Finite‐field method with unbiased polarizable continuum model for evaluation of the second hyperpolarizability of an open‐shell singlet molecule in solvents

The static second hyperpolarizability γ of the complexes composed of open‐shell singlet 1,3‐dipole molecule involving a boron atom and a water molecule in aqueous phase are investigated by the finite‐field (FF) method combined with a standard polarized continuum model (PCM) and with a newly proposed unbiased PCM (UBPCM). On the basis of the comparison with the results calculated by the FF method using the full quantum and the quantum‐mechanical/molecular‐mechanical and molecular‐dynamics (QM/MM‐MD) treatments, the present FF‐UBPCM method is demonstrated to remedy the artificial overestimation of the γ caused by standard FF‐PCM calculations and to well reproduce the FF‐QM/MM‐MD and FF‐full‐QM results with much lower costs. © 2013 Wiley Periodicals, Inc.     

锂掺杂胺化物中氮原子配位数效应对结构和非线性光学性质的影响

采用MP2／6—311＋＋G（d,p）方法得到了含有不同氮原子配位数的系列锂掺杂胺化物的几何结构,并使用MP2／6．311＋＋G（2d,p）方法计算了该系列的非线性光学性质．结果表明：相对于未掺杂体系,锂掺杂极大地增加了体系的一阶超极化率（β0）,其中1的β0值是掺杂前的3238倍;体系的风随着氮原子配位数的增加而显著增加,具有3个配位氮原子的1的风值达到2．8×10^5a．u．另外,频率依赖的一阶超极化率（β（-ω;ω,0）和β（-2ω;ω,0））也表现了同样的趋势．     

Accurate calculations of dynamic first hyperpolarizability: Construction of physically justified slater‐type basis sets

An efficient procedure for construction of physically rationalized Slater‐type basis sets for calculations of dynamic hyperpolarizability is proposed. Their performance is evaluated for the DFT level calculations for model molecules, carried out with a series of functionals. Advantages of new basis sets over standard d‐aug‐cc‐pVTZ and recently developed LPOL‐(FL,FS) Gaussian‐type basis sets are discussed. © 2014 Wiley Periodicals, Inc.     

Evaluation of the molecular static and dynamic first hyperpolarizabilities

By considering two prototypical π‐conjugated compounds, several technical aspects associated with the evaluation of the first hyperpolarizabilities have been addressed in this article, that is, (i) the automatization of the Romberg's scheme to improve the numerical accuracy in the finite field method, (ii) the evaluation of the frequency dispersion at correlated levels using approximate schemes, and (iii) the deviations from Kleinman's symmetry conditions. It results from this study that accurate numerical derivatives can be obtained by resorting to the Romberg's method and by analyzing the Romberg's table in terms of two quantities, the field error and the iteration error. Indeed, the resulting first hyperpolarizability values are in close agreement with those obtained using an analytical differentiation procedure. The reliability of the multiplicative and additive approximate schemes to describe the frequency dispersion at correlated levels from using HF (Hartree‐Fock) frequency dispersion has been confirmed to be limited to large wavelengths or far‐from‐resonance wavelength regions. Kleinman's symmetry conditions have been assessed, showing that for off‐diagonal components of these two π‐conjugated compounds, the deviations could be substantial. Nevertheless, good accuracy can be achieved for experimentally related quantities like β_HRS because the diagonal tensor components are dominant. © 2014 Wiley Periodicals, Inc.     

Influence of Spiral Framework on Nonlinear Optical Materials

A series of spiral donor–π–acceptor frameworks (i.e. 2 – 2 , 3 – 3 , 4 – 4 , and 5 – 5 ) based on 4‐nitrophenyldiphenylamine with π‐conjugated linear acenes (naphthalenes, anthracenes, tetracenes, and pentacenes) serving as the electron donor and nitro (NO₂) groups serving as the electron acceptor were designed to investigate the relationships between the nonlinear optical (NLO) responses and the spirality in the frameworks. A parameter denoted as D was defined to describe the extent of the spiral framework. The D value reached its maximum if the number of NO₂ groups was equal to the number of fused benzene rings contained in the linear acene. A longer 4‐nitrophenyldiphenylamine chain led to a larger D value and, further, to a larger first hyperpolarizability. Different from traditional NLO materials with charge transfer occurring in the one‐dimensional direction, charge transfer in 2 – 2 , 3 – 3 , 4 – 4 , and 5 – 5 occur in three‐dimensional directions due to the attractive spiral frameworks, and this is of great importance in the design of NLO materials. The origin of such an enhancement in the NLO properties of these spiral frameworks was explained with the aid of molecular orbital analysis.     

