A solvatochromic method for determining second-order polarizabilities of organic molecules

Paley, Mark S.; Harris, J. M.; Looser, Herbert; Baumert, J.‐C.; Bjorklund, G. C.; Jundt, D. H.; Twieg, Robert J.

doi:10.1021/jo00277a007

Cited by 218 publications

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“…The strong solvatochromism observed for 2a, [23] and semiempirical calculations of the hyperpolarizabilities in 2a and 3, [24] indicated a low-lying HOMO-LUMO electronic transition having sizable charge transfer, and therefore possible NLO capabilities for 2a and 3 as second-order NLO chromophores. The structure of 2a being centrosymmetric (space group P1), it is not surprising that Kurtz-Perry powder tests [25] confirm that 2a exhibits no efficiency in secondharmonic generation.…”

Section: Resultsmentioning

confidence: 99%

New Tetrathiafulvalene-π-Spacer-Acceptor Derivatives: Synthesis, Crystal Structure, Optical and Electrochemical Properties

et al. 2000

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4‐[2‐tetrathiafulvalenyl‐ethenyl]pyridine (1) has been prepared from a Wittig reaction between formyltetrathiafulvalene and 4‐picolyltriphenylphosphonium chloride hydrochloride. Conversion of the pyridine moiety of 1 by reaction with methyl iodide leads to 4‐[2‐tetrathiafulvalenyl‐ethenyl]‐1‐methylpyridinium iodide (2a). Neutralization of 1 with a large excess of L‐tartaric acid affords 4‐[2‐tetrathiafulvalenyl‐ethenyl]‐1‐methylpyridinium hydrogen tartrate (3). These TTF‐π‐spacer‐acceptor compounds have been characterized by elemental analysis, and IR and 1H NMR spectroscopy. The crystal structure of 2a has been determined by X‐ray diffraction. The cation is essentially planar. Examination of the bond lengths in 2a, UV/Vis spectra and CV data, and calculations indicate that an intramolecular charge transfer occurs in the studied compounds, although it is rather limited, and larger in 2a and 3 than in 1.

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Section: Resultsmentioning

confidence: 99%

New Tetrathiafulvalene-π-Spacer-Acceptor Derivatives: Synthesis, Crystal Structure, Optical and Electrochemical Properties

et al. 2000

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“…One simple test of the validity of this approximation was to examine the cyanine compounds 4 asymmetry was induced in the normally symmetric chromophore by sequentially substituting hydrogen atoms upon the methyl groups on one end of the molecule with fluorine atoms. Increases in bond-length alternation from the initially bond-equivalent symmetrical cyanine were observed as the number of fluorines in the molecule increased.…”

Section: Resultsmentioning

confidence: 99%

An investigation of the interrelationships between linear and nonlinear polarizabilities and bond-length alternation in conjugated organic molecules.

Gorman

Marder

1993

Proc. Natl. Acad. Sci. U.S.A.

237

148

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A computational method was devised to explore the relationship of charge separation, geometry, molecular dipole moment (p), polarizability (a), and hyperpolarizabilities (,B, y) in conjugated organic molecules. We show that bond-length alternation (the average difference in length between single and double bonds in the molecule) is a key structurally observable parameter that can be correlated with hyperpolarizabilities and is thus relevant to the optimization of molecules and materials. By using this method, the relationship of bond-length alternation, it, a, 3, and y for linear conjugated molecules is ilustrated, and those molecules with maximized a, 3, and y are described. The first coefficient, a, is the linear polarizability and is related to the first derivative of the dipole moment with respect to E. The higher-order terms (3 and y are referred to as the first and second hyperpolarizabilities. The polarization associated with these higher-order coefficients is responsible for second-and third-order NLO effects. In this paper, we discuss a computational method that predicts structural features ofmolecules that have maximized a, B, and 'yfor a given molecular length. Throughout, we will emphasize what we believe to be a key experimentally accessible structural parameter, bond-length alternation, and illustrate the correlation between it and the NLO response.Prototypical organic chromophores for second-order nonlinear optics contain a polarizable r-electron system and donor and acceptor groups to create an asymmetric polarizability in the molecule. It has been recently hypothesized that there is an optimal combination of donor/acceptor strengths that will maximize 8 (1 (Fig. la). Thus, the aromatic ground state impedes electronic polarization in an applied field and effectively reduces the donor and acceptor strengths of a given pair connected by an aromatic bridge. The visible absorption maximum and extinction coefficients of merocyanines ( Fig. 1 b and c) are sensitive to the dielectric properties of the surrounding medium. Although solvatochromic behavior is usually interpreted solely as a change in the electronic distribution at a fixed nuclear geometry (4), for merocyanines it has been shown that the molecular geometry also undergoes significant changes as well (5)(6)(7)(8)(9)(10)(11)

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“…ahead, NLO molecules, which are well known materials, appear promising for the development of electro-optical ultra-fast switches and frequency modulators for tunable laser devices, thanks to their large conjugated electronic systems that undergo low energy and high intensity, CT type, p-p* transitions. [7][8][9][10] The two-level model, restricted to the interplay between the ground and the first excited states, is generally applied in order to evaluate the first hyperpolarizability, b, which represents the second-order NLO efficiency of these materials. [11][12][13][14] The aim of the present study is to analyze in depth the UV-vis spectra of a number of alkylthiophene copolymers with different percentages of monomeric units functionalized with a donor-acceptor azobenzene chromophore ( Figure 1).…”

Section: Discussionmentioning

confidence: 99%

Electronic Transitions of Polyalkylthiophenes Partially Derivatized with NLO Chromophores: A Theoretical and Experimental Study

Lanzi

Bertinelli

Paganin

et al. 2006

Macro Chemistry & Physics

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Summary: The UV‐vis spectral profiles of some alkylthiophene copolymers in CHCl3 solutions, variously substituted with an azobenzenic NLO chromophore have been carefully analyzed and distinct intensity contributions have been assigned to the overlapped electronic transitions appearing in the lower energy part of the spectra. The different spectral behaviours are influenced by the chromophore content, the length of the alkylic side‐chain of the plastifying comonomer and, more significantly, by the number of the carbon atoms in the oligomethylenic spacer between the chromophoric group and the conjugated polythiophenic chain. This latter finding can be correlated with the strong steric hindrance caused by chromophore crowding in close proximity to the polymeric backbone. As the intensity distributions may be reasonably compared with the NLO properties, identification of the above parameters and of their role is an important step towards the synthesis of polyalkylthiophenes with predictable electronic properties and the development of materials with enhanced NLO characteristics.Graphical surfaces of the highest‐occupied (HOMO)s and the lowest unoccupied (LUMO) molecular orbitals involved in the first three π–π* electronic transitions of the chromophoric system.magnified imageGraphical surfaces of the highest‐occupied (HOMO)s and the lowest unoccupied (LUMO) molecular orbitals involved in the first three π–π* electronic transitions of the chromophoric system.

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A solvatochromic method for determining second-order polarizabilities of organic molecules

Cited by 218 publications

References 0 publications

New Tetrathiafulvalene-π-Spacer-Acceptor Derivatives: Synthesis, Crystal Structure, Optical and Electrochemical Properties

New Tetrathiafulvalene-π-Spacer-Acceptor Derivatives: Synthesis, Crystal Structure, Optical and Electrochemical Properties

An investigation of the interrelationships between linear and nonlinear polarizabilities and bond-length alternation in conjugated organic molecules.

Electronic Transitions of Polyalkylthiophenes Partially Derivatized with NLO Chromophores: A Theoretical and Experimental Study

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