Bioinspired non-aromatic compounds emitters displaying aggregation independent emission and recoverable photo-bleaching

Aggregation dependence is a universal feature for fluorophores, ranging from classical planar fluorescent dyes displaying aggregation-caused quenching (ACQ) and propeller-shaped AlEgens that exhibit aggregation-induced emission (ME). In this work, we report compounds emitters (CA-PDA) that display aggregation-independent fluorescence owing to the formation of robust intramolecular, rather than intermolecular hydrogen bonding. We achieved CA-PDA by synthesis of an amide from citric acid (CA) and propane diamine (PDA). Quantum chemistry calculations suggest the CA-PDA compounds have closed structures facilitated by intramolecular hydrogen bonds, which forces the lone pair electrons on oxygen and nitrogen to within 2.9 angstrom. Then the strong electron clustering generates a pseudo conjugated effect and leads to blue emission. This emission exhibits recoverable photobleaching, as UV irradiation only temporally breaks the intramolecular hydrogen bonds, which may form again upon relaxation. CA-PDA can be used in cell imaging as well as in probes for Hg2+ and sulfur-containing amino acids. We expect that the strategy of a bioinspired intramolecular hydrogen bonds facilitated compounds emitters will provide a new avenue toward advanced fluorescent materials.