nonlinear optics of organic molecules and polymers pdf

Nonlinear Optics Of Organic Molecules And Polymers Pdf

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Third-order nonlinear processes In molecules and polymers

Theoretical nonlinear optics equivalence between mesoionic and polyenic bridges in push-pull compounds. In this work we report a semiempirical investigation with the purpose of establishing an equivalence in terms of the value of the first static hyperpolarizability, b 0 , of push-pull compounds of the type electron-acceptor A - bridge - electron-donor D , either formed by polyenic bridges or by mesoionic bridges, keeping unchanged both D and A groups.

The ground state geometries of the molecules were optimized via AM1 using Mopac93r2 program. Our results indicate that a bridge formed by a single mesoionic ring can be equivalent to seven or more conjugated double bonds, depending on the ring, reaffirming that mesoionic rings constitute promising materials for photonics applications. Keywords: hyperpolarizabilities, polyenes, mesoionic. The synthesis of new organic materials with applications to nonlinear optics has attracted considerable attention from many areas of knowledge, especially from materials science, due to their photoluminescence, conductivity and nonlinear optics properties.

The interest in organic materials for nonlinear optics has been stimulated by the expectation of lower cost, faster optical response, higher versatility, possibility of tuning the structure in terms of their nonlinear optical properties, and nonlinear optics susceptibilities comparable or superior to conventional materials. Marder et al. Their objectives were the optimization of the bridge length, in terms of the number of conjugated double bonds [n] and also the introduction of new electron donor and acceptor groups that could lead to high experimental values of b 0.

On the other hand, Moura et al. Moura et al. Consequently, we can now in principle design new and efficient compounds for nonlinear optics, based on purely theoretical reasonings, via semiempirical calculations. In particular, in that work, we suggested mesoionic rings as a promising alternative to polyenic bridges in intensifying nonlinear optics properties. Important questions concerning the structure of mesoionic compounds, in general, can be addressed. In that discussion, we have cited some of our X-ray diffration and theoretical studies on mesoionic compounds, from which we concluded that there are regions of positive and negative charges, each presenting both electron and charge delocalizations.

Based on this discussion, we introduced a new notation for the structures of mesoionic compounds, Figure 2a , which we believe more accurately represents both the bonding situation and the chemical patterns of reactivity of such compounds.

In summary, we have postulated the following definition: mesoionic rings are cyclic dipolar structures in which the positive and negative charges are both separated and delocalized within the p eletron system.

Electrons are delocalized over two regions separated by bonds which are essentially single bonds. The first excited state of the mesoionic ring represents an electron transfer of one electron from the p system located at the HOMO region to the p system at the LUMO region, a situation that results in a high dipole moment change upon excitation.

These push-pull characteristics generally lead to high hyperpolarizabilities, which can then be further maximized through adequate substitution of electron-donor and electron-acceptor groups. Being organic molecules, mesoionic compounds can be further modified in order to enchance their intrinsic separation of charges. To corroborate our theoretical findings, we have been designing and synthesizing mesoionic compounds to be useful as promising materials for nonlinear optics with the following rings: 1,3-dithioliumthiolate, 12,13,9 1,3,4-thiadiazoliumphenylaminide, 14 1,2,4-triazoliumthiolate, 15 1,2,4-oxadiazoles, 16,17 1,3,4-triazoliumselenolates, 18 1,3-thiazoliumthiolates.

Furthermore, we have also measured the nonlinear optics properties of these mesoionic compounds through experimental techniques: Z-scan which allows the determination of the nonlinear refractive index, n 2 , from which one can infer values for the second hyperpolarizability g, a microscopic property related to nonlinear third order process , and optical Kerr gate which allows one to investigate the dynamics of third-order processes. The trends displayed by our experimental values agree with the AM1-TDHF predictions and may be understood qualitatively in terms of a two-level system.

The optical gate experiments, in which we used Kerr's effect, revealed that the response time for these mesoionic compounds are less than 60 fs at nm. The largest measured value of b 0 we obtained for the 3-methyl p -chlorophenyl p -isopropylphenyl -1,3-thiazoliumthiolate mesoionic was 10 esu , 23 which is only 2. More recently, we have also carried out some studies on intensity dependent transmission and laser-induced fluorescence in liquid solutions of some mesoionic systems. Our results indicate that two-photon absorption TPA is the dominant mechanism which causes the observed behavior.

