Second-order Nonlinear Optical Chromophores Research Articles

High-throughput virtual screening of organic second-order nonlinear optical chromophores within the donor-π-bridge-acceptor framework.

In view of the theoretical importance and huge application potential of second-order nonlinear optical (NLO) materials, it is of great significance to conduct high-throughput virtual screening (HTVS) on a compound library to find candidate NLO chromophores. Under the donor-π-bridge-acceptor structural framework, a virtual compound library (size = 27 090) was constructed by enumeration of structural fragments. The kernel property adopted for optimization is the static first hyperpolarizability (β0). By combining machine learning and quantum chemical calculations, we have performed an HTVS procedure to sieve NLO chromophores out, and the response mechanism of the selected optimal NLO chromophores was examined. We have found: (a) The multi-layer perceptron/extended connectivity fingerprint combination with 20% selection ratio gives the highest prediction accuracy for the studied systems. (b) The two optimal donors are bis(4-diphenylaminophenyl)aminyl and bis(4-tert-butylphenyl)aminyl; the optimal π-bridges are composed of two thiophenyl, selenophenyl or furanyl units; and the two optimal acceptors are tri-s-triazinyl and 2,3-dicyanopyrazinyl. (c) The no. 1 candidate molecule can exhibit a calculated β0 equal to 8.55 × 104 a.u. (d) The difference in NLO responses of the optimal 16 molecules comes from the synergistic interaction of ES1, Δμ and f, by employing the two-level model. In addition, the sizable Δμ and f allow the studied optimal molecules to obtain a large NLO response in the meantime keeping a not-too-low excitation energy (retaining good optical transparency in the restricted range of the visible spectrum region). (e) With further modification on the acceptor, the designed DPA-π-TRZ-A' (A' = CN or NO2, π = oligo-thiophenyl or selenophenyl) systems can exhibit a rather large NLO response (maximum β0 = 3.17 × 105 a.u.), hence should have considerable potential as second-order NLO chromophores. With the above observations, we expect to provide some insight for the research community into the HTVS of organic second-order NLO chromophores.

Nonlinear optical materials based on fluorinated polyurethane-imides and their application in waveguide devices

Two monomers, a second-order nonlinear optical azo chromophore C containing a tricyanofuran electron acceptor and a dihydroxyethyl nitrogen electron donor, and a bisphenol AF-type diether dianhydride (BPAFDA), were designed and synthesized. Fluorinated polyurethaneimide (PUI) electro-optic (EO) waveguide materials were prepared using the synthesized monomers polymerized with 4,4′-diphenylmethane diisocyanate (MDI). The structures of the synthesized chromophore C, BPAFDA, and polymers of PUI were characterized by 1HNMR and FTIR, and the thermal properties of the polymers were characterized by DSC and TGA. The prepared PUI exhibited good film-forming properties with glass transition temperatures (Tg) between 160–169°C and over 300°C at 5% thermal weight loss in a nitrogen atmosphere. The experimental results showed that the fluorinated PUIs possessed an EO coefficient of 56–60 p.m./V at 1550 nm and the optical propagation loss of the polymer waveguide was between 1.3–1.4 dB/cm at 1550 nm. Using PUI as the core material of the waveguides, EO modulators with Mach-Zehnder (MZ) structure were designed and prepared, showing good EO modulation performance at 1550 nm.

