NMR‐Parameter und CNDO/2‐Berechnungen von einfachen Cyaninen, Merocyaninen und Oxonolen

Radeglia, R.; Gey, E.; Steiger, Th.; Kulpe, S.; Lück, R.; Ruthenberg, M.; Stierl, M.; Dähne, S.

doi:10.1002/prac.19743160508

Cited by 30 publications

(4 citation statements)

References 17 publications

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“…The values obtained are in good agreement with those reported in the literature (Radeglia et al, 1972;Radeglia, 1973;Radeglia et al, 1974) (+ 0.6) corresponds remarkably to the variation of the chemical shift (+ 60 p.p.m.). In Fig.…”

Section: Molecular Modellingsupporting

confidence: 91%

Structure of 1,5-bis(dimethylamino)-1,5-diphenylpentadienylium perchlorate and modelling of pentadienylium salts (cyanine dyes)

Declercq¹,

Dubourg²,

Payrastre³

et al. 1996

Acta Crystallogr Sect B

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C21H25N2+.CIO4 -(orange crystals), Mr = 404.9, orthorhombic; P212121, a = 7.810(2), b = 15.007(3), c = 18.326 (3)/~, V = 2147.8 (7)/~3. Graphitemonochromated Mo Kc~ source at room temperature; A = 0.71069A,, /z = 0.22 mm -l, Z = 4; F(000) = 856, Dx = 1.25 g cm -3, R = 0.057 for 1392 independent data. As for the unsubstituted pentamethinium dyes, the chain lies in an all-trans planar configuration. Molecular modelling calculations reproduce the Xray structure with good accuracy, even in the case of more crowded pentadienylium cations, i.e. 1,5-bis(dimethylamino)-1,3,5-triphenylpentadienylium perchlorate.

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Section: Molecular Modellingsupporting

confidence: 91%

Structure of 1,5-bis(dimethylamino)-1,5-diphenylpentadienylium perchlorate and modelling of pentadienylium salts (cyanine dyes)

Declercq¹,

Dubourg²,

Payrastre³

et al. 1996

Acta Crystallogr Sect B

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“…Here, we simply stress the oscillatory behavior of the H−H coupling constants traceable to alternation of the C−C bond orders (BOA) and hence of the C−C bond lengths (BLA). As is well-known, the degree of oscillation is larger in polyenes (where BLA is maximum), whereas it vanishes in symmetric cyanines , (characterized by equalized C−C bond lengths).…”

Section: Resultsmentioning

confidence: 78%

First- and Second-Order Polarizabilities of Simple Merocyanines. An Experimental and Theoretical Reassessment of the Two-Level Model

2008

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Taking four merocyanines [(CH3)2N-(CHCH)n-C(CH 3)O; n = 1-4] (Mc1-4) as test D-A systems, we performed a close experimental and theoretical examination of the two level model with reference to its ability to provide correct predictions of both absolute values and dependence on the conjugation path length of first- and second-order molecular polarizabilities. By (1)H NMR spectroscopy merocyanines Mc1-4 were found to be approximately 1:1 mixtures of two planar conformers with cis and trans arrangements of the C(CH 3)O electron-acceptor group and all trans structure of the polyene like fragment. The degree of bond length alternancy (BLA) in the -(CHCH)n- fragment, was quantified by extensive full geometry optimizations at both semiempirical and ab initio level. DFT (6-31G**/B3LYP) optimized geometries were considered to be most reliable and were used for calculations of the excited-state properties. The applicability of the two level model, reducing the general sum-over-states (SOS) expansion to only one term involving the ground state (g) and the lowest-lying (1)(pipi*) CT state (e), was checked by analysis of fluorescence and near UV absorption spectra. Measurements of the basic two-level model quantities ( Ege, microge and Deltamicro(eg)), by which the dominant components of alpha and beta tensors are expressed (alpha XX , beta XXX , X identical with long molecular axis), were designed to give approximate free-molecule values. It is proposed, in particular, an adjustment of the solvatochromic method for the determination of Deltamicro(eg), based on accurate measurements of absorption spectral shifts in n-hexane/diethyl ether mixtures with small diethyl ether volume fractions. Such an approach led to Mc1-4 beta XXX 's matching well in both value and n-dependence with EFISH data reported in the literature for similar merocyanines. For the fluorescent Mc4, the results were qualitatively well reproduced by an approach, which combines absorption and fluorescence solvent shifts. All the measured quantities were calculated for both trans and cis Mc1-4 by three semiempirical INDO-based approaches aiming at evaluating the performances of different integral parametrizations and CI extensions: ZINDO/S, CS INDO SCI, CS INDO SDCI. In all cases, alpha XX and beta XXX were found to rise proportionally to about n (1.3) and n (2), respectively, in qualitatively good agreement with the experimental values. As to the absolute values, however, experimental alpha XX 's and beta XXX 's were best reproduced by CS INDO SDCI combining Ohno-Klopman parametrization and CI including both single and double excitations. The validity of the two-level model was checked by comparison with converged SOS calculations for the longest chain merocyanine (Mc4) and finite field calculations of linear polarizabilities for all of the four dyes (Mc1-4).

