Luminescent materials that change their light-emitting properties in response to external stimuli could provide interesting new approaches for novel storage materials, sensors, security materials, and information displays.
Typically, such materials can either be switched from “on” to “off” or between two different colors. It has not previously been possible to switch between three different stable colors with materials containing only a single luminescent substance. In the journal Angewandte Chemie, Takashi Kato and Yoshimitsu Sagara from the University of Tokyo (Japan) have now introduced a liquid-crystalline material that can be switched back and forth between three different colors by means of thermal and mechanical stimuli.
The new material consists of two dumbbell-shaped organic compounds—one small and one large, both consisting of a branched arrangement of aromatic six-membered rings. The large molecule contains an anthracene component as the luminescent group (luminophore). This mixture of molecules aggregates to form liquid crystals. Molecules in a liquid-crystalline state are partially ordered like in a crystal, but are mobile like in a liquid. Liquid crystals are most commonly found in liquid-crystal displays.
The Japanese researchers prepared thin films of their special liquid crystals. Under UV light, these films glow red-orange. Mechanical shearing, such as rubbing, at 90 °C changes the arrangement of the liquid crystals—the rubbed areas now appear green. This new, green phase is stable between room temperature and 146 °C. This amazing film can do more: both the red-orange and green phases can be changed to a yellow one by rubbing at room temperature. Heating to 145 °C and subsequent cooling to room temperature changes the green and yellow back to red-orange.
If this luminescent mixture can be incorporated into materials such as structural polymers, the thermal and stress histories for the materials are easily detected by bright luminescence color changes. Knowledge of these histories is useful for the maintenance of the materials systems, which include coatings and plastics. In addition, artists may be interested in these materials because of the beauty of the luminescence colors and the ease of writing/erasing and stability of the generated images.Author: Takashi Kato, University of Tokyo (Japan), http://kato.t.u-tokyo.ac.jp/index-e.html
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201100914
Seeing on the Quick: New Insights into Active Vision in the Brain
15.08.2018 | Eberhard Karls Universität Tübingen
New Approach to Treating Chronic Itch
15.08.2018 | Universität Zürich
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur
What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...
08.08.2018 | Event News
27.07.2018 | Event News
25.07.2018 | Event News
15.08.2018 | Physics and Astronomy
15.08.2018 | Earth Sciences
15.08.2018 | Physics and Astronomy