KYNURENIC ACID — I. SPECTROSCOPIC PROPERTIES

Abstract— The presence of different ground state species in ionic and/or keto s enol equilibrium has been demonstrated by studying NMR, IR and UV spectroscopic properties of kynurenic acid and related quinoline derivatives. The optical and emission properties of kynurenic acid and related compounds are thus very sensitive to pH conditions. Fluorescence and intersystem crossing (ISC) quantum yields have been measured in various solvents. The first excited singlet state is probably very short‐lived in neutral aqueous solution. The triplet state is long‐lived (10 μs) as shown by 353 nm laser flash spectroscopy. A high ISC quantum yield and a large molar extinction coefficient make it easy to detect the T1→ Tn transient (Δmax≃ 570 nm).

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