Side-Chain Engineering of Boron β-Dialdiminate Homopolymer for Solvent-Dependent Emission Properties.

Abstract

Luminescent materials that respond to changes in microscopic chemical conditions are essential for visualizing and evaluating molecular environments. Boron complexes are often employed as robust scaffolds for constructing such responsive systems because of their inherent stimuli-responsive properties. However, in the case of nonresponsive luminophores, the absence of these intrinsic features limits their range of applications. In this study, environment-responsive luminescent homopolymers based on the boron β-dialdiminate complex are developed, which is intrinsically less responsive, by introducing optimized side chains. As a key finding, the triethylene glycol-decorated polymer exhibits more intense luminescence in chloroform but weaker luminescence in N,N-dimethylformamide. Structural analyses using NMR and size-exclusion chromatography suggest that this polymer forms larger aggregates in polar solvents because of the solvophobicity of its main chain, while the polar side chains assist in maintaining adequate dispersibility of these aggregates. Photophysical measurements indicate that interchromophore interactions within the aggregates should be responsible for the reduced luminescence in polar solvents. These findings suggest that side-chain engineering should be an effective strategy for creating stimuli-responsive polymers from otherwise nonresponsive luminophores.