A distinctive example of the cooperative interplay of structure and environment in tuning of intramolecular charge transfer in second-order nonlinear optical chromophores

The strongly enhanced cooperative influence of medium polarity and organic structural design on the first hyperpolarizability beta of a novel family of highly polarizable azinium-(CH=CH-thienyl)-dicyanomethanido chromophores 1-3 is described. The dyes can be efficiently synthesized by regioselective protonation/alkylation of the corresponding bidentate anion precursors. Consecutive annelation of the pyridyl ring of 1 (pyridine-->quinoline-->acridine) and medium polarity effects are responsible for an extraordinarily variable range of intramolecular charge transfer (ICT), leading to a large set of pi-electron distribution patterns. Accordingly, systems with remarkably different zwitterionic/quinoid character in the ground and excited states present beta values in a broad range, eventually switching from negative to positive. Our investigation is based on a combination of experimental (UV/Vis spectroscopy, multinuclear NMR spectroscopy, and electrooptical absorption measurements) and computational (ab initio) approaches. It is shown that: 1) beta and mubeta are dramatically influenced, even by orders of magnitude, by a complex, non-monotonic interplay of structure and medium action, which in turn affects molecular ICT and bond length alternation (BLA), 2) the computations, validated by different experimental data, are to be recommended as an extremely useful tool in the search for a greatly improved set of molecular nonlinear optical (NLO) responses (in the case of 1-3 they show that such conditions may be attained only in a narrow and limited range of dielectric constants in which the annelation effect operates most efficiently), and 3) the search for the most favorable molecular NLO response of a highly polarizable chromophore both in solution and in solid matrices should simultaneously take into account not only the molecular design supplemented by annelation effects but also the polarity of the medium.     

Optical colours and polarization of a model reflection nebula

Simple models of a reflection nebula in the form of a plane-parallel slab containing smooth spherical solid particles in submicron size range have been considered. Single scattering has been assumed. The effect of varying the composition and size distribution function of the grains have been brought out in the calculations using Mie theory of scattering. The analytical part of the geometry of the problem has been treated quite rigorously and the resulting expression for nebular intensity has been presented in a somewhat new form. In this paper, the case of the star behind the nebula has been examined. A comparison of the theoretical results with the observations of the Merope nebula shows that the dirty ice grains with index of refraction about 1·3–0·1i and size parametera ₀ = 0·5μ give reasonable agreement with the colours. Simultaneously, the polarization in the visual and blue wavelength bands agree approximately up to offset angle of 6 minutes of arc. The larger offset angles pose an intriguing problem. The general trends of nebular colours and polarization with variation of real and imaginary parts of index of refraction and the size distribution parameter have been tabulated to serve as a guide for further study of reflection nebulae with the star in the rear. A part of this work was presented at the first scientific meeting of the Astronomical Society of India, held on 27 and 28 February 1974 at Hyderabad. An erratum to this article is available at .     

Ca0．80Zn0．20Te晶体的生长及性能研究

用本实验室合成的Ca0．80Zn0．20Te多晶料为原料，采用改进的布里奇曼法在镀碳和未镀碳的石英安瓿中生长出Ca0．80Zn0．20Te晶锭。使用X射线衍射仪对合成产物及晶锭进行了分析，生长晶体的X射线衍射峰尖锐，摇摆谱对称，表明晶锭的结晶性能较好；用IRPrestige-21红外光谱仪分析了晶体的红外透射光谱，测试结果表明安瓿镀碳后生长的晶体位错密度小，均匀性较好，电阻率优于未镀碳安瓿生长的晶体；晶体的蚀坑密度在10^3-10^4cm^-2之间，比未镀碳安瓿生长的晶体低1个数量级。     

Entanglement,superselection rules and supersymmetric quantum mechanics

In this paper we show that the energy eigenstates of supersymmetric quantum mechanics (SUSYQM) with non-definite “fermion” number are entangled states. They are “physical states” of the model provided that observables with odd number of spin variables are allowed in the theory like it happens in the Jaynes–Cummings model. Those states generalize the so-called “spin-spring” states of the Jaynes–Cummings model which have played an important role in the study of entanglement.     

Regioselective synthesis of 1,2- vs 1,3-squaraines

Squaraines have been known for many decades as very stable and versatile vis-NIR absorbing dyes. They have found applications for example as sensitizers in organic photovoltaics and photodetectors. The most common squaraine structure is the 1,3-regioisomer. Their 1,2-regioisomers are seldom mentioned and unanimously regarded as side products. A facile direct synthesis of 1,2-squaraines, highlighting the role played by reaction conditions and electronic factors, is described. The first electrochemical characterization of these dyes is also shown.     