The TPA cross-sections measured have values ranging from 0. In this work, as part of a complete theoretical investigation of the nonlinear optics properties of molecular systems with charge transfer, we attempt to establish an equivalence, in terms of calculated first static hyperpolarizabilities, b 0 , between compounds with polyenic bridges Figure 2b and compounds with mesoionic rings Figure 2a , maintaining unchanged, for both cases, the electron-donor and electron-acceptor groups.

Accordingly, we intend to answer the following question: for a given pair of A and D substituents, which size of polyenic bridge possesses a value of b 0 equivalent to the value of the compound with a mesoionic bridge? In this work, we considered polyenic bridges with one up to ten double bonds and also considered eight different types of mesoionic rings Figure 3 , totaling 48 different calculated mesoionic compounds.

The symbols inside the parenthesis indicate, for example, that the described mesoionic SSS , has sulfur atoms in positions a , b and c. The adopted methodology consisted of two steps: i the ground state geometries for all molecules were optimized with the semiempirical method AM1 implemented in MOPAC 93r2 program, 28 and ii the value of b 0 was calculated through method TDHF, also implemented in this program.

In this table, structure 2[10] means that the electron donating group is a julolidinyl and the electron receptor group is the N,N' -diethylthiobarbituric acid and the molecule has ten double bonds in the polyenic bridge. The corresponding mesoionic compounds are listed in the columns. For example, the SSS in the 2[10] row, means: the ring where a, b and c are all S, with the same substituent groups D and A of compound 2[10]. From previous papers, 8 we know that the presence of D and A groups connected to the mesoionic ring in the correct locations produces an increase in b 0.

These positions are see Figure 2 : the right side negative part of the mesoionic ring for an electron-donor group D, and the left side positive part of the mesoionic ring for an electron-accepting group A. Indeed, the right part of the mesoionic ring is an electron rich region and is associated with the HOMO, and the presence of an electron donor substituent group increases b 0. Likewise, the left part of the ring has an electron deficient character and is associated with the LUMO.

Thus, b 0 can be intensified via the presence of an electron withdrawal group in this position. We observed that the substitution of a sulphur atom by an oxygen atom in a mesoionic ring increases b 0. This occurs for all calculated mesoionic compounds, even for molecules with different D and A groups and mainly oxygen atoms located at a and b positions. Even so, this quantity is equivalent to a b 0 for a molecule with a polyenic bridge of approximately four to five double bonds, as in structure 6[n] Figure 4.

The only exception is the 1[n] structure, where the highest calculated b 0 was, instead, for the OOO mesoionic ring. Comparing the calculated b 0 for each mesoionic compound, we can notice the number of double bonds in a polyenic bridge that would be necessary, in order for it to be equivalent to a maximum calculated b 0 value of a mesoionic ring.

For example, for mesoionic compounds with SSS ring and groups D and A equal to the structure 2[n], the calculated b 0 was x10 esu. In order to answer our initial question, we can point out that, in average, considering our highest calculated b 0 for the OOS ring, it is necessary for a polyenic bridge to possess from seven up to ten double bonds to be equivalent, in terms of b 0 , to a compound containing a mesoionic ring.

This fact places us in position to invest in the synthesis of these mesoionic compounds for application in nonlinear optics, since the synthesis of a system that has ten conjugated double bonds may often become difficult.

Figure 4 shows the graphs of the dependence of the value of b 0 with the number of double bonds in the polyenic bridges for each type of structure considered. Indeed, for all cases, there exists an increase in the value of b 0 with the number of double bonds in the polyenic chain.

However, when we reach a critical number of double bonds, a saturation of the trend occurs in b 0. This adds evidence, justifying our work in the synthesis of compounds containing mesoionic rings. For these, we are now in position of suggesting that mesoionic rings are more efficient bridges than polyenes for the design of materials for nonlinear optics. Maya, E. A , , Prasad, P. Tykwinski, R. B , Kanis, D. Chemla, D. Marder, S. T; Tiemann, B.

