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Synthesis
1. Triple bonds
Hay-Glaser coupling [20] and Sonogashira coupling [21] reactions are useful tools for direct
introduction of triple bonds to the polymer backbones. Hay-Glaser reaction, one of the earliest
oxidative homo-coupling reaction, is widely used for the construction of polydiynes (PDYs) [22].
The problem of stoichiometric imbalance is avoided since sole component is involved. As a result,
PDYs with high polymerization degree can be easily obtained. Conjugated polyelectrolytes
(CPEs) are well-known for their distinguished functions as fluorescent transducers or biosensors
[23]. The ionic pendants impart good solubility to the CPEs in aqueous media despite their
conjugated skeleton. Moreover, the hydrophilic ionic moieties and the hydrophobic backbones
endow CPEs with amphiphilic characteristics. As illustrated in Scheme 2, the tetraphenylethene
(TPE)-containing diyne monomers 1 and 2 can undergo homo-coupling at 50oC in the presence of
CuCl and TMEDA in dichlorobenzene, generating water-soluble CPEs 5 and 6 after subsequent
quaternization [24]. Thanks to the typical AIE-active TPE units, the polymers exhibit strong solidstate
emission and are responsive to biomolecules such as heparin, bovine serum albumin, human
serum albumin, calf thymus DNA and RNA. Additionally, 6 also functions as a fluorescent
visualizer for in vivo cell imaging with high contrast and good biocompatibility. The conjugated
backbones of CPEs provide plentiful binding sites for biomolecules via hydrophobic interaction,
which greatly improves the sensitivity of fluorescent probe to the targeted molecules.