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“…The intermediate character of merocyanines between polyenes and SPC is reflected in various structural observables and in their UV-visible absorption behaviour. So, X-ray diffraction 9 and NMR spectroscopy [10][11][12][13] revealed, along the polymethine chain of merocyanines, a pbond order alternation of the polyene type, but a chargedensity alternation characteristic of SPC. Furthermore, the absorption maxima of the color band of merocyanines were found to exhibit a dependence on the chain length intermediate between those of SPC and polyenes.…”

Section: Introductionmentioning

confidence: 99%

Photoisomerization of simple merocyanines: a theoretical and experimental comparison with polyenes and symmetric cyanines

Baraldi

Momicchioli

Ponterini

et al. 2002

Phys. Chem. Chem. Phys.

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The structure and electronic spectra of merocyanines are intermediate between those of acyclic polyenes and cationic symmetric cyanines of comparable sizes, shifting from one to the other as a result of a solvent polarity change. In this paper we address, both theoretically and experimentally, the question of how the photochemical behaviour of simple merocyanines compares with that of polyenes and symmetric cyanines. After a brief theoretical re-appraisal of the absorption maxima dependence on the chain length in the three classes of chromogens, we analyse the calculated potential-energy curves for two photoisomerization coordinates of a polyene, a symmetric cyanine and a merocyanine of comparable sizes. The results concerning both the energy curves and the nature of the relevant electronic states, particularly the TICT (twisted intramolecular charge transfer) character of the S 1 state at the perpendicular geometry, reveal the existence of a near relationship between merocyanines and symmetric ionic polymethines, traceable back to their being odd-alternant systems. The presence of a low-lying 1 (np*) state at the trans geometry and the associated solvent-modulated vibronic coupling with the 1 (p H p L *) state dominate the experimentally accessible photochemical behaviour of two simple merocyanines and make it peculiar with respect to those of both polyenes and symmetric ionic cyanines.y Dedicated to Professor Dr Z. R. Grabowski and Professor Dr J. Wirz on the occasions of their 75th and 60th birthdays. Fig. 1 Dominant resonance structures in strepto polymethinecyanines (SPC), strepto polymethinemerocyanines (SPMC) and acyclic polyenes (AP).

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NMR‐Parameter und CNDO/2‐Berechnungen von einfachen Cyaninen, Merocyaninen und Oxonolen

Cited by 30 publications

References 17 publications

Structure of 1,5-bis(dimethylamino)-1,5-diphenylpentadienylium perchlorate and modelling of pentadienylium salts (cyanine dyes)

Structure of 1,5-bis(dimethylamino)-1,5-diphenylpentadienylium perchlorate and modelling of pentadienylium salts (cyanine dyes)

First- and Second-Order Polarizabilities of Simple Merocyanines. An Experimental and Theoretical Reassessment of the Two-Level Model

Photoisomerization of simple merocyanines: a theoretical and experimental comparison with polyenes and symmetric cyanines

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