7-Azaindole: the low-temperature near-UV/vis spectra and electronic structure

• Published in: Journal of molecular structure Vol. 354; no. 1; pp. 37 - 47
• Main Author: Ilich, Predrag
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.1995
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/0022-2860(95)08856-Q

7-Azaindole is isolated in an argon matrix and its absorption, fluorescence and phosphorescence are analyzed by comparison with indole spectra and indo s 1 calculations. The absorption origin is a distinct band at 289.9 nm, but we could not identify the second {π∗, π} transition in the spectrum. We predict it to be weak and near-degenerate with a pyridine-type {π∗, n} transition. The origin of the well-structured phosphorescence emission, at 414.9 nm, is strongly blue-shifted in comparison to the previously reported phosphorescence of 7-azaindole in hydrocarbon glasses. A long phosphorescence lifetime, τ = 3.78 s, indicates the S 0{gp} ← T 1{π∗} radiative transition. The Φ P Φ F ratio in 7-azaindole is smaller by an order of magnitude in the argon matrix and two orders of magnitude in glycerol/water glass, in comparison to that of indole. The sensitivity to protic media indicates that an S 0{n} ← T k{π∗} transition is responsible for the emission loss. No dimerizaton of 7-azaindole and tautomerization to 7 H-pyrrolo[2,3- b]pyridine was observed in the argon matrix or glycerol/water glass; however, association with indole is suggested by phosphorescence band shifts and emission loss. It is expected that these features will further the use of 7-azaindole as a spectroscopic marker in a variety of environments.