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.     

NLOPredict: visualization and data analysis software for nonlinear optics

A data analysis and visualization program was developed to assist in the interpretation of second-order nonlinear optical (NLO) processes, including vibrational sum-frequency generation and electronically resonant second harmonic generation. A novel diagrammatic approach allows concise visual representations of the resonant NLO molecular response. By mapping the predicted NLO response as a function of molecular orientation, molecular modeling results can be combined with experimental measurements for orientational analysis. A method is developed and implemented to predict the nonlinear optical properties of the amide backbones in complete proteins with known structures. NLOPredict is available for most computer operating systems from http://sda.iu.edu/nlopredict/.     

Boosted Second Harmonic Generation of a Chiral Hybrid Lead Halide Resonant to Charge Transfer Exciton from Metal Halide Octahedra to Ligand

Chiral hybrid organic–inorganic metal halides (HOMHs) offer an ideal platform for the advancement of second-order nonlinear optical (NLO) materials owing to their inherent noncentrosymmetric structures. The enhancement of optical nonlinearity of chiral HOMHs could be achieved by matching the free exciton and/or self-trapped exciton energy levels with desired NLO frequencies. However, the current scarcity of resonance modes and low resonance ratio hamper the further improvements of NLO performance. Herein, we propose a new resonant channel of charge transfer (CT) excited states from metal halide polyhedra to organic ligand to boost the second-order optical nonlinearity of chiral HOMHs. The model lead halide (C₇H₁₀N)PbBr₃ (C₇H₁₀N=1-ethylpyridinium) exhibits a drastically enhanced second harmonic generation in resonance to the deep CT exciton energy, with intensity of up to 111.0 times that of KDP and 10.9 times that of urea. The effective NLO coefficient has been determined to be as high as ~40.2 pm V⁻¹, balanced with a large polarization ratio and high laser damage threshold. This work highlights the contribution of organic ligands in the construction of a resonant channel for enhancing second-order NLO coefficients of metal halides, and thus provides guidelines for designing new chiral HOMHs materials for advanced nonlinear photonic applications.     

(NH4)Bi2(IO3)2F5: An Unusual Ammonium‐Containing Metal Iodate Fluoride Showing Strong Second Harmonic Generation Response and Thermochromic Behavior

An ammonium‐containing metal iodate fluoride compound, (NH₄)Bi₂(IO₃)₂F₅, featuring a two‐dimensional double‐layered framework constructed by [BiO₂F₅]^6? and [BiO₄F₄]^9? polyhedra, as well as [IO₃]^? groups, was successfully synthesized. The well‐ordered alignment of these SHG‐active units leads to an extraordinary strong SHG response of 9.2 times that of KDP. Moreover, this compound possesses a large birefringence (Δn=0.0690 at 589.3 nm), a wide energy band gap (E_g=3.88 eV), and a high laser damage threshold (LDT; 40.2×AgGaS₂). In particular, thermochromic behavior was observed for the first time in this type of compound. Such multifunctional crystals will expand the application of nonlinear optical materials.     

The Use of Second‐Harmonic Generation to Study Diffusion through Films under a Liquid Phase

Knowledge of the diffusion of chemicals through buried films is important for a wide variety of systems—from sensing to drug delivery. Herein, we show that second‐harmonic generation (SHG) can be used to follow the diffusion through a thin film buried under a liquid in situ. More specifically, the diffusion of 4‐(4‐diethylaminostyryl)‐1‐methylpyridinium iodide through zeolite precursor films of different thickness is followed. The diffusion coefficients are calculated according to Fick’s law.     

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.     

磺基水杨酸盐的晶体结构和倍频效应

用X射线单晶衍射法测定了三水合二（5－磺基水杨酸）钙（C（14）H1（10）O（12）S2Ca·3H2O，1）和二水合（5－磺基水杨酸）二钾（C7H4O6SK2·2H2O，2）的晶体结构·化合物1属单斜晶系，空间群为Pn。，晶胞参数a＝5．604（1），B＝18．560（4），c＝10．006（2），β＝102．19（3）°，Z＝2，最终R＝0．0244．化合物2属正交晶系，空间群Pbca，晶胞参数a＝25．841（5），b＝12．186（2），c＝7．739（2），Z＝8，最终R＝0．0308．化合物1粉末倍频效应为2．86倍KH2PO4，其厘米级单晶体的紫外端吸收边经在375nm附近     

Rb3VO(O2)2CO3: A Four‐in‐One Carbonatoperoxovanadate Exhibiting an Extremely Strong Second‐Harmonic Generation Response

