Guest Chromophores Research Articles

Design and preparation of novel Diels\u2013Alder crosslinking polymer and its application in NLO materials

Principally novel crosslinking nonlinear optical and optoelectronics system based on Diels–Alder reaction was designed. The copolymer of methyl methacrylate and anthracen-9-ylmethyl methacrylate (PMMA-AMA) was used as a host polymer; chromophore ETO was used as guest chromophore; chromophore ETO and N,N-(methylenediphenyl)bismaleimide were used as crosslinker. The thermodynamic property of crosslinking system studied by differential scanning calorimeter (DSC) showed us that the glass transition temperature was about 65 °C and the crosslinking temperature was varied between 80 and 120 °C The crosslinking reactive speed and effectiveness were studied by ultraviolet absorption and infrared absorption spectroscopy with spectral resoluiotn 1 cm−1. These results have indicated that the cross linking process could be finished at 110 °C for 20 min. Surprisingly, such EO polymer showed us a large EO coefficient of about 96.3 pm/V at wavelength 1 µm and excellent long term stability about 85% with respect to its initial value and can be kept after 250 h of heating at 80 °C.

Facile Cucurbit[8]uril-Based Supramolecular Approach To Fabricate Tunable Luminescent Materials in Aqueous Solution.

Light-emitting materials with tunable properties may offer fascinating applications in optoelectronic devices, fluorescent sensors, and imaging agents. Herein, a new supramolecular approach based on host-guest interactions that greatly decreases the number of required synthetic steps and produces a system with tunable and dynamical photophysical properties was developed. Because of the novel electronic distributions of the chromophore guest within the rigid hydrophobic cavity of the cucurbit[8]uril host in this system, color tuning of emissions such as cyan, yellow, green, and white light with efficiency increased fluorescence lifetime, and quantum yield was easily achieved by simple addition of the host in aqueous solution. Stimulus-responsive tuning of color has long been an important area of research into light emissions. The current study distinguishes itself by its combination of simple steps using a single synthetic receptor and a single organic fluorophore guest in a single solution. Our results may provide a promising advancement of the fabrication of smart and tunable luminescent materials.

Design and preparation of novel polyarylene ether materials based on Diels–Alder reaction as the crosslinker for electrooptical modulators

Novel crosslinkable organic linear electro-optical (EO) material based on polyarylene ether as the main chain host polymer was designed and prepared. The host polymer with rigid aromatic has demonstrated a good compatibility with the guest chromophore. Long side chain with anthracene ensured the crosslinkable reaction and appropriate glass transition temperature of the host polymer (55 °C). The EO r33 tensor coefficient for this novel EO material has been magnitude of 66 pm/V at 1310 nm and the excellent long term stability at 85 °C. These parameters permit to consider their application in fabrication of organic electro optical devices. The semi-empirical and DFT quantum chemical simulations were performed for 4 principal chromophores to clarify a role of cross-linker in the enhancement of the ground state dipole moments and effective hyperpolarizabilities.

A systematic, quantum-mechanical, finite-order approach for the quantitative determination of molecular internal electric fields in guest–host systems from Stark spectroscopy

Within a host molecular system, such as cofactors in proteins, active sites in metal–organic frameworks, and dopants in semiconductor solids, a guest molecule experiences a very specific environment that includes interaction with electrostatic forces. As a supramolecular complex with a defined structure, the host will generate a defined net Coulombic force that undoubtedly influences the properties of its guest, including reactivity. This internal electric field experienced by a guest chromophore in a host matrix can be quantitatively determined at the molecular level using Stark spectroscopy, which is the application of an external electric field during spectral collection. Analysis of Stark spectra is typically performed using a truncated classical approach. However, a potentially more accurate quantum-mechanical approach based on perturbation theory was developed and previously described challenges to its implementation are overcome by the rigorous protocol reported here to achieve convergence for this theoretically infinite-order approach. In addition, a comparison of methods to calculate the required input for the approach (electronic properties, specifically transition energies and transition dipole moment) is made, ranging from semiempirical to time-dependent density functional to ab initio methods, which further reveals the governing aspects of this quantum-mechanical Stark effect analysis. The approach is illustrated with a biological guest–host system, the heme protein myoglobin, but an examination of theoretical aspects of the approach show that it is expected to have wider applicability to the quantitative measurement of internal electric fields in guest–host systems in general.

Research of the optimum molar ratio between guest and host chromophores in binary chromophore systems for excellent electro-optic activity

A series of binary chromophore systems were designed and prepared. The optimum molar ratio (OMR) between guest and host chromophores was first systematically explored in the BCSs. When at the OMR, there is the biggest EO coefficient growth rate.

Encapsulation of Ln(III) Ions/Dyes within a Microporous Anionic MOF by Post-synthetic Ionic Exchange Serving as a Ln(III) Ion Probe and Two-Color Luminescent Sensors.

A new anionic framework {[Me2NH2]0.125[In0.125(H2L)0.25]⋅xDMF}n (1) with one-dimensional (1D) channels along the c axis of about 13.06×13.06 Å(2), was solvothermally synthesized and well characterized. Post-synthetic cation exchange of 1 with Eu(3+), Tb(3+), Dy(3+), Sm(3+) afforded lanthanide(III)-loaded materials, Ln(3+)@1, with different luminescent behavior, indicating that compound 1 could be used as a potential luminescent probe toward different lanthanide(III) ions. Additionally, compound 1 exhibits selective adsorption ability toward cationic dyes. Moreover, the RhB@1 realized the probing of different organic solvent molecules by tuning the energy transfer efficiency between two different emissions, especially for sensing DMF. This work highlights the practical application of luminescent guest@MOFs as sensors, and it paves the way toward other one/multi-color luminescent host-guest systems by rational selection of MOF hosts and guest chromophores with suitable emissive colors and energy levels.

Improved solubility and stability of 7-hydroxy-4-methylcoumarin at different temperatures and pH values through complexation with sulfobutyl ether-β-cyclodextrin

The inclusion complex of 7-hydroxy-4-methylcoumarin (7H4MC) with sulfobutyl ether-β-cyclodextrin (SBE-β-CD) was investigated by means of UV–vis, circular dichroism and 1H NMR spectroscopy in phosphate buffer solutions at different temperatures and pH values. The stoichiometric ratio of the complexation was found to be 1:1 and the stability constants (KC) were estimated from phase solubility analysis. The thermodynamic parameters of standard Gibbs free energy change, ΔGo, enthalpy change, ΔHo, and entropy change, ΔSo, for the complexation process were obtained by using the van’t Hoff equation and Gibbs–Helmholtz equation. The large negative ΔHo and the small negative or positive ΔSo (|ΔHo|>|TΔSo|) demonstrated that the inclusion interaction was an enthalpy-driven process. The positive signal of circular dichroism indicated that 7H4MC penetrated the cavity in such a way that the transition moment of the guest chromophore was parallel to the long axis of SBE-β-CD cavity. Moreover, the 1H NMR spectrum showed that the entire 7H4MC molecule, except the hydroxyl group, was included in the SBE-β-CD cavity.

Melt-Extruded Films of a Commercial Polymer with Intense Chiral Optical Response of Achiral Guests

The degree of circular polarization (g-value) of infrared and UV–vis bands of melt-extruded syndiotactic polystyrene (s-PS) films of different thickness, as induced by cocrystallization with a nonracemic guest ((R)-(−) or (S)-(+) carvone), and of their nonracemic and achiral guests has been studied. The induced circular dichroism (CD) phenomena, both for polymer host and for chromophore guests, are maximized for films with thickness of few micrometers. Surprisingly, for all the examined thicknesses and spectral ranges, the chiral response of the considered achiral guests (azulene and 4-nitroaniline) is definitely higher than for the chirality-inducing nonracemic guest (carvone). This clearly indicates that the origin of the chiral optical response is extrinsic to the site of photon absorption. In agreement with this extrinsic nature, a comparison of g-value for host and guest peaks of melt-extruded and spin-coated s-PS films indicates that the observed chiral response is an extensive property. The reported results also confirm that the intense chiral responses of s-PS films are associated with a nonracemic helical morphology of crystallites, as induced by the nonracemic guest.