Multipolar symmetric squaraines with large two-photon absorption cross-sections in the NIR region

The two-photon absorption (TPA) properties of two extended symmetric squaraine dyes are thoroughly characterized from the experimental and quantum-chemical point of view. The two molecules are specially engineered to have a multipolar structure with increasing complexity, D-π-A-π-D and A'-π-D-π-A-π-D-π-A', respectively. The experimental TPA spectra, measured by means of the Z-scan technique in the femtoseconds regime, display considerably high values of TPA cross sections (σ(TPA)) for both molecules. In particular, the squaraine with the more extended structure shows the highest value of σ(TPA) ever reported for this class of molecules. CIS and TDDFT calculations of the one and two-photon absorption properties are carried out to clarify the origin of the observed TPA properties and fully characterize the electronic properties of these compounds. The calculations, in good agreement with the experimental data, suggest that the origin of this exceptionally high σ(TPA) can be ascribed to the presence of a peripheral A' group, that increases the density of excited states involved in the TPA process.     

Studies on the Middle-phase Microemulsion of Lauric-N-methylglucamide

The phase behaviour of the middle-phase microemulsion for the quaternary system lauric-N-methylglucamide （MEGA-12）/n-butanollalkane/water has been studied with Winsor type, δ-γ, fishlike and novel ε-β fishlike phase diagrams. A series of phase inversions Winsor I （2）→Ⅲ（3）→Ⅱ （ 2 ） were observed for the three kinds of phase diagrams. The phase types, the phase volumes and the range of alcohol concentrations from the beginning to the end of the middle-phase microemulsion were obtained from Winsor phase diagram. From δ-γ, fishlike phase diagram, the physicochemical parameters, such as the mass fraction of n-butanol in the hydrophile-lipophile balanced inteffacial layer, A^s, the coordinates of the start and end points of the middle-phase microemulsion, and the solubilities of MEGA-12 and n-butanol in alkane phase were calculated. The novel ε-β fishlike phase diagram was also presented. From this kind of diagram, the above experimental phenomena were observed and the physicochemical parameters were calculated precisely. The novel fishlike phase diagram has advantages over the Winsor and δ-γ fishlike phase diagrams in the evaluation of the solubilization power of the microemulsion and calculation of the related physicochemical parameters.     

Reduction of steroidal dicarbonyl compounds with poly(n-isopropyliminoalane)

Reduction of 6,17- and 6,20-dioxo-3α,5-cyclo-5α-steroids with poly(N-isopropyliminoalane) (HAlN-i-Pr)₆ yields 6α-hydroxyketones as the major products. The unexpected reduction outcome observed in the case of some steroidal ketoaldehydes is discussed. Treatment of methyl lithocholate 16 and methyl 3β-hydroxy-5α-etianate 18 with the same hydride is also reported.     

Crystal structure,spectroscopy and magnetism of binuclear complexes of mercury and lanthanides; the Ln(NCS)(HMPA)4(μ-SCN)2HgCl(SCN) type

A series of lanthanide compounds of type Ln(NCS)(HMPA)₄,(μ-SCN)₂HgCl(SCN) (Ln = Pr, Nd, Eu) were synthesized and grown in the form of single crystals.

The crystal structure of the neodymium complex was determined by X-ray diffraction. Its space group is Cc, with the following unit cell parameters; a = 17.338(3) Å, b = 15.795(3) Å, c = 21.828(4) Å, β = 107.65(3)°. The structure has an unexpected architecture in which one Cl^? ion, four SCN^? ions, and four oxygen atoms of HMPA groups are engaged in the metal ion coordination.

The binuclear complex is composed of two types of subunits; seven coordinated Nd (III) and four coordinated Hg (II). The results obtained were compared with the earlier published data on the crystal structures of polynuclear complexes with ions of the IIa group (Zn or Cd). Luminescence, excitation of luminescence and absorption spectra of lanthanide (Pr, Nd, Eu) single crystals, as well as vibrational IR and Raman spectra at 293, 77 and 4K, were recorded. Non-trivial results of reabsorption of the d-level of Pr(III) emission by ³H₄ → ³ P_J, ₁D² transitions were observed with simultaneous detection of emission from the ³P₀ level after excitation in the UV region. The experimental oscillator strengths of the transitions were determined from the absorption spectra and parametrized in terms of the Judd-Ofelt intensity parameters Ω_λ (λ = 2, 4, 6).

Satisfactory results for the calculation with low errors of estimation of the parameters were obtained for a crystal of the Nd-Hg compound, which reproduced the intensities of the electronic transitions well. Positive values of Ω_λ were evaluated for Pr(III) after including the ³H₄ → ³F₂ hypersensitive transition (obeying selection rules δJ = 2, δL = 2) in the calculations.

Based on the above results, the radiative rate constant can be determined. Strong vibronic components were found in the low temperature spectra for both types of ligands involved in metal ion coordination. The vibronic transitions are mainly associated with modes of groups directly coordinated to the metal ions. Electron-phonon coupling including the resonant vibronic effect was analysed based on IR and Raman data.

Magnetic susceptibility measurements were carried out down to 1.7 K. Correlation of the spectra and magnetic properties with details of the structure of the title compound was studied.