Vibrational spectra and structures of long-chain streptocyanine dyes

Effects of electron-vibration interactions and vibrational polarizabilities

Kazuhiko Furuya, Hajime Torii, Yukio Furukawa, Mitsuo Tasumi

    Research output: Contribution to journalArticle

    9 Citations (Scopus)

    Abstract

    The structural and vibrational properties of streptocyanine dyes, expressed as [(CH3)2N(CH)xN(CH3) 2]+C1O4 (called SCx in this paper) with x = 2n + 1 (n = 0-10), are examined by measuring the infrared (IR) and Raman spectra in solution and in the polycrystalline state (for x = 1, 3, 7, 9) and by carrying out density functional calculations at the BHandHLYP/6-31G* level. It is shown that the strong IR bands observed and calculated in the 1800-800 cm-1 region arise from the normal modes containing large contributions from the vibrations along the bond-alternation coordinate of the conjugated chains. As the conjugated chain becomes longer, the strongest IR band shifts toward the lower-wavenumber side, inducing noticeable changes in the spectral pattern, and the total IR intensity increases significantly. The shifts to lower wavenumbers and the changes in the spectral pattern are explained by the decrease in the intrinsic wavenumber of the bond-alternation mode. A two-state model Hamiltonian, which involves electron-vibration interaction of the bond-alternation mode, reasonably explains the IR intensity enhancement. In the Raman spectra of SC7 and SC9, a few strong bands appear in solution which are not seen in the polycrystalline state. These Raman bands are considered to arise from the same vibrational modes as the strong IR bands, as in the case of similar Raman bands observed previously for SC5 in solution. The relative Raman intensities of the bands are, however, larger in the spectra of SC7 and SC9. These results provide strong evidence for the validity of the mechanism proposed previously that the electron-vibration interaction in the conjugated chain and the intermolecular interaction with the perchlorate ions (existing at various positions near the conjugated chain in solution) give rise to the strong Raman intensities of these bands. It is also suggested that the appearance of these bands is a good signature of the large vibrational contributions to the polarizability tensors in this type of conjugated molecules. The diagonal and off-diagonal force constants of the CC stretches in the conjugated chains are analyzed. It is.shown that the conjugated chains of streptocyanine dyes are more strongly correlated than those of neutral polyene chains.

    Original languageEnglish
    Pages (from-to)11203-11211
    Number of pages9
    JournalJournal of Physical Chemistry A
    Volume104
    Issue number47
    Publication statusPublished - 2000 Nov 30

    Fingerprint

    Vibrational spectra
    vibrational spectra
    Coloring Agents
    dyes
    Infrared radiation
    vibration
    Electrons
    electrons
    alternations
    interactions
    Raman scattering
    Polyenes
    Hamiltonians
    Raman spectra
    Density functional theory
    Tensors
    shift
    perchlorates
    Molecules
    vibration mode

    ASJC Scopus subject areas

    • Physical and Theoretical Chemistry

    Cite this

    Vibrational spectra and structures of long-chain streptocyanine dyes : Effects of electron-vibration interactions and vibrational polarizabilities. / Furuya, Kazuhiko; Torii, Hajime; Furukawa, Yukio; Tasumi, Mitsuo.

    In: Journal of Physical Chemistry A, Vol. 104, No. 47, 30.11.2000, p. 11203-11211.

    Research output: Contribution to journalArticle

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    abstract = "The structural and vibrational properties of streptocyanine dyes, expressed as [(CH3)2N(CH)xN(CH3) 2]+C1O4 (called SCx in this paper) with x = 2n + 1 (n = 0-10), are examined by measuring the infrared (IR) and Raman spectra in solution and in the polycrystalline state (for x = 1, 3, 7, 9) and by carrying out density functional calculations at the BHandHLYP/6-31G* level. It is shown that the strong IR bands observed and calculated in the 1800-800 cm-1 region arise from the normal modes containing large contributions from the vibrations along the bond-alternation coordinate of the conjugated chains. As the conjugated chain becomes longer, the strongest IR band shifts toward the lower-wavenumber side, inducing noticeable changes in the spectral pattern, and the total IR intensity increases significantly. The shifts to lower wavenumbers and the changes in the spectral pattern are explained by the decrease in the intrinsic wavenumber of the bond-alternation mode. A two-state model Hamiltonian, which involves electron-vibration interaction of the bond-alternation mode, reasonably explains the IR intensity enhancement. In the Raman spectra of SC7 and SC9, a few strong bands appear in solution which are not seen in the polycrystalline state. These Raman bands are considered to arise from the same vibrational modes as the strong IR bands, as in the case of similar Raman bands observed previously for SC5 in solution. The relative Raman intensities of the bands are, however, larger in the spectra of SC7 and SC9. These results provide strong evidence for the validity of the mechanism proposed previously that the electron-vibration interaction in the conjugated chain and the intermolecular interaction with the perchlorate ions (existing at various positions near the conjugated chain in solution) give rise to the strong Raman intensities of these bands. It is also suggested that the appearance of these bands is a good signature of the large vibrational contributions to the polarizability tensors in this type of conjugated molecules. The diagonal and off-diagonal force constants of the CC stretches in the conjugated chains are analyzed. It is.shown that the conjugated chains of streptocyanine dyes are more strongly correlated than those of neutral polyene chains.",
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    AU - Furuya, Kazuhiko

