Laser-induced fluorescence and single vibronic level emission spectroscopy of chiral (R)-1-aminoindan and some of its clusters in a supersonic jet

Abstract

Two low energy conformers of the chiral (R)-1-aminoindan molecule are identified in supersonic jet and their ground and excited states vibrational spectroscopy has been investigated by laser-induced fluorescence (LIF) excitation and single vibronic level (SVL) emission spectroscopy. Ab initio calculations confirm the existence of two lowest-energy structures, where the amino group is in equatorial position with its lone pair directed opposite to the aromatic electron cloud. Harmonic frequencies have been calculated for these two conformers at the DFT level with B3LYP functional. A low-frequency progression of 118 cm⁻¹ and 114 cm⁻¹, respectively, appears in the fluorescence excitation spectrum of the two conformers, with its ground state counterpart at ∼147 cm⁻¹. It has been assigned to the puckering motion coupled with the ring flapping mode. The other calculated low-frequency mode corresponds to the puckering motion coupled with the ring twisting mode and its ground state frequency has been observed at 119 cm⁻¹ and 111 cm⁻¹ from SVL spectra. Both conformers form similar 1 ∶ 1 water clusters, whose 0–0 transitions are shifted to the blue by 41 cm⁻¹ and 44 cm⁻¹, respectively, and whose SVL spectra are similar. