Photoinduced flip-flop of amphiphilic molecules in lipid bilayer membranes.

We demonstrate localized photoinduced flip-flop of stilbazolium markers in model lipid bilayer membranes. The flip-flop mechanism and dynamics are determined by combined two-photon excited fluorescence and second-harmonic generation microscopy. Upon illumination of labeled membranes with a femtosecond laser beam, two-photon absorption induced photoisomerization provokes a significant increase in the cis- marker population whose flip-flop rate was determined to be at least a thousand times faster than that for transmarkers, allowing the possibility of fast targeted control of the local interleaflet distribution of markers in biological membranes.