Ln‐N‐MOFs ${\hbox{}{{\hfill 2\atop \hfill \infty }}}$ [Ln₂Cl₆(4,4′‐bipy)₃] ? 2(4,4′‐bipy). Accordingly, the luminescence properties of the complexes with Ln=Y, Sm, Eu, Gd, Tb, Dy, ( 1 , 4 – 8 ) were determined, showing an antenna effect through a ligand–metal energy transfer. The highest efficiency of luminescence is observed for the terbium‐based compound 7 displaying a high quantum yield (QY of 86 %). Excitation with UV light reveals typical emission colors of lanthanide‐dependent intra 4f–4f‐transition emissions in the visible range (Tb^III: green, Eu^III: red, Sm^III: salmon red, Dy^III: yellow). For the Gd^III‐ and Y^III‐containing compounds 6 and 1 , blue emission based on triplet phosphorescence is observed. Furthermore, ligand‐to‐metal charge‐transfer (LMCT) states, based on the interaction of Cl^? with Eu^III, were observed for the Eu^III compound 5 including energy‐transfer processes to the Eu^III ion. Altogether, the model complexes give further insights into the luminescence of the related MOFs, for example, rationalization of Ln‐independent quantum yields in the related MOFs.     

Oxidative addition of boron–boron, boron–chlorine and boron–bromine bonds to platinum(0)

The synthesis and spectroscopic characterisation of the new diborane(4) compounds B₂(1,2-O₂C₆Cl₄)₂ and B₂(1,2-O₂C₆Br₄)₂ are reported together with the diborane(4) bis-amine adduct [B₂(calix)(NHMe₂)₂] (calix=Bu^tcalix[4]arene). B–B bond oxidative addition reactions between the platinum(0) compound [Pt(PPh₃)₂(η-C₂H₄)] and the diborane(4) compounds B₂(1,2-S₂C₆H₄)₂, B₂(1,2-O₂C₆Cl₄)₂ and B₂(1,2-O₂C₆Br₄)₂ are also described which result in the platinum(II) bis-boryl complexes cis-[Pt(PPh₃)₂{B(1,2-S₂C₆H₄)}₂], cis-[Pt(PPh₃)₂{B(1,2-O₂C₆Cl₄)}₂] and cis-[Pt(PPh₃)₂{B(1,2-O₂C₆Br₄)}₂] respectively, the former two having been characterised by X-ray crystallography. In addition, the platinum complex [Pt(PPh₃)₂(η-C₂H₄)] reacts with XB(1,2-O₂C₆H₄) (X=Cl, Br) affording the mono-boryl complexes trans-[PtX(PPh₃)₂{B(1,2-O₂C₆H₄)}] as a result of oxidative addition of the B–X bonds to the Pt(0) centre; the chloro derivative has been characterised by X-ray crystallography.     

The split-cavity oscillator: a high-power E-beam modulator andmicrowave source

A compact device, called a split-cavity oscillator, whose self-excited oscillating electromagnetic field converts a large-area steady electron beam into one that is highly density modulated, is described. It does this in a short beam travel length, easing both space-charge and pinching limitations. Thus, high currents are possible without requiring a magnetic guide field. Methods for converting the modulated output beam into high-power microwaves are discussed, as are ways to phase-lock several oscillators together. Analytic theory, numerical simulations, and experiments describing the device are presented     

库仑加线性位基态解析解

应用新发展的单一轨迹积分方法求解库仑加线性位的基态量子波函数,得到基态能量和波函数的一般解析表达式,并讨论了解的收敛性.应用此方法讨论了重夸克偶素系统.