Oxygen doped SiC nanocrystals: first principles study of the optical properties

We have studied a typical spherical SiC nanocrystal with a diameter of 1.2 nm (Si₄₃C₄₄H₇₆) using linear combination of atomic orbitals in combination with pesudopotential density functional calculation. The role of fluorine and oxygen impurities was investigated on the electronic and optical properties of the Si₄₃C₄₄H₇₆ nanocrystal. Total energy calculations show that the fluorine doped Si₄₃C₄₄H₇₆ nanocrystals are unstable. Oxygen doped Si₄₃C₄₄H₇₆ have different binding energies in various substitutional and interstitial defects. The maximum binding energy of the oxygen at carbon substitutional defect is about ?0.5 eV and at interstitial defect is ?0.18 eV. The HOMO-LUMO gap of the pure Si₄₃C₄₄H₇₆ is about 6.71 eV and after doping with oxygen changes on the order of 0.1 eV. Our studies show that the refractive index of the doped Si₄₃C₄₄H₇₆ nanocrystal significantly dispersed in comparison with pure SiC nanocrystal especially at the range of 6 to 8 eV.     

Linear and nonlinear optical properties of azobenzene derivatives

The results of computations of spectroscopic parameters of lowest–lying electronic excited states of azobenezene derivatives are presented. The analysis of experimentally recorded spectra was supported by quantum chemical calculations using density functional theory. The theoretically determined resonant (two-photon absorption probabilities) and non-resonant (first-order hyperpolarisability) nonlinear optical properties are also discussed, with an eye towards the performance of recently proposed long-range corrected (LRC) schemes (LC–BLYP and CAM–B3LYP functionals). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Probing the linear and nonlinear optical properties of nitrogen-substituted carbon nanotube

In view of their intriguing structural and electrical properties, the linear and nonlinear optical (NLO) responses of six carbon nanotube (CNT) molecules substituted by nitrogen atoms at one end have been explored by using the CAM-B3LYP method. Molecules 1, 2 and 3 were obtained by increasing the lengths of the CNTs, and 1-Li, 2-Li and 3-Li were constructed by doping one Li atom into the N-substituted end of 1, 2 and 3 (mentioned above), respectively. Two effective approaches have been proposed to increase nonlinear optical properties(NLO): increasing the length of the CNT as well as doping one Li atom into the N-substituted end. The results show that both the linear polarizabilities (α(0)) and nonlinear first hyperpolarizabilities (β(tot)) values increase with increasing the lengths of the CNTs: 188 of 1 < 307 of 2 < 453 of 3 for α(0) and 477 of 1 < 2654 of 2 < 3906 au of 3 for β(tot). Significantly, compared with the non-doped CNTs, the β(tot) values are remarkably enhanced by doping one Li atom into the N-substituted end: 477 of 1 < 23258 of 1-Li, 2654 of 2 < 37244 of 2-Li, and 3906 of 3 < 72004 au of 3-Li. Moreover, the β(vec) values show a similar trend to the β(tot) values. Our results may be beneficial to experimentalists in exploring high-performance nonlinear optical materials based on CNT.     

Intraband optical activity of semiconductor nanocrystals

Here we review our three recently developed analytical models describing the intraband optical activity of semiconductor nanocrystals, which is induced by screw dislocations, ionic impurities, or irregularities of the nanocrystal surface. The models predict that semiconductor nanocrystals can exhibit strong optical activity upon intraband transitions and have large dissymmetry of magnetic‐dipole absorption. The developed models can be used to interpret experimental circular dichroism spectra of nanocrystals and to advance the existing techniques of enantioseparation, biosensing, and chiral chemistry.     

ctDNA与离子型表面活性剂相互作用的共振瑞利散射法研究

利用共振瑞利散射光谱(RRS)方法研究了ctDNA与离子型表面活性剂的相互作用.结果表明:阳离子表面活性剂通过静电、疏水等作用在ctDNA表面聚集,造成ctDNA的RRS大大增强;阴离子表面活性剂对吖啶橙(AO)与ctDNA的相互作用有协同作用,能使AO-ctDNA的RRS信号大大增强.     

