Laser Q-switching by organic solvents

The role of the solvent in the passive Q-switching of lasers by solutions of organic dyes has been examined in detail. It was found that several pure organic solvents could themselves partially Q-switch the laser, in the absence of the dye. This behaviour was observed for both ruby and neodymium: glass lasers. Pulse-widths as short as 20 nsec were occasionally recorded. Peak powers up to 2 MW have been observed using 1-chloronaphthalene to switch a ruby laser. It is proposed that Q-switching arises from an enhancement of reflectivity of the liquid, during the evolution of the laser pulse, through the formation of a periodic refractive index modulation in the liquid by the action of standing waves.Research Fellow, attached from Royal Holloway College.     

«Living polymers» in organic solvents: Bicopper (II) tetracarboxylate solutions

Summary Viscoelastic solutions of a binuclear copper(II) tetracarboxylate (Cu₂S₈) in tert-butylcyclohexane (TBC) have been investigated by rheology and small-angle neutron scattering techniques. The data are analysed in the theoretical framework of the so-called ?living polymers?. The Cu₂S₈ aggregates are semi-rigid thin heterogeneous molecular threads undergoing scission/recombination reactions. Structural and dynamical correlations have been made with the thermotropic columnar phase and some lyotropic swollen mesophases of the system. The simplicity of the composition and structural constitution enables to avoid the usual salt and composition problems of the aqueous analogues and also to deduce some most probable behaviours related to the scission mechanisms, chain flexibility and dynamics of stress relaxation. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. Member of CNRS.     

芘在离子液体及常规溶剂中的激光闪光光解研究

利用纳秒级时间分辨激光光解装置,以Nd:YAG激光器三倍频后的355 nm激光作为激发光源,研究了芘在常规溶剂乙腈、丙酮、环己烷、1-丁基-3-甲基咪唑六氟磷酸离子液体([Bmim][PF6])、N-丁基吡啶四氟硼酸离子液体([BuPy][BF4])以及三乙基庚基铵双三氟甲磺酰亚胺(R4NNTf2)的瞬态光解行为,比较...     

Laser printing and characterization of semiconducting polymers for organic electronics

Hybrid organic/inorganic thin-film transistors (TFTs) with bottom-contact configuration were fabricated using the Laser Induced Forward Transfer (LIFT) process. The semiconducting polymer P3HT was laser printed from a donor to a receiver substrate in order to form the active layer of the TFTs. With a single laser pulse, P3HT pixels were successfully printed. The printed material was analyzed morphologically by means of Optical Microscopy and its thickness was measured by profilometry. In addition, structural characterization of P3HT thin films before and after laser printing took place by using UV-Visible absorption spectroscopy and X-Ray Diffraction. It was found that the crystallinity of the investigated films is improved upon annealing. An organic thin-film transistor (OTFT) with laser printed P3HT pixel as a channel layer was then fabricated. The OTFTs indicated a field-effect mobility up to 2.23?10^?4 cm²/Vs and an on/off ratio on the order of 10–100.     

Phase behaviour of hyperbranched polymers in demixed solvents

Hyperbranched polymers have attracted increased interest because of their tunable properties, which are affected by their architecture and a wide range of different functional groups. Many applications of hyperbranched polymers have been proposed based on their liquid–liquid phase behaviour. In recent years, the Lattice Cluster Theory (LCT) has been used to consider the impact of the architecture on the phase behaviour of hyperbranched polymers. In the theoretical framework of the LCT, the chain architecture is included in the Helmholtz energy, so all derived properties are influenced by polymer architecture. Until now, the application of the LCT in the field of hyperbranched polymers has been limited to ternary systems composed of one polymer with an arbitrary chain structure, one trimer and one solvent. This paper aims to extend the LCT to a ternary system that includes two polymers with an arbitrary chain structure and one solvent occupying one lattice site. In contrast to previous studies, the ternary system consists of Boltorn H20?+?butan-1-ol?+?water, where all of the binary subsystems show demixing behaviour. Whereas experimental data are reported in the literature for the binary subsystems Boltorn H20?+?water and butan-1-ol?+?water, no experimental information is available for the binary subsystem Boltorn H20?+?butan-1-ol. Therefore, the phase behaviour of this subsystem was measured using the visual method. The paper discusses the possibility of predicting the ternary phase behaviour with the LCT in combination with the modified Wertheim theory based on knowledge of the phase behaviour of the corresponding binary subsystems. To verify the theoretical results, the ternary phase equilibria at constant temperature were also measured. In addition, the dependence of the thermodynamic properties on the special production lot of the commercially available Boltorn H20 is discussed.     

