Jacques A. Delaire

Spirooxazine- and spiropyran-doped hybrid organic-inorganic matrices with very fast photochromic responses

Both spirooxazine and spiropyran dyes have been embedded into two different hybrid matrices, which were formed from hydrolysis and cocondensation between diethoxydimethylsilane and zirconium propoxide and between methyldiethoxysilane (DH) and triethoxysilane (TH) respectively. The nature and the kinetics of the photochromic response depend strongly on the hydrophobic/hydrophilic balance (HHB) of the hybrid material. The HHB controls the competition between direct and reverse photochromism. The photochromic behaviour of the strongly hydrophobic spirooxazine-doped DH/TH coatings is direct, highly efficient (ΔA>1), reversible and extremely fast (thermal bleaching time constant, k=0.2 s -1 ). The photochromic kinetics of this hybrid material are, to the best of our knowledge, much faster than those reported for spirooxazine in any other solid matrix.

Azo-azulene derivatives as second-order nonlinear optical chromophores

The molecular and solid state nonlinear optical (NLO) properties of several (phenylazo)-azulenes are investigated. In particular, (4-nitrophenylazo)-azulene (2b) exhibits a quadratic hyperpolarizability (beta(vec)) of 80 x 10(-30) cm5esu recorded at 1.907 microm by the electric field-induced second-harmonic (EFISH) technique. This molecular material, which crystallizes in the monoclinic noncentrosymmetric space group Pc, exhibits an efficiency 420 times that of urea in second-harmonic generation. The origin of the optical nonlinearity in azo-azulene is discussed in relation with crystal structures and semiempirical calculations within the INDO/SOS formalism, and compared with that of the well known disperse red one (DR1) organic dye.

Optical limitation induced by gold clusters: Mechanism and efficiency

The optical limiting effect induced by gold clusters was measured as a function of excitation wavelength. The limiting effect is most efficient below 530 nm, and decreases towards the red. Two different behaviors are seen in the time-resolved signals in the nanosecond and picosecond ranges. These behaviors have different time delays for the amplitude maxima and for the fluence thresholds where nonlinear effects are observed. This suggests that two types of scattering centers are responsible for the optical limitation. The fast mechanism, which reaches a maximum amplitude in less than 1 ns, occurs at relatively high fluence and for short pulses and is assigned to the vaporization of metal particles. It is more pronounced for large clusters where the absorbed light energy is primarily highly confined. The slow mechanism, which develops in a few nanoseconds, is assigned to the energy transfer from the gold particles to the surrounding solvent and to the formation of solvent bubbles. At lower fluence and for smaller size clusters, only the second mechanism is observed in the nanosecond range, because the efficient dissipation of energy from the small clusters to the solvent, which produces bubbles, precludes metal-particle vaporization.

Solar photodegradation of pesticides in water by sodium decatungstate

Solar photodegradation in aqueous solutions of phenol, 4-chlorophenol, 2,4-dichlorophenol, bromoxynil, atrazine, imidachloprid and oxamyl, in the presence of two photocatalysts titanium dioxide TiO2 and sodium decatungstate Na4W10O32 is reported. TiO2 appears to be the most efficient photocatalyst concerning the rate of photodegradation and mineralization of the pure compounds. However, when the pesticides are used in formulated solutions, the decatungstate anion becomes as efficient or even more efficient than TiO2. The mechanism of the photodegradation in the presence of Na4W10O32 is investigated by nanosecond flash-photolysis experiments, and is compared to the one proposed for TiO2. The difference of reactivity between the two photocatalysts is accounted by the different primary processes of the mechanisms. The formulation effect is investigated with two model surfactants SDS and Triton X100, and 2-chlorophenol as a model pesticide.

Π‐Stacking Functionalization of Carbon Nanotubes through Micelle Swelling

We report on a new, original and efficient method for pi-stacking functionalization of single-wall carbon nanotubes. This method is applied to the synthesis of a high-yield light-harvesting system combining single-wall carbon nanotubes and porphyrin molecules. We developed a micelle-swelling technique that leads to controlled and stable complexes presenting an efficient energy transfer. We demonstrate the key role of the organic solvent in the functionalization mechanism. By swelling the micelles, the solvent helps the non-water-soluble porphyrins to reach the micelle core and allows a strong enhancement of the interaction between porphyrins and nanotubes. This technique opens new avenues for the functionalization of carbon nanostructures.

Study of the mechanisms of the photodegradation of atrazine in the presence of two photocatalysts: TiO2 and Na4W10O32

The mechanisms of the photodegradation of atrazine under direct photolysis and in the presence of two different photocatalysts, TiO2 and Na4W10O32, are investigated by the means of GC/MS, total radioactivity counting, HPLC and TLC analysis on 14C ring-labelled atrazine solutions. Integration of photo- and biodegradation processes is studied.

Quantum efficiency of energy transfer in noncovalent carbon nanotube/porphyrin compounds

We report on the quantum yield of excitation energy transfer in noncovalently bound nanotube/porphyrin compounds. Evidence for energy transfer is gained from photoluminescence excitation experiments. We perform a quantitative evaluation of the transfer quantum yield in the case of (6,5) nanotubes through three independent methods: quantitative photoluminescence excitation measurements, evaluation of the luminescence quenching of the donor (porphyrin) and ultrafast transient absorption measurements. The latter shows a tremendous increase in the porphyrin recovery rate upon incorporation in the compound. All these measurements consistently lead to an exceptional quantum yield: η∼1(10−5<1−η<10−3).

Ruthenium(II) Complexes for Two‐Photon Absorption‐Based Optical Power Limiting

Long-lived excitation: Novel bifluorene-substituted 1,10-phenanthroline-based RuII coordination complexes are presented (see picture). They fulfil several requirements for optimized optical power limiting in the visible-NIR, as they are stable, soluble and transparent at low laser fluences. The two-photon absorption of these complexes are strongly related to those of the ligand.

Photoinduced orientation in poly(vinylcinnamate) and poly(7-methacryloyloxycoumarin) thin films and the consequences on liquid crystal alignment

Thin films of poly(vinylcinnamate) and poly(7-methacryloyloxycoumarin) have been exposed to linearly polarized UV light. The resulting anisotropic films have been characterized by using UV, conventional and polarization modulation FTIR spectroscopies. In particular, several internal vibrational modes have been used as structural probes to examine the orientation of groups in the irradiated polymers. These experiments provide new information about the photoinduced anisotropy in these photocrosslinkable polymers upon irradiation with linearly polarized UV light, and an orientation mechanism is proposed. This mechanism is confirmed by studying the liquid crystal alignment induced by PVCi and poly(7-methacryloyloxycoumarin). Finally, the stability of the photoalignment process is discussed.

Excitation transfer in functionalized carbon nanotubes.

Tailoring the properties of carbon nanotubes by functionalizing their side-wall is one of the key challenges towards the realization of carbon nanotube-based optoelectronic devices. This technique aims at combining the remarkable transport properties of the tube with the versatility of the optical properties of organic molecules. Herein, we achieve p-stacking functionalization of nanotubes with hydrosoluble porphyrins.