Chinese Scientists Have Made Significant Progress In the Field of Organic Long Afterglow

In 2019, Huang Wei, an academician of the Chinese Academy of Sciences and chief scientist of the Northwestern Polytechnical University's Flexible Electronics Research Institute and An Zhongfu of the Nanjing University of Technology's Advanced Materials Research Institute, led the team to make another major breakthrough in the field of organic long-lasting luminescence. A series of new polymer long afterglow materials were introduced. Related results published online in Nature-Communication on September 18 in this year.

 

Long afterglow luminescence refers to a luminescence phenomenon, in which the luminescent material can continue to emit light for several seconds to several hours after the excitation light source is removed. The long afterglow luminous material is commonly known as "the pearl of the night", and can emit a dazzling light even in the dark, and is regarded as a rare treasure by ancient emperors.

 

Long afterglow luminescent materials are widely used in night emergency indications, instrument displays, optoelectronic devices, and defense and military fields. Especially in recent years, with its long life, large Stokes shift, and abundant excited state properties, it has been used in some frontier scientific fields such as anti-counterfeiting, encryption, and biological imaging.

 

Compared with inorganic light storage materials, room temperature organic long afterglow materials have the advantages of better biocompatibility, electrical conductivity, low cost, and easy modification of the structure. In recent years, organic long afterglow materials have developed rapidly. However, such materials are mainly concentrated in small crystal molecules and host-guest doping systems. Due to the crystallinity of crystal small molecule systems and phase separation of host-guest doping systems, the actual material application is restricted. Polymer materials have many advantages such as flexibility, light weight, spin coating, stretchability, etc., and show great application potential in the field of flexible electronics.

 

However, how to achieve long afterglow emission of polymer materials is one of the challenges in this field. In response to this problem, the technical innovation team led by Huang Wei and An Zhongfu proposed that by locking the light-emitting unit through ionic bonds, the long-lasting luminescence of ionic polymers was achieved with the synergistic effect of polymer covalent bonds, and the emission life was  up to 2.1 s. Experimental data and theoretical calculations indicate that the reason for the long-lasting afterglow of such polymer materials is that ionic bonds inhibit the non-radiative transitions of the light-emitting unit. This design concept applies not only to aromatic polymer material systems, but also to non-aromatic polymer material systems.

 

In addition, for the first time, they have reported the long-lasting emission of polymers that depend on the excitation wavelength, enabling the afterglow color to be adjustable from blue to orange. And, such materials can still maintain long visible afterglow at temperatures up to 170 degrees Celsius.

 

This research result gives traditional polymer materials new properties, coupled with a wide range of materials and low cost, and has great application prospects in flexible display, lighting, data encryption, and biomedical fields.

 

As an international pioneer of organic long-glow afterglow, Huang Wei's team has been committed to the development of new organic long-glow afterglow materials, research on new mechanisms, and exploration of new applications. After achieving long-lasting luminescence in a single-component organic semiconductor, and the first realization of colorful long-afterglow emission under a single organic crystal material, this research achievement once again achieved a major breakthrough in the field of long-afterglow emission.