共振瑞利散射测定痕量甲胎蛋白含量研究

用共振瑞利散射光谱研究磷钼杂多酸与甲胎蛋白的相互作用的过程中,发现其结合会引起共振瑞利散射(RRS),最大RRS峰均位于480 nm。在一定浓度范围内,AFP浓度与散射强度成正比,这样就产生了一种新的利用共振光散射强度定量测定甲胎蛋白的方法。本文对该反应体系的适宜反应条件、主要影响因素、散射强度与AFP浓度的关系、方法的灵敏度等,进行了比较研究。发现不同的杂多酸对于甲胎蛋白的检出限(3σ)在5.2~78μg.L-1之间,其中以磷锑钼酸体系灵敏度最高,对于甲胎蛋白(AFP)的检出限为2.5μg.L-1。该方法具有操作简便、灵敏度高、线性范围宽等优点。考察了共存物质的干扰影响,获得了满意的结果。     

Structure and nonlinear optical properties of copper phthalocyanine thin films

This paper describes a joint study of the structure and nonlinear optical properties of vacuum evaporated thin films of copper phthalocyanine (CuPc for brevity). Film thickness ranges from 50 to 500 nm. The anisotropic paramagnetic resonance of Cu⁺⁺ ions reveals that the Pc rings lie almost parallel to the substrate plane with however a large angular distribution (30° FWHM). Third harmonic optical generation measurements performed at 1.064 m and 1.907 m fundamental wavelengths give respectively an average value of the cubic susceptibility ⁽³⁾(-3,)=(4±0.4)·10^–12 e.s.u. and (2.1+-0.2) · 10^-12 These values, although significantly higher than for a common ionic crystal, are about one order of magnitude lower than in conjugated 1-D systems, which shows that the 2-D -electron delocalization is less profitable than the 1-D one. Besides third harmonic, we have also observed second harmonic generation. Its polarization dependence is characteristic of a quadratic susceptibility enhanced in one direction, almost perpendicular to the substrate, withd _eff comprised between 30 and 60 · 10^-9 e.s.u. The possible origins ofd _eff are discussed.     

Characterization of the optical properties of color pastes for the design of optical phantoms mimicking biological tissue

Clinicians need a way to rapidly and reliably test the correct functioning of near‐infrared spectroscopy (NIRS)–based oximeters. Therefore, optical phantoms for quality assessment of NIRS oximeters are needed. The fabrication of such phantoms that mimic the optical properties of biological tissue in the NIR range represents a challenge. To enable their development, the aim was to characterize the absorption and scattering spectra of different dyes. The optical properties of silicone SILPURAN 2420 with 11 color pastes of type ELASTOSIL were measured in the 500 to 1000 nm range by a spectrometer with an integrating sphere. In addition, two commercial frequency‐domain NIRS devices, the ISS OxiplexTS and the ISS Imagent, were used to assess the optical properties at specific wavelengths. The evaluated colors present mostly features in the visible range below 650 nm, but two colors include peaks in the near‐infrared region, simulating low tissue oxygenation values. These colors were used to create an optical phantom, which matched the designed StO₂ value within an error of only 4%. This set of dyes already enables simulating many different spectra, thus achieving a first step on the way to a long‐term stable comparison and validation method.      

A DFT study on the second-order nonlinear optical properties of the plenary mixed-metal polyoxometalate

The redox and second-order nonlinear optical (NLO) properties of organic–inorganic hybrid polyoxoanions [LNbOEMe₃]^3 ? , [LNbOEPh₃]^3 ?  (L = α-{PW₁₁O₃₉}^7 ? , E = Si, Ge, Sn, Pb) are investigated by density functional theory method. The element substitution effects on the molecular nonlinear response have been analysed. The results show that the computed β₀ values depend on both E (E = Si < Ge < Sn < Pb) and the organic groups connected with E. For [LNbOEPh₃]^3 ?  (L = α-{PW₁₁O₃₉}^7 ? , E = Si, Ge, Sn, Pb), the analysis of major contributions to β₀ value suggests that the charge transfer from organic group to Keggin polyanion plays the key role in NLO response; the polyanion acts as a donor, whereas the organic group acts as an acceptor in [LNbOEPh₃]^3 ? . Our results show that this kind of organic–inorganic hybrid compound possesses larger molecular second-order polarisability and might be a potential NLO material.     

Second-order nonlinear optical properties ofp-dimethylaminobenzylidene-1,3-indandione (DABI) measured by EFISH in dioxane

The second-order nonlinear optical properties of p-dimethylaminobenzylidene-1,3-indandione (DABI) have been measured using electric field-induced second-harmonic generation (EFISH) at wavelengths of 1064 nm and 1907 nm in dioxane. The absolute values of the microscopic hyperpolarizabilities are ^{1064 nm}=1064×10^–40 m⁴ V^–1 and ^{1907 nm}=150×10^–40 m⁴ V^–1.The condensation of 1,3-indandione with substituted aromatic aldehydes offers a pathway to a class of molecules with extended -electron systems. In the case of DABI, semiempirical calculations and a simple, two-level model indicate that the relatively high values of the microscopic hyperpolarizability are due to several factors which, in combination, positively enhance the electron donor-acceptor group-induced polarizability of DABI. The nonlinear optical properties of DABI are compared with experimental data for 2-methyl-4-nitroaniline (MNA).     

