Azo-azulene derivatives as second-order nonlinear optical chromophores

The molecular and solid state nonlinear optical (NLO) properties of several (phenylazo)-azulenes are investigated. In particular, (4-nitrophenylazo)-azulene (2b) exhibits a quadratic hyperpolarizability (beta(vec)) of 80 x 10(-30) cm5esu recorded at 1.907 microm by the electric field-induced second-harmonic (EFISH) technique. This molecular material, which crystallizes in the monoclinic noncentrosymmetric space group Pc, exhibits an efficiency 420 times that of urea in second-harmonic generation. The origin of the optical nonlinearity in azo-azulene is discussed in relation with crystal structures and semiempirical calculations within the INDO/SOS formalism, and compared with that of the well known disperse red one (DR1) organic dye.     

Nonlinear optical molecular switches as selective cation sensors

This work demonstrates that the recognition of cations by molecular switches can give rise to large contrasts of the second-order nonlinear optical (NLO) properties, which can therefore be used as a powerful and multi-usage detection tool. The proof of concept is given by evidencing, by means of ab initio calculations, the ability of spiropyran/merocyanine systems to selectively detect alkali, alkaline earth, and transition-metal cations.     

Acido-triggered nonlinear optical switches: benzazolo-oxazolidines

This work is the continuation of our previous experimental and theoretical studies aiming at designing efficient nonlinear optical (NLO) switches derived from the benzazolo-oxazolidine core. Here, we report the synthesis and the characterization of the linear and nonlinear optical properties of benzothiazolo[2,3-b]oxazolidine acidochromes by means of hyper-Rayleigh scattering as well as quantum chemical calculations. It is shown that these new derivatives incorporating a benzothiazole subunit exhibit very high static first hyperpolarizability values in their acido-generated form. On the basis of previously reported NLO responses of indolino- and benzimidazolo-oxazolidines, structure-properties relationships within the benzazolo-oxazolidine series are proposed.     

Family of site-selective molecular optical switches

[reaction: see text] We describe the design, synthesis, and characterization of a family of thiol-reactive optical switches for labeling proteins and other biomolecules. Site-selective introduction of photochromic probes within biomolecules is being used as part of a new approach for optical control of biomolecular interactions and activities within cells. The thiol-reactive photochromic probes described in this report include a spironaphthoxazine and five spirobenzopyrans. The location of the thiol-reactive group on the spirobenzopyran is different for each probe; this feature can be used to control the geometry of the optical switch within a bioconjugate. The photochromes undergo rapid and reversible, optically driven transitions between a colorless spiro (SP) state and a brightly colored merocyanine (MC) state. The MC absorption of a spironaphthoxazine conjugate is red shifted by more than 100 nm compared to the equivalent spirobenzopyran, which may be exploited for the independent control of the MC to SP transition for up to two different spironaphthoxazine and spirobenzopyran conjugates within the same sample.     

Inorganic supramolecular compounds with 3-D chiral frameworks show potential as both mid-IR second-order nonlinear optical and piezoelectric materials

Two inorganic supramolecular compounds, (Hg(6)P(3))(In(2)Cl(9)) (1) and (Hg(8)As(4))(Bi(3)Cl(13)) (2), which have chiral 3-D host frameworks with guest moieties filling the helical tunnels, have been synthesized. They both have large second-harmonic generation efficiencies, and compound 2 also exhibits obvious single-crystal piezoelectric performance. Theoretical studies from first-principles calculations were performed on their nonlinear optical (NLO) and piezoelectric properties, and results indicate that good NLO and piezoelectric materials can be obtained by designing both complicated polycations and polyanions with large molecular polarizability as functional components rather than traditional single polyanions.     

Mixed electric-magnetic second-order nonlinear optical response of helicenes

The mixed electric-magnetic second-order nonlinear optical responses of oriented films of helicenes have been computed ab initio using the random phase approximation method and compared to the pure electric-dipole counterpart. It turns out that the mixed electric-magnetic responses can be of the same order of magnitude as the pure electric-dipole counterpart when there is no donor/acceptor (D/A) substituent or these D/A pairs are weak, i.e., when the pure electric-dipole response is small. When adding strong D/A substituents, the pure electric-dipole response increases substantially and much more than its mixed electric-magnetic counterpart. Consequently, the ratio between the mixed electric-magnetic and pure electric responses decreases. Although there is no general rule, the mixed responses evolve as a function of substitution quasi similarly to the pure electric contribution. This study confirms therefore the possibility of tuning the mixed electric-magnetic response by employing appropriate chiral molecules.     

