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.
Address (URL): http://dx.doi.org/10.1021/jp911180n