Enabling Visible-Light-Charged Near-Infrared Persistent Luminescence in Organics by Intermolecular Charge Transfer.

Visible light is a universal and user-friendly excitation source; however, its use to generate persistent luminescence (PersL) in materials remains a huge challenge. Herein, the concept of intermolecular charge transfer (xCT) is applied in typical host-guest molecular systems, which allows for a much lower energy requirement for charge separation, thus enabling efficient charging of near-infrared (NIR) PersL in organics by visible light (425-700 nm). Importantly, NIR PersL in organics occurs via the trapping of electrons from charge-transfer aggregates (CTAs) into constructed trap states with trap depths of 0.63-1.17 eV, followed by the detrapping of these electrons by thermal stimulation, resulting in a unique light-storage effect and long-lasting emission up to 4.6 h at room temperature. The xCT absorption range is modulated by changing the electron-donating ability of a series of acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile-based CTAs, and the organic PersL is tuned from 681 to 722 nm. This study on xCT interaction-induced NIR PersL in organic materials provides a major step forward in understanding the underlying luminescence mechanism of organic semiconductors and these findings are expected to promote their applications in optoelectronics, energy storage, and medical diagnosis.

Visualizing Dynamic Mechanical Actions with High Sensitivity and High Resolution by Near-Distance Mechanoluminescence Imaging.

Proportionally converting the applied mechanical energy into photons by individual mechanoluminescent (ML) micrometer-sized particles opens a new way to develop intelligent electronic skins as it promises high-resolution stress distribution visualization and fast response. However, a big challenge for ML sensing technology is its low sensitivity in detecting stress. In this work, a novel stress distribution sensor with the detection sensitivity enhanced by two orders of magnitude is developed by combining a proposed near-distance ML imaging scheme with an improved mechano-to-photon convertor. The enhanced sensitivity is the main contributor to the realization of a maximum photon harvesting rate of ≈80% in the near-distance ML imaging scheme. The developed near-distance ML sensor shows a high sensitivity with a detection limit down to ≈kPa level, high spatial resolution of 254 dpi, and fast response with an interval of 3.3 ms, which allows for high-resolution and real-time visualization of complex mechanical actions such as irregular solid contacts or fluid impacts, and thus enables use in intelligent electronic skin, structural health monitoring, and human-computer interaction.