Associate Professor Yang Zhiyong of the School of Chemistry and Associate Professor Huang Huahua of the School of Materials Science and Engineering at Sun Yat-sen University have jointly developed an ultra-long phosphorescent and ultrastable polymer-based room-temperature phosphorescent material with excellent adhesion, water resistance, and toughness. The relevant results were recently published in Science Advances.
Previously, Associate Professor Yang Zhiyong's research group carried out a series of studies on polymer-based organic room-temperature phosphorescent materials. In the latest research, they obtained TpB@PVB and TpBe@PVB films with phosphorescence lifetimes approaching 6s and afterglow durations exceeding half a minute by physically doping commercial triphenylamine derivatives (TpB and TpBe) into polyvinyl butyral resin (PVB), respectively. This is currently the system with the longest phosphorescence lifetime among the reported polymer-based luminescent materials. More importantly, this material's luminescence is extremely stable, resistant to water, impact, and collision. Studies have shown that the phosphorescence emission of this type of PVB material requires activation by ultraviolet light. After continuous UV irradiation of the film for 40s, the strongest phosphorescence performance can be achieved. This activation process is reversible; this reversibility can be applied to optical printing and erasure.
Yang Zhiyong, one of the corresponding authors of the paper, said that by testing singlet oxygen signals, comparing activation processes in atmospheres with different oxygen contents, infrared spectroscopy, and other experimental means, the researchers proved that the system involves oxygen consumption and photocrosslinking during the first photoactivation process, forming a more stable crosslinked network in the PVB matrix. In addition, the lone pairs of electrons in the B and O of the boric acid group can increase the rate of intersystem crossing (ISC) from the singlet state to the triplet state of excitons, thereby achieving longer-lived luminescence of triphenylamine molecules.
To clarify the influence of each component of PVB on the luminescence, the researchers prepared three films with different substrates using the same method, including TpB@PVBt, TpB@PVAc, and TpB@PVA. Studies have shown that the PVB substrate has a dual network structure of strong hydrogen bonds and hydrophobicity, which can effectively reduce the non-radiative transition of triplet excitons and isolate the quenching of triplet excitons by moisture and oxygen in the air, thus significantly stabilizing and prolonging the luminescence of triphenylamine derivatives.
The researchers have explored the comprehensive performance and potential applications of this type of polymer-based ultra-long luminescent material in depth. In order to better simulate actual application scenarios, natural water (rainwater, river water, lake water, seawater, etc.) was directly used for water resistance experiments. They found that after the film was immersed for more than 1 month, the phosphorescence spectrum of TpB did not change significantly and could still emit an afterglow of nearly half a minute. In view of the fact that this material combines the advantages of photoactivated organic room-temperature phosphorescence, adhesion, impact resistance, and water resistance, the researchers designed an advanced anti-counterfeiting label with its own glue—the first self-adhesive, real-time freshness certification, and reusable advanced label.
Huang Huahua, one of the corresponding authors of the paper, said that this work proposes a strategy to stabilize triplet excitons with a "rigid-flexible" double network structure of hydrogen bonds and hydrophobicity, and develops a polymer-based phosphorescent material with an ultra-long phosphorescence lifetime based on PVB as the substrate and triphenylamine derivatives (TpB and TpBe) as the light-emitting materials. Moreover, this material exhibits excellent luminescence stability, such as water resistance and impact resistance, and combined with the strong adhesion of the PVB substrate itself, the easy availability of raw materials, and simple preparation, this type of polymer-based phosphorescent material has very high application value in the fields of anti-counterfeiting encryption and luminescent devices.
Related paper information: https://doi.org/10.1126/sciadv.adk3354
