A phenomenological,kinematical model of the coronal magnetic fields in terms of thin flux tubes rising from the photosphere

A kinematical model is necessary for understanding the gross structure of the coronal magnetic field and its slow evolution in consistency with the small scale structure of the photospheric fields. Here we have developed a preliminary phenomenological model in terms of flux tubes of flux amounts ≈ 10¹⁷ − 10^18.5 Mx rising across the inner corona in the form of arches and opening out in the outer corona. In contrast to Parker’s estimate, this model is consistent with the observed spans of the chromospheric fibrils and x-ray arches. It is also consistent with the number of flux tubes present above the photosphere as estimated from the observed abundance of spicules.     

Twisted bimesitylene-based oxadiazoles as novel host materials for phosphorescent OLEDs

The D_2d-symmetric bimesitylene core has been exploited for designing novel host materials required in the construction of phosphorescence-based organic light emitting devices. The oxadiazole-functionalized twisted bimesitylenes are found to exhibit high band gap (triplet energies), and excellent glass transition temperatures and thermal stabilities for ready exploitation as host materials. The electron-transporting ability and respectable luminance efficiencies with triplet dopants (up to 19.0 cd/A) allow oxadiazole-functionalized bimesitylenes as promising materials for phosphorescence-based light emitting devices, namely PHOLEDs.     

Organometallic chemistry of chiral diphosphazane ligands: Synthesis and structural characterisation

The diphosphazane ligands of the type, (C₂₀H₁₂O₂)PN(R)P(E)Y₂ (R = CHMe₂ or (S)-*CHMePh; E = lone pair or S; Y₂ = O₂C₂₀H₁₂ or Y = OC₆H₅ or OC₆H₄Me-4 or OC₆H₄OMe-4 or OC₆H₄Bu^t-4 or C₆H₅) bearing axially chiral 1,1'-binaphthyl-2,2′-dioxy moiety have been synthesised. The structure and absolute configuration of a diastereomeric palladium complex, [PdCl₂{ηsu2}-((O₂C₂₀H₁₂)PN((S)-*CHMePh)PPh₂] has been determined by X-ray crystallography. The reactions of [CpRu(PPh₃)₂Cl] with various symmetrical and unsymmetrical diphosphazanes of the type, X₂PN(R)PYY′ (R = CHMe₂ or (S)-*CHMePh; X = C₆H₅ or X₂ = O₂C₂₀H₁₂; Y=Y′= C₆H₅ or Y = C₆H₅, Y′ = OC₆H₄Me-4 or OC₆H₃Me₂-3,5 or N₂C₃HMe₂-3,5) yield several diastereomeric neutral or cationic half-sandwich ruthenium complexes which contain a stereogenic metal center. In one case, the absolute configuration of a trichiral ruthenium complex, viz. [Cp*Ruη₂-Ph₂PN((S)-*CHMePh)*PPh (N₂C₃HMe₂-3,5)Cl] is established by X-ray diffraction. The reactions of Ru₃(CO)₁₂ with the diphosphazanes (C₂₀H₁₂O₂)PN(R)PY₂ (R = CHMe₂orMe; Y₂=O₂C₂₀H₁₂or Y= OC₆H₅ or OC₆H₄Me-4 or OC₆H₄OMe-4 or OC₆H₄Bu^t-4 or C₆H₅) yield the triruthenium clusters [Ru₃(CO)₁₀{η-(O₂C₂₀H₁₂)PN(R)PY₂}], in which the diphosphazane ligand bridges two metal centres. Palladium allyl chemistry of some of these chiral ligands has been investigated. The structures of isomeric η³-allyl palladium complexes, [Pd(η³-l,3-R′₂-C₃H₃){η²-(rac)-(0₂C₂₀H₁₂)PN(CHMe₂)PY₂}](PF₆) (R′ = Me or Ph; Y = C₆H₅ or OC₆H₅) have been elucidated by high field two-dimensional NMR spectroscopic and X-ray crystallographic studies.     

Enhanced photocatalytic degradation of monocrotophos in aqueous solution over titania hybridised with beta-zeolite

Photocatalytic degradation of monocrotophos has been carried out in a slurry type batch reactor. The reaction variables were optimised to obtain maximum degradation efficiency. The degradation rate of monocrotophos is significantly higher for acidic solutions than for alkaline solutions. It is also observed that the high concentration environment of the pollutant formed around the hybridised TiO2, enhances the mineralisation rate of monocrotophos. Hence an increase in relative photonic efficiency is obtained.     

A new type of intermediate, C+(BCH3)11- <--> C(BCH3)11, in a Grob fragmentation coupled with intramolecular hydride transfer. A nonclassical carbocation ylide or a carbenoid?

