# Stimuli‐Responsive Supramolecular Polymers of Mono‐ and Bis‐triazolylphenylazoaniline‐Functionalized Copillar[5]Arenes: With Distinctive Binding Modes

## TL;DR

Researchers created responsive supramolecular polymers that change structure based on pH and light, showing different behaviors depending on their chemical design.

## Contribution

The study introduces pH- and photo-responsive supramolecular polymers with distinct binding modes based on functionalized copillar[5]arenes.

## Key findings

- Protonation of copillar[5]arene 1 significantly enhances its supramolecular polymerization compared to its neutral form.
- Copillar[5]arene 2 forms a 1:1 complex with DMP5 through cavity binding, linking two aniline groups from separate molecules.
- Polymerization and morphology are tunable by pH and light, as confirmed by NMR, UV–vis, and FE-SEM analyses.

## Abstract

Mono‐ and bis‐triazolylphenylazoaniline‐functionalized copillar[5]arenes 1 and 2 were synthesized forming linear supramolecular polymers with dual pH and photo responsiveness. Upon acidification, copillar[5]arene 1 undergoes protonation, converting its aniline group into a primary ammonium ion (1‐H), which significantly enhances its supramolecular polymerization compared to 1. Designed as an AB‐type supramolecular polymer, 1‐H exhibits distinct polymerization behavior in contrast to neutral copillar[5]arene 2, which forms a 1:1 supramolecular polymer with dimethoxypillar[5]arene (DMP5). Copillar[5]arene 2 is believed to bind DMP5 through its cavity, linking two aniline groups from separate molecules to form a two component supramolecular polymer. The degree of polymerization of 1‐H and the 1:1 ratio of 2 and DMP5 can be controlled by adjusting the pH, as confirmed by pH‐ and concentration‐dependent 1H‐NMR and diffusion‐ordered spectroscopy (DOSY) experiments. UV–vis spectroscopy and FE‐SEM were further used to examine the effects of photoirradiation on polymer morphology and absorption at varying concentrations.

Mono‐ and bis‐functionalized copillar[5]arenes 1 and 2 form pH‐ and photo‐responsive supramolecular polymers. Protonation of 1 enhances polymerization (1‐H), differing from neutral 2, which forms a 1:1 complex with DMP5 via cavity binding. Polymerization and morphology are tunable by pH and light, as shown by NMR, UV–vis, and FE‐SEM analyses.