Thioflavin-T derivatives with controlled AIE and ACQ properties as potential one-photon and two-photon amyloid...

Aggregates of organic dyes are not only interesting from a fundamental science perspective but also have significant implications in application as Aggregation Induced Emission (AIE) and Aggregation Caused Quenching (ACQ) dyes. Here, we present BF₂-functionalized benzothiazoles, sharing the same core, but various electron-donating, amino groups substituted at the amino nitrogen by alkyl or aromatic groups and 1,4-phenylene acting as a conjugated bridge between donor and acceptor. Difference between alkyl/aromatic donors results in the opposite ACQ/AIE mechanisms, i.e., in the water environment dyes with alkyl-donors exhibit ACQ, whereas those with aryl-donors demonstrate AIE. Here, we evaluate how AIE or ACQ affects the performance of dyes as amyloid probes, in relation to the form of the dyes (monomers or aggregates) which are bound to amyloids. For this propose we measured one-photon properties like absorption, fluorescence, fluorescence quantum yield, fluorescence lifetime, and binding constants. Additionally, we evaluated two-photon properties and presented that 2PA can be used to distinguish between the form of a dye (monomer vs aggregate) upon binding to amyloids. Since our dyes differ only in one functional group (aryl/alkyl amine), evaluation of their structure-properties relationship as fluorescent probe is highly beneficial for better understanding of ACQ/AIE luminogens interaction with amyloids.