Minh Lequan

Boron derivatives containing a bithiophene bridge as new materials for non-linear optics

New molecules with dimesitylboron as the acceptor group and bithiophene as the unsaturated chain have been synthesized and their non-linear optical properties investigated. The theoretical first hyperpolarizabilities determined by calculations are compared with experimental results.

Trivalent boron as acceptor chromophore in asymmetrically substituted 4,4′-biphenyl and azobenzene for non-linear optics

[4′-(Dimethylamino)biphenyl-4-yl]dimesitylborane (BNB) and [4′-(dimethylamino)phenylazophenyl-4-yl]dimesitylborane (BNA) have been prepared and studied by a solvatochromic technique. The high second-order hyperpolarisability coefficients βCT determined by this technique, 37 and 240 × 10–30 esu, respectively, show that this new family of materials is of interest for non-linear optics.

POLYURETHANES CONTAINING BORON CHROMOPHORES AS SIDECHAINS FOR NONLINEAR OPTICS

Abstract An azo-dye containing dimesityl boron as the electron acceptor group is synthesized and incorporated as side chains in polyurethane matrices. These new polymers have been poled under an external electrical field by the corona technique. They exhibit high nonlinear response and a remarkable temporal stability. It appears that the poling time is a crucial parameter not only in terms of obtaining a good second harmonic response but also in the temporal stability.

Crystal structures and non-linear optical properties of borane derivatives

[4′-(Dimethylamino)biphenyl-4-yl]dimesitylborane (BNB) and 4-[4′-(Dimethylamino)pnenylazo]phenyldimesityl-borane (BNA) have been investigated by X-ray diffraction; crystallographic data were used to calculate dipole moments in the ground state and the hyperpolarizability coefficient βo was measured by the EFISH technique for each derivative. The results show that the trivalent boron group is an efficient electron acceptor compared to other known acceptors such as the nitro group. Organoboron derivatives are promising candidates for nonlinear optical materials.

Hyperpolarizability of tetraorganotin compounds determined by the hyper-Rayleigh scattering technique

Abstract The hyperpolarizability of non-polar tetraorganotin molecules with Td symmetry has been investigated by the hyper-Rayleigh scattering technique. The results show that, in spite of the absence of a dipolar contribution to the hyperpolarizability tensor, the value of β is significantly high.

Light-induced orientation of a low absorbing phosphine oxide azo-dye/PMMA copolymer: towards a trade-off between transperancy and photoinduced non-linearity

Abstract All-optical poling at a significant spectral distance from resonance is investigated in a new phosphine oxide azo-dye PMMA copolymer (PO-MA) showing increased transparency with respect to Disperse Red 1 (DR1), together with large second-order properties. Trade-off between all-optical poling efficiency and resonant absorption of the non-linear polymer is considered in detail. Consequences for the device conversion efficiency are discussed.

A new zwitterionic salt for non-linear optics: {4′-[methyl(diphenyl)phosphonio]biphenyl-4-yl}triphenylborate

The synthesis of {4′-[methyl(diphenyl)phosphonio]biphenyl-4-yl}triphenylborate (PBB) and 4′-(diphenylphosphino)biphenyl-4-yl(methyl)diphenylphosphonium hexafluorophosphate (PBP) is described. The properties of PBP and PBB are investigated by absorption and fluorescence spectroscopy. Diphenylphosphine is found to be a weaker donor group than the triphenylborate anion. The variation of dipole moment between excited and ground states as well as the hyperpolarisability coefficient, determined for PBB by solvatochromic methods, shows that this compound is promising for second-harmonic generation.

Phosphine oxides as novel acceptor groups in molecules presenting non-linear optical properties

In search for molecules possessing high hyperpolarizabilities, β, the diphenylphosphine oxide group is used as a novel acceptor. Three phosphorus model compounds were synthesized and their non-linear optical (NLO) properties investigated. The results obtained from EFISH measurements are complemented by semi-empirical calculations performed with the AM1 hamiltonian method taking account of the angle, θ, between the dipole moment, µ, and the vector part of the tensor, β. Their high non-linear efficiencies [βx(O)=38–63 × 10–30 esu] make these compounds interesting for their potential use as NLO materials.

Non-linear optical properties of polymers bearing pendent phosphine oxide chromophores

Abstract Polymethacrylates and polyurethanes containing covalently bound organophosphorus NLO chromophores have been synthesized and characterized. These polymers contain a high concentration of NLO chromophores. Film samples obtained by spin coating and poled by the corona method show large second harmonic coefficients (ifd 33 =70 to 135 pm V −1 ) measured at 1064 run. The bulky size and the local polarity of the diphenylphosphoryl acceptor group contribute to the high glass transition temperature (ifT g = 120 to 163 °C) and to the good temporal stability of these materials.

A new class of electrically conducting organometallic salts with an unprecedented metallocene stack. Preparation and crystal structures of η5-cyclopentadienyl-η6-tri- and hexa-methylbenzeneiron(II) tetracyano-p-quinomethanides

Redox reactions between [(cp)FeAr]+I–(cp =η5-C5H5; Ar = 2,4,6-Me3C6H3 or C6Me6; readily prepared from the parent PF6 salts by exchange with Kl on anionic resin) and tetracyanoquinodimethane (TCNQ), afford electrically conducting, single crystals of the title compounds whose structures reveal, as a consequence of the difference in size of the two parallel planar ligands, one-dimensional segregated stacks of organometallic cations and TCNQ½– anions, a situation unique in metallocene complexes with electron acceptors.