Moura, G. Simas, A. Cheung, K. C , 47 , C , 48 , C , 49 , Srivastava, R. Carpenter, G. Lira, B. Bezerra, A. Bezerra Jr. Rakov, N. Optics , 40 , Menezes, L. Stewart, J. Babudri, F. Patro, B. Williams, J. Stewart, S. Received: October 10, Published on the web: March 9, All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License.

Services on Demand Journal. Introduction The synthesis of new organic materials with applications to nonlinear optics has attracted considerable attention from many areas of knowledge, especially from materials science, due to their photoluminescence, conductivity and nonlinear optics properties.

Methodology In this work, we considered polyenic bridges with one up to ten double bonds and also considered eight different types of mesoionic rings Figure 3 , totaling 48 different calculated mesoionic compounds.

References 1. How to cite this article.

Nonlinear Optical Properties of Organic Molecules and Crystals V1

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Nonlinear Optical Effects in Organic Polymers

Second-order nonlinear optical NLO materials have played a very important role in laser technology since the invention of the laser. The materials have been developed from inorganic crystals to organic molecules and polymers. The search for new second-order NLO materials with better performance has continuously been in the frontier of materials science and optical engineering.

Organic semiconductors as active materials in thin-film electronic devices such as alkynes, heterocycles, dyes, ferrocenes, spiranes, or porphyrins, with special geometries and certain electronic molecular parameters, which possess nonlinear optical NLO properties and offer several major advantages over their inorganic counterparts, are presented in this chapter. There are a number of simple and versatile techniques that can be employed for the deposition of these important classes of materials. The matrix-assisted pulsed laser evaporation MAPLE technique provides advantages with regard to making organic films of different morphologies on different types of substrates.

Skip to main content Skip to table of contents. Advertisement Hide. This service is more advanced with JavaScript available. Nonlinear Optical Effects in Organic Polymers.

Synthesis and Nonlinear Optical Studies on Organic Compounds in Laser-Deposited Films

Theoretical nonlinear optics equivalence between mesoionic and polyenic bridges in push-pull compounds. In this work we report a semiempirical investigation with the purpose of establishing an equivalence in terms of the value of the first static hyperpolarizability, b 0 , of push-pull compounds of the type electron-acceptor A - bridge - electron-donor D , either formed by polyenic bridges or by mesoionic bridges, keeping unchanged both D and A groups. The ground state geometries of the molecules were optimized via AM1 using Mopac93r2 program. Our results indicate that a bridge formed by a single mesoionic ring can be equivalent to seven or more conjugated double bonds, depending on the ring, reaffirming that mesoionic rings constitute promising materials for photonics applications. Keywords: hyperpolarizabilities, polyenes, mesoionic. The synthesis of new organic materials with applications to nonlinear optics has attracted considerable attention from many areas of knowledge, especially from materials science, due to their photoluminescence, conductivity and nonlinear optics properties. The interest in organic materials for nonlinear optics has been stimulated by the expectation of lower cost, faster optical response, higher versatility, possibility of tuning the structure in terms of their nonlinear optical properties, and nonlinear optics susceptibilities comparable or superior to conventional materials.

Nonlinear Optical Properties of Organic Molecules and Crystals, Volume 1 discusses the nonlinear optical effects in organic molecules and crystals, providing a classical distinction between quadratic and cubic processes. This book begins with a general overview of the basic properties of organic matter, followed by a review on the benefits derived from quantum-chemistry-based models and growth and characterization of high quality, bulk organic crystals and waveguided structures. A case study focusing on a specific material, namely urea, which exemplifies a situation in which transparency in the UV region has been purposely traded for nonlinear efficiency is also deliberated. This text concludes with a description of a type of trade-off between the unpredictable orientation of molecules in crystalline media, polarity of liquid-crystalline structures, and dominant electronic contribution to the electro-optic effect. This publication is beneficial to solid-state physicists and chemists concerned with nonlinear optical properties of organic molecules and crystals. Introduction II.

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Preparation of the Inclusion Complex-Type Nonlinear Optical Polymer

1 comments

Amancai P.

Upon complexation, the DR1 and SP molecules are free to align themselves along an applied electric field and show high order parameters of approximately 0.

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