The Orange Side of Disperse Red 1: Humidity‐Driven Color Switching in Supramolecular Azo‐Polymer Materials Based on Reversible Dye Aggregation

Abstract

Humidity detection, and the quest for low-cost facile humidity-sensitive indicator materials is of great interest for many fields, including semi-conductor processing, food transport and storage, and pharmaceuticals. Ideal humidity-detection materials for a these applications might be based on simple clear optical readout with no power supply, i.e.: a clear color change observed by the naked eye of any untrained observer, since it doesn't require any extra instrumentation or interpretation. Here, the introduction of a synthesis-free one-step procedure, based on physical mixing of easily available commercial materials, for producing a humidity memory material which can be easily painted onto a wide variety of surfaces and undergoes a remarkable color change (approximately 100 nm blue-shift of λ ) upon exposure to various thresholds of levels of ambient humidity is reported. This strong color change, easily visible to as a red-to-orange color switch, is locked in until inspection, but can then be restored reversibly if desired, after moderate heating. By taking advantage of spontaneously-forming reversible 'soft' supramolecular bonds between a red-colored azo dye and a host polymer matrix, a reversible dye 'migration' aggregation appearing orange, and dis-aggregation back to red can be achieved, to function as the sensor.

Controlled disassembly of azobenzene cellulose-based thin films using visible light

“…These changes on the molecular scale can result in large changes in the entire material, and azobenzene-containing materials have been developed for a wide variety of shape-changing applications such as drug delivery via photo driven assembly/disassembly, to fabricate surface relief holographic optical gratings, employed as sunlight-driven photo-actuators, for photoalignment, and as humidity driven sensor devices. 14,21,[27][28][29][30][31][32] Generally, these materials are fabricated out of synthetic polymers. However, in response to the negative impact of synthetic polymers on the environment, a shift towards biodegradable and bio-based polymers has received much recent attention.…”

Easily Prepared and Reusable Films for Fast-Response Rewritable Light Printing

“…Color-changing technologies responding to light, − temperature, − water, − and force − have provided new strategies to design paper with rewritable ability. ,− Photochromism, as a promising technology, could be used to design and fabricate rewritable paper. Now, many photochromic materials have been prepared by incorporating organic dyes (typically, spiropyran − or diarylethene − ) into conventional paper.…”

Layers and Multilayers of Self-Assembled Polymers: Tunable Engineered Extracellular Matrix Coatings for Neural Cell Growth

“…Chromophores, such as azobenzene, can be added to the LbL assembly process through chemical means or through soft bonds . The addition of photoswitches to biologically relevant polymers creates new biomaterials that exhibit optical properties while remaining biologically permissive.…”