Verbenone-based push–pull chromophores with giant first hyperpolarizabilities: A new structure–property correlation study

Novel chromophores Ch1–8 based verbenone bridge with various strong donors and acceptors were designed for applications in nonlinear optics, and the nonlinear optical (NLO) properties of those verbenone-type chromophores were systematically investigated using the bond length alteration (BLA) theory, two states model (TSM) and sum-over-states (SOS) model. The results show that several verbenone-based chromophores possess remarkably large molecular second-order hyperpolarizabilities, which is due to its electron distribution close to the cyanine limit, the appropriate strength of acceptor, rather large change in dipole moment and low excitation energy. Computed hyperpolarizability (β_tot) of Ch6 also approach an outstanding 2922 × 10⁻³⁰ esu in TFE. The hyperpolarizability density analyses and two states model (TSM) were carried out to make a further insight into the origination of molecular nonlinearity of this unique system, suggesting that tuning structure of acceptor and polarity of the medium have great influence on the second-order nonlinear optical properties. More importantly, chromophores Ch1–Ch8 exhibited distinct features in two-dimensional second order NLO responses, and the strong electro-optical Pockels effect and optical rectification responses. The excellent electronic sum frequency generations (SFG) and difference frequency generations (DFG) effect are observed in these verbenone-type chromophores. These chromophores have a possibility to be appealing second-order nonlinear optical (NLO) materials, data storage materials and DSSCs materials from the standpoint of large β values, high LHE, and excellent two-dimensional second order NLO responses.     

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/.     

A new approach to highly electrooptically active materials using cross-linkable, hyperbranched chromophore-containing oligomers as a macromolecular dopant

A new, practical approach to a variety of highly electrooptically active polymers for device development is described. It involves the use of a new thermally cross-linkable, hyperbranched oligomer containing nonlinear optical (NLO) chromophores as a macromolecular dopant in a common host polymer. A series of NLO polymeric blends were readily formulated and showed large and stable electrooptic (EO) coefficients (up to 65 pm/V). In comparison with previously studied linear NLO polyimides and guest-host polymers doped with molecular chromophores and even linear NLO analogous oligomers, this new approach offers clear advantages for device development in terms of improved poling efficiency, larger EO coefficients, good temporal stability, and versatile material formulation.     

含咔唑生色团的有机芳香杂环分子的二阶非线性光学性质

采用密度泛函理论B3LYP/6-31G^*方法, 对一系列含咔唑生色团的有机芳香杂环分子进行结构优化, 并采用有限场(FF)和含时密度泛函理论(TD-DFT)方法在6-311G^**水平上探讨了体系的二阶非线性光学(NLO)性质和电子光谱. 结果表明, 咔唑取代基推或拉电子能力的改变和引入芳香杂环对研究分子的极化率α和二阶NLO系数β值都有较大影响. 当取代基分别连有拉电子硝基和推电子羟基, 以及引入呋喃杂环都可以使体系分子的β值随分子的最大吸收波长λ_max的增大而减小(蓝移). 该系列化合物兼具有很大的二阶非线性响应与良好的透光范围, 避免了“非线性-透光性”矛盾, 可能在非线性材料领域中有很大的潜在应用价值.     

Probing organic field effect transistors in situ during operation using SFG

In this communication, we report results obtained using surface-sensitive IR+Visible Sum Frequency Generation (SFG) nonlinear optical spectroscopy on interfaces of organic field effect transistors during operation. We observe remarkable correlations between trends in the surface vibrational spectra and electrical properties of the transistor, with changes in gate voltage (VG). These results suggest that field effects on electronic conduction in thin film organic semiconductor devices are correlated to interfacial nonlinear optical characteristics and point to the possibility of using SFG spectroscopy to monitor electronic properties of OFETs.     

Self-consistent approach for simplifying the molecular interpretation of nonlinear optical and multiphoton phenomena

A method is developed for simplifying molecular interpretations of nonlinear optical phenomena. General sum-over-states expressions derived from perturbation theory can be written identically and self-consistently as simple products of lower-order effects. Electric dipole-allowed expressions for the nonlinear polarizability reduce to straightforward formulas directly connected to intuitive molecular properties without sacrificing mathematical rigor. This approach is sufficiently general to allow its application in treating electronic, vibrational, and vibronic interactions for both parametric (passive) processes (e.g., wave-mixing spectroscopies, sum- and difference-frequency generation, harmonic generation, etc.) and nonparametric (active) processes (e.g., hyper-Raman spectroscopy, multiphoton absorption, etc.). Explicit examples for sum-frequency generation and for four-wave mixing provide a convenient context for interpreting higher order nonlinear optical processes.     

