Determination of the structure of 7-azaindole in the electronic ground and excited state using high-resolution ultraviolet spectroscopy and an automated assignment based on a genetic algorithm

Abstract

The rotationally resolved electronic spectra of four different isotopomers of 7-azaindole (IH-pyrrolo(2,3-b)pyridine) have been measured in order to obtain the geometric structure in the electronic ground and excited state. The electronic origins of the rotationally resolved UV spectra overlap strongly and an assigned fit to single rovibronic lines is hardly possible. We performed an automatized fit based on the genetic algorithm to assign all four spectral components simultaneously and extract the molecular constants. The resulting inertial parameters were used to determine the structure of 7-azaindole in the ground and electronically excited state. It was found that the pyridine moiety expands on electronic excitation, while the pyrrole ring showed only minor geometric changes. From the hybrid-type spectra of three isotopomers, the direction of the Ã∣A′(ππ*)– ∣A′ transition dipole moment for the transition was found to be −21°. Evaluation of the individual line shapes yielded an excited state lifetime of 2.55 ns for 7-azaindole.