Gold Nanocage Assemblies for Selective Second Harmonic Generation Imaging of Cancer Cell

Second harmonic generation (SHG) imaging using near infrared laser light is the key to improving penetration depths, leading to biological understanding. Unfortunately, currently SHG imaging techniques have limited capability due to the poor signal‐to‐noise ratio, resulting from the low SHG efficiency of available dyes. Targeted tumor imaging over nontargeted tissues is also a challenge that needs to be overcome. Driven by this need, in this study, the development of two‐photon SHG imaging of live cancer cell lines selectively by enhancement of the nonlinear optical response of gold nanocage assemblies is reported. Experimental results show that two‐photon scattering intensity can be increased by few orders of magnitude by just developing nanoparticle self‐assembly. Theoretical modeling indicates that the field enhancement values for the nanocage assemblies can explain, in part, the enhanced nonlinear optical properties. Our experimental data also show that A9 RNA aptamer conjugated gold nanocage assemblies can be used for targeted SHG imaging of the LNCaP prostate cancer cell line. Experimental results with the HaCaT normal skin cell lines show that bioconjugated nanocage‐based assemblies demonstrate SHG imaging that is highly selective and will be able to distinguish targeted cancer cell lines from other nontargeted cell types. After optimization, this reported SHG imaging assay could have considerable application for biology.     

Theoretical Investigations of Nonlinear Optical Properties of Transition Metal Cluster Anions

In the framework of density functional theory （DFT）, the electronic excitations and nonlinear optical （NLO） properties of six binuclear transition metal cluster anions with the formula of [Ch2M-（μ-Ch）2-M＇CN]^2- （M = Mo, W; Ch = S, Se; M＇ = Cu, Ag） have been systemically investigated at both cases of gas phase and DMF solution. The obtained electronic absorption spectra reveal that the element replacements of metals M and ligands Ch have significant influence on the absorptions, especially on the low-lying ones. In addition, the transitions of μ-Ch→M are dominant for the low-lying excitations, whereas the transitions of M＇→M as well as Ch→M are mainly responsible for the higher excitations. The calculated molecular first and second hyperpolarizabilities present the remarkable element substitution and solvent effects. The analyses show that the transitions involving μ-Ch→M charge transfer make the critical contributions to the first hyperpolarizability t, and that the charge transfers from the moieties of MCh4 to M＇CN as well as those of μ-Ch→M and M＇→M are responsible for the second hyperpolarizability y. Moreover, the introduction of solvent leads to the results that the transitions within the moieties of MCh4 and M＇CN make larger contributions to the hyperpolarizability, especially to γ.     

Front Cover: Investigation of the Second Harmonic Generation at the Water–Vacuum Interface by Using Multi‐Scale Modeling Methods (ChemistryOpen 1/2023)

The Front Cover shows the interfacial selectivity of second harmonic generation at the water‐vacuum interface, which is targeted in this work. In more details, the molecular first hyperpolarizability responses have been calculated by combining classical molecular dynamics and quantum chemistry simulations, and our model was able to distinguish between the bulk and the interfacial contributions. More information can be found in the Research Article by Tárcius N. Ramos et al.     

二阶超极化率γ的Hartree-Fock极限值的再研究

用有限场(FF)方法,在ROHF/x-aug-cc-pVXZ(x=1～5或7,X=T,Q)水平上计算了C,N,O,F,OH和OH⁺等开壳层原子和分子、离子的二阶超极化率γ.与闭壳层原子和分子的计算结果相类似,γ随基组的增大出现一个拐点.拐点对应的γ值与数字轨道计算的γ值符合得较好,其平均相对误差分别为1.79%(x-aug-cc-pVTZ)和1.91%(x-aug-cc-pVQZ),故计算二阶超极化率γ不需使用g函数.进一步研究表明,用x-aug-cc-pVTZ系列基组不仅可以得到γ的Hartree-Fock极限值,而且可以用来作较准确的二阶超极化率相关效应的计算.