Recently, researchers from the Institute of flexible electronics of Northwestern Polytechnic University (Center for advanced science of flexible electronics) and the Institute of information materials and nanotechnology of Nanjing University of Posts and telecommunications have made new progress in realizing the response behavior of photochromic materials. The research results are "on-demand printing by adjusting photochromic response behavior on demand through different countervailing ions" Regulation of photochromic behavior through various countermeasures for high-level security printing, published online in the top international journal science advances.
In recent years, a lot of research interests have been attracted by smart responsive optoelectronic materials, which have significant changes in optoelectronic properties under external stimulation. Researchers at home and abroad have developed a series of photochromic, photochromic, thermochromic and electrochromic functional materials. At present, they have been successfully used in various optical and optoelectronic fields, such as information display, security, anti-counterfeiting, information sensing, biological imaging and so on. Among them, the unique response properties of these materials open up a new way for the development of new optical information storage and encryption and optical anti-counterfeiting technology. Now, researchers have made a series of important work in the development of new intelligent response materials for optical information storage and security protection.
Photochromic molecules have become important materials for advanced photon applications, including fluorescence imaging, intelligent lens, optical data storage and anti-counterfeiting. The research focus in this field is to develop new photochromic molecules and effectively regulate the photochromic behavior of these materials to meet the requirements of different photoelectric applications. At present, the conventional strategy to control the response behavior of photochromic materials is to introduce electron donor or acceptor substituents into the molecules. However, the photochromic materials usually have a constant color rendering performance and rate under the same light conditions. In addition, the regulation of photochromic behavior often needs complex chemical synthesis and complicated purification process, which makes the regulation of photochromic behavior inconvenient and inefficient. Therefore, it is of great scientific significance to realize the simple, fast and efficient regulation of photochromic response.
To solve this problem, the researchers proposed a new strategy to control photochromic response by using counterions. The dye containing spirolactam showed photoinduced ring opening reaction, which resulted in significant changes in absorption or photoluminescence properties. Because the stability of the open-loop isomers in these molecules is very low, the negatively charged nitrogen atom will destroy the stability of the open-loop form. Based on this, the team coordinated the zinc ion with the crystal violet lactone derivative, reduced the negative charge density of the nitrogen atom through induction effect, stabilized the open-loop isomer, and changed the counterbalance ion that has a direct impact on the central charge density of zinc (II) ion The photochromic response rate was successfully controlled. Therefore, using zinc (II) salt water solution as ink, the encrypted information can be printed on the safety paper coated with crystal violet lactone to record the hidden information. When ultraviolet light is used continuously, the recorded information can be clearly displayed.
The photochromic materials with different discoloration rate will be obtained after coordination of crystal violet lactone and different zinc salts. Different zinc (II) salt solution can be used as ink to achieve a higher level of safety printing. Different illumination time will show different information. Only knowing the accurate illumination time can get the correct information. This work provides a unique solution for realizing the response behavior of smart response optoelectronic materials and effectively regulating this cutting-edge scientific problem. It is expected to make some contribution to the development of new smart materials and promote their practical application in the field of information protection and optical anti-counterfeiting. (source: Northwest Polytechnic University)