title: Absorption and fluorescence spectra of ring-substituted indole-3-acetic acids.
abstract: 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.
authors.affiliation: Faculty of Agronomy, Svetosimunska cesta 25, 10000 Zagreb, Croatia.
authors.forename: Dejana
authors.initials: D
authors.lastname: Carić
authors.forename: Vladislav
authors.initials: V
authors.lastname: Tomisić
authors.forename: Marina
authors.initials: M
authors.lastname: Kveder
authors.forename: Nives
authors.initials: N
authors.lastname: Galić
authors.forename: Greta
authors.initials: G
authors.lastname: Pifat
authors.forename: Volker
authors.initials: V
authors.lastname: Magnus
authors.forename: Milan
authors.initials: M
authors.lastname: Soskić
mesh_terms: D006863:Hydrogen-Ion Concentration; D007210:Indoleacetic Acids / Q000737:chemistry*; D015394:Molecular Structure; D013050:Spectrometry, Fluorescence / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
chemical_list: D007210:Indoleacetic Acids