Squaraines and croconaines are organic dyes characterized by intense absorption in the visible or near‐infrared spectral regions with applications ranging from biology to material sciences. They are commonly synthesized by condensation reactions of oxocarbonic acids (squaric or croconic acid, respectively) with electron‐rich aromatic compounds in high‐boiling organic solvents. Here, a simple, cost‐effective, and environmentally benign process was developed for the synthesis of indolenine‐based squaraines and croconaines under solvent‐free conditions. Protocols based on conventional thermal heating, mechanochemical milling, and IR‐light activation were compared.

中文翻译：

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合成吲哚烯基胍基和可可碱的无溶剂反应：热加热，机械化学研磨和红外辐射的比较

鱿鱼碱和藏红花碱是有机染料，其特征是在可见光或近红外光谱区具有强吸收性，其应用范围从生物学到材料科学。它们通常是由含氧碳酸（分别为方酸或巴豆酸）与高沸点有机溶剂中富电子芳族化合物的缩合反应合成的。在此，开发了一种简单，经济高效且对环境无害的方法，用于在无溶剂条件下合成基于吲哚烯的方酸和可卡因。比较了基于常规热加热，机械化学研磨和红外激活的协议。