7-AZAINDOLE - THE LOW-TEMPERATURE NEAR-UV VIS SPECTRA AND ELECTRONIC-STRUCTURE/

7-Azaindole is isolated in an argon matrix and its absorption, fluores cence and phosphorescence are analyzed by comparison with indole spect ra and INDO/Sl calculations. The absorption origin is a distinct band at 289.9 nm, but we could not identify the second {pi,pi} transition in the spectrum. We predict it to be weak and near-degenerate with a p yridine-type {pi,n} transition. The origin of the well-structured pho sphorescence emission, at 414.9 nm, is strongly blue-shifted in compar ison to the previously reported phosphorescence of 7-azaindole in hydr ocarbon glasses. A long phosphorescence lifetime, tau = 3.78 s, indica tes the S-0{pi} <-- T-1{pi} radiative transition. The Phi(P)/Phi(F) r atio in 7-azaindole is smaller by an order of magnitude in the argon m atrix and two orders of magnitude in glycerol/water glass, in comparis on to that of indole. The sensitivity to protic media indicates that a n S-0{n} <-- T-k {pi} transition is responsible for the emission loss . No dimerizaton of 7-azaindole and tautomerization to 7H-pyrrolo[2,3- b]pyridine was observed in the argon matrix or glycerol/water glass; h owever, association with indole is suggested by phosphorescence band s hifts and emission loss. It is expected that these features will furth er the use of 7-azaindole as a spectroscopic marker in a variety of en vironments.