Professor Zhiyong Yang's research group, from the School of Chemistry, Sun Yat-sen University, collaborated with the research team of Professor Huahua Huang, from the School of Materials Science and Engineering, Sun Yat-sen University, and has developed an ultralong afterglow and super stable polymer-based room-temperature phosphorescent material with excellent adhesion, water resistance, and toughness. The relevant findings were recently published in Science Advances.
Previously, Professor Yang's research group has carried out a series of studies on polymer-based organic room-temperature phosphorescent materials. In their latest study, by physically doping commercial triphenylamine derivatives (TpB and TpBe) into polyvinyl butyral resin (PVB), they produced TpB@PVB and TpBe@PVB films with phosphorescence lifetimes close to 6s, and the afterglow lasted more than half a minute. This is the system with the longest phosphorescence lifetime among the currently reported polymer-based luminescent materials. More importantly, this material's luminescence is extremely stable and is both water-resistant and impact and collision-resistant. The study shows that the phosphorescence emission of these PVB materials requires activation by ultraviolet light. After continuous ultraviolet light irradiation for 40s, the film can achieve the strongest phosphorescence performance, and this activation process is reversible. This reversibility can be used for light printing and erasing.
Co-corresponding author of the paper, Professor Yang, explained that through testing singlet oxygen signals, comparing the activation processes in different oxygen-containing atmospheres, infrared spectroscopy, etc., the research team demonstrated that the system involves oxygen consumption and photocrosslinking during the first photoactivation process. In the PVB matrix, a more stable crosslinked network was formed. In addition, the lone pairs of electrons of the boron and oxygen in the boric acid group can increase the rate of intersystem crossing (ISC) of excitons from the singlet state to the triplet state, thereby allowing the triphenylamine molecules to emit light with a longer lifetime.
In order to elucidate the effects of each component of the PVB on the luminescence, the research team prepared three films with different substrates using the same method: TpB@PVBt, TpB@PVAc, and TpB@PVA. The study demonstrates that the PVB substrate has a dual-network structure with both strong hydrogen bonds and hydrophobicity, which can effectively reduce the non-radiative transitions of the triplet excitons and effectively isolate the quenching of the triplet excitons by moisture and oxygen in the air, thereby significantly stabilizing and prolonging the luminescence of the triphenylamine derivatives.
The research team delved into the comprehensive properties and potential applications of this type of polymer-based ultralong afterglow material. To better simulate actual application scenarios, they used natural water (rainwater, river water, lake water, seawater, etc.) to conduct water resistance experiments. They discovered that after soaking the film for more than a month, the TpB's phosphorescence spectrum did not change significantly, and the afterglow still lasted for nearly half a minute. Given that this material integrates light-activated organic room-temperature phosphorescence, adhesion, impact resistance, and water resistance, the research team designed an advanced anti-counterfeiting label with built-in glue -- the first self-adhesive, real-time freshness certification, and reusable advanced label.
Co-corresponding author of the paper, Professor Huang, stated that this study proposes a strategy to stabilize triplet excitons using a "rigid-flexible" dual-network structure of hydrogen bonds and hydrophobicity, and developed a polymer-based phosphorescent material with an ultralong phosphorescence lifetime, which uses PVB as the substrate and triphenylamine derivatives (TpB and TpBe) as the luminescent bodies. Moreover, this material exhibits excellent luminescence stability in terms of water resistance, impact resistance, etc., and due to the strong adhesion of the PVB substrate itself, and the fact that the raw materials are readily available and easy to prepare, this type of polymer-based phosphorescent material has extremely high application value in the fields of anti-counterfeiting and encryption, and luminescent devices.
Related Paper Information: https://doi.org/10.1126/sciadv.adk3354