In solvolysis of alkyl halides Hal-(CH(2))(n)-C(BCH(3))(11)(-) (n = 2, 5, 6, but not 3, 4, or 7) and protonation of alkenes CH(2)=CH-(CH(2))(n)(-)(2)-C(BCH(3))(11)(-) (n = 3, 6, 7, but not 4 or 5) carrying the icosahedral electrofuge -C(BCH(3))(11)(-) attached through its cage carbon atom, generation of incipient positive charge on C(alpha) (as shown in Scheme 1 in the article) leads to simultaneous cleavage of the C(beta)-C(BCH(3))(11)(-) bond. The products are a C(alpha)=C(beta) alkene and a postulated intermediate C(+)(BCH(3))(11)(-) <--> C(BCH(3))(11), trapped as the adduct Nu-C(BCH(3))(11)(-) by one of the nucleophiles (Nu(-)) present. The reaction kinetics is E1, first order in the haloalkylcarborane and zero order in [Nu(-)], and the elimination appears to be concerted, as in the usual E2 mechanism. The process is best viewed as a Grob fragmentation. The loss of the longer chains involves intrachain hydride transfer from the C(alpha)-H bond to an incipient carbocation on C(delta)(') or C(epsilon)(') via a five- or six-membered cyclic transition state, respectively. The electronic structure of the postulated intermediate is believed to lie between those of a nonclassical carbonium ylide C(+)(BCH(3))(11)(-) and a carbenoid C(BCH(3))(11) whose electronic ground state resembles the S(2) state of ordinary carbenes.     

Studies on oxidations with IBX: oxidation of alcohols and aldehydes under solvent-free conditions

A variety of allylic and benzylic alcohols are oxidized to their respective carbonyl compounds with IBX under solvent-free conditions at ca. 60-70 °C. It has also been found that some of the aromatic aldehydes also undergo oxidation when heated with IBX at 90 °C under solvent-free conditions; notably, this transformation does not occur under the otherwise identical but heterogeneous conditions.     

Blue light-emitting and hole-transporting amorphous molecular materials based on diarylaminobiphenyl-functionalized bimesitylenes

The diarylaminobiphenyl-functionalized bimesityls and exhibit amorphous nature, high thermal stability and excellent blue emission in the solid state. They serve as both hole-transporting and emissive materials in OLEDs for blue emission with high external quantum efficiencies.     

Effect of energy above laser-induced damage thresholds in the micromachining of silicon by femtosecond pulse laser

A 400 nm second harmonic Ti : sapphire femtosecond laser was applied to structure silicon base on a direct-write process in air. A series of lines were ablated with pulses of 300-fs duration at varying power densities ranging from 50 to 100 nJ of energy on 2″ silicon (1 1 1) wafers. In this event, we investigate and report extensive laser induced thermal damage and redeposition encompassing the ablated lines at high energy levels above the damage threshold of the silicon. In addition, the effect of polarisation on the direction of micromachining is also observed and discussed. The resolution and quality of these lines were also found to hold a linear relationship to the laser energy up to its thermal threshold limit.     

Rearrangements in Scholl Reaction

Rearrangements in Scholl reaction are mostly serendipitous. The design of molecular precursors is what seems to guide the course of rearrangement. This review consolidates different classes of precursors used in Scholl reaction and their accompanying rearrangements that include aryl migration, migration followed by cyclization and skeletal rearrangements involving ring expansion, ring contraction and both, under the reaction conditions. The attempt in collating heretofore-reported examples in this review is to guide designing appropriate precursors to predictably achieve complex molecular structures or nanographenes or defect-nanographenes via rearrangement.     

Laser singulation of thin wafer: Die strength and surface roughness analysis of 80 μm silicon dice

In this paper, we have studied the characteristics of silicon dice, singulated using a high-power-high-repetition-rate femtosecond laser. The die strength and surface roughness, of the die side walls, are evaluated for different laser parameters such as pulsewidth and repetition rate. Since, the 80-μm-thick wafers used in this study were polished on both sides, die-edge roughness plays a decisive factor in determining the die strength when compared to backside roughness and wafer thickness as is the case in other studies. Excellent side wall average surface roughness of 0.35 μm is obtained at pulsewidth of 214 fs and repetition rate of 4.33 MHz using an average laser power of 15.5 W. Die strength is measured via the 3-point bending test. Strength reduction, due to die side wall surface defects that are induced through the wafer dicing process, is evaluated through die strength and surface roughness analysis. Die strength of a silicon dice is characterized as the first step in prediction and prevention of die failure during the package assembly, reliability test and working life. Improvement in the die side wall surface roughness is observed with the usage of nitrogen gas assist as compared to that obtained in air.