Properties of a Stilbene-Containing Gemini Photosurfactant:  Light-Triggered Changes in Surface Tension and Aggregation

Abstract

A new photosurfactant has been synthesized, and its photoreactions in water, interfacial properties, and changes in aggregation have been characterized. The compound is a stilbene-containing gemini photosurfactant (SGP), which is of interest because the headgroup spacer is a stilbene chromophore, and it may be prepared initially in the trans (E-SGP) form. Molecular simulations show that UV-induced reactions cause significant changes in molecular conformation and especially the relative orientation of hydrophobic chains. 1H nuclear magnetic resonance, UV−vis absorption, and liquid chromatography−mass spectroscopy results are consistent with photodimerization in aqueous solutions. Irradiation causes significant changes in surface tension (maximum Δγ = −12 mN m-1) and wettability (Δθ = −15° on hydrophobic glass). Furthermore, small-angle neutron scattering shows the initial E-SGP form is present as large vesicle-like aggregates whereas the UV-induced dimer gives small 20 Å spherical charged micelles. These results demonstrate the importance of molecular design for generating effective and efficient photosurfactants.