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.