Structural control of side-chain chromophores to achieve highly efficient electro-optic activity.

A series of chromophores J1-J4 have been synthesized based on julolidine donors modified with different rigid steric hindrance groups. Compared with the chromophore (J1) without the isolation group, chromophores J2, J3 and J4 show better stability. Structural analysis and photophysical property measurements were carried out to compare the molecular mobility and steric hindrance effect of the different donor-modified chromophores. All of these chromophores with isolation groups showed superb thermal stabilities with high thermal decomposition temperatures above 250 °C. Furthermore, with rigid steric hindrance, chromophores J3 and J4 showed more enhanced thermal stabilities with thermal decomposition temperatures of 269 °C and 275 °C, respectively. Density functional theory was used to calculate the hyperpolarizability (ß), and the high molecular hyperpolarizability of these chromophores can be effectively translated into large electro-optic coefficients. The electro-optic coefficients of poled films containing 20 wt% of these new chromophores doped in amorphous polycarbonate were 127, 266 and 209 pm V-1 at 1310 nm for chromophores J1-J3, respectively, while the film containing chromophore J4 showed the largest r33 value of only 97 pm V-1 at 25 wt%. These results indicated that the introduced isolation group can reduce intermolecular electrostatic interactions, thus enhancing the macroscopic electro-optic activity, while the size of the isolation group should be suitable.

Nonlinear optical chromophores based on Dewar's rules: enhancement of electro-optic activity by introducing heteroatoms into the donor or bridge.

In this work, we investigated the enhancement of the electro-optic response by introducing electron-rich heteroatoms as additional donors into the donor or bridge of a conventional second-order nonlinear optical chromophore. A series of chromophores C2-C4 based on the same tricyanofuran acceptor (TCF) but with different heteroatoms in the alkylamino phenyl donor (C2 or C3) or thiophene bridge (C4) have been synthesized and systematically investigated. Density functional theory calculations suggested that chromophores C2-C4 had a smaller energy gap and larger first-order hyperpolarizability (ß) than traditional chromophore C1 due to the additional heteroatoms. Single crystal structure analyses and optimized configurations indicate that the rationally introduced heteroatom group would bring larger ß and weaker intermolecular interactions which were beneficial for translating molecular ß into macro-electro-optic activity in electric field poled films. The electro-optic coefficient of poled films containing 25 wt% of these new chromophores doped in amorphous poly-carbonate afforded values of 83 and 91 pm V(-1) at 1310 nm for chromophores C3 and C4, respectively, which are two times higher than that of the traditional chromophore C1 (39 pm V(-1)). High r33 values indicated that introducing heteroatoms to the donor and bridge of a conventional molecular structure can efficiently improve the electron-donating ability, which improves the ß. The long-chain on the donor or bridge part, acting as the isolation group, may reduce inter-molecular electrostatic interactions, thus enhancing the macroscopic EO activity. These results, together with good solubility and compatibility with the polymer, show the new chromophore's potential application in electro-optic devices.

The synthesis of new double-donor chromophores with excellent electro-optic activity by introducing modified bridges.

A series of chromophores y1­y3 based on the same bis(N,N-diethyl)aniline donor and the tricyanofuran acceptor (TCF) linked together via the modified thiophene π-conjugation with different isolated groups have been synthesized and systematically investigated in this paper. Density functional theory (DFT) was used to calculate the HOMO­LUMO energy gaps and first-order hyperpolarizability (ß) of these chromophores. Besides, to determine the redox properties of these chromophores, cyclic voltammetry (CV) experiments were performed. After introducing the isolation group into the thiophene, reduced energy gaps of 1.03 and 1.02 eV were obtained for chromophores y2 and y3, respectively, much lower compared to chromophore y1 (ΔE = 1.13 eV). These chromophores showed better thermal stability with their decomposition temperatures all above 220 °C. Besides, compared with results obtained from the chromophore (y1) without the isolated group, these new chromophores show better intramolecular charge-transfer (ICT) absorption. Most importantly, the high molecular hyperpolarizability (ß) of these chromophores can be effectively translated into large electro-optic (EO) coefficients (r33) in poled polymers. The electro-optic coefficient of poled films containing 25% wt of these new chromophores doped in amorphous polycarbonate (APC) afforded values of 149, 139 and 125 pm V(−1) at 1310 nm for chromophores y1­y3, respectively. Besides, when the concentration was increased, the film containing chromophores y1 and y3 showed obvious phase separation, while the film with chromophore y2 showed the maximum r33 value of 146 pm V(−1). Moreover, the electro-optic film prepared with these new chromophores showed greater stability. High r33 values indicated that the double donors of the bis(N,N-diethyl)aniline unit can efficiently improve the electron-donating ability and the isolated groups on the thiophene bridge can reduce intermolecular electrostatic interactions, thus enhancing the macroscopic EO activity. These properties, together with the good solubility, suggest the potential use of these new chromophores as advanced material devices.

Synthesis and characterization of a novel second-order nonlinear optical chromophore based on a new julolidine donor.