Tunable Two-color Luminescence and Host–guest Energy Transfer of Fluorescent Chromophores Encapsulated in Metal-Organic Frameworks

Co-assembly of chromophore guests with host matrices can afford materials which have photofunctionalities different from those of individual components. Compared with clay and zeolite materials, the use of metal–organic frameworks (MOFs) as a host structure for fabricating luminescent host–guest materials is still at an early stage. Herein, we report the incorporation of a laser dye, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), into stilbene-based and naphthalene-based MOF systems. The resulting materials exhibit blue/red two-color emission, and the intensity ratio of blue to red fluorescence varies in different planes within the MOF crystal as detected by 3D confocal fluorescence microscopy. The observed changes in ratiometric fluorescence suggest the occurrence of energy transfer from MOF host to DCM molecules, which can be further confirmed by periodic density functional theoretical (DFT) calculations. Moreover, selective changes in luminescence behavior are observed on treating the guest@MOF samples with volatile organic compounds (methanol, acetone and toluene), indicating that these host–guest systems have potential applications as fluorescence sensors. It can be expected that by rational selection of MOF hosts and guest chromophores with suitable emissive colors and energy levels, a wide variety of multi-color luminescent and energy-transfer systems can readily be prepared in a similar manner.

Electro-optic properties of a bi-chromophore norbornene polymer brush system

A selection of poly(norbornene-exo-dicarboximide) brush-type polymers decorated with a pendent azobenzene dye have been prepared for use as electro-optic (EO) hosts. These polymer brushes were employed as EO polymer hosts for a high molecular hyperpolarizability phenyl vinylene thiophene vinylene (FTC) chromophore guest. These polymer brushes contained methoxy or cyano azobenzene substituents, which were able to manipulate the π-electronic polarization, refractive index, and EO activity. The concentration of the azobenzene dye was increased from 6 to 38%, in order to find the optimum and to maximise the EO coefficient. The refractive index of the mixtures could also be tuned by changing the azobenzene content. Ultimately an EO coefficient of nearly 95 pm/V could be realized using a methoxy substituted azobenzene brush at a concentration of 25% with an added FTC chromophore.

Second-order nonlinear optical susceptibilities in nonelectrically poled guest–host polymers with tricyanofuran chromophores

In this manuscript, we describe the current manuscript describes the second-order nonlinear optical susceptibility of guest–host polymers possessing chromophores with strongly electron-accepting tricyanofuran (TCF). Chromophores substituted with different numbers of hydroxyl groups were prepared. Our experimental results demonstrated that the guest–host polymers exhibited nonlinear optical susceptibilities simply upon annealing at temperatures higher than the glass transition point of the host polymers even in the absence of applied external DC electric fields. Nonelectrical poling behaviors were only available for the materials possessing hydroxyl-group-functionalized chromophores. The results indicate that chemisorption of the hydroxyl groups on the substrate led to the orientation order of the guest chromophores. The orientation order of the chromophores was reproduced well by the model of poled polymers in previous studies.

