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Absorption and fluorescence spectra of ring-substituted indole-3-acetic acids

2004; Elsevier BV; Volume: 111; Issue: 3 Linguagem: Inglês

10.1016/j.bpc.2004.06.006

1873-4200

Dejana Carić, Vladislav Tomišić, Marina Kveder, Nives Galić, Greta Pifat, Volker Magnus, Milan Šoškić,

Synthesis and Biological Evaluation

The absorption and fluorescence spectra of indole-3-acetic acid (1), a plant growth regulator (auxin) and experimental cancer therapeutic, 29 ring-substituted derivatives and the 7-aza analogue (1H-pyrrolo[2,3b]pyridine-3-acetic acid) are compared. Two to four absorbance maxima in the 260–310-nm range are interpreted as overlapping vibronic lines of the 1La←1A and 1Lb←1A transitions. Two further maxima in the 200–230-nm region are assigned to the 1Ba←1A and 1Bb←1A transitions. 4- and 7-Fluoroindole-3-acetic acid exhibit blue shifts with respect to 1, most other derivatives show red shifts. All indole-3-acetic acids studied, with the exception of chloro-, bromo- and 4- or 7-fluoro-derivatives, fluoresce at 345–370 nm when excited at 275–280 nm. 7-Azaindole-3-acetic acid emits at 411 nm. The fluorescence quantum yield of 6-fluoroindole-3-acetic acid significantly exceeds that of 1 (0.3); the other derivatives have lower quantum yields. The plant-growth promoting activity of the ring-substituted indole-3-acetic acids studied correlates with the position of the 1Bb←1A transition band.