Characterization of the human myocardium by optical coherence tomography

Imaging of cardiac tissue structure plays a critical role in the treatment and understanding of cardiovascular disease. Optical coherence tomography (OCT) offers the potential to provide valuable, high‐resolution imaging of cardiac tissue. However, there is a lack of comprehensive OCT imaging data of the human heart, which could improve identification of structural substrates underlying cardiac abnormalities. The objective of this study was to provide qualitative and quantitative analysis of OCT image features throughout the human heart. Fifty human hearts were acquired, and tissues from all chambers were imaged with OCT. Histology was obtained to verify tissue composition. Statistical differences between OCT image features corresponding to different tissue types and chambers were estimated using analysis of variance. OCT imaging provided features that were able to distinguish structures such as thickened collagen, as well as adipose tissue and fibrotic myocardium. Statistically significant differences were found between atria and ventricles in attenuation coefficient, and between adipose and all other tissue types. This study provides an overview of OCT image features throughout the human heart, which can be used for guiding future applications such as OCT‐integrated catheter‐based treatments or ex vivo investigation of structural substrates.     

Effect of dehydrogenation/hydrogenation on the linear and nonlinear optical properties of Li@porphyrins

In the present work, Li@porphyrins and their derivatives were designed in order to explore the effect of dehydrogenation/hydrogenation on linear and nonlinear optical properties. Their stable structures were obtained by the M06-2X method. Moreover, the M06-2X method showed that dehydrogenation/hydrogenation has greatly influences polarizabilities (α (0) values) and hyperpolarizabilities (β (tot) and γ (tot) values): α (0) values ranged from 331 to 389 au, β (tot) values from 0 to 2465 au, and γ (tot) values from -21.2?×?10(4) to 21.4?×?10(4) au. This new knowledge of the effect of dehydrogenation/hydrogenation on nonlinear optical properties may prove beneficial to the design and development of high-performance porphyrin materials.     

Substituent effects on the electronic structures and nonlinear optical properties of Li-doped nano-carbon bowl

A series of Li-corannulene-(NH₂)_n and Li-corannulene-(NO₂)_n (n = 1, 2, 5) compounds have been theoretically designed and investigated using density functional theory. In this work, two models are systematically investigated to explore the important factors for enhancing the static first hyperpolarizability by introducing the substitution group. It is revealed that energy gaps (E_gap) between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of all compounds are in the range of 4.149–4.934 eV. Different DFT methods are adopted to calculate polarizabilities and the first hyperpolarizabilities of Li-corannulene-(NH₂)_n and Li-corannulene-(NO₂)_n (n = 1, 2, 5) compounds. It is revealed that polarizability values of the systems increase with increasing number of NH₂/NO₂ substitution group. Moreover, it is found that the first hyperpolarizabilities of Li-corannulene-(NO₂)_n are larger than those of Li-corannulene-(NH₂)_n, which can be attributed to the lower transition energies. In contrast to the NH₂ substitution group, NO₂ substitution group can be more powerful in increasing the first hyperpolarizability of Li-doped corannulene. We hope that this study can provide a new idea for designing nonlinear optical materials using the NH₂ and NO₂ groups.     

Cell imaging and manipulation by nonlinear optical microscopy

Advances in the technologies for labeling and imaging biological samples drive a constant progress in our capability of studying structures and their dynamics within cells and tissues. In the last decade, the development of numerous nonlinear optical microscopies has led to a new prospective both in basic research and in the potential development of very powerful noninvasive diagnostic tools. These techniques offer large advantages over conventional linear microscopy with regard to penetration depth, spatial resolution, three-dimensional optical sectioning, and lower photobleaching. Additionally, some of these techniques offer the opportunity for optically probing biological functions directly in living cells, as highlighted, for example, by the application of second-harmonic generation to the optical measurement of electrical potential and activity in excitable cells. In parallel with imaging techniques, nonlinear microscopy has been developed into a new area for the selective disruption and manipulation of intracellular structures, providing an extremely useful tool of investigation in cell biology. In this review we present some basic features of nonlinear microscopy with regard both to imaging and manipulation, and show some examples to illustrate the advantages offered by these novel methodologies.     