Second-Order Nonlinear Optical Susceptibilities of Nonelectrically Poled DR1–PMMA Guest–Host Polymers

Guest-host nonlinear optical polymers have attracted considerable interest due to their applications in fast electro-optical modulators and wavelength converters. In general, the electrical poling procedures, for which high DC external fields are applied, are necessary for aligning guest chromophores in polar order and activating the second-order nonlinearity. We present the nonelectrical poling behaviors for guest-host polymers: DR1 (4-[ethyl (2-hydroxyethyl) amino]-4'-nitroazobenzene) is the guest, and PMMA (poly (methyl methacrylate)) is the host. Second-order nonlinear optical susceptibility was induced in the conventional guest-host polymers after annealing at temperatures above the glass transition points of the host polymer even without applying the external fields. This phenomenon did not occur in the side-chain polymers, where the guests were directly bonded to the host chains. The guest polar alignments were most likely generated from the guest hydroxyl groups chemisorbing on the substrates. The polar alignments of the guest formed not only near the surface of the substrate, but also inside the host polymers. The optimized conditions for the SHG conversion were examined in the context of the polymer film thickness and guest concentration. The nonelectrical poling techniques described in this study are useful for enhancing the surface nonlinearity in the several materials, and they will be useful for further developments in nanophotonics and plasmonics.

Racemic synthetic polymers and chirality

This review is mainly devoted to the chiral-optical behavior in the solid state of racemic synthetic polymers, which are able to form co-crystalline phases with low molecular mass guest molecules and whose chirality is induced by non-racemic (also temporary) guest molecules. The article starts with the description of chiral features relevant for the synthesis of stereoregular polymers. Subsequently, the chirality of chain helicity and the related phenomena of macromolecular amplification of chirality, both in solution and in the solid state, are discussed. The final part of the article describes the recent achievement of robust chiral-optical films being constituted by a racemic commercial host polymer and achiral guest chromophores.

Second harmonic generation in NLO polymers excited by Surface Plasmon enhanced electric field induced by femtosecond optical pulses

We will report second harmonic generation (SHG) in nonlinear optical (NLO) polymers excited by surface plasmon enhanced optical fields. The surface plasmon (SP) polariton was excited in an attenuated total reflection geometry having the Kretchmann configuration. The NLO polymers, consisting of Disperse Red1 as guest chromophores and poly (methyl methacrylate) as host materials, were coated upon the Ag layers. Our experimental results indicated that the SHG signal intensity from the polymer coated Ag films was more than 10 times higher than that from the non-coated Ag films. The SHG autocorrelation traces excited by SP-enhanced fields were also studied and the correlation time was shorter than 150 fs, the temporal resolutions of the present spectrometer.

Photo-induced denitrogenation of triazoline moieties for efficient photo-assisted poling of electro-optic polymers

Efficient room temperature poling of a guest–host electro-optic (EO) polymer is achieved by photo-induced denitrogenation of triazoline moieties. The host polymer (P1) with Δ2-1,2,3-triazoline groups on the backbone is synthesized by 1,3-dipolar cycloaddition polymerization between a bis-N-phenylmaleimide and an aromatic bis-azide. The guest chromophore (C1) is a push–pull compound with a strong dialkylaminophenyl donor and a CF3–TCF acceptor. By irradiating the thin films of P1 with a compact UV lamp at 365 nm, the angular and asymmetric 1,2,3-triazoline structures can be readily converted into a more straight and symmetrical aziridine structure by losing nitrogen. This photo-induced denitrogenation provides the clean conversion to form an aziridine-based polymer P2. This high efficiency conversion process is insensitive to the light-absorbing nonlinear optical chromophores, and the reaction rate can be controlled by the irradiation power and the thin film UV absorbance. Upon the photo-induced denitrogenation, considerable structural change of the polymer backbone provides sufficient rotational freedom to the chromophores for the poling of EO polymers. This has been verified by the demonstration of high field poling (up to 250 V μm−1) and large EO activity at RT for thin films containing 20–25 wt% of chromophore C1 in P1, which can be efficiently activated by photochemical denitrogenation of triazoline moieties by irradiating with low-power UV light.