Synthesis and second-order nonlinear optical properties of new chromophores containing benzimidazole, thiophene, and pyrrole heterocycles

A new series of thermally stable benzimidazole-based nonlinear optical (NLO) chromophores 4 and 5 have been developed. These chromophores possess a thienylpyrrolyl π-conjugated system attached to functionalized benzimidazole heterocycles. This feature leads to robust chromophores with excellent solvatochromic properties, high thermal stabilities and good molecular optical nonlinearities.     

Alkali metal doping effect on static first hyperpolarizabilities of PMI chains

An ab initio study of the effect on nonlinear optical (NLO) properties of medium-size polymethineimine (PMI) chains caused by doping with an alkali metal atom along the backbone is presented. Both the electronic and (preliminary) vibrational static first hyperpolarizabilities are investigated. Doping leads to the injection of an excess electron into the PMI chain, which is accompanied by major enhancement of its NLO response. Along with the hyperpolarizability, other electronic and structural properties depend strongly upon the position of doping along the chain. The vibrational contribution is larger than the corresponding electronic one for most of the cases studied.     

Optical, redox, and NLO properties of tricyanovinyl oligothiophenes: comparisons between symmetric and asymmetric substitution patterns

A series of tricyanovinyl (TCV)-substituted oligothiophenes was synthesized and investigated with a number of physical methods including UV/Vis, IR, and Raman spectroscopy, nonlinear optical (NLO) measurements, X-ray diffraction, and cyclic voltammetry. Mono- or disubstituted oligomers were prepared by the reaction of tetracyanoethylene with mono- or dilithiated oligomers. The comparative effects of the symmetric and asymmetric substitutions in the electronic and molecular properties have been addressed. These oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison with unsubstituted molecules. The analysis of the electronic properties of the molecules was assisted by density functional theory calculations, which are in excellent agreement with the experimental data. TCV substitution influences the energies of the frontier orbitals, especially with respect to the stabilization of LUMO orbitals. X-ray structural characterization of a monosubstituted oligomer exhibits pi-stacking with favorable intermolecular interactions. NLO results agree with the role of the intramolecular charge-transfer feature in the asymmetric samples. These results furthermore exalt the role of conformational flexibility in the disubstituted compounds and reveal an unexpected nonlinear optical activity for symmetric molecules. Regarding the electronic structure, the interpretation of the vibrational data reflects the balanced interplay between aromatic and quinoid forms, finely tuned by the chain length and substitution pattern. The electronic and structural properties are consistent with the semiconducting properties exhibited by these materials in thin film transistors (TFTs).     

A relaxation study of poled nonlinear optical polymers by infrared reflection-absorption spectroscopy

The relaxation of poled nonlinear optical (NLO) chromophores in polymer films was characterized by infrared (i.r.) reflection-absorption spectroscopy. Both a guest-host system and a photocrosslinkable polymer system were investigated. Polymethylmethacrylate doped with either 2-methyl-4-nitroaniline or 4(4′-nitrophenylazo)aniline was studied. The photocrosslinkable polymer system, polyvinylcinnamate doped with 3-cinnamoyloxy-4-[4-(N,N-diethylamino)-2-cinnamoyloxy phenyl azo]nitrobenzene was also investigated. Doped NLO active molecules were aligned using the corona poling technique. i.r. spectra as a function of time were used to monitor the relaxation behavior of the oriented dyes after poling. Relaxation of NLO molecules was followed at various characteristic vibrational frequencies. The relaxation behavior of both systems were found to be consistent with those studied by the second harmonic generation technique.     