A new chromophore HK containing the cis,cis-1,7-diethoxy-3-isopropyljulolidine group as a novel electron-donor, thiophene as a π-conjugated bridge and a tricyanofuran (TCF) acceptor has been synthesized and systematically investigated in this paper. Its corresponding chromophore FTC using 4-(diethyl amino)benzyl as the electron donor group was also prepared for comparison. This is the first time that the cis,cis-1,7-diethoxy-3-isopropyljulolidine group was introduced into NLO materials. Density functional theory (DFT) was used to calculate the HOMO-LUMO energy gap and first-order hyperpolarizability (ß) of the new chromophore. The HOMO-LUMO gap was also investigated by cyclic voltammetry (CV). Upon using the cis,cis-1,7-diethoxy-3-isopropyljulolidine group as the donor, a reduced energy gap of 1.007 eV was obtained compared with chromophore FTC (ΔE = 1.529 eV). The high molecular hyperpolarizability of the new chromophore can be effectively translated into large electro-optic (EO) coefficients (r33) in poled polymers. The doped films containing the new chromophore HK showed a value of 72 pm V(-1) at the concentration of 25 wt% at 1310 nm. This value is almost two times higher than the EO activity of the usually reported traditional (N,N-diethyl) aniline nonlinear optical (NLO) chromophore FTC. High r33 values indicated that the new julolidine donor can efficiently improve the electron-donating ability and reduce intermolecular electrostatic interactions, thus enhancing the macroscopic EO activity. These properties, together with good solubility, suggest the potential use of the new chromophore in advanced materials devices.

Synthesis of novel nonlinear optical chromophore to achieve ultrahigh electro-optic activity.

A new diene-conjugated chromophore WJ1 was synthesized with high yield of 36% through an H-bonding induced Vilsmeier reaction. By simple guest-host doping, a large electro-optic efficiency of 337 pm V(-1) at 1310 nm and excellent temporal stability at 75 °C have been achieved in poled films of WJ1/APC with a high loading density of 40 wt%.

Improved coupling technique of ultracompact ring resonators in silicon-on-insulator technology.

In order to improve the coupling coefficient between a bus waveguide and a bent waveguide of an ultracompact microring to obtain the critical coupling, a design using a bent bus waveguide with reduced width is provided to maintain a better phase matching and increase the coupling. A full vectorial finite difference model, specifically suited for high index contrast and smaller size waveguides, for example, a waveguide in the silicon-on-insulator (SOI) technology, is developed. As a validation, the straight and bent waveguides are simulated using this model, whose results are compared with the results deduced from the measurement results of the ultracompact ring resonators in SOI technology. Also, the model solver is performed to simulate the design, and an experiment is implemented to testify the design.

The formation of thymidine-based T-tetramers with remarkable structural and metal ion size effects.

We present direct ESI Q-TOF MS and X-ray evidence for remarkable structural and metal ion size effects on the formation of thymidine-based T-tetramers. The conventional H-bond acceptors on the ribose and deoxyribose may disfavor the formation of T-tetramers, and in the series of alkali metal ions, lithium did not induce T-tetramer due to its small ion size. Sodium, potassium, rubidium and caesium could produce thymidine-based T-tetramers. Furthermore, rubidium and caesium could induce T-pentamers and dimeric T-pentamers probably due to their larger ion sizes.

Novel perfluorodiphenylphosphinic acid lanthanide (Er or Er-Yb) complex with high NIR photoluminescence quantum yield.

A perfluorodiphenylphosphinic acid lanthanide (Er or Er-Yb) complex is synthesized by a one-pot process from perfluorotriphenylphosphine oxide and lanthanide (Er or Er-Yb) chloride; the photoluminescence quantum efficiency reaches 0.98% for the erbium complex and 3.5% for the erbium-ytterbium complex, about 50 times and 175 times, respectively, higher than the usual erbium organic complexes with the hydrogen-containing ligands.

Near-infrared luminescence properties of erbium complexes with the substituted phthalocyaninato ligands.

Two homoleptic bis(phthalocyaninato) erbium(III) complexes Er[Pc(beta-OR/R)4]2 and two half-sandwich phthalocyaninato erbium(III) complexes (acac)Er[Pc(beta-OR/R)4] (OR = 1-n-pentyloxy and R = tert-butyl) have been investigated. Then we studied the near-infrared luminescence properties of the compounds. When the phthalocyanine ligands were excited, half-sandwich phthalocyaninato erbium(III) complexes showed strong near-infrared luminescence at 1540 nm while homoleptic bis(phthalocyaninato) erbium(III) complexes showed no signals. The full width at half maximum (FWHM) centered at 1540 nm in the emission spectrum of the half-sandwich complexes in solution and in solid state are 67 nm and 78 nm respectively, which shows potential for optical-amplification applications. Erbium-doped standard polymethyl-methacrylate (PMMA) matrix which was synthesized has also displayed NIR emission.

One-step synthesis of highly water-soluble LaF(3):Ln(3+) nanocrystals in methanol without using any ligands.

Water-soluble infrared-to-visible fluorescent LaF(3) nanocrystals doped with different lanthanide ions (Er(3+)/Yb(3+), Eu(3+), Nd(3+), Tb(3+)) have been synthesized in methanol without using any ligands. These nanocrystals are easily dispersed in water, producing a transparent colloidal solution. The colloids of the Er(3+)/Yb(3+), Eu(3+), Nd(3+), Tb(3+) doped nanocrystals exhibit strong luminescence in the visible and near-infrared spectral regions.