Intermolecular exciton-exciton annihilation in phospholipid vesicles doped with [Ru(bpy)(2)dppz](2+)
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The ultrafast photophysics of [Ru(bpy)(2)dppz](2+) (dppz = dipyrido[3,2-a:2',3'-c]-phenazine) embedded into the walls of phospholipid vesicles has been studied by femtosecond time-resolved pump-probe spectroscopy. While [Ru(bpy)(2)dppz](2+) has been studied intensively with respect to its intramolecular charge transfer processes, which are associated with the well known light-switch effect, this study focuses on intermolecular energy transfer processes taking place upon dense packing of the complexes into a phospholipid membrane composed of dipalmitoyl-t-a-phosphatidylglycerol, which can be thought of as a simplistic model of a cellular membrane. The data indicate additional quenching of excited [Ru(bpy)(2)dppz](2+) upon increasing the pump-pulse intensity. Hence, the observed photophysics, which is assigned to the presence of intermolecular exciton-exciton annihilation at high pump-intensities, might be related to the ultrafast photophysics of [Ru(bpy)(2)dppz](2+) when used as a chromophore to stain cells, an effect that may be taken into account during the employment of novel cellular markers based on Ru polypyridine complexes. (C) 2015 Elsevier B.V. All rights reserved.