Patrizio Salice - Photophysics of Squaraine Dyes: Role of Charge-Transfer in Singlet Oxygen Production and Removal

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  Publication Details (including relevant citation   information): Salice, Patrizio, Arnbjerg, Jacob,   Pedersen, Brian Wett, Toftegaard, Rasmus, Beverina, Luca, Pagani,   Giorgio A., Ogilby, Peter R., J. Phys. Chem. A,   2010, 114 (7), pp 2518-2525

  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 ?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.

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