Synthesis of new type of nonlinear optical chromophores: The introduction of a novel aromatic amine donor 1-oxajulolidine to enhance the electro-optical activity of organic second-order nonlinear optical materials

Developing new organic second-order nonlinear optical chromophores with a new electron donor is crucial for enhancing performance of electro-optic (EO) materials. A series of new second-order nonlinear optical chromophores (J1, JS and JO) with new electron donor 1-Oxajulolidine have been designed and synthesized. Ref1, Ref2 and Ref3 with N, N-diethylaniline (DEA), 4-anisole and julolidine as electron donor had also been synthesized for comparison. The result of TGA and DSC tests suggested that the decomposition temperature of the chromophores was higher than 260 °C. As the UV–vis absorption spectra of chromophores in solution, maximum absorption (λmax) of the chromophores J1 with 1-Oxajulolidine group presented red-shift compared to Ref1 and Ref2, but blue-shift to Ref3. Nevertheless, chromophore with 1-Oxajulolidine presented more obvious solvatochromic behavior from dioxane to dichloromethane. Density functional theory had been used to calculate HOMO-LUMO energy gaps and β of these chromophores. The r33 values of guest-host EO polymers Ref1/APC, J1/APC, JS/APC and JO/APC with a loading density of 10 wt% were obtained as 7.5, 9.6, 15.3 and 13.5 pm V−1, respectively. The above result clearly indicated that r33 of J1/APC (9.6 pm V−1) was 27% higher than that of Ref1/APC (7.5 pm V−1). The electro-optic coefficient of JS with the same conjugate bridge and acceptor was higher than that of FTC in the same doping concentration. As revealed by the above results, the introduction of the polycyclic structure of 1-Oxajulolidine, containing two electron-rich atoms (N and O), could efficiently enhance the electro-optical performance. Furthermore, λmax of JS in doped film showed blue-shift compared with FTC which exhibited a promising potential for tackling nonlinearity and transparency trade-off in second-order nonlinear optical (NLO) materials.

Thieno [2,3-b] indole-based second-order nonlinear optical chromophores with high thermal stability and good nonlinear optical performance

Tow novel second-order nonlinear optical (NLO) chromophores A4, A5 containing the thieno [2,3-b] indole (TI) group as a novel electron-donor, ethylene as a p-conjugated bridge and malononitrile, 2-(3-cyano-4-methyl-5-phenyl-5-(trifluoromethyl) furan-2 (5H)-ylidene) malononitrile (CF3-TCF) as the acceptor have been synthesized and systematically investigated in this paper. These TI-based chromophores showed significantly high thermal stability. The UV–vis spectra indicated that the TI-based chromophores had a red-shift compared to the carbazole-based chromophores both in solid state and in solution. The HOMO-LUMO energy gaps and hyperpolarizability (β) of the chromophore A5 is calculated by Density functional theory (DFT), it shows that A5 has a narrow energy gap and big β. In short, the TI-based chromophore A5 we synthesized exhibited high thermal stability and good NLO activity.

Cyclometalated Ir(III) Complexes with Curcuminoid Ligands as Active Second-Order NLO Chromophores and Building Blocks for SHG Polymeric Films

The second-order nonlinear optical (NLO) properties of iridium(III) complexes having two cyclometalated 2-phenylpyridines and curcumin or tetrahydrocurcumin as ancillary ligand have been investigated both in solution and as guest in a polymeric organic matrix. In solution, these complexes are characterized by a significant second-order NLO response, as determined by the Electric Field Induced Second Harmonic (EFISH) technique, like the related complex with acetylacetonate. Whereas the low second-harmonic generation response of a composite film of [Ir(2-phenylpyridine)2(acetylacetonate)] in polymethyl methacrylate was not stable and fell down to zero upon turning off the electric field. A good and stable response was obtained with a film based on the iridium(III) complex bearing two cyclometalated 2-phenylpyridines and curcumin.

The synthesis of second-order nonlinear optical chromophores with conjugated steric hindrance for electro-optics at 850 nm

We show the strategy of introducing a suitable conjugated site-isolator on the bridge of a nonlinear optical chromophore to significantly improve the electro-optic activity at the shortwave infrared window (850 nm) for electro-optic modulation.

