Curcumin-based aggregation-induced-emission fluorogens as a bioprobe

This project is dedicated to synthesize and characterize new curcuminoids luminogens, aggregation-induced-emission (AIE) active molecules with bright red/near-infrared (NIR) emission. Certain studies have demonstrated that curcumin could decrease A? deposits in animal models, but its use as a bioprobe is limited because of its low water solubility, short emission wavelength, brain barrier impermeability, and rapid metabolism. On the other hand, synthetically modified analogues, curcuminoids, have shown improved properties for efficient sensing of A? species in vivo. To overcome the disadvantages possessing curcumin molecule four main strategies will be employed to develop a system that matches the requirements for in vivo bioimaging or sensing: (a) Synthesize all isomers of di- and tri-methoxy substituted curcuminoids and study the influence of their mutual orientations on the photophysical and photochromic properties. (b) Increase the hydrogen bonding interactions by attaching a hydroxy group (OH) or a sulfonic group (SO3H) to the phenyl ring, which is supposed to address the issue of low water solubility. (c) Incorporate a strong electron-accepting BF2 group into the ?-diketone moiety of curcumin in order to significantly shift the emission to the red and produce a large Stokes shift. Such donor-acceptor-donor (D-A-D) type of molecules was developed in 2015 and is the most promising AIEgen in terms of NIR emission. (d) Attach the rotor tetraphenylethene (TPE) to the phenyl ring to suppress any non-radiative decay pathways occurring due to free rotation, thus enhancing its AIE activity. The work described here should deepen our understanding of the AIE process and enable the luminescent behavior to become more predictable and controllable. Although attaching AIE-enabling units to aggregation-caused quenching dyes has successfully transformed many of them into AIE ones, there still some unsuccessful examples that indicate other factors co-exist to non-radiatively consume the energy in aggregates, which competes with the AIE process. These factors will be explored in this proposal.