Peteris Augustovs

Synthesis and properties of 1,3-dioxo-1H-inden-2(3H)-ylidene fragment and (3-(dicyanomethylene)-5,5-dimethylcyclohex-1-enyl)vinyl fragment containing derivatives of azobenzene for holographic recording materials

New glassy 1,3-dioxo-1H-inden-2(3H)-ylidene fragment und (3-(dicyanomethylene)-5,5-dimethylcyclohex-1-enyl)vinyl fragment containing push-pull type derivatives of azobenzene able to create thin layers have been synthesized. Thin films of synthesized glasses for holographic recording were prepared using spin coating technique from saturated chloroform solution. Holographic grating recording in films of 6a-b, 7 and 12 has been experimentally studied at 633 and 532 nm in both transmission and reflection modes with p-p recording beam polarizations. The film 12 was found to be the most efficient at both wavelengths in transmission mode exhibiting the maximum self-diffraction efficiency of 9.9% at 633 nm, and 15.3% at 532 nm. The film of 6a was the most efficient in reflection mode with the maximum selfdiffraction efficiency of about 3%.

Effect of Light Polarization on Holographic Recording in Glassy Azocompounds and Chalcogenides

Light polarization effects on a holographic grating recording in a glassy chalcogenide a-As40S15Se45 film has been experimentally studied and compared with previously studied glassy molecular azobenzene film 8a at 633, using s − s,p − p, CE-1 and CE-2 circular-elliptic recording-beam polarizations (differing by light electric field rotation directions). The azocompound exhibited much higher self-diffraction efficiency (SDE) and diffraction efficiency whereas chalcogenide was more sensitive. Their recording efficiency polarization dependences also were different. SDE up to 45% was achieved in 8a with p − p and up to 2.6% in a-As40S15Se45 with CE-2 polarized recording beams. The polarization changes in the diffraction process were studied as well in these and other materials (11, 16, 19 and a-As2S3 film, LiTaO3:Fe crystal). It was found that light polarization changes in the process of diffraction from gratings recorded vectorially by s−p polarizations depended on chemical composition, wavelength, and exposure time. Vector gratings with SDE up to 25% were recorded in 8a, rotating a linear polarization by 90°. No light polarization changes were found in azobenzene 19 and chalcogenide films and in LiTaO3:Fe crystal, thus showing a vector recording of scalar holograms. The recording mechanisms in azocompounds and chalcogenides are discussed and compared.

Thermal, glass-forming, nonlinear optical and holographic properties of push-pull type azochromophores with triphenyl moieties containing isophorene and pyranylidene fragments

Molecular organic compounds with electron donating fragment bounded through π-conjugated system with electron acceptor fragment, as well as with incorporated triphenyl groups in their molecules show potential for creating cheap and simple solution processable materials with nonlinear optical properties. Additional insertion of azobenzene fragment in their structures makes them also possible to form holographic volume and surface relief gratings (SRG) after exposure to laser radiation, which could be useful for holographic data storage. For these purposes polymers are generally used. However, their application is complicated and challenging task as in every attempt to obtain the same polymer it will have different physical properties. On the other hand, the synthetic procedure of molecular glasses is more simple as their structure and physical properties are strongly defined. Unfortunately, there is still no clear relation between compound organic structures and their thermal, glass-forming and optical properties. In order to investigate the above mentioned regularities, we have synthesized and investigated ten molecular glassy organic compounds with three different fragments as main backbones of the molecules: indene-1,3-dione (WE-1, WE-2, WE-3), isophorene (IWK-1D, IWK-2M, IWK-2D) and pyranylidene (DWK-2TB, ZWK-2TB, JWK-2TB, ZWK-3AZO). Compounds containing isophorene fragment in their molecules had the highest NLO efficiencies (d33 up to 125.7 pm/V for IWK-2D) and also were the most effective holographic data storage compounds with holographic self diffraction efficiency 13% and holographic diffraction efficiency 20%, also for IWK-2D, but their thermal stability (Td from 288°C to 295°C) and glass transition (Tg from 90°C to 105°C) values were just average. Pyranylidene type compounds had the highest thermal stability and highest glass transition (Tg from 115°C to 180°C). But their ability to form and maintain amorphous structure were low and they had average NLO efficiencies (d33 up to 66.2 pm/V for ZWK-2TB) and average holographic self diffraction efficiency 2% and holographic diffraction efficiency 8% for ZWK-3AZO. The molecules with just azobenzene fragment and indene-1,3-dione as electron acceptor has the lowest thermal (Td from 250°C to 282°C, Tg from 70°C to 98°C) and also the lowest holographic properties with holographic diffraction and self diffraction efficiencies at 4% for WE-1 and lower for other compounds. Nevertheless, some of the investigated molecular glasses show potential as multifunctional optical materials.