A nonlinear optical (NLO) carbonatoperoxovanadate, Rb₃VO(O₂)₂CO₃, was synthesized through a simple solution‐evaporation method in phase‐pure form. Single‐crystal X‐ray diffraction revealed that the structure of Rb₃VO(O₂)₂CO₃ consists of important noncentrosymmetric (NCS) chromophores, that is, π‐delocalized (CO₃)^2? groups, a second‐order Jahn–Teller (SOJT) distortive V⁵⁺ cation, and π‐localized distorted O₂^2? groups, as well as charge‐balancing polarizable Rb⁺ ions. The powder second‐harmonic generation (SHG) measurements indicated that Rb₃VO(O₂)₂CO₃ is phase‐matchable (Type I) and exhibits a remarkably strong SHG response circa 21.0 times that of potassium dihydrogen phosphate (KDP), which is the largest efficiency observed among carbonate NLO materials. First‐principles calculation analysis suggests that the extremely large SHG response of Rb₃VO(O₂)₂CO₃ is attributed to the synergistic effect of the cooperation of all the constituting NCS chromophores.     

The Large Second‐Harmonic Generation of LiCs2PO4 is caused by the Metal‐Cation‐Centered Groups

We evaluated the individual atom contributions to the second harmonic generation (SHG) coefficients of LiCs₂PO₄ (LCPO) by introducing the partial response functionals on the basis of first principles calculations. The SHG response of LCPO is dominated by the metal‐cation‐centered groups CsO₆ and LiO₄, not by the nonmetal‐cation‐centered groups PO₄ expected from the existing models and theories. The SHG coefficients of LCPO are determined mainly by the occupied orbitals O 2p and Cs 5p as well as by the unoccupied orbitals Cs 5d and Li 2p. For the SHG response of a material, the polarizable atomic orbitals of the occupied and the unoccupied states are both important.     

A2SnS5: A Structural Incommensurate Modulation Exhibiting Strong Second‐Harmonic Generation and a High Laser‐Induced Damage Threshold (A=Ba,Sr)

Structural modulations have been recently found to cause some unusual physical properties, such as superconductivity or charge density waves; however, thus‐induced nonlinear optical properties are rare. We report herein two unprecedented incommensurately modulated nonlinear optical sulfides exhibiting phase matching behavior, A₂SnS₅ (A=Ba, Sr), with the (3+1)D superspace groups P2₁2₁2(00γ)00s or P2₁(α0γ)0, featuring different modulations of the [Sn₂S₇]_∞ belts. Remarkably, Ba₂SnS₅ exhibits an excellent second harmonic generation (SHG) of 1.1 times that of the benchmark compound AgGaS₂ at 1570 nm and a very large laser‐induced damage threshold (LIDT) of 8×AgGaS₂. Theoretical studies revealed that the structural modulations increase the distortions of the Sn/S building units by about 44 or 25 % in A₂SnS₅ (A=Ba, Sr), respectively, and enhance significantly the SHG compared with α‐Ba₂SnSe₅ without modulation. Besides, despite the smaller E_g, the A₂SnS₅ samples exhibit higher LIDTs owing to their smaller thermal expansion anisotropies (Ba₂SnS₅ (1.51)<Sr₂SnS₅ (2.08)<AgGaS₂ (2.97)).     

Giant Enhancement of Second Harmonic Generation Accompanied by the Structural Transformation of 7‐Fold to 8‐Fold Interpenetrated Metal–Organic Frameworks (MOFs)

Interpenetration in metal–organic frameworks (MOFs) is an intriguing phenomenon with significant impacts on their properties, and functional applications. Herein, we show that a 7‐fold interpenetrated MOF ( 1 ) is transformed into an 8‐fold interpenetrated MOF by the loss of DMF in a single‐crystal‐to‐single‐crystal manner. This is accompanied by a giant enhancement of the second harmonic generation (SHG ca. 125 times) and two‐photon photoluminescence (ca. 14 times). The strengthened π–π interaction between the individual diamondoid networks and intensified oscillator strength of the molecules aid the augment of dipole moments and boost the nonlinear optical conversion efficiency. Large positive and negative thermal expansions of 1 occur at 30–150 °C before the loss of DMF. These results offer an avenue to manipulate the NLO properties of MOFs using interpenetration and provide access to tunable single‐crystal NLO devices.     

非线性光学环氧聚合物的近程结构对二次谐波产生弛豫特性的影响

设计合成了三种具有不同主链化学结构的二阶非线性光学功能化环氧聚合物,并对其化学结构进行了表征,考察了聚合物近程结构对材料极化后二次谐波产生弛豫特性的影响。极化后线型聚合物链节的扭转弹性回复是二次谐波产生弛豫的主要原因,在温度处于Ｔｇ 以下或Ｔｇ 附近时玻璃化转变温度的高低决定了二次谐波产生弛豫的快慢;聚合物交联后有助于提高二次谐波产生的稳定性,但此时聚合物单个链节结构的柔顺性成为影响二次谐波产生弛豫的主要原因,刚性越大,材料将具有更稳定的二次谐波产生性能。极化聚合物的二次谐波产生弛豫过程非常复杂,需要综合考虑聚合物材料的近程和远程结构因素。     

