The solid-state [2 + 2] cycloaddition of vitamin K₃ (VK3) polymorphs has been systematically reexamined, overcoming the limitations of powder-based studies by focusing on single-crystal behavior. Using THz micro-Raman and FTIR-ATR vibrational spectroscopies combined with X-ray diffraction and solid-state density functional theory (DFT) calculations, we unveil distinct photoreactivity and stereoselectivity in both polymorphs. Monochromatic irradiation at the absorption tail preserved the crystal integrity, enabling a detailed investigation of the reaction outcomes. While both polymorphs undergo photoreaction, their transformations proceed via distinct crystal-to-crystal processes, yielding cis-syn and cis-anti dimers selectively. The photochemical pathway to the formation of the cis-isomers is analyzed by quantum mechanical calculations. These findings highlight the critical role of polymorphism in solid-state photochemistry while questioning the conventional dichotomy between defect-driven and purely topochemical mechanisms.

中文翻译：

---

解开固态 [2 + 2] 维生素 K3 环加成反应中的多态性控制：来自单晶辐照的见解

维生素 K₃ （VK3） 多晶型物的固态 [2 + 2] 环加成反应已被系统地重新检查，通过关注单晶行为克服了基于粉末的研究的局限性。使用太赫兹微拉曼和 FTIR-ATR 振动光谱，结合 X 射线衍射和固态密度泛函理论 （DFT） 计算，我们揭示了两种多晶型物中不同的光反应性和立体选择性。吸收尾部的单色照射保留了晶体的完整性，从而能够详细研究反应结果。虽然两种多晶型物都发生光反应，但它们的转化通过不同的晶体到晶体过程进行，选择性地产生顺式-syn 和顺式-抗二聚体。通过量子力学计算分析形成顺式异构体的光化学途径。这些发现强调了多态性在固态光化学中的关键作用，同时质疑了缺陷驱动和纯拓扑化学机制之间的传统二分法。