Regioregular Poly(p-phenylene iminoborane): A Strictly Alternating BN-Isostere of Poly(p-phenylene vinylene) with Stimuli-Responsive Behavior

Abstract

Incorporation of BN units into π-conjugated organic com­pounds, as substitutes for specific CC couples, often leads to new hybrid materials with modified physical and chemical properties. Poly(p-phenylene iminoborane)s are derived from well-known poly(p-phenylene vinylene) (PPV) by replacement of the vinylene groups by B=N linking units. Herein, an unprecedented poly(p-phenylene imino­borane) is presented that features a strictly alternating sequence of BN units along the main chain. The synthesis thereof was achieved by AB-type polymerization of a monomer featuring an N and a B ter­minus. Monodisperse oligomers with up to three BN units in the chain were additionally prepared and structurally characterized. Associated with the introduction of a dipole in the regioregular backbone struc­ture, they display notable fluorescence already in solution and large Stokes shifts, distinct from their previously reported BBNN-sequenced congeners. All compounds show aggregation-induced emission en­hancement (AIEE) properties. Computational studies provided evi­dence for emission from either locally excited (LE) or twisted intramo­lecular charge transfer (TICT) states. These processes can be option­ally addressed by various stimuli, giving rise to dual emission, solvato­chromic, thermochromic, and reversible mechanochromic behavior.