Elmars Zarins

Nonlinear optical properties of low molecular organic glasses formed by triphenyl modified chromophores

The series of organic molecular glasses have been studied as possible candidates for nonlinear optical (NLO) applications. Amorphous phase formation of investigated materials is ensured by the presence of bulky triphenyl substituents in molecular structure of NLO chromophores. Linear optical properties as well as NLO coefficients and thermal stability of NLO activity for the 13 molecular materials in glassy thin solid films have been determined. For the benzylidene-1,3-indandione chromophore containing compound the highest d33 value equal to 280 pm/V was measured under the 1064 nm excitation. Among the investigated compounds uppermost achieved thermal sustainability of NLO response was 108 °C. The relationship between number of triphenyl substituents and increased thermal sustainability of nonlinear response was observed.

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%.

Pyranylidene indene-1,3-dione derivatives as an amorphous red electroluminescence material

The organic light-emitting diode (OLED) has promising applications in flat-panel displays and novel light sources. Thus far, OLED structures have mostly been made by thermal evaporation in vacuum. An alternative approach is to use small molecules that form amorphous (glassy) structures from solutions. Such compounds can be used in ink-jet printing technologies and result in reduced OLED prices. We present an original red fluorescent organic compo- und 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-methyl-4H-pyran-4-ylidene)-1H-indene-1, 3(2H)-dione (ZWK1), and its derivative 2-(2,6-bis(4-(bis(2-(trityloxy)ethyl) amino)styryl)-4H- pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK2), where the methyl group is replaced with a 4-substituted-styryl group. This change could improve the formation of glassy structures. The thickness of the electroluminescent layer in the device is optimized to the higher power efficiency and obtains: ITO/PEDOT:PSS (40 nm)/ZWK1 (95 nm)/LiF (1 nm)/Al (100 nm), and ITO/PEDOT:PSS (40 nm)/ZWK2 (85 nm)/LiF (1 nm)/Al (100 nm). The maximum of electroluminescence (EL) spectra for the device with the ZWK1 compound is 667 nm, which corresponds to the CIE coordinates x = 0.65 and y = 0.34. The power and luminance efficiency at a luminance of 100 cd/m 2 is 0.63 lm/W and 1.78 cd/A, respectively. Adding an additional 4-substituted-styryl group to the ZWK1 molecule shifts the maximum of EL spectra to the red region (705 nm) and decreases the efficiencies by one order. C 2011 Society of Photo-Optical

Synthesis of Red Luminescent Non Symmetric Styryl-4H-Pyran-4-Ylidene Fragment Containing Derivatives for Organic Light-Emitting Diodes

New organic glassy non symmetric styryl- derivatives of 2(2,6-substituted-4H-pyran-4-ylidene)-malononitrile, 2(2,6-substituted-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione and 2(2,6-substituted-4H-pyran-4-ylidene)-pyrimidine-2,4,6(1H,3H,5H)-trione were synthesized. They form thin solid amorphous films from volatile organic solvents (DCM and chloroform). Their spectral properties have been studied.

Synthesis, optical, and thermal properties of glassy trityl group containing luminescent derivatives of 2-tert-butyl-6-methyl-4H-pyran-4-one

In this work we present simple preparation of original trityl group containing glassy luminescent 6-styryl substituted derivatives of 2-(2-tert-butyl-4H-pyran-4-ylidene)malononitrile (DWK-1TB), 2-(2-tert-butyl-4H-pyran-4-ylidene)-2- ethyl-2-cyanoacetate (KWK-1TB), 2-(2-tert-butyl-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK-1TB) and 5-(2-tert-butyl-4H-pyran-4-ylidene)pyrimidine-2,4,6(1H,3H,5H)-trione (JWK-1TB). Their optical properties have been investigated. The absorption maxima of synthesized glasses is in region from 425 nm to 515 nm and emission maxima is from 470 nm to 625 nm in solution of dichloromethane. But absorption maxima of their solid films is from 425 nm to 500 nm and emission maxima is in range from 570 nm to 710 nm. Incorporation of bulky trityloxy ethyl groups combining with existing tert-butyl groups results in thin solid films formation of synthesized glasses from volatile organic solvents (chloroform, dichloromethane) without them being doped in any polymer. This makes them perspective for potential applications in organic light-emitting diodes and organic lasers by simple luminescent layer composition with cheap wet-casting approaches. All glasses show good thermal stability with thermal decomposition temperatures from 264° to 318°C and glass transition values up to 158°C for DWK-1TB. These thermal properties of synthesized glasses could make them also useful for potential applications in other optical materials such as materials for nonlinear optics.

