Researchers design tunable, self-recovering dyes for use in next-generation smart devices

October 24, 2019

The building blocks of rationally designed chemicals are simple elements: carbon, hydrogen, oxygen and so on. These elements can be combined in myriad ways to accomplish a variety of chemicals with different characteristics. Even the same chemical can be treated differently - with pressure or heat, for example - to show drastically different properties. A simpler version is to think of how water can be boiled to cook pasta or frozen to become ice - the same ingredient can be made into two different states via temperature treatment.

Now, researchers are working to better control how the chemicals respond to treatment, as well as how to reverse the chemicals back to their original state with little to no interference. Such control would allow scientists to prepare the sensing systems of environmental stimuli, as well as continuously repeat the sensing.

A team of researchers at Yokohama National University has achieved such results with a specific compound that can emit light and has potential applications in the next generation of smart devices such as wearable devices and anti-counterfeiting paintings. They published their results online on September 12, ahead of print in Chemical Communications.

The compound is a derivative of thiophene, which is a dye with mechanochromic luminescence properties -- it changes color under physical change. It starts emitting a violet glow under the irradiation of UV light, but as it is exposed to mechanical stimuli, such as grinding, the violet glow shifts slightly to blue. Another external intervention can make the compound heal and become violet again.

"Mechanochromically luminescent (MCL) dyes have recently attracted considerable interest on account of their potential applications," said Suguru Ito, paper author and associate professor in the Department of Chemistry and Life Science in the Graduate School of Engineering Science at Yokohama National University. "However, it is still very difficult to rationally design MCL dyes with desired characteristics."

In this study, however, researchers discovered that by adding another chemical called DMQA, the dye changed to orange under mechanical stimuli. The dye did not need more external stimuli to revert back to violet either.

"We combined two kinds of rational design guidelines for tuning the luminescent properties, resulting in the desired -- and unprecedented-- characteristics of high-contrast, self-recovering dyes," Ito said.

The first rational design guideline is that the recovery behavior of the dye can be attributed to the length of the alkyl group in the compound -- a longer chain of carbon atoms with hydrogens in the dye allows the dye to recrystallize and heal in time. The second is that by mixing with DMQA, the color range between the original state and ground state differ greatly.

"The next step is to establish a rational design guideline to control the dye's responsiveness to mechanical stimuli," Ito said. "My ultimate goal is to develop an innovative pressure-sensing system by rationally creating a material that can change its emission color in stages in response to mechanical stimuli of different intensity."

With such control, Ito could use mechanical stimuli to precisely induce a specific and intended response. A little pressure could shift the violet glow to blue, a little more pressure pushes the glow closer to red. A system with such ability would allow for stepwise changes and recoveries by the stimulus, which could be highly beneficial in the next generation of smart materials, according to Ito.
-end-
Minako Ikeya and Genki Katada, both of the Department of Chemistry and Life Science in the Graduate School of Engineering Science at Yokohama National University, also authored the paper.

This work was supported in part by the Japan Society for the Promotion of Science KAKENHI Grant Number 18H04508 in Grant-in-Aid for Scientific Research on Innovative Areas "Soft Crystals: Area No. 2903".

Yokohama National University (YNU or Yokokoku) is a Japanese national university founded in 1949. YNU provides students with a practical education utilizing the wide expertise of its faculty and facilitates engagement with the global community. YNU's strength in the academic research of practical application sciences leads to high-impact publications and contributes to international scientific research and the global society. For more information, please see: https://www.ynu.ac.jp/english/

Yokohama National University

Related Color Articles from Brightsurf:

Envision color: Activity patterns in the brain are specific to the color you see
Researchers at the National Eye Institute (NEI) have decoded brain maps of human color perception.

OPD optical sensors that reproduce any color
POSTECH Professor Dae Sung Chung's team uses chemical doping to freely control the colors of organic photodiodes.

What laser color do you like?
Researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland have developed a microchip technology that can convert invisible near-infrared laser light into any one of a panoply of visible laser colors, including red, orange, yellow and green.

Increasing graduation rates of students of color with more faculty of color
A new analysis published in Public Administration found that student graduation rates improve as more faculty employed by a college or university share sex and race/ethnic identities with students.

How much color do we really see?
Color awareness has long been a puzzle for researchers in neuroscience and psychology, who debate over how much color observers really perceive.

Stretchable variable color sheet that changes color with expansion and contraction
Toyohashi University of Technology research team have succeeded in developing a variable color sheet with a film thickness of 400 nanometers that changes color when stretched and shrunk.

High color purity 3D printing
ICFO researchers report on a new method to obtain high color purity 3D objects with the use of a new class of nanoparticles.

Building a better color vision test for animals
University of Cincinnati biologists modified simple electronics to create a color vision test for fiddler crabs and other animals.

The color of your clothing can impact wildlife
Your choice of clothing could affect the behavioral habits of wildlife around you, according to a study conducted by a team of researchers, including faculty at Binghamton University, State University of New York.

Recovering color images from scattered light
Engineers at Duke University have developed a method for extracting a color image from a single exposure of light scattered through a mostly opaque material.

Read More: Color News and Color Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.