Photochromism of 1,2-bis(2-methyl-5-phenylthien-3-yl)perfluorocyclopentene in liposomes

A photochromic dithienylethene, 1,2-bis(2-methyl-5-phenylthien-3-yl)perfluorocyclopentene (1), was synthesized and incorporated into the lipid bilayer of liposomes as a strategy for demonstrating the potential for complete photocontrol over the permeability of a lipid membrane. Absorption spectroscopy and differential scanning calorimetry (DSC) were used to characterize the photochromism and inclusion of 1 in dipalmitoylphosphatidylcholine (DPPC) large unilamellar liposomes (LUVs), respectively. Absorption studies confirm that the photoisomerization of 1 in DPPC LUVs is completely reversible, although hindered due to the more restrictive and rigid environment posed by the lipid bilayer. DSC studies strongly suggest that 1 is partially buried in the hydrocarbon core of the bilayer, interacting primarily with the C2–C8 methylene region of the acyl chains of DPPC. Photoinduced changes in the membrane permeability of DPPC LUVs were assessed by monitoring changes in the fluorescence of an encapsulated fluorophore, 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS), upon photocycling 1 between the two photoisomers using ultraviolet and visible light. The fluorescence studies show that release of encapsulated HPTS is not observed following the irradiations. Thus, the photoisomerization of 1 does not lead to a large disruption in the local lipid order within the bilayer.