Frustrated element-blocks: A new platform for constructing unique stimuli-responsive luminescent materials

Abstract

Element-blocks, the minimum heteroatom-containing functional units, are versatile building blocks for constructing functional polymers. In this focus review, we explain the new concept of developing stimuli-responsive luminochromic materials based on frustrated element-blocks. Herein, we termed “frustrated” element-blocks as those that show a relatively larger degree of structural relaxation in the excited state but are structurally restricted. As a result, frustrated element-blocks can have unique stimuli-responsive luminochromic behaviors. As a representative example, the stimuli-responsive properties of frustrated boron clusters are initially illustrated, and a series of their luminochromic properties, such as mechano- and thermochromism, are described. Next, we designed fused complexes for suppressing intramolecular motion to obtain frustrated boron complexes that display constant emission in both the solution phase and solid-state to produce mechanochromic luminescent materials. Finally, generating the frustrated state by polymerization is explained. These polymers display unique luminochromic behaviors, such as thermochromism in solution, mechanochromism in the solid-state and vapochromism. Finally, the stimuli-responsive luminochromic behaviors of frustrated element-block-containing polymers and their mechanisms are illustrated, mainly by examples from our recent works.