A Facile Supramolecular Approach towards Strategic Fluorescence Switching and Recognition-Controlled Photoreduction

A supramolecular system design strategy to control photoreduction is reported. 1,4,5,8-naphthalenediimide (NDI) was used as the core unit to synthesize two different sets of ionic aromatic amphiphiles (AA), one incorporating the NDI with an aliphatic chain (denoted NDI) and the other with a phenoxy-based chain (denoted NDI-Phe). These systems form self-assembled structures which are different to those in their monomeric states and which can selectively be photoreduced to generate the radical anion (NDI-Phe^.−) and dianion (NDI²⁻) in the presence of dicarboxylic acids as the counter anion (CA). Interestingly, fluorescence (FL) switching was detected in the different redox states. The reduction mechanisms and the kinetics were found to be different for these two sets of AAs and the reduction kinetics were further controlled by the structurally different CAs. This unexpected observation reveals molecular recognition in the controlled-assembly systems. The changes in spectroscopic output upon an electronic input have been described as a simple “off/on” FL switch. The appealing “bottom-up” approach toward molecular device fabrication is possible only in molecular assembly systems such as these.