Dendronized tricyanopyrroline‐based chromophores in nonlinear optical active host polymer

We synthesized new nonlinear optical (NLO) chromophores containing a 3,5‐bis(3,5‐bisbenzyloxy‐benzyloxy)‐benzoate dendron. Tricyanopyrroline (TCP)‐based chromophores were designed and prepared by virtue of its strong electron withdrawing property. A soluble polyimide containing 6‐({4‐[2‐(1‐allyl‐4‐cyano‐5‐dicyanomethylene‐2‐oxo‐2,5‐dihydro‐1H‐pyrrol‐3‐yl)‐vinyl]‐phenyl}‐butyl‐amino)‐hexanoyl group in the side chain was also prepared as an NLO active host polymer. A benzoate dendron was tethered at two different binding positions of the chromophore to yield two different guest molecules. Thin‐film composites of these dendronized chromophores dissolved in the NLO active polyimide host were employed to fabricate the electro‐optic (EO) samples. The EO properties of new NLO polyimides containing dendronized chromophores were compared with those of the sample with nondendronized plain chromophores. The effect of a bulky dendron on the EO properties was investigated using an in situ reflection technique. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5064–5076, 2008     

Nonlinear optical chromophores with pyrrole moieties as the conjugated bridge: enhanced NLO effects and interesting optical behavior

A series of nonlinear optical (NLO) chromophores were successfully prepared, in which pyrrole moieties were the conjugated bridge. In comparison with their analogues containing furan or thiophene groups as the bridge, these chromophores demonstrated similar or enhanced NLO effects (up to 3.3 times) and interesting optical behavior. While the acceptor groups were malononitrile (Mal), 3-phenyl-5-isoxazolone (Iso), and 1,3-diethylthiobarbituric acid (Bar), the chromophores exhibited much blue-shifted maximum absorption wavelengths (lambda max) (up to 36 nm); however, the lambda max of the chromophore containing tricyanovinyldihydrofuran (TCF) as acceptor became much longer than that of the analogue (up to 75 nm).     

Linear and nonlinear optical properties of a macrocyclic trichromophore bundle with parallel-aligned dipole moments

A macrocyclic trichromophore bundle 1 with parallel-aligned dipole moments has been synthesized to study the influence of aggregation and orientation of a nonlinear optical (NLO) chromophore on its optical properties. The linear and nonlinear optical properties of 1 and a single chromophore standard 2 have been studied by UV-vis absorption, fluorescence, solvatochromic spectrometry, and hyper-Rayleigh scattering (HRS). Reduced first-order hyperpolarizability beta, hypsochromic shift, enhanced solvatochromic shifts, and fluorescence quenching for individual chromophores were observed when 1 was compared with 2. Analysis of the data showed that the transition dipole moment changes only slightly when the chromophores are parallel aligned in the bundle architecture. However, the apparent hyperpolarizability of the individual chromophores decreased significantly by about 20%. The reduction in beta for the individual chromophores in 1 is largely due to the hypsochromic shift, i.e., excitation energy increase of the interband (charge-transfer) energy gap and the reduced difference between the ground-state and excited-state dipole moments. The hypsochromic shift and fluorescence quenching are consistent with exciton theory. Possible reasons for the enhanced solvatochromic shift are discussed.     

Theory of time-resolved sum-frequency generation and its applications to vibrational dynamics of water

A molecular theory of time-resolved sum-frequency generation (SFG) has been developed. The theoretical framework is constructed using the coupled-oscillator model in the adiabatic approximation. This theory can treat not only the vibrational spectroscopy but also vibrational dynamics. An application of this theory is also provided for estimation of the time constants of the intermolecular vibrational energy transfer between water molecules. This approach can be used for molecular analysis of the experimental results of Shen at al. on the SFG studies of vibrational dynamics of water.     

Unique Vibrational Features as a Direct Probe of Specific Antigen–Antibody Recognition at the Surface of a Solid‐Supported Hybrid Lipid Bilayer

Here, we demonstrate how sum frequency generation (SFG), a vibrational spectroscopy based on a nonlinear three‐photon mixing process, may provide a direct and unique fingerprint of bio‐recognition; This latter can be detected with an intrinsically discriminating unspecific adsorption, thanks to the high sensitivity of the second‐order nonlinear optical (NLO) response to preferential molecular orientation and symmetry properties. As a proof of concept, we have detected the biological event at the solid/liquid interface of a model bio‐active antigen platform, based on a solid‐supported hybrid lipid bilayer (ss‐HLB) of a 2,4‐dinitrophenyl (DNP) lipid, towards a monoclonal mouse anti‐DNP complementary antibody.     