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.

Synthesis and Physical Properties of Red Luminescent Glass Forming Pyranylidene and Isophorene Fragment Containing Derivatives

© 2012 Zarins et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Synthesis and Physical Properties of Red Luminescent Glass Forming Pyranylidene and Isophorene Fragment Containing Derivatives

Solution processable piperazine and triphenyl moiety containing non-symmetric bis-styryl-DWK type molecular glasses with light-emitting and amplified spontaneous emission properties

A series of 2,6-bis-styryl-4H-pyran-4-ylidene fragment containing glassy organic compounds with chemically stable bonding of amorphous phase promoting bulky triphenyl moieties through piperazine structural fragment (DWK-T dyes) in a form of 2-(5,5,5-triphenylpentyl)piperazin-1-yl)styryl)-substituent have been synthesized and investigated as the potential gain medium component for organic solid state laser applications. Physical properties of the dyes vary and are mostly depending from the other styryl-substituent attached to the 4H-pyran-4-ylidene backbone fragment in 6-position. Thermal stability of synthesized dyes is above 312°C with the glass transitions from 97°C to 109°C. Obtained neat spin-cast films based on these compounds exhibit photoluminescence with λmax in range from 672 nm to 695 nm, ASE λmax from 690 nm to 704 nm with ASE threshold values in range from 327 μJ/cm2 to 1091 μJ/cm2. Parameters are mostly influenced by the electron affinities of various 4-substituents in 6-styryl-fragment. The proposed synthetic approach could be useful for obtaining stable covalently bonded bulky triphenyl group containing glassy dyes while the synthetic design allows to acquire different non-symmetric 2,6-bis-styryl-4H-pyran-4-ylidene fragment containing compounds for infra-red light-emitting and light amplification systems.

Investigation of photoluminescence and amplified spontaneous emission properties of cyanoacetic acid derivative (KTB) in PVK amorphous thin films

In this work photoluminescence and amplified spontaneous emission properties of new original 2-cyanoacetic acid derivative in different concentration mixed in polyvinyl carbazole (PVK) matrix were investigated. Ethyl 2-(2-(4-(bis(2- (trityloxy)ethyl)amino)styryl)-6-tert-butyl-4H-pyran-4-ylidene)-2-cyanoacetate (KTB) is recently synthesised nonsymmetric red light emitting laser dye, that in previous experiments with neat thin films showed low amplified spontaneous emission (ASE) threshold value. Based on PVK high refractive index it has been used as a polymer to ensure the preparation of good planar waveguide. Luminescence quenching is expected in neat amorphous thin films according to previous experiments which reduces photoluminescence quantum yield and increases ASE excitation threshold energy. It could be overcome by a decrease of the intermolecular interactions between laser active molecules by doping them in polymer matrix thereby decreasing photoluminescence quenching effect in the system by increasing distance between organic molecules which in turn results in lowering ASE excitation threshold energy. The lowest threshold value of ASE was achieved at 20wt% of KTB molecule in PVK matrix. Ability to significantly decrease intermolecular interactions and excitation threshold energy of investigated compound in host-guest systems makes it promising to be used as a laser dye in preparation of organic solid state lasers.

Optical and amplified spontaneous emission of neat films containing 2-cyanoacetic derivatives

During the last two decades, small organic molecules have been widely studied for potential applications in organic solid-state lasers due to low-cost production, simple processing possibility and physical property tuning ability through chemical structure synthetic modifications. One of the most investigated and applied compound in dye lasers is 4- (dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM). It has shown remarkable properties as a dye in solid-state lasers. One of the drawbacks of this compound is high intermolecular interactions which reduce emission efficiency. Therefore it can be applied only in doped systems in low concentration (around 2 wt%). Recently we have demonstrated that incorporation of bulky triphenyl groups in the low molecular mass organic compounds enables the ability to form good optical quality transparent glassy films by solution processing. Additional such bulky groups reduce intermolecular interaction thus increase photoluminescence quantum yield in the thin film. In the presentation, we will show optical properties of new 2-cyanoacetic derivatives where two different bulky groups (9H-carbazole fragment and triphenyl group) are attached to molecule electron donating and accepting parts. Synthesized compounds have light absorption from 400nm to 600nm and photoluminescence from 600 nm up to 800 nm. Dyes with only one incorporated electron donating fragment showed 16% PLQY and ASE excitation threshold values (below 52 μJ/cm2) in neat thin films. Two electron donating fragment containing molecules have PLQY of 7% and ASE excitation threshold 223 μJ/cm2.