Photoinduced Anisotropy of IWK-2D Azobenzene Molecular Glassy Films

We have experimentally studied photoinduced anisotropy (PA) of holographic gratings in IWK-2D [precise chemical notation: 2-(3-(4-((4-(bis (2-(trityloxy) ethyl) amino) phenyl) diazenyl) styryl)-5,5-dimethylcyclohex-2-enylidene) malononitrile] azobenzene molecular glassy films in transmission and reflection modes using a special simultaneous holographic recording and readout setups which enabled measurements of PA time evolution. PA manifested itself by diffraction efficiency difference with linear s- and p-polarizations. Three different types of polarization holographic gratings were recorded and studied using p-p, L-L and L-R polarized beams creating different recording interference patterns. Atomic force microscope (AFM) was used to study the surface profile changes. Experimental evidence was obtained that the transmission mode PA was due to the both recorded surface relief and volume polarization gratings whereas the reflection mode PA was due to the recorded surface relief gratings. The main PA features were similar for all three types of polarization gratings whereas details were different. PA properties of IWK-2D films were notably distinctive from those of previously studied films.

Recording and self-enhancement of dynamic polarization gratings in degenerate four-wave-mixing geometry

Scalar and vectorial degenerate four-wave-mixing (DFWM) in azobenzene molecular K-RJ-4-3 [N,N-bis(5,5,5- tryphenylpentyl)-4-((4-tritylphenyl)diazenyl)aniline] and in chalcogenide a-As2S3 glassy films is experimentally investigated. A coherent self-enhancement (CSE) of holographic gratings (HG) in this geometry was experimentally confirmed, for the first time to our knowledge, thus establishing a new method of HG recording, the DFWM CSE recording. Scalar linear s-s, p-p and circular R-R(right) polarizations and orthogonal linear s-p and circular L(left)-R polarizations were used for HG recording with 2 μm period at 532 nm. In the case of K-RJ-4-3 film L-R polarizations were the most efficient enabling the maximum DFWM efficiency ρmax=14.5% whereas in the case of a-As2S3 film s-s polarizations were the best with ρmax=6.0%. DFWM CSE recording has exhibited a different polarization dependence compared to normal DWFM recording. CSE factor ρ/ρ0 (ρ0 being the initial ρ) was the highest for K-RJ-4-3 film (6.8) with s-s polarizations compared to 3 for a-As2S3 film with p-p polarizations. Two-wave HG recording was also studied for comparison.

Synthesis and Properties of New Glassy Molecular and Oligomer Azocompounds Suitable for Holographic Recordings

Molecular diphenylamine derivative containing two azochromophores has been synthesized. Compound showed formation of stable amorphous glassy phase with good optical quality. Functionalization with bulky trityl- group was carried to further improve physical properties of material. Two types of azochromophore containing polymeric materials, azochromophore in side chain containing aromatic polyether and azochromophores in both, main and side chain, containing polyester were also synthesized. Samples for holographic recording were prepared using spin coating technique from saturated chloroform solution. Holographic recording experiments have been made using 532 and 633 nm lasers. All compounds showed ability of forming laser induced diffraction gratings.