基于分子间侧向氢键作用的电光材料制备及性能

通过重氮耦合和酯化等反应制备了一系列侧向含有酰胺基团的偶氮苯类非线性光学生色团, 并将其与聚合物进行掺杂或通过分子间的侧向氢键作用制备了主客体型及超分子型的电光薄膜材料. 生色团的结构通过核磁共振谱(¹H NMR, NMR)、 红外光谱(IR)、 质谱(MS)和元素分析(EA)等进行了表征, 结果表明, 生色团形成了分子间的氢键作用. 通过紫外-可见(UV-Vis) 光谱研究了材料的极化性能. 相比主客体型电光薄膜材料, 由分子间侧向氢键作用形成的超分子型电光薄膜材料无需与聚合物基体材料复合, 更有利于提高材料的生色团含量、 极化取向度及稳定性. 通过Teng-Man简单反射法研究了主客体型和超分子型电光材料的二阶非线性光学性质, 结果表明, 基于分子间侧向氢键作用形成的超分子体系具有更大的电光系数.     

Synthesis and Optical Properties of HyperbranchedPAEKs Containing Porphyrin and Its Metal Derivatives简

Novel functional hyperbranched poly(aryl ether ketone)s(HPAEKs) bonded with nonlinear optical chromophores(meso-tetrakis(4-hydroxyphenyl) porphyrin, THPP and its metal derivatives) were synthesized and characterized by 1H-NMR and UV-Vis absorption spectra. The incorporation of chromophores into HPAEKs endowed HPAEKs novel NLO and OL properties. Indeed, dendritic architecture allowed for maximum dispersion of the chromophores, avoided aggregation, more optical limiting property was obtained. Simultaneously, they retained the excellent properties of the materials, particularly in thermal stability. Their optical properties were evaluated by nonlinear optical analyses and optical limiting. The results showed that these polymers possessed good optical limiting(OL) property and large nonlinear optical(NLO) susceptibilities(ca. 10 12esu). All polymers containing chromophores presented excellent thermal stability(DT5 524.17 °C).     

有机二阶非线性光学发色团的研究进展

近年来,科学家们通过引进杂环片段、采用双(或多)官能化以及运用分子间弱相互作用等方法,在二阶非线性光学发色团的性能优化方面取得了较大进展.结合本课题组的研究,对此领域的研究进行了较全面的综述,并特别针对“非线性-透光性”矛盾的解决途径进行了较为详细的介绍.     

Direct metal-metal interaction contributions to quadratic hyperpolarizability: a study on dirhenium complexes

We present a comparative study of the metal-metal interaction effect on the static quadratic hyperpolarizabilities of two typical dinuclear rhenium clusters. The electronic structures, excitation spectra, dipolar moments, static polarizabilities, and quadratic hyperpolarizabilities of the two complexes with direct metal-metal interactions have been computed and analyzed with the use of high-level DFT/TDDFT methods. The geometries and the first intense excitations agree with the relevant reported measurements. The orbital decomposition scheme ( J. Phys. Chem. A 2006, 110, 1014-1021) has been applied to analyze the relationship between the electronic structures and nonlinear optical (NLO) properties of these two complexes. We propose an unprecedented NLO response mechanism featuring the contribution of the direct metal-metal interaction transition process in these dinuclear rhenium complexes. This contribution positively enhances the quadratic hyperpolarizability and relates to the intensity of the metal-metal interactions of the complexes. The results are helpful to the development of NLO chromophores in polynuclear metal clusters through the molecular design technique.     

Variational calculation of vibrational linear and nonlinear optical properties

A variational approach for reliably calculating vibrational linear and nonlinear optical properties of molecules with large electrical and/or mechanical anharmonicity is introduced. This approach utilizes a self-consistent solution of the vibrational Schrodinger equation for the complete field-dependent potential-energy surface and, then, adds higher-level vibrational correlation corrections as desired. An initial application is made to static properties for three molecules of widely varying anharmonicity using the lowest-level vibrational correlation treatment (i.e., vibrational M?ller-Plesset perturbation theory). Our results indicate when the conventional Bishop-Kirtman perturbation method can be expected to break down and when high-level vibrational correlation methods are likely to be required. Future improvements and extensions are discussed.