Using phenothiazine as electron donor for new second-order nonlinear optical chromophore

A novel chromophore based on the phenoxazine and tricyanofuran acceptor linked together via thiophene as the bridges have been synthesized by the conventional technique and systematically investigated. Structure analysis and photophysical properties were carried out to investigate the new structure chromophore. Density functional theory was used to calculate the hyperpolarizability (β) and the result shows that chromophore A showed a lower energy gap. In addition, chromophore A displayed good thermal stability with the onset decomposition temperature over 240 °C. These results showed that chromophore A, which had good thermal stability and nonlinear optical properties was a promising candidate for practical use.

The Progress in the Field Auxiliary Donors and their Application in Novel Organic Second-Order Nonlinear Optical Chromophores

Conversion efficiency between electrical and optical signals is very important for the development of modern information technologies. Due to their advantages in half-wave voltage, bandwidth, cost and integration, as well as organic electro-optic (EO) parameters, these materials are widely studied and used in microwave photonic devices. Second order nonlinear optical (NLO) chromophores, as the core of organic EO materials have an increasing interest in this branch. Auxiliary donors present a new direction for the design and improvement of organic NLO chromophores. In this short review, the advantages, theoretical calculations and experimental results of auxiliary donors are reviewed and discussed in detail.

Three-stage pH-switchable organic chromophores with large nonlinear optical responses and switching contrasts.

Three-stage pH-switchable organic second-order nonlinear optical (SO NLO) chromophores are synthesized and characterized by wavelength-dependent linear and nonlinear spectroscopy. The chromophores exhibit huge SO NLO responses in their "on" stages, and large switching contrasts between adjacent stages in both SO NLO response and fluorescence quantum yield, with moreover different "on/off" sequences for closely related compounds.

Synthesis and characterization of new second-order NLO chromophores containing the isomeric indolizine moiety for electro-optical materials

To further explore the potential application of the indolizine donor group in nonlinear optical (NLO) chromophores, we have designed and synthesized new push-pull chromophores (MPI-1)-V-TCF and (MPI-3)-V-TCF, having isomeric 3(1)-methyl-2-phenylindolizin-1(3)-yl (MPI-1(3)) electron donor and TCF acceptor, and compared them with dimethyl aniline (DMA) analogues. The Uv-Vis (linear optical) properties and solvatochromic behavior were also investigated; theoretical predictions of molecular NLO characteristics were done on the basis of the DFT calculations. The indolizine-based chromophores have high thermal stability: the decomposition temperature is 348 °C for (MPI-1)-V-TCF and 343 °C for the (MPI-3)-V-TCF, which is by 10–15 °C higher than that for the chromophore DMA-V-TCF. An important role is played by the bulky phenyl group, which prevents the aggregation of chromophores in guest-host doped polymer films. In NLO activities, the doped (MPI-1)-V-TCF/PMMA and (MPI-3)-V-TCF/PMMA films display the NLO coefficient, d33, values of 40 and 42 pm/V, correspondingly, at the chromophore load of 20 wt%.

Janus second-order nonlinear optical dendrimers: their controllable molecular topology and corresponding largely enhanced performance.

A new type of Janus dendrimers, consisting of two different side dendrons with the dipole orientation of the second-order nonlinear optical (NLO) chromophore moieties partially in a non-centrosymmetric direction, was intelligently designed and synthesized in order to enhance the macroscopic NLO performance and break through the limitation of NLO efficiency in the current molecular topological structure of azo chromophore-based polymers. This kind of Janus dendritic structure was constructed by the combination of convergent and divergent methods, with the utilization of a powerful "click chemistry reaction". The obtained three dendrimers, D-13N, D-17N and D-21N, show very high NLO performance, especially the dramatically enhanced NLO coefficient of 299 pm V-1 for D-13N, which is the highest value ever reported for polymers containing a simple azo chromophore. The new dendrimers provide a clear structure-properties relationship between high NLO efficiency and the controllable molecular topology with the non-centrosymmetrical alignment of dipole orientation, thus opening up a new avenue for the further development of NLO dendrimers with high performance and more importantly providing some clues for the rational design of functional dendrimers with controllable molecular topology.

