Chameleonic, Light Harvesting Photonic Gels Based on Orthogonal Molecular Fibrillization

The preparation of smart photonic gels composed of two orthogonally self-assembled fibrillar networks is reported. The molecular gelators are a light acceptor derived from 4-amino-1,8-naphthalimide and an acridine-based energy donor. Fibrillar orthogonal assembly of both chromophores is a requisite for light harvesting to be observed which results in emission from the naphthalimide-based acceptor upon irradiation of the acridine-derived donor with a significant Stokes shift of ca. 200 nm. Energy transfer is present both in the form of molecular gels in acetonitrile and in the solid-like xerogels and efficiently visualized both by fluorescence spectroscopy and confocal laser scanning microscopy. The chameleonic, stimuli responsive behavior is linked to the fact that the gel network formed by the acridine derivative can be selectively disassembled by means of temperature changes or chemical species. For example, the light harvesting process can be switched off/on by addition of HCl or NaOH respectively, affording a new type of stimuli responsive photonic soft materials.