Alain Fort

Chromophores with Strong Heterocyclic Acceptors: A Poled Polymer with a Large Electro-Optic Coefficient

Syntheses of a series of conjugated donor-acceptor chromophores, based on a strongly electron-withdrawing heterocyclic acceptor, have led to compounds with large second-order optical nonlinearities. Incorporation of one of these chromophores into polycarbonate at 20 percent weight loading yielded, after poling at 150 volts per micrometer, a polymer film with an electro-optic coefficient, r33, of 55 picometers per volt at 1.313 micrometers. This value is roughly twice that of lithium niobate. A variant of one of these chromophores exhibited improved thermal stability as needed for use in polymers with higher glass transition temperatures. The chromophore was soluble in common organic solvents, had a scalar product of the dipole moment, μ, and the molecular first hyperpolarizability, β (corrected for dispersion), of roughly 5000 × 10−48 electrostatic units, and showed less than 10 percent decomposition after heating for 20 minutes in air and at 200°C in an inert organic solvent.

A two-state description of (hyper) polarizabilities of push-pull molecules based on a two-form model

Abstract We have established analytical structure/(hyper)polarizability relationships for donor-acceptor conjugated molecules, within the framework of the two-state approximation. In this two-form model, a molecule is described as a mixture between neutral and charge-separated resonance forms. We defined a parameter MIX, characterizing the mixing between the limiting-resonance forms, that is measurable in solution. MIX is proportional to the change in dipole between the ground and excited states. We studied analytically the variation of (hyper)polarizabilities with MIX. Finally, we showed how this model can account for external perturbation, such as the solvent electric reaction field.

Role of surface plasmon in second harmonic generation from gold nanorods

The role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength. In addition to photoluminescence, a peak of second harmonic is observed and is found to depend on the polarization and wavelength of the fundamental frequency laser beam. In particular, the authors found similarities between extinction spectra of the nanoparticles and spectra of emmitted second harmonic. This behavior can be explained by resonant excitation of localized surface plasmon resonances.

LARGE QUADRATIC HYPERPOLARIZABILITIES WITH DONOR-ACCEPTOR POLYENES FUNCTIONALIZED WITH STRONG DONORS. COMPARISON WITH DONOR-ACCEPTOR DIPHENYLPOLYENES

Abstract Donor-acceptor polyenes and carotenoids of defined and increasing length, bearing electron-donating ferrocene or julolidine moieties, and formyl or dicyanovinyl electron-withdrawing end groups have been prepared in order to achieve enhanced quadratic optical nonlinearities. The variation of their quadratic hyperpolarizability β in solution was investigated using the electric field induced second harmonic (EFISH) generation technique, and was compared to the behavior of two series of soluble push-pull diphenylpolyenes. The chainlength behavior for each series of homologous compounds can be modeled by μs(0) = kna relationships with respect to the number n of double bonds in the polyenic chain, the exponent value a depending markedly on the end groups. Steeper increases were observed with the ferrocene donor moiety as compared to the strong julolidine donor group, and with the stronger dicyanovinyl acceptor (a = 2.4 and 1.45), as compared to the weak formyl acceptor (a = 1.6 and 1.3). In contrast, the series of push-pull diphenylpolyenes display the weakest dependencies, and show very little influence of the terminal acceptor substituents on the length behavior (a ≈ 1).

Quasi-solitonic behavior of self-written waveguides created by photopolymerization

We investigated the condition of unique self-written channel and multichannel propagation inside bulk photopolymerizable materials. Light was introduced in the medium by a single-mode optical fiber. At a very low beam power of 5 muW , a unique uniform-channel waveguide without any broadening was obtained by polymerization. When the input power is increased to 100 muW , the guide becomes chaotic and multichannel. We connected two fibers separated by a 1-cm distance. The results open the door to studies of the optical and electro-optical properties of photopolymerized guides doped by nonlinear optical chromophores and to possible applications in integrated optical devices.

Nonlinear optical chromophores containing dithienothiophene as a new type of electron relay

Nonlinear optical (NLO) donor-acceptor (D-A) chromophores containing a fused terthiophene, namely dithienothiophene (DTT) as electron relay, and various strength acceptors were synthesized to evaluate the relays role in the solvatochromism as well as in the molecular nonlinearity, µβ(0). Their solvatochromic behavior, which is dependent on acceptor strength, is correlated to their µβ(0). The static quadratic hyperpolarizability, β(0), of DTT-containing chromophores was determined by EFISH measurements. From the comparison of µβ(0) values of D-A chromophores based on oligothiophenes, it was assessed that DTT as relay is significantly more efficient compared to bithiophene (the same number of conjugated double bonds) and terthiophene. An additional merit of DTT is that chromophores containing DTT have a noticeably high thermal stability.

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.

Rewritable optical data storage in azobenzene copolymers

We propose to encode optical information through the localized depoling of polar chromophores in thin films of grafted polymeric materials with a femtosecond near IR laser source. This disorientation is promoted through the photoisomerization of the azo-dye component induced by a twophoton absorption process. We show that the resulting localized loss in second harmonic generation efficiency can be exploited in data storage applications. The low irradiation powers used allow for a recycling by reheating and repoling the films leading to a rewritable system.

The linear and non-linear optical properties of some conjugated ferrocene compounds with potent heterocyclic acceptors

Abstract We have synthesized donor-acceptor chromophores containing ferrocene as the donor and several different heterocyclic acceptors. In each case the chromophores have an intense band at low energy which is ascribed to a metal to ligand charge-transfer band. Neutral compounds containing the 1,3-diethyl-2-thiobarbituric acid and dicyanomethylene-2,3-dihydrobenzothiophene-1,1-dioxide acceptors have large first molecular hyperpolarizabilities (β) in comparison to a previously examined compound 1-ferrocenyl-2- E -(4nitrophenyl)ethylene, as measured by electric field induced second harmonic generation (EFISH), in chloroform, with 1.907,μm fundamental radiation. Incorporation of 1-ferrocenyl-4- E,E (4-nitrophenyl)butadiene into polymethylmethacrylate at 2% molar loading, yielded after poling at 100 V μm −1 , a polymer film with an r 33 = 0.8 pm V −1 measured at 820 nm.

Synthesis and stability studies of conformationally locked 4-(diarylamino)aryl- and 4-(dialkylamino)phenyl-substituted second-order nonlinear optical polyene chromophores

A series of chromophores with high second-order nonlinearities has been synthesized; the chromphores consist of triarylamine or dialkylarylamine donors linked by a conformationally locked polyene bridge to a dicyanomethylidene acceptor. The use of bridges of this type, combined with the replacement of dialkylarylamine with triarylamine donors, leads to high thermal stability without adverse affects on the nonlinear optical properties of the chromophores.