Jump to main content
Jump to site search

Issue 4, 2004
Previous Article Next Article

Electronic structure and photochemistry of squaraine dyes: basic theoretical analysis and direct detection of the photoisomer of a symmetrical squarylium cyanine

Author affiliations

Abstract

The photoisomerization kinetics of a squaraine dye has been the object both of experimental investigation and of interpretation in the framework of a qualitative theoretical model formulated by the aid of simple HMO calculations and orbital symmetry considerations. Such a model has first confirmed that the electronic structure and the spectroscopic properties of symmetrical squaraines are related to those of the parent cyanines, with ketocyanines as intermediate systems. Extension of the approach to structures twisted by 90° about a polymethine bond has then provided insight into the electronic aspects and the mechanism of the photoisomerization of the squaraine under study. The reaction, previously indirectly investigated by fluorescence analysis, has been directly monitored by laser flash photolysis. These experiments indicate that, while photoisomerization is likely the main radiationless decay route from the spectroscopic minimum of the lowest excited singlet state (S1), the cis photoisomer is produced with only a 1% yield, likely because of an unfavourable cis/trans branching ratio from the perpendicular minimum of the S1-state potential energy surface. In contrast with what found for symmetrical cyanines, an increase in the solvent polarity was found to accelerate both the direct, excited-state reaction and, to a much larger extent, the ground-state back-isomerization. Such observations are consistent with predictions of the theoretical model and provide a clue for the identification of the isomerization coordinate.

Graphical abstract: Electronic structure and photochemistry of squaraine dyes: basic theoretical analysis and direct detection of the photoisomer of a symmetrical squarylium cyanine

Back to tab navigation

Publication details

The article was received on 04 Dec 2003, accepted on 03 Feb 2004 and first published on 23 Feb 2004


Article type: Paper
DOI: 10.1039/B315605B
Photochem. Photobiol. Sci., 2004,3, 396-402

  •   Request permissions

    Electronic structure and photochemistry of squaraine dyes: basic theoretical analysis and direct detection of the photoisomer of a symmetrical squarylium cyanine

    F. Momicchioli, A. S. Tatikolov, D. Vanossi and G. Ponterini, Photochem. Photobiol. Sci., 2004, 3, 396
    DOI: 10.1039/B315605B

Search articles by author

Spotlight

Advertisements