Laser spectroscopic characterization of supersonic jet cooled 2,6-diazaindole (26DAI)

In this article, we present the laser spectroscopic investigation of a nitrogen rich indole derivative, 2,6-diazaindole (26DAI) in the gas phase for the first time. Laser induced fluorescence (LIF) and two-color resonant two-photon ionization (2C-R2PI) spectroscopies were carried out to understand the role of N-insertion on the electronic excitation of indole derivatives. The band origin for S1←S0 electronic transition was observed at 33915 cm-1, which was red shifted by 713 cm-1 and 1317 cm-1 from that of 7-azaindole and indole, respectively. The single vibronic level fluorescence (SVLF) spectroscopy of the molecule depicted a large Franck-Condon activity till 2500 cm-1 for ground state vibrational modes. The experimental vibrational frequencies from the SVLF spectrum were compared to Franck-Condon simulated frequencies at two different level of theories. The more accurate results were found at B3LYP-D4/def2-TZVPP, than the more energy demanding MP2/cc-pVDZ level. Fluorescence-dip infrared (FDIR) spectrum was recorded to determine the N-H stretching frequency of the molecule in the ground state, which was observed at 3524 cm-1. The photoionization efficiency spectroscopy was performed to measure the ionization energy of the molecule as 71866 cm-1, which is significantly higher as compared to 7-azaindole and indole. Thus, the above study suggests that the N-rich biomolecules appear to have a considerably lower risk of photodamage. The current investigation can shed light on to the nature’s way of stabilizing bio-relevant molecules with a possible N-insertion mechanism.