title: Photophysics of squaraine dyes: role of charge-transfer in singlet oxygen production and removal.
abstract: The unique optical properties of squaraines render these molecules useful for applications that range from xerography to photodynamic therapy. In this regard, squaraines derived from the condensation of nitrogen-based heterocycles and squaric acid have many promising attributes. Key solution-phase photophysical properties of six such squaraines have been characterized in this study. One feature of these molecules is a pronounced absorption band in the region approximately 600-720 nm that has significant spectral overlap with the fluorescence band (i.e., the Stokes shift is small). As such, effects of emission/reabsorption yield unique excitation wavelength dependent phenomena that are manifested in quantum yields of both fluorescence and sensitized singlet oxygen production. Comparatively small squaraine-sensitized yields of singlet oxygen production and, independently, large rate constants for squaraine-induced deactivation of singlet oxygen are consistent with a model in which there is appreciable intra- and intermolecular charge-transfer in the squaraine and squaraine-oxygen encounter complex, respectively. The results reported herein should be useful in the further development of these compounds for a range of oxygen-dependent applications.
authors.affiliation: Department of Materials Science and INSTM, University of Milano-Bicocca, via Cozzi, 53, I-20125, Milano, Italy.
authors.forename: Patrizio
authors.initials: P
authors.lastname: Salice
authors.forename: Jacob
authors.initials: J
authors.lastname: Arnbjerg
authors.forename: Brian Wett
authors.initials: BW
authors.lastname: Pedersen
authors.forename: Rasmus
authors.initials: R
authors.lastname: Toftegaard
authors.forename: Luca
authors.initials: L
authors.lastname: Beverina
authors.forename: Giorgio A
authors.initials: GA
authors.lastname: Pagani
authors.forename: Peter R
authors.initials: PR
authors.lastname: Ogilby
mesh_terms: D003503:Cyclobutanes / Q000737:chemistry*; D004563:Electrochemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry*; D010777:Photochemistry; D011789:Quantum Theory; D026082:Singlet Oxygen / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D003503:Cyclobutanes; D005456:Fluorescent Dyes; D010636:Phenols; C480596:squaraine; D026082:Singlet Oxygen