Nature of the electronic transitions in thiacarbocyanines with a long polymethine chain

    Authors

    R. S. Lepkowicz; O. V. Przhonska; J. M. Hales; J. Fu; D. J. Hagan; E. W. Van Stryland; M. V. Bondar; Y. L. Slominsky;A. D. Kachkovski

    Comments

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    Abbreviated Journal Title

    Chem. Phys.

    Keywords

    cyanine dyes; symmetry breaking; solitonic charge wave; symmetrical and; asymmetrical forms; charge density; excited-state absorption; saturable; absorption; anisotropy; EXCITED-STATE ABSORPTION; NEGATIVE-DEFECT TRANSPOLYACETYLENE; SOLITON; MODEL COMPOUNDS; SQUARYLIUM MOLECULES; FINITE-LENGTH; POLYACETYLENE; CATIONS; DYES; DYNAMICS; SYSTEMS; Chemistry, Physical; Physics, Atomic, Molecular & Chemical

    Abstract

    A detailed experimental investigation and quantum-chemical analysis of symmetric cyanines of different conjugation lengths have been performed with the goal of understanding the nature of the electronic transitions in molecules that possess a long chromophore. The nature of electronic transitions in cyanines with a relatively short chromophore (inside the cyanine limit) has already been investigated and many properties of these molecules are well understood. However, little is known about the nature of the transitions beyond the cyanine limit. Their unusual properties, which were proposed by Tolbert and Zhao to be connected with symmetry breaking, still remain unexplored. The analysis of the spectral data in various solvents and results of femtosecond pump-probe saturable absorption measurements enable us to conclude that an increase in the length of the chain leads to a symmetry breaking and the appearance of two forms with symmetrical and asymmetrical distributions of the charge density in the ground state. For thiacarbocyanines, symmetry breaking is predicted and observed for a pentacarbocyanine dye. Quantum-chemical calculations provide additional proof of this hypothesis. The excited-state absorption properties of a pentacarbocyanine in the visible region are also reported. For the first time we have observed an excited-state cross-section that is larger (approximate to3x) than the ground state cross-section at the peak spectral position. (C) 2004 Elsevier B.V. All rights reserved.

    Journal Title

    Chemical Physics

    Volume

    305

    Issue/Number

    1-3

    Publication Date

    1-1-2004

    Document Type

    Article

    Language

    English

    First Page

    259

    Last Page

    270

    WOS Identifier

    WOS:000224321000027

    ISSN

    0301-0104

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