A Photophysical Study of the α-Carboline (1-Azacarbazole) Aggregation Process

• Published in: Photochemistry and photobiology 2012-03, Vol.88 (2), p.277-284
• Main Authors: García-Fernández, Emilio, Carmona, Carmen, Muñoz, María A., Hidalgo, José, Balón, Manuel
• Format: Article
• Language: English
• Subjects: Carbolines - chemistry; Dimerization; Fluorescence; Hydrogen Bonding; Indoles - chemistry; Kinetics; Light; Photochemical Processes; Pyridines - chemistry; Solvents; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Temperature; Thermodynamics
• ISSN: 0031-8655; 1751-1097
• DOI: 10.1111/j.1751-1097.2011.01056.x

This paper reports a comprehensive photophysical study of the aggregation process of 1‐azacarbazole, or α‐carboline (9H‐pyrido[2,3‐b]indole), AC, in low polar aprotic solvents by using absorption, steady state and time‐resolved fluorescence spectroscopic techniques. To ascertain the characteristics of the aggregation process we have studied the changes produced by the increase of the AC concentration and the decrease of the temperature on the absorption and fluorescence spectra of the AC monomer. Previously, to aid the interpretation of these results, the hydrogen bonding interactions of the AC monomer with pyridine, PY, and indole, IND, have been also analyzed. The results obtained from these studies reveal that, under our experimental conditions, AC does not form doubly hydrogen bonded cyclic dimers, (AC)2, but singly hydrogen bonded open dimers, AC–AC, and open higher aggregates, (–AC–)n. The formation of these species shifts to the red the absorption spectrum of the AC monomer and quenches its fluorescence. In low polar aprotic solvents α‐Carboline (1‐Azacarbazole), AC, forms hydrogen bonded open dimers, AC–AC, and higher open aggregates (–AC–)n, that quench the fluorescence.