Alkyl Chain Introduction: In Situ Solar‐Renewable Colorful Organic Mechanoluminescence Materials

Mechanoluminescence (ML) materials are environmentally friendly and emit light by utilizing mechanical energy. This has been utilized in light sources, displays, bioimaging, and advanced sensors. Organic ML materials are strongly limited to application by in situ unrepeatable ML. Now, in situ solar‐renewable organic ML materials can be formed by introducing a soft alkyl chain into an ML unit. For the first time, the ML from these polycrystalline thin films can be iteratively produced by simply recrystallizing the fractured crystal in situ after a contactless exposure to sunlight within a short time (≤60 s). Additionally, their ML color and lifetime can be also easily tuned by doping with organic luminescent dyes. Therefore, large‐area sandwich‐type organic ML devices can be fabricated, which can be repeatedly used in a colorful piezo‐display, visual handwriting monitor, and sensitive optical sensor, showing a lowest pressure threshold for ML of about 5 kPa. Solar‐renewable colorful organic mechanoluminescence (ML) materials are induced by introduction of alkyl chains. Colorful ML from a polycrystalline thin film can be repeated interactively and totally for preliminary sandwich‐type ML device applications by simply recrystallizing the fractured crystal in situ after non‐contact exposure to sunlight in less than one minute.