Organic Second-Order Nonlinear Optical Chromophores Modified by Isolation Groups

Organic Second-Order Nonlinear Optical Chromophores Modified by Isolation Groups

Synthetic, Optical and Theoretical Study of Alternating Ethylenedioxythiophene-Pyridine Oligomers: Evolution from Planar Conjugated to Helicoidal Structure towards a Chiral Configuration.

A series of alternating 3,4-ethylenedioxythiophene-alkynylpyridine oligomers (DA)n with increased solubility are synthesized and their photophysical properties and nonlinear optical properties are investigated. Their quadratic polarizabilities are determined from hyper-Rayleigh scattering experiments to obtain information on their conformations in solution. These chromophores, based on the alternation of electron-rich (D) and electron-deficient (A) moieties, exhibit optical properties that arise from the combination of dipolar and helicoidal features in the (DA)n homologue series where n=1-4. The transition from dipolar conjugated planar structures (n=1, 2) to helicoidal structures (n=3, 4) is clearly evidenced by results from symmetry-sensitive second-order nonlinear optical experiments. This suggests an approach towards highly efficient chiral chromophores for second-order nonlinear optics. Interestingly, this structural evolution also has significant impact on the photophysical properties: both absorption and fluorescence emission show bathochromic and hyperchromic shifts with increasing number of repeating units in the dipolar planar derivatives (n=1-2) but show saturation effects in the helicoidal structures (n=2-4). In addition, the helicoidal structures show sizeable two-photon absorption at 700-750 nm (40-100 GM) for compounds lacking either electron-donating or electron-withdrawing substituents.

Second-Order Nonlinear Optical Properties of Carboranylated Square-Planar Pt(II) Zwitterionic Complexes: One-/Two-Dimensional Difference and Substituent Effect.

Zwitterionic complexes have been the subject of great interest in the past several decades due to their multifunctional application in supramolecular chemistry. Herein, a series of internally stable charge-compensated carboranylated square-planar Pt(II) zwitterionic complexes have been explored by density functional theory aim to assessing their structures, the first hyperpolarizabilities, first hyperpolarizability densities, and electronic absorption spectra. It is found that the first hyperpolarizabilities of two-dimensional (2D) structure complexes are much larger with respect to the one-dimensional complex. It is ascribed to the lower transition energy and more obvious charge transfer, which can be further illustrated by their large amplitude and separate distribution of first hyperpolarizability density. In addition, the first hyperpolarizabilities of 2D complexes can be further significantly modified by introducing electron-donating/withdrawing groups on the carborane cage. As a consequence, we believe that these 2D zwitterionic complexes can behave as novel second-order nonlinear optical chromophore with a promising future.

Synthesis and Characterization of Novel Second-Order Nonlinear Optical Chromophore with Multi-Hydroxyl Groups Donor

ABSTRACTNew electro optical chromophore with 4-(bis(2-hydroxyethyl)amino)-2,6-dipropoxybenzaldehyde as electron donor was synthesized and characterized by 1H NMR spectra and mass spectra. Four hydroxyl groups were introduced to the electron donor, which could be easily reacting with carboxyl, isocyanate, anhydride, and so on, to afford us second-order nonlinear optical polymers. Chromophore T showed us good solubility in common solvents, thermal stability (above 200°C) and expected Uv-vis absorption. In this article, polymethyl methacrylate (PMMA) doped with chromophore T at different loading density was prepared to second- order nonlinear optical films by spin coating. These films showed us large second-order nonlinear optical coefficients, 13.5, 19.7, 24.3, and 26.4 pm/V for the second-order nonlinear optical films with chromophore loading density of 10 wt%, 20 wt%, 30 wt%, and 40 wt%, respectively.

