Journal of the American Chemical Society, Vol.142, No.23, 10308-10313, 2020
Molecular-Pump-Enabled Synthesis of a Daisy Chain Polymer
The assembly of a kinetically trapped daisy chain polymer under redox control has been achieved with a self-complementary monomer using an energy ratchet mechanism. The monomer is composed of a molecular pump at one end and a cyclobis(paraquat-p-phenylene) (CBPQ(4+)) ring at the other end. The pump and ring are linked together by a long collecting chain. When the monomer is reduced to its radical state, it self-assembles into a supramolecular daisy chain polymer on account of radical-pairing interactions. When all of the bipyridinium radical cations are quickly oxidized to dications, the CBPQT(4+) rings are forced to thread onto the collecting chains, forming an out-of-equilibrium, kinetically trapped daisy chain polymer. This polymer can be switched reversibly back to the supramolecular polymer by reduction, followed by depolymerization to afford the monomer as a result of slow oxidation. This proof-of-concept investigation opens up opportunities for synthesizing mechanically interlocked polymers using molecular machines.