Modulation of π-Conjugation of Polymer Main Chain Containing π-Extended Benzoxaborin by Molecular Addition

We synthesize novel cyclic boronic acids incorporated into the main-chain π-conjugated system. The optical measurements under basic conditions reveal that the oligomer binds one-to-one to the sugar containing the cis-1,2-diol structure at the cyclic boronic acid moiety. In particular, the binding is accompanied by a bathochromic shift in absorption and emission spectra. The π-conjugated polymer maintained similar characteristics to the oligomer but showed emission in the longer wavelength region (λPL = 493–525 nm) where the color change was clearly detectable before and after the coordination of diols. Theoretical calculations with density functional theory reveal that the diol bonding to the cyclic boronic acid moiety elevates the energy levels of frontier molecular orbitals, especially the highest occupied molecular orbital. This study demonstrates that the introduction of cyclic boronic acid into π-conjugated polymers is effective for detecting diols with emission color change under mild conditions as well as for manipulating the electronic structures of polymer main chains.