Supramolecular Oligourethane Gel with Multicolor Luminescence Controlled by Mechanically Sensitive Hydrogen-Bonding.

Nan Jiang,Dongxia Zhu,Martin R Bryce,Bing Li,Shi-Hao Ruan,Xing-Man Liu

doi:10.1021/acs.chemmater.0c01620

Abstract

We report a new type of mechanically sensitive multicolor luminescent oligourethane gel (OUA-gel). The conformation of the oligomeric chains can be controlled by changing the strength of hydrogen bonds. The optical properties of the oligomers are highly dependent on the conformations which vary in response to mechanical stresses and phase transitions. The design relies on the introduction of a single mechanical chromophore, aurintricarboxylic acid, with propeller-like, spatially crowded, and highly twisted conformations, and the presence of three carboxyl groups, which provide multidirectional hydrogen-bonding opportunities. Introducing dimethylsulfoxide (DMSO) as an additional H-bond acceptor molecule leads to a viscous OUA-gel which exhibits multiemission colors because of changes in the chain conformation within the matrix, which are induced by different strengths of H bonds. The conformation can be adjusted by mechanical force or temperature, both of which influence the H-bonding. The multifunctional and multicolored mechanochromism of the OUA-gel has great promise in sensing applications. The results represent a substantial step toward understanding the mechanism of polychromism in soft materials and the molecular design of advanced smart materials.

Highlights

We report a new type of mechanically sensitive multicolor luminescent oligourethane gel (OUA-gel)
Mechanochromic materials change color when mechanical pressure is applied. They have great potential as smart materials, for example, as sensors, memory devices, and displays.[1−5] A visual change in color can be induced by altering the chemical identity, intermolecular interactions, or orientation of chromophores under mechanical stress.[6,7]
The design of mechanical chromophores is challenging.[22−27] Most of the reported materials change between two colors in response to mechanical stimuli and only a few exhibit multicolor changes and they generally have complex structures.[28−31] the design

Summary

Introduction

We report a new type of mechanically sensitive multicolor luminescent oligourethane gel (OUA-gel). We explored the self-assembling gelation behavior arising from interactions among amide, carbonyl, and sulfone groups in oligourethane derivatives.[39] In the present work, we observed the formation of OUA-gel at the molecular level by atomic force microscopy (AFM) (Figure S3). The cross-linking network collapses under mechanical stimuli and the twisted molecular chains are forced into a more planar conformation, which increases the effective conjugation length (ECL) resulting in red-shifted emission.

Results

Conclusion