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    N2 - The structural and vibrational properties of streptocyanine dyes, expressed as [(CH3)2N(CH)xN(CH3) 2]+C1O4 (called SCx in this paper) with x = 2n + 1 (n = 0-10), are examined by measuring the infrared (IR) and Raman spectra in solution and in the polycrystalline state (for x = 1, 3, 7, 9) and by carrying out density functional calculations at the BHandHLYP/6-31G* level. It is shown that the strong IR bands observed and calculated in the 1800-800 cm-1 region arise from the normal modes containing large contributions from the vibrations along the bond-alternation coordinate of the conjugated chains. As the conjugated chain becomes longer, the strongest IR band shifts toward the lower-wavenumber side, inducing noticeable changes in the spectral pattern, and the total IR intensity increases significantly. The shifts to lower wavenumbers and the changes in the spectral pattern are explained by the decrease in the intrinsic wavenumber of the bond-alternation mode. A two-state model Hamiltonian, which involves electron-vibration interaction of the bond-alternation mode, reasonably explains the IR intensity enhancement. In the Raman spectra of SC7 and SC9, a few strong bands appear in solution which are not seen in the polycrystalline state. These Raman bands are considered to arise from the same vibrational modes as the strong IR bands, as in the case of similar Raman bands observed previously for SC5 in solution. The relative Raman intensities of the bands are, however, larger in the spectra of SC7 and SC9. These results provide strong evidence for the validity of the mechanism proposed previously that the electron-vibration interaction in the conjugated chain and the intermolecular interaction with the perchlorate ions (existing at various positions near the conjugated chain in solution) give rise to the strong Raman intensities of these bands. It is also suggested that the appearance of these bands is a good signature of the large vibrational contributions to the polarizability tensors in this type of conjugated molecules. The diagonal and off-diagonal force constants of the CC stretches in the conjugated chains are analyzed. It is.shown that the conjugated chains of streptocyanine dyes are more strongly correlated than those of neutral polyene chains.

    AB - The structural and vibrational properties of streptocyanine dyes, expressed as [(CH3)2N(CH)xN(CH3) 2]+C1O4 (called SCx in this paper) with x = 2n + 1 (n = 0-10), are examined by measuring the infrared (IR) and Raman spectra in solution and in the polycrystalline state (for x = 1, 3, 7, 9) and by carrying out density functional calculations at the BHandHLYP/6-31G* level. It is shown that the strong IR bands observed and calculated in the 1800-800 cm-1 region arise from the normal modes containing large contributions from the vibrations along the bond-alternation coordinate of the conjugated chains. As the conjugated chain becomes longer, the strongest IR band shifts toward the lower-wavenumber side, inducing noticeable changes in the spectral pattern, and the total IR intensity increases significantly. The shifts to lower wavenumbers and the changes in the spectral pattern are explained by the decrease in the intrinsic wavenumber of the bond-alternation mode. A two-state model Hamiltonian, which involves electron-vibration interaction of the bond-alternation mode, reasonably explains the IR intensity enhancement. In the Raman spectra of SC7 and SC9, a few strong bands appear in solution which are not seen in the polycrystalline state. These Raman bands are considered to arise from the same vibrational modes as the strong IR bands, as in the case of similar Raman bands observed previously for SC5 in solution. The relative Raman intensities of the bands are, however, larger in the spectra of SC7 and SC9. These results provide strong evidence for the validity of the mechanism proposed previously that the electron-vibration interaction in the conjugated chain and the intermolecular interaction with the perchlorate ions (existing at various positions near the conjugated chain in solution) give rise to the strong Raman intensities of these bands. It is also suggested that the appearance of these bands is a good signature of the large vibrational contributions to the polarizability tensors in this type of conjugated molecules. The diagonal and off-diagonal force constants of the CC stretches in the conjugated chains are analyzed. It is.shown that the conjugated chains of streptocyanine dyes are more strongly correlated than those of neutral polyene chains.

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