A Highly Effective Biomimetic Method for Simultaneously Enhancing the Stability and Functionality of Merocyanine Photoacids

Merocyanine photoacids (MCHs) have found applications in chemical, material, energy, and biomedical areas, and are currently being investigated for industrial applications. Hydrolysis, relatively high dark acidity, and moderate solubility in water are the major concerns for their practical applications. Inspired by the structure of the cell membrane, we incorporated the most commonly used MCH into sodium dodecyl sulfate (SDS) micelles. NMR and UV-vis absorption studies indicated that the MCH was located near the surface of the micelle with the positively charged indolinium moiety in the micelle and the neutral phenol moiety exposed to water. The location allows the MCH to be protected by SDS while still being able to release protons to the aqueous solution. In the presence of 15 mM of SDS, the half-life of the MCH in aqueous solutions increased over a hundred times to nearly half a year. In addition, the solubility increased by several orders of magnitude and the dark acidity decreased, which significantly enhances its capability of photo pH-modulation. Structure modification with a dodecoxyl group, together with the addition of SDS, essentially stopped the hydrolysis.