Andrejs Tokmakovs
University of Latvia
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Featured researches published by Andrejs Tokmakovs.
Journal of Materials Chemistry | 2012
Kaspars Traskovskis; Igors Mihailovs; Andrejs Tokmakovs; A. Jurgis; Valdis Kokars; Martins Rutkis
The incorporation of trityl and triphenylsilyl groups into low molecular weight molecules allows the formation of stable molecular glasses. A series of materials based on the N-phenyldiethanolamine core was synthesized bearing different azobenzenes and benzylydene-1,3-indandione as active chromophores. Molecular hyperpolarizability of the synthesized compounds was calculated by a restricted Hartree–Fock method with basis 6-31G(d,p) and measured in solutions by hyper-Rayleigh scattering. Non-linear optical (NLO) activity of the thin glassy films was confirmed after a corona poling procedure. Thermal sustainability of the NLO response of up to 85 °C was achieved. Quantum chemical calculations of the compounds revealed increased steric bulk and conformational freedom of the triphenylsilyl moiety. While the presence of the triphenylsilyl group results in more stable glasses and increased material nonlinearity, in the case of trityl groups, measured glass transition temperatures are higher.
Proceedings of SPIE, the International Society for Optical Engineering | 2006
Martins Rutkis; Aivars Vembris; V. Zauls; Andrejs Tokmakovs; Egils Fonavs; A. Jurgis; Valdis Kampars
Second order non linear optical (NLO) properties of sPMMA based host-guest systems containing eight dimethylaminobenzylidene -1, 3 - indandione (DMABI) related chromophores have been investigated by means of quantum chemical calculations and SHG experimental characterization. Ab initio calculations with basis set 6-31G were used for molecular geometry determination as well as in the calculations of molecular hyperpolarizability by FF approach. Influence of the chromophore concentration on the host-guest film NLO performance was obtained by SHG Maker fringe experiments. The highest value of d53233 =80 pm/V (frequency corrected value d033 =12 pm/V) at chromophore concentration 15 %wt have been recorded for tret-butyl substituted DMABI chromophore.
Molecular Crystals and Liquid Crystals | 2008
Mārtiņš Rutkis; A. Jurgis; Valdis Kampars; Aivars Vembris; Andrejs Tokmakovs; Valdis Kokars
Reliability to forecast SHG efficiency using two sets of non linear optical (NLO) chromophore figures of merit (FOM) was tested. One of them predicts that SHG efficiency d 33 of the poled guest-host polymer is proportional to ground state dipole ∼ μg, another to ∼ 1/μg. Correlation of maximal achieved second order NLO efficiency of the PMMA based systems containing eight dimethylaminobenzylidene-1, 3-indandione (DMABI) related chromophores with proposed FOM have been analyzed. The best correlations were obtained with second set of FOM, especially if high dipole moment (μg > 7D) chromophores are included in analysis.
IOP Conference Series: Materials Science and Engineering | 2012
Andrejs Tokmakovs; Mārtiņš Rutkis; Kaspars Traskovskis; Elmars Zarins; Lauma Laipniece; Valdis Kokars; Valdis Kampars
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.
Journal of Materials Chemistry C | 2016
Kaspars Traskovskis; Valdis Kokars; Andrejs Tokmakovs; Igors Mihailovs; Edgars Nitiss; M. V. Petrova; Sergey Belyakov; Martins Rutkis
A series of organic push–pull type chromophores using indane-1,3-dione 5-carboxylic acid (IDCA) and novel 1,3-bis(dicyanomethylidene)indane 5-carboxylic acid (CICA) electron acceptor fragments have been synthesized and characterized. NMR and X-ray analysis revealed that condensation reactions with the CICA fragment were stereoselective and yielded benzylidenes and azomethines with E double bond configurations. Due to the non-planar geometry these compounds are chiral and were acquired as a racemic mixture. The subsequent functionalization of the carboxylic acid group with 5,5,5-triphenylpentan-1-ol yielded solution-processable glass forming materials (6, 8, 10, 13) with glass transition temperature values of 76–134 °C. The nonlinear optical (NLO) properties of these compounds were characterized using quantum chemical calculations and second harmonic generation (SHG) measurements in corona-poled thin glassy films. The twisted geometry of the CICA based materials was shown to be beneficial to the macroscopic NLO performance due to the less pronounced solid phase stacking compared to the flat IDCA based compounds. The presence of site isolating groups at both the acceptor and donor ends of the molecule in compound 13 resulted in a considerable NLO efficiency increase. Non-centrosymmetric crystals of CICA based N,N-dimethylaminobenzylidene 7b were obtained and showed a SHG response comparable to urea.
Journal of Physics: Conference Series | 2007
Mārtiņš Rutkis; A Jurgis; Valdis Kampars; Aivars Vembris; Andrejs Tokmakovs; Valdis Kokars
Maximal achieved second order non linear optical (NLO) efficiency of the PMMA based host – guest systems containing eight dimethylaminobenzylidene -1, 3 - indandione (DMABI) related chromophores have been analysed. Two contradicting sets of NLO chromophore figure of merit (FOM) equations were tested. One of them predicts that NLO efficiency of the poled polymer host -guest film is proportional to ground state dipole d33 ~ 1/μg, another to d33 ~ 1/μg. The best correlations for the maximal achieved nonlinearity were obtained with second set of FOM, especially if high ground state dipole (μg > 7D) chromofores are included in analysis.
Optics Express | 2017
Edgars Nitiss; Andrejs Tokmakovs; Kaspars Pudzs; Janis Busenbergs; Martins Rutkis
In this paper we describe the principles of operation as well as the fabrication and testing steps of an all-organic waveguide modulator. The modulator comprises an SU-8 core and an electro-optic host-guest polymer cladding. The polymer properties are tuned in order to achieve single mode operation. We used direct-write laser lithography in two steps for the preparation of the devices. The electro-optic coefficient of the polymer is estimated from observing the modulation of the device operated in push-pull mode.
Proceedings of SPIE | 2013
Elmars Zarins; Andrejs Tokmakovs; Zane Kalnina; Valdis Kokars; Martins Rutkis; Andris Ozols; Peteris Augustovs; Kristine Lazdovica; Valdis Kampars
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.
Proceedings of SPIE | 2012
Kaspars Traskovskis; Igors Mihailovs; Andrejs Tokmakovs; Valdis Kokars; Martins Rutkis
New molecular design of obtaining molecular glasses has been developed by linking triphenylmethyl moieties to chromophore core by flexible C-C bridge. Compounds capable of forming stable amorphous phase with good optical quality have been acquired with increased chemical and thermal sustainability compared to the previously reported design. NLO activity of compounds has been measured after corona discharge polling. Compared to previously synthesized trityloxy fragment containing compounds increase of d33 coefficient by up to 17 times was achieved for the same chromophore core containing compounds.
Proceedings of SPIE | 2011
Kaspars Traskovskis; Igors Mihailovs; Andrejs Tokmakovs; Valdis Kokars; Valdis Kampars; Martins Rutkis
In given study a new structural design of molecular NLO materials is presented where amorphous phase formation is achieved by introduction of bulky trityl and triphenylsilyl substituents. Obtained materials formed stable organic glasses with good optical quality and glass transition temperatures notably exceeding ambient. NLO activity was successfully measured in samples that underwent corona discharge poling. The comparison of both enhancer groups revealed, that trityl group increases thermal sustainability of material, while triphenylsilyl group better promotes formation and stability of amorphous phase.