Synthesis of novel polyarylate with elecrooptical chromophores as side chain as electro-optic host polymer

Two novel soluble polyarylates with different nonlinear optical chromophores as the side chains were prepared and characterized by UV–visible spectra, nuclear magnetic resonance, and infrared spectroscopy. The titled polymers show us good thermal stability; the thermal decomposition temperature values were 201 and 253 °C, respectively, for polymer sPAR-CTCF and sPAR-CTCP. The glass transition temperatures were 139 and 122 °C for sPAR-CTCF and sPAR-CTCP, respectively. Chromophore FTC-wl was doped in these polymers as a guest chromophore to form binary chromophore electro-optic (EO) system. And super large EO coefficients (124 pm/V) were found from FTC-wl-doped sPAR-CTCP binary chromophore system at high chromophore loading density.

Chiral Optical Films Based on Achiral Chromophore Guests

Films constituted by an achiral host polymer and an achiral guest chromophore, which exhibit intense chiral optical responses for both host and guest peaks in the infrared as well as in the UV-visible regions, have been obtained. Such films can have any thickness from the nanoscale up to the macroscopic scale. This unexpected chiral optical behavior is easily achieved by crystallization of a robust commercial stereoregular host polymer (syndiotactic polystyrene, s-PS) from the amorphous phase as induced by a nonracemic guest, followed by exchange of the nonracemic guest with the achiral guest, leading to the formation of polymer-host/chromophore-guest cocrystalline phases. This finding opens the possibility to achieve s-PS-based films with chiral optical response at selected wavelengths. It has been also found that the chiral optical cocrystalline phase of s-PS with azulene exhibits a monoclinic δ-clathrate form with equal proportions of left- and right-handed helices. This confirms that the observed chiral optical behavior arises by the nonracemic native morphology of the crystalline regions, which has been induced by the temporary nonracemic guest.

Multi-colour emission from dye doped polymeric nanotubes by host–guest energy transfer

Emission chromaticity tuning in polymeric nanotubes was achieved by transfer of excitation energy from a polymer host matrix poly(N-vinylcarbazole) (PVK) to incorporated luminescent chromophore guests (Coumarin 6 and Nile red). Nanotubes were synthesized in densely packed arrays by solution assisted template wetting. Un-doped PVK tubes displayed blue luminescence while Coumarin 6 and Nile red doped tubes exhibited characteristic green and red luminescence with minimal PVK emission, confirming effective host–guest energy transfer. The emission spectral data of single nanotubes, and indicated that, by varying the type and relative concentrations of the dopant dyes, nanotube emission could be tuned from the blue, through green and yellow, to the red and, ultimately, to white, while maintaining excellent color purity.

Supramolecular Chemistry: Induced Circular Dichroism to Study Host−Guest Geometry

In this laboratory experiment, students obtain information about the structure of a host−guest complex from the interpretation of circular dichroism measurements. The value and sign of the induced circular dichroism (ICD) on an achiral chromophore guest when it complexes with a cyclodextrin can be related to the guest penetration and its orientation relative to the cyclodextrin. This experiment examines the complexation of dimethyl 2,3-naphthalenedicarboxylate with 2-hydroxypropyl-α-, -β-, and -γ-cyclodextrins in aqueous medium.

Optical Properties of Nanostructures Obtained by Encapsulation of Cation Chromophores in Y Zeolite

Several unsaturated cation chromophores have been prepared by ship-in-the-bottle synthesis in the supercages of Y zeolite as a host. The guests were encapsulated into the zeolite in their H+ form in the liquid phase. The chromophores were assembled inside the void space of the zeolite through the reaction of the different aldehydes, 3-phenyl-2-propynal (A), trans,trans-2,4-hexadienal (B), and trans-2-pentenal (C), with the N,N-dimethylaniline. The appropriate synthesis involved using an N,N-dimethylaniline/aldehyde molar ratio of 2:1. The host−guest chromophores obtained have been fully characterized by chemical analysis, spectroscopic methods (FTIR and UV/vis), N2 adsorption isotherms, powder X-ray diffraction, and scanning electron microscopy. Fluorescence studies provided direct evidence that the cation species are located inside the zeolite supercages of these host−guest chromophore materials.