中心对称双酞菁铥LB膜二次谐波产生特性

利用二次谐波产生(SHG)方法研究了中心对称分子稀土夹心双酞菁铥(TmPc₂) Langmuir-Blodgett (LB)膜二阶非线性光学特性, 测量了二次谐波强度随入射基频光入射角的关系, 并对其二阶非线性产生机制进行了讨论. 实验结果表明, TmPc₂分子LB膜具有较好的二次谐波信号, 二次谐波信号强度的最大值在基频光入射角为45°的地方, 其二阶非线性极化率χ⁽²⁾和分子超极化率β分别为1.152×10^-8和1.905×10^-30 esu. 通过测量样品二次谐波信号的偏振特性, 并与理论分析相比较, 得出其二阶非线性起源于电四极子作用机制.     

Optical Second Harmonic Generation and Relaxation Dynamics of Aligned Azo-Dyes in Sol-Gel Derived Organic-Inorganic Film

An Azo-dye doped organic-inorganic hybrid film was prepared by the sol-gel technique, and optical second-harmonic (SH) nonlinearities were measured as a function of the poling conditions. Azo-dye molecules dispersed in poly-vinylpyrrolidone were complexed with the hydrolyzed silicon-alkoxide. The Maker-fringe pattern composed of a fine oscillating pattern on a broad component, and the highest second-order nonlinear coefficient, d ₃₃, was 0.83 pm/V when poled at 175°C and 4 kV. The analysis of the decay curves of the SH intensities at 150–190°C predicted the relaxation time of about 3 years at room temperature.     

N原子对取代NH_4H_2PO_4盐类晶体的二次谐波发生的影响(英文)

从N—H键在取代NH4H2 PO4盐的 [AH]4 [H2 PO4]类晶体中的突出作用出发 ,作者对几个 [AH]4 [H2 PO4]型晶体的二次谐波发生进行理论上的研究 (这里A =伯、仲、叔胺 )。并对这一类晶体的二次谐波发生和其亚结构单元 [AH]+ 中N原子上的净电荷之间的依赖关系进行了估计。     

Combined Second Harmonic Generation and Fluorescence Analyses of the Structures and Dynamics of Molecules on Lipids Using Dual-Probes: A Review

Revealing the structures and dynamic behaviors of molecules on lipids is crucial for understanding the mechanism behind the biophysical processes, such as the preparation and application of drug delivery vesicles. Second harmonic generation (SHG) has been developed as a powerful tool to investigate the molecules on various lipid membranes, benefiting from its natural property of interface selectivity, which comes from the principle of even order nonlinear optics. Fluorescence emission, which is in principle not interface selective but varies with the chemical environment where the chromophores locate, can reveal the dynamics of molecules on lipids. In this contribution, we review some examples, which are mainly from our recent works focusing on the application of combined spectroscopic methods, i.e., SHG and two-photon fluorescence (TPF), in studying the dynamic behaviors of several dyes or drugs on lipids and surfactants. This review demonstrates that molecules with both SHG and TPF efficiencies may be used as intrinsic dual-probes in plotting a clear physical picture of their own behaviors, as well as the dynamics of other molecules, on lipid membranes.     

Pb2BO3Cl: A Tailor‐Made Polar Lead Borate Chloride with Very Strong Second Harmonic Generation

A meticulously designed, polar, non‐centrosymmetric lead borate chloride, Pb₂BO₃Cl, was synthesized using KBe₂BO₃F₂ (KBBF) as a model. Single‐crystal X‐ray diffraction revealed that the structure of Pb₂BO₃Cl consists of cationic [Pb₂(BO₃)]⁺ honeycomb layers and Cl^? anions. Powder second harmonic generation (SHG) measurements on graded polycrystalline Pb₂BO₃Cl indicated that the title compound is phase‐matchable (type I) and exhibits a remarkably strong SHG response, which is approximately nine times stronger than that of potassium dihydrogen phosphate, and the largest efficiency observed in materials with structures similar to KBBF. Further characterization suggested that the compound melts congruently at high temperature and has a wide transparency window from the near‐UV to the mid‐IR region.     

Conserved Hydrogen Bonded Tartrate Frameworks: Inclusion of Amines and Implications for Second Harmonic Generation

A series of anilinium cations with various functional groups as substituents has been chosen to form salts with l-tartaric acid and d-dibenzoyl tartaric acid. The salts show second harmonic generation activities comparable to urea. The tartrate frameworks provide conformationally rigid hydrogen bonded frameworks for the incorporation of these cations. The SHG activity of these salts appear to depend upon the type of framework provided by the tartrate anions, which in turn decides the orientation of the cations.