Novel crosslinked polyurethanes with second-order nonlinear optical effects

A series of push–pull chromophores (R-HANB) based on 4′(N,N′-dihydroxyethyl)amino-4-nitro azobenzene has been designed and synthesized. R-HANB chromophores show a strong tendency to undergo intramolecular charge transfer and show high nonlinear optical effects. During the poling process, the trimer of hexamethylene diisocyanate reacted with R-HANB to give four various thermosetting polyurethanes simultaneously at higher temperature. The second harmonic generations (SHG) of three crosslinked polyurethane films are fairly high and stable at ambient temperature. The real-time measurement of SHG intensity vs. poling voltage indicates that orientation of chromophores is still feasible in this crosslinked system.     

Novel low-melting salts with donor-acceptor substituents as targets for second-order nonlinear optical applications

We synthesized several novel low-melting ionic salts with donor-acceptor substituents and investigated their possible applications as second-order nonlinear optical materials.     

Influence of thiazole regioisomerism on second-order nonlinear optical chromophores

Two series of matched and mismatched donor–thiazole–acceptor chromophores have been synthesized to disclose the role that the orientation of the thiazole ring plays on their second-order nonlinear optical (NLO) properties. Whereas previous theoretical studies predict that the matched systems show markedly higher NLO responses, our experimental results do not parallel this trend, showing differences between regioisomers much lower than those predicted.     

Tunable resonance hyper-Raman spectroscopy of second-order nonlinear optical chromophores

Two-photon-resonant hyper-Raman spectra are reported for three "push-pull" conjugated organic chromophores bearing -NO(2) acceptor groups, two dipolar and one octupolar. The excitation source is an unamplified picosecond mode-locked Ti:sapphire laser tunable from 720 to 950 nm. The linear resonance Raman spectra of the same molecules are measured using excitation from the laser second harmonic. Excitation on resonance with the lowest-lying band in the linear absorption spectrum yields nearly identical resonance Raman and resonance hyper-Raman spectra. However, excitation into a region that appears to contain more than one electronic transition gives rise to different intensity patterns in the linear and nonlinear spectra, indicating that different transitions contribute differently to the one-photon and two-photon oscillator strength. The promise of the hyper-Raman technique for examining electronic transitions that are both one- and two-photon allowed is discussed.     

Conformational diastereoisomers of PPh3 coordinated to stereogenic metal centres as molecular optical switches

The specific rotation of (R_Fe,R,M)-4 switches sign upon epimerisation to (R_Fe,S,P)-5. X-Ray crystallographic studies suggest that inversion of the propeller configuration of the coordinated PPh₃ ligand is a major contributor to the switch of specific rotation. A simple model for predicting the conformational diastereoisomeric forms of PPh₃ is presented, suggesting future routes towards the design of molecular optical switching devices.     

Highly efficient and thermally stable second-order nonlinear optical polymers

Several functionalized polyurethanes with highly active nonlinear optical chromophores were prepared. The alignment of the chromophores in poled samples exhibited an extended temporal stability due to the hydrogen bonding between the urethane linkage. Thermally stable polyetherimides with an excellent long-term stability of nonlinear activity were also developed. The detailed characterization, including thermal and optical properties, indicated very promising features for photonics applications of these polymers.     

Optically-induced second-order nonlinear optical effect in polyvinyl alcohol photopolymers

IR induced picosecond nonlinear optical effects in polyvinyl alcohol photopolymer is investigated. The second harmonic generation (SHG) is studied versus the pump power and delaying time between the pump and probing beam (λ=1.55 and 1.32 μm, respectively). The phenomena are explained within a framework of fifth-order nonlinear optical susceptibilities. An explanation of the observed dependences is given within a framework of photostimulated vibrations, which enhance acentric electron-phonon anharmonicity. Temperature dependences of the observed phenomena fully confirm the electron-phonon anharmonic origin of the observed effect.     

Photocrosslinkable second-order nonlinear optical polymers synthesized by cationic copolymerization

Photocrosslinkable second-order nonlinear optical (NLO) polymers were synthesized from cationic copolymerization of a vinyl ether monomer bearing 4′-nitrobiphenyl-4-oxy group as the NLO chromophore with a vinyl ether monomer bearing cinnamoyl group as the photoreactive moiety. To obtain a suitable poling method involving photocrosslinking, which is capable of inducing a higher and more stable second-order nonlinear coefficient, d₃₃, for NLO polymer films, some poling procedures were investigated. An optimized poling method was as follows. Ultraviolet (UV) irradiation is performed for 90 sec during poling at 50°C for 20 min, followed by poling at 150°C for 20 min. By using this poling method NLO polymer films exhibited a higher and considerably stable d₃₃ value at room temperature, even though they had rather lower glass transition temperatures before photocrosslinking. Some photocrosslinking mechanism for NLO polymers investigated here were considered.     

