Photodimerization Processes in Self-Assembled Chiral Oligo(p-phenylenevinylene) Bolaamphiphiles

An oligo(p-phenylene vinylene) (OPV) amphiphile has been synthesized with a positively charged head group on one end and a hydrophilic ethyleneglycol wedge on the other. In water, this bolaamphiphile forms vesicles consisting of a monolayer in which the OPV surfactants are organized in a helical head-to-tail fashion. Mass spectrometry analysis and reversed-phase high performance liquid chromatography (RP-HPLC) reveals that because of the presence of two double bonds in the OPV units, photo-induced [2+2] cycloaddition takes place resulting in polymerization of the surfactants. Performing RP-HPLC allowed the OPV dimer to be isolated in a sufficient amount to perform a variety of one- and two-dimensional NMR experiments. These experiments show a highly stereoselective photochemical cycloaddition process resulting in a regioselective head-to-tail dimerization with a stereoselective syn arrangement.