Enhancement of CsLiB(6)O(10) surface-damage resistance by improved crystallinity and ion-beam etching

The surface laser-induced damage threshold (LIDT) of CsLiB(6)O(10) (CLBO) crystal was enhanced twofold with improved crystallinity and ion-beam etching. For crystals with high crystal quality (bulk LIDT, 15.0-19.0 GW/cm(2)), the surface LIDT was 1.4-fold higher than for those with conventional crystal quality (bulk LIDT, 9.0-12.0 GW/cm(2)). In addition, removal of residual surface-polishing compounds by means of ion-beam etching can further enhance the surface LIDT by another 1.5-fold. Thus, CLBO crystals with high crystal quality and ion-beam etching are now more reliable for high-power UV light generation.     

Room temperature ionic liquids from 20 natural amino acids

We first succeeded in synthesizing ionic liquids from 20 natural amino acids. Amino acid ionic liquids dissolved native amino acids, despite water-free conditions. Furthermore, these ionic liquids are soluble in various organic solvents, such as chloroform. Effects of acidity, hydrogen bonding ability, and steric factors on the properties of these ionic liquids were analyzed as the function of side groups.     

Total Synthesis of (±)-Hirsutene via Pd-Promoted Cycloalkenylation Reaction

Beginning with trans-2-methyl-4-cyclohexenecarboxylic acid (9), a total synthesis of linear triquinane sesquiterpene (±)-hirsutene (1) has been accomplished. An acid catalyzed intramolecular conjugate addition (7→6a) and a Pd²⁺-promoted highly stereocontrolled cyclization (5→4) were utilized for the key step of the sequence. Interestingly, some synthetic intermediates exhibited cytotoxicity.     

Dynamics of excited and ionic states of N,N,N′,N′-tetramethyl-p-phenylenediamine in poly(methyl methacrylate) under ablation condition

The nanosecond transient dynamics of N,N,N′,N′-tetramethyl-p-phenylenediamine in poly(methyl methacrylate) has been investigated under ablation condition. Time-resolved spectroscopic data can be interpreted in terms of the dynamics of the lowest excited singlet and triplet states and the cation of TMPD. The decay processes of all the detected transients became rapid with an increase in the laser fluence. It is shown directly that TMPD absorbs about eight 248 nm photons during a nanosecond laser pulse at the ablation threshold of 220 mJ/cm². These results are well explained by cyclic multiphotonic absorption mechanism where dopant transients work as repetitive absorbers of laser photons.     

Studies on the syntheses of heterocyclic compounds—DXLV : An alternative synthesis of the protoberberine ring system

The reaction of 3,4-dihydro-6,7-dimethoxyisoquinoline (11) with 1-bromobenzocyclobutene (10) gave, in one step, 2,3-dimethoxyprotoberberinium bromide (15), which was easily converted into the tetrahydroprotoberberine (16).     

Chelation-assisted hydroesterification of alkenes catalyzed by rhodium complex

[reaction: see text] The hydroesterification of alkenes with 2-pyridylmethanol (1) catalyzed by Rh(4)(CO)(12) is described. The reaction is accelerated by the presence of a pyridine ring in the alcohol 1. The reaction is applicable to various alkenes, both terminal and internal alkenes.     

Synthesis and optical properties of π-conjugated polymers and oligomers bearing hexaphenylbenzene and tetraphenyl ethene units

π-Conjugated polymers (CPs) and oligomers (COs) bearing hexaphenylbenzene (HPB) and tetraphenyl ethene (TPE) units were synthesized by Sonogashira and Suzuki–Miyaura coupling reactions. The optical properties of the CPs and COs were investigated by UV–vis, photoluminescence (PL), and fluorescence lifetime (τ) measurements. The PL intensities of the solutions of the CPs and COs synthesized by Sonogashira coupling were reduced upon addition of poor solvent like water, which is attributed to aggregation-caused quenching. In contrast, the CP and COs bearing the TPE unit synthesized by Suzuki–Miyaura coupling exhibited aggregation-induced emission enhancement in solution. This difference in fluorescence behavior is discussed herein in terms of the molecular sizes, conformations in solution, and τ values of the CPs and COs.     

Electrospray ionization mass spectrometry of metal complexes. Gas phase formation of a binuclear copper(II)–5-Br-PADAP complex

The complexes formed from copper(II) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP or HL) in aqueous methanol solution was studied by electrospray ionization mass spectrometry. The solution of a 1:1 complex of Cu(II) with 5-Br-PADAP showed five peaks assignable to a binuclear complex [Cu₂L₂(AcO)]⁺ and mononuclear complexes [CuL]⁺, [CuL(H₂O)]⁺, [CuL(AcOH)]⁺ and [CuL(HL)]⁺ (AcO=acetate). Collision activated dissociation revealed the relative order of bonding strengths; Cu–L>Cu–HL>CuL–AcOH>CuL–H₂O. The peak intensities of the binuclear complex showed second-order dependency on those of the mono complex. As for the solution of Ni(II)–5-Br-PADAP, no binuclear complex was observed in the mass spectra. Thus, it was suggested that [Cu₂L₂(AcO)]⁺ was formed by the fast gas phase reaction: 2[CuL]⁺+AcO⁻[Cu₂L₂(AcO)]⁺.     

Fission of metal clusters: A comparison of jellium model calculations and shell correction method calculations

We investigate the fission process Ag²⁺₂₃ → Ag⁺₁₂ + Ag⁺₁₁ in order to compare total energies that calculated by the shell correction method and jellium models. A cavity potential and a Woods-Saxon-type potential are used as the shell potential for the shell correction method, with which the single-particle energy levels are calculated. Shell corrections are obtained by using the Balian-Bloch formula and by smoothing the discrete energy levels in the shell potentials. The jellium model calculations are performed in the framework of the local spin density functional approximation. The conventional jellium model and stabilized jellium model are used. Although the qualitative agreement between the shell correction method calculations and the stabilized jellium calculations is very good, an improvement of the liquid drop energy will be necessary for the satisfactory quantitative agreement. © 1996 John Wiley & Sons, Inc.