Synthesis and second-order nonlinear optical properties of push-pull BODIPY derivatives

A series of boron dipyrromethene derivatives bearing an electron-donating 4-(dimethylamino)phenylethynyl group and an electron-withdrawing 4-nitrophenylethynyl group in the opposite 2- and 6-positions have been synthesized by Knoevenagel condensation followed by sequential Sonogashira coupling reactions. The compounds have been fully characterized with various spectroscopic methods. Their electrochemical properties have also been studied by cyclic voltammetry in CH₂Cl₂. It has been found that expansion of the π systems by introduction of the 4-dodecyloxystyryl or 4-(dimethylamino)phenylethynyl group results in lowering of the first oxidation potential, while the first reduction potential remains relatively unaffected. The second-order nonlinear optical properties of these compounds have also been studied by electric-field-induced second-harmonic generation method in CHCl₃. The values of the dot product μ·β are in the range from 94×10^?48 to 330×10^?48 esu at 1907 nm, depending the substituents at the 3- and 5-positions.     

盐酸氨基脲的二阶非线性光学性质研究

非线性光学(NLO)材料在光学信息处理、远程通讯等光电子学领域有着重要的应用,有效地预测和设计出二阶非线性光学材料所必需的非中心对称晶体,提高材料的综合性能是这一领域的研究热点。标题化合物盐酸氨基脲是以尿素为分子母体的有机离子型化合物,具有将有机和无机材料的优异性能集于一身的结构优势,是综合性能优的材料之一。     

Synthesis and features of nonlinear optical switches based on dithienylethene unit

Two nonlinear optical (NLO) chromophores C1 and C2 based on dithienylethene were designed and synthesized as the ultraviolet NLO switches. The open/close behavior of C1 and C2 were investigated through the UV–vis spectra. Through quantum chemical calculations of the dipole moments, first and second hyperpolarizabilities, etc. we analyzed both opening and closure states of C1 and C2. The NLO switch ability of the chromophores were studied through monitoring of the SHG at the opening/closure states, which were performed under illumination of fourth harmonic generation of the nanosecond Nd:YAG laser (λ?=?266?nm). The obtained results indicated that the maximal SHG changes were observed at energy density equal to about 90?J/m², and the samples C1, 2′ closure states possess significantly higher value of the second order susceptibility compared to the opening states. After switching off of the external UV light, the induced second order susceptibilities remain up to 150?h without a decrease, which indicated that the obtained chromophores have the potential application as the NLO switches applied in photonics.     

Exceptionally large second-order nonlinear optical response in donor-graphene nanoribbon-acceptor systems

Graphene nanoribbon (GNR) has been used, for the first time, as an excellent conjugated bridge in a donor-conjugated bridge-acceptor (D-B-A) framework to design high-performance second-order nonlinear optical materials. Owing to the unique diradical planar conjugated bridge of GNR, D(NH(2))-GNR-A(NO(2)) exhibits exceptionally large static first hyperpolarizability (β(0)) up to 2.5×10(6) a.u. (22000×10(-30) esu) for H(2)N-(7,3)ZGNR-NO(2) (ZGNR=zigzag-edged GNR), which is about 15 times larger than the recorded value of β(0) (1470×10(-30) esu) for the D-A polyene reported by Blanchard-Desce et al. [Chem. Eur. J. 1997, 3, 1091]. Interestingly, we have found that the size effect of GNR plays a key role in increasing β(0) for the H(2)N-GNR-NO(2) system, in which the width effect of GNR perpendicular to the D-A direction is superior to the length effect along the D-A direction.     

螺旋双芴体系二阶非线性光学性质的ZINDO-SOS理论研究

用密度泛函B3LYP/631G*方法优化螺旋双芴的几何构型,在获得稳定构型的基础上,用半经验ZINDO方法计算体系的激发能和跃迁偶极矩,然后代入完全态求和公式得到体系的二阶极化率.结果表明,螺旋双芴具有较大的二阶极化率、较小的色散行为以及在可见光范围内透明等优点,是具有很好应用前景的非线性光学材料.