One-pot three-component tandem polymerization toward functional poly(arylene thiophenylene) with aggregation-enhanced emission characteristics

The development of efficient multicomponent tandem polymerization is attractive but challenging, owing to the limitations such as the required strict stoichiometric balance, the poor solubility and low molecular weight of the polymer products, etc. In this work, an efficient one-pot three-component polymerization of alkyne, carbonyl chloride and ethyl 2-mercaptoacetate was reported. The polymerization of aromatic diyne (1), diaroyl chloride (2), and ethyl 2-mercaptoacetate (3) catalyzed by Pd(PPh₃)₂Cl ₂/CuI proceeded smoothly under mild conditions at room temperature without strict stoichiometric balance of the monomers, affording poly(arylene thiophenylene) (P1) with high molecular weights (M_w up to 156 000) in excellent yields (up to 97%). Single crystal structure of model compound 4 was obtained, aiding in verification of the complete transformation to the desired polymer product. The thiophene-containing conjugated polymer possesses good solubility in common organic solvents, good film-forming ability and high thermal stability. Meanwhile, the polymer shows typical aggregation-enhanced emission behavior: its solution is weakly emissive, but turns to be highly emissive when nanoaggregates or thin films are formed. Furthermore, thin film of P1 shows high refractive indices (n = 1.9461-1.6668) in a wide wavelength region of 400-1000 nm, which can be further modulated by UV irradiation. Well-resolved fluorescent photopattern can be generated by exposure of the thin film of P1 under UV irradiation through a copper photomask. The polymer also serves as an efficient fluorescent chemosensor for Ru³⁺ with high sensitivity and selectivity, and the quenching constants for the sensing are up to 8.8 × 10⁵ L mol^-1. This work provides a new polymerization concept and an efficient approach toward functional conjugated polymer materials, overcoming the limitations of multicomponent polymerization.