Syntheses and structures’ influence on the nonlinear optical properties of o-ferrocenylbenzoate compounds

Two complexes containing o-ferrocenylbenzoate [o-⁻OOCH₄C₆Fc, Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)] components: {[Pb(η²-o-OOCH₄C₆Fc)₂(phen)](NO₃)} (phen = phenanthroline) (1) and {[Zn(η²-o-OOCH₄C₆Fc)₂(bpe)](CH₃OH)}_n (bpe = 1,2-bis(4-pyridyl) ethene) (2) have been synthesized and structurally characterized by single crystal X-ray diffraction. 1 gives a discrete mononuclear framework, 2 features an infinite 1-D chain structure constructed by the bpe linking two adjacent zinc (II) ions. The third-order nonlinear optical (NLO) properties of complexes 1, 2 and the reactant o-NaOOCH₄C₆Fc were determined by Z-scan techniques in DMF solution. The results show that the structures of complexes have great impact on NLO properties. Complex 1 and o-NaOOCH₄C₆Fc display self-defocusing behaviors, while complex 2 exhibits strong self-focusing effect. The solution-state differential pulse voltammograms of complexes 1, 2 and o-NaOOCH₄C₆Fc were investigated as well. The results reveal that the half-wave potential of the ferrocenyl moieties is strongly influenced by the Pb(II) or Zn(II) ions in complexes 1 and 2.     

Theoretical study of geometrical and nonlinear optical properties of pyridinum N-phenolate betaine dyes

This paper presents an ab initio quantum chemical investigation of the geometrical structures and the non-linear optical properties (NLO) of three structural isomers of pyridinium N-phenolate betaine dye. The ground state geometrical parameters and the first-order hyperpolarizabilities were calculated using the Hartree-Fock (HF) as well as the second-order perturbation Møller-Pleset (MP2) method with the 6–31G, 6–31G(d), 6–31G(d,p), 6–31+G(d), 6–31++G(d,p), 6–311+G(d), aug-cc-PVDZ and the recently developed Z3PolX basis sets. Moreover, the first-order hyperpolarizability was calculated at the coupled cluster singles and doubles (CCSD/6–31+G(d)) level of theory. The analysis of the results of calculations for the investigated isomers indicates that there are important differences in their NLO activities. Additionally, it was shown that Z3PolX basis set works reasonable well for betaine dyes.

Synthesis,characterisation, optical and nonlinear optical properties of thiazole and benzothiazole derivatives: a dual approach

In the present investigation, we employ a dual approach consisting of experimental and computational techniques to synthesise and characterise the Schiff-base including the moieties of nitrophenyl (3), nitrothiazole (5) and nitrobenzothiazole (7). The synthesised Schiff bases are confirmed by FT-IR, ¹H-NMR and UV-visible spectroscopic techniques. The experimental UV-visible spectroscopic results are compared to the theoretically calculated TD-DFT results. There is a reasonably good agreement between the experimental and the theoretically calculated spectroscopic results. We also calculate the third-order nonlinear optical (NLO) polarizability (γ) of above entitled derivatives using finite field (FF) approach and DFT methods. The compound 7 shows an amplitude of γ as large as 124.15×10⁴ a. u., which is found to be several times larger than that of para-nitroaniline. Moreover, the partial and total density of states (PDOS and TDOS) along with electrostatic potential maps are calculated to get more physical insights into the structure-property relationship and electronic communications between terminal donor and central core acceptor moieties in the synthesised compounds. The present investigation highlights the significance of indigenously synthesised nitrothiazole and nitrobenzothiazole compounds as efficient NLO materials, which may evoke the interest of scientific community in such efficient NLO materials for their potential utilization in device applications.     

Computational investigation on redox-switchable nonlinear optical properties of a series of polycyclic p-quinodimethane molecules

The polycyclic p-quinodimethanes are proposed to be the novel candidates of the high-performance nonlinear optical (NLO) materials because of their large third order polarizabilities (γ). We investigate the switchable NLO responses of a series of polycyclic p-quinodimethanes with redox properties by employing the density functional theory (DFT). The polycyclic p-quinodimethanes are forecasted to exhibit obvious pure diradical characters because of their large y ₀ index (the y ₀ index is a value between 0 [closed-shell state] and 1 [pure biradical state]). The γ values of these polycyclic p-quinodimethanes and their corresponding one-electron and two-electron reduced/oxidized species are calculated by the (U)BHandHLYP method. The γ values of polycyclic p-quinodimethanes and their corresponding one-electron reduced species are all positive and significantly different. The large differences of the γ values are due to a change in the transition energy and are related to the different delocalization of the spin density, which demonstrates that the NLO switching is more effective on one-electron reduction reactions. Therefore, the study on these polycyclic p-quinodimethanes provides a guideline for a molecular design of highly efficient NLO switching.