Naphthalene-embedded spiropyran derivative-A type of conjugated expanded material with solid-state photochromic properties and tunable color switching range

• Published in: Journal of molecular structure 2024-12, Vol.1318, p.139404, Article 139404
• Main Authors: Liu, Tongli, Li, Jiu-Long, Xie, Zhipeng, Huang, Congshu, Wang, Jingjing, Zhang, Chuyi, Sha, Jianang, Wang, Lu
• Format: Article
• Language: English
• Subjects: Conjugated expanded spiropyran; Solid-state photochromism; Stimulus-responsive material; Tunable color switching range
• ISSN: 0022-2860
• DOI: 10.1016/j.molstruc.2024.139404

•Proposing a novel strategy to construct a conjugated expanded spiropyran, SP-Naph.•SP-Naph exhibits excellent photochromic properties in the solid state.•SP-Naph displays an enhanced solid-state photochromic rate.•SP-Naph possesses a tunable color switching range.•SP-Naph shows broad prospects in anti-counterfeiting and information encryption. Due to the limited free volume in the solid state, spiropyrans generally exhibit photochromic properties in solution or mixed thin films. However, few spiropyrans can display the photoisomerization process in the solid state. One conventional solution for solid-state photochromism is to embed the spiropyran on polymer chains or introduce bulky groups to create an efficient free volume in the solid state. In this article, we attempt to introduce large conjugated fragments on the spiropyran backbone to construct a donor-acceptor (D-A) building block that not only possesses an enlarged π-electron system with enhanced electronic delocalization capability but also exhibits an improved free volume for efficient solid-state photoisomerization. Through this strategy, we have successfully embedded the naphthalene ring on the spiropyran backbone to obtain a novel D-A type conjugated building block, SP-Naph, which exhibits excellent solid-state photochromic performance and reversibility. Furthermore, the D-A structure of SP-Naph significantly tuned its photochromic color-switching range to blue. Consequently, SP-Naph was successfully applied in optical printing and invisible inks. The excellent solid photochromic properties make it exhibit remarkable photochromic effects, indicating significant potential for optical printing and anti-counterfeiting applications.