Synthesis and Spectroscopic Characterization of New NIR Absorbing (2‐Thienyl)‐ and (4‐Dialkylaminoaryl)‐substituted Croconic Acid Dyes

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Abstract
By condensation of croconic acid (7) with 2‐(dialkylamino)‐thiophenes 6a–d and with 3‐(dialkylamino)phenols 9a–c the deeply colored, sparingly soluble croconic acid dyes (“croconines”) 8a–d and 10a–c, respectively, have been prepared. These croconines have been characterized by UV/Vis, IR, and 1H‐NMR spectrometry. They exhibit strong electronic absorption bands in the near infrared (NIR) region (λmax ≈ 750–850 nm; cf. Table 1).

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