Title

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

Authors

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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