Synthesis and characterization of electro-optic polyurethane-imide and fabrication of optical waveguide device

The novel electro-optic (EO) polymers of fluorinated cross-linkable Y-type polyurethane-imides (PUI) were designed and synthesized by polycondensation of second-order non-linear optical azo-based chromophores, phenyl diisocyanate, and aromatic dianhydride. Molecular structural characterization for the resulting polymers was achieved by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, and gel permeation chromatography. The resulting polymers exhibited good film-forming properties, high glass transition temperature in the range from 186°C to 198°C and thermal stability up to 300°C, high EO coefficient ( γ33 = 43–60 pm/V) at 1550 nm wavelength, good stabilization of electrically induced chromophore dipole alignment and low optical propagation losses in the range of 1.5–1.7 dB/cm at 1550 nm, which are suitable for the EO modulators. Using the synthesized EO PUI as the active core material and of a fluorinated polyimide as cladding material, we have designed and fabricated the high-performance polymer waveguide Mach-Zehnder EO modulators. Obvious modulation was observed by application of ac voltage signal to the EO modulators.

Intramolecular photo-induced electron transfer in nonlinear optical chromophores: Fullerene (C60) derivatives

The push-pull functionalized fullerenes consisting of multi-N,N-diethylamine donors covalently attached to N-methylpyrrolidine derivative of C60 have been designed and investigated. The structures and first hyperpolarizabilities of these fullerene derivatives were calculated using density functional theory. Furthermore, absorption spectra of the complexes along with electron density difference maps corresponding to the most intense electronic transitions were achieved by time-dependent density functional theory. It suggests that with the growing numbers of N,N-Dimethylanilin acting as electron-donating group, the polarizabilities, dipole moments and the first hyperpolarizabilits increase, however, transition energies of the crucial electronic transitions decrease and the absorption wavelength shows bathochromic effect. The excitation transitions have significant charge transfer character and, as a consequence, the novel complexes can behave as second-order nonlinear optical chromophores, in which the N,N-Dimethylanilin act as donors towards fullerenes.

Synthesis and characterization of two novel second-order nonlinear optical chromophores based on julolidine donors with excellent electro-optic activity

Second order NLO chromophores with julolidine donor.

Synthesis and characterization of one novel second-order nonlinear optical chromophore based on new benzoxazin donor

One novel second order nonlinear optical chromophore based on benzoxazin donor and tricyanovinyldihydrofuran acceptor linked together via thiophene bridge has been synthesized and characterized. According to cyclic voltammetry measurement, chromophore Z showed low energy gap. In addition, chromophore Z displayed good thermal stability with the onset decomposition temperature over 221°C. The electro-optic coefficient of a poled film containing 25wt% of chromophore Z doped in polymethylmethacrylate afforded a value of 64pm/V at 1310nm. The result showed that chromophore Z, which had good thermal stability and high r33 values after poling in films, was a promising candidate for practical use.

Comparative studies on structure–nonlinearity relationships in a series of novel second-order nonlinear optical chromophores with different aromatic amine donors

A series of second-order nonlinear optical chromophores containing an identical π-bridge and electron acceptor but different, aromatic amine electron-donating groups have been synthesized and systematically investigated. The donors studied here include traditional donors carbazole, triphenylamine and N,N-diethylaniline and novel donor phenothiazine, phenoxazine and N-(4-methoxyphenyl)phenoxazine. The ultraviolet absorption, solvatochromic, redox properties, density functional theory calculations, thermal stabilities and electro-optic activities of these chromophores were systematically studied to compare the strength of the donors and illustrate the structure–performance relationships within six chromophores. The results show that the new donors have stronger electron-donating ability than traditional donors. Moreover, they show reduced energy gap, much larger molecular quadratic hyperpolarizability (μβ) and r33 value. Exemplified by the N-(4-methoxyphenyl)phenoxazine chromophore, it showed nearly three times higher μβ and more than four times higher r33 value than that of the N-hexylcarbazole containing chromophore.