Polarons in organic conjugated polymers

An unified treatment of the electronic structure of organic conjugated polymers based on a renormalization approach is presented. The changes in the electronic structures of trans-polyacetylene, poly-(p-phenylene), polypyrrole and polythiophene, brought about by the presence of polarons in these systems, are studied. For all systems, two localized states, which can be interpreted as the symmetric and antisymmetric combinations of soliton wavefunctions, are created at the central gap.     

Co（Ⅱ）,Ni（Ⅱ）非有机溶剂液—液萃取行为的研究

In PEG-Eriochrome cyanine R-(NH4)2SO4 system the liquid-liquid extraction behaviour of Co(II) and Ni(II) without organic solvents was investigated. We found that Ni(II) was almost extracted by PEG phase while Co(II) was not extracted in the water solutions of NaAc-HAc (pH=5) and (NH4)2SO4. Thus Co(II) was quantitatively separated from mixed solutions of Ni(II) and Co(II) ions.     

Solvent polarity scales: determination of new ET(30) values for 84 organic solvents

The solvent polarity parameter E_T(30) is newly measured from the solvatochromism of the betaine dye 30 for 84 solvents and re‐measured for 186 additional ones. The results are organized in a database. It is shown that the validity of linear solvation energy relationships used for the determination of secondary E_T(30) values is limited to non‐hydrogen‐bond donor solvents. Relationships with the chain length n are given for the determination of tertiary E_T(30) values of the homologous H(CH₂)_nY solvent series. The parameter E_T(30) is orthogonal to the function of the refractive index (n² ? 1) / (2n² + 1). For non hydrogen‐bond donor solvents, this allows to enter E_T(30) as an almost pure electrostatic parameter in a new linear solvation energy relationship. Copyright © 2014 John Wiley & Sons, Ltd.     

ESR studies on the pressure and temperature dependence of electron self-exchange kinetics between tetrathiafulvalene (TTF) and its radical cation in ionic liquids and organic solvents

The question whether chemical reactions and diffusion processes in ionic liquids are comparable with those taking place in classical organic liquids is a current issue in the literature. Pressure- and temperature-dependent investigations on simple electron self-exchange reactions between the two partners of a redox couple are good tools to get a better understanding of how the solvent influences such reactions. The electron self-exchange reaction between tetrathiafulvalene (TTF) and its radical cation has been investigated in two ionic liquids and two organic solvents using electron spin resonance (ESR) line broadening experiments at variable temperature and pressure. Rate constants are reported for the ionic liquids 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim⁺][Tf₂N^?]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim⁺][Tf₂N^?]) within a temperature range of 298 K ≤ T ≤ 368 K and a pressure range of 0.1 MPa ≤ p ≤ 100 MPa. The self-exchange reaction of the redox couple [TTF/TTF^?+] has been found to be diffusion-controlled in the used ionic liquids over the entire temperature range. The observed rate constants in ionic liquids at higher pressures are larger than those predicted by common diffusion, and suggest that the electron transfer takes place within a solvent cage. Also, the self-exchange reaction of the [TTF/TTF^?+] redox couple in classical solvents (dimethylphthalate (DMP) and acetonitrile) was investigated and compared to the results with those obtained in ionic liquids. The high viscosity of the ionic liquids makes it difficult to extract the electron transfer rate constants reliably, making interpretation within the framework of the Marcus Theory impossible.     

Route to ferromagnetism in organic polymers

Employing a rigorous theoretical method for the construction of exact many-electron ground states we prove that interactions can be employed to tune a bare dispersive band structure such that it develops a flat band. Thereby, we show that pentagon-chain polymers with electron densities above half filling may be designed to become ferromagnetic or half metallic.     

Self-assembly of length-tunable gold nanoparticle chains in organic solvents

The one-dimensional coagulation of gold colloidal particles dispersed in organic solvent was investigated with transmission electron microscopy. The results indicate that the length of the nanoparticle chains can be modulated by changing the concentration of the solutions. It was also demonstrated that the wetting of the substrate surface hardly influenced the morphology of the nanoparticle chains, which revealed that the particle chains had been formed in the solution before deposition on the substrates. A general theoretical interpretation is provided to explain the linear coagulation of gold colloidal particles, on the basis of the asymmetrical distribution of the charges absorbed on the surface of the gold colloidal particles, as well as the action of the solvent molecules. Received: 8 April 2002 / Accepted: 1 July 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-025/361-9983, E-mail: jhliao@seu.edu.cn     

Direct optical excitation of singlet oxygen in organic solvents

Efficient excitation of singlet oxygen is demonstrated for several organic solvents (CS₂, CCl₄, and C₆F₁₄) that are irradiated using LED in the visible spectral range in the absorption bands of the O₂-O₂ collision complexes at the corresponding cooperative transitions. It is shown that the two-photon interaction of the pumping radiation in the Herzberg I band of molecular oxygen with its excitation to the ³Σ _u ⁺ state and the subsequent collisional relaxation to the ¹Σ _g and ¹Δ _g singlet states contributes to the excitation of singlet oxygen.     

Laser performance of perylenebis (dicarboximide) dyes with long secondary alkyl chains

The laser performance and related photophysical properties of two very soluble perylene dyes with long chain secondary alkyl groups were investigated in cyclohexane solution. With a dye laser as pump source a tuning range of 555–580 nm was obtained at an optimum concentration of 3×10^–4 M. The quantum efficiencies (=0.29 and 0.21) were better than 1/2 that of rhodamine 6G. No photodegradation was observed over an excitation period of several hours.     

Temperature-responsive polymers in mixed solvents: competitive hydrogen bonds cause cononsolvency

If two good solvents become poor for a polymer when mixed, the solvent pair is called a cononsolvent pair. The sharp reentrant coil-to-globule-to-coil transition of a poly(N-isopropylacrylamide) chain observed in the mixed solvent of water and methanol is shown to be caused by the competitive hydrogen bonding by water and methanol molecules onto the polymer chain. On the basis of a new statistical-mechanical model for competitive hydrogen bonds, the mean square end-to-end distance is theoretically calculated and compared with experiment. The chain sharply collapses at the molar fraction xm approximately 0.2 of methanol, stays collapsed up to xm approximately 0.4, and finally recovers the swollen state at xm approximately 0.6. Such a reentrant coil-globule transition takes place because the total number of hydrogen bonds along the chain exhibits a similar square-well-type depression as a result of the competition.     

Electron paramagnetic resonance of sonicated powder suspensions in organic solvents

The chemical effects of the acoustic cavitation generated by ultrasound translates into the production of highly reactive radicals. Acoustic cavitation is widely explored in aqueous solutions but it remains poorly studied in organic liquids and in particular in liquid/solid media. However, several heterogeneous catalysis reactions take place in organic solvents.Thus, we sonicated trimethylene glycol and propylene glycol in the presence of silica particles (SiO₂) of different sizes (5–15 nm, 0.2–0.3 µm, 12–26 µm) and amounts (0.5 wt% and 3 wt%) at an ultrasound frequency of 20 kHz to quantify the radicals generated. The spin trap 5,5-dimethyl-1-pyrrolin–N-oxide (DMPO) was used to trap the generated radicals for study by electron paramagnetic resonance (EPR) spectroscopy. We identified the trapped radical as the hydroxyalkyl radical adduct of DMPO, and we quantified it using stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a quantitation standard. The concentration of DMPO spin adducts in solutions containing silica size 12–26 µm was higher than the solution without particles. The presence of these particles increased the concentration of the acoustically generated radicals by a factor of 1.5 (29 µM for 0.5 wt% of SiO₂ size 12–26 µm vs 19 µM for 0 wt%, after 60 min of sonication). Ultrasound produced fewest radicals in solutions with the smallest particles; the concentration of radical adducts was highest for SiO₂ particle size 12–26 µm at 0.5 wt% loading, reaching 29 µM after 60 min sonication. Ultrasound power of 50.6 W produced more radicals than 24.7 W (23 µM and 18 µM, respectively, at 30 min sonication). Increased temperature during sonication generated more radical adducts in the medium (26 µM at 75 °C and 18 µM at 61 °C after 30 min sonication). Acoustic cavitation, in the presence of silica, increased the production of radical species in the studied organic medium.