Here we describe a new BODIPY-based membrane probe (1) that provides an alternative to dialkylcarbocyanine dyes, such as DiI-C18, that can be excited in the blue spectral region. Compound 1 has unbranched octadecyl chains at the 3,5-positions and a meso-amino function. In organic solvents, the absorption and emission maxima of 1 are determined mainly by solvent acidity and dipolarity. The fluorescence quantum yield is high and reaches 0.93 in 2-propanol. The fluorescence decays are well fitted with a single-exponential in pure solvents and in small and giant unilamellar vesicles (GUV) with a lifetime of ca. 4 ns. Probe 1 partitions in the same lipid phase as DiI-C18(5) for lipid mixtures containing sphingomyelin and for binary mixtures of dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC). The lipid phase has no effect on the fluorescence lifetime but influences the fluorescence anisotropy. The translational diffusion coefficients of 1 in GUVs and OLN-93 cells are of the same order as those reported for DiI-C18. The directions of the absorption and emission transition dipole moments of 1 are calculated to be parallel. This is reflected in the high steady-state fluorescence anisotropy of 1 in high ordered lipid phases. Molecular dynamic simulations of 1 in a model of the DOPC bilayer indicate that the average angle of the transition moments with respect to membrane normal is ca. 70°, which is comparable with the value reported for DiI-C18.

Biomedical Research Institute Hasselt University Agoralaan Building C 3590 Diepenbeek Belgium

Department of Chemistry Katholieke Universiteit Leuven Celestijnenlaan 200f bus 02404 3001 Leuven Belgium

Department of Life and Environmental Physics Horia Hulubei National Institute for Physics and Nuclear Engineering Reactorului 30 Măgurele 077125 Romania

Division of Theoretical Chemistry and Biology KTH Royal Institute of Technology School of Biotechnology Roslagstullsbacken 15 S 106 91 Stockholm Sweden

INSERM UMR S850 Faculté de Pharmacie Université de Limoges 2 rue du Docteur Marcland 87025 Limoges Cedex France

LCSN EA1069 Faculté de Pharmacie Université de Limoges 2 rue du Dr Marcland 87025 Limoges Cedex France

Regional Centre of Advanced Technologies and Materials Department of Physical Chemistry Faculty of Science Palacký University tř 17 listopadu 12 771 46 Olomouc Czech Republic

Service de Chimie des Matériaux Nouveaux Université de Mons Place du Parc 20 B 7000 Mons Belgium

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