Photocontrolled template-directed synthesis of complementary double helices assisted by amidinium–carboxylate salt bridge formation

The template-directed imine-bond forming reactions between chiral amidines or achiral carboxylic acids monomers bearing a formyl or an amino group at one end were remarkably accelerated 34- or 10-fold in chloroform in the presence of the corresponding optically inactive carboxylic acid dimer or optically active amidine dimer linked by a trans-azobenzene unit as the template, respectively. The cis-azobenzene-linked carboxylic acid template markedly slowed the monomer conversions, and hence a reversible photocontrolled dimerization was achieved by light-induced cis–trans isomerization upon alternative irradiation with UV and visible light.