Multifunctional Pt(II)-Based Metallo-Supramolecular Polymer with Carboxylic Acid Groups: Electrochemical, Mechanochemical, Humidity, and pH Response
Chanchal Chakraborty, Utpal Rana, Satoshi Moriyama, Masayoshi Higuchi
Abstract
We report multifunctional Pt(II)-based metallo-supramolecular polymer with carboxylic acid groups (polyPtC). The polymer showed multi-stimuli-responsive emission to electrochemical redox, mechanical force, humidity, and pH. It also exhibited humidity-responsive ionic conductivity. Furthermore, it displayed electrofluorochromism. The emission switching between the two transition states (3MLCT/3LLCT and 3MMLCT) was based on the reversible changes of the interchain Pt–Pt interaction in polyPtC, which was caused by the secondary interaction or the crystalline–amorphous transition. The ionic conductivity of polyPtC was responsible for the humidity and the real-time humidity sensor with the polymer film was demonstrated on interdigitated Pt-electrodes. A solid-state electrochromic device with the polymer film was successfully fabricated to show reversible yellow-to-black electrochromism. In addition, it was revealed by the electrofluorochromic study that the pristine 3MLCT/3LLCT emission was quenched in the electrochemically reduced state (the black state), because the radical anion species of the ligand (tpy·–) generated at the negative potential caused the repulsion among the polymer chains, expanded the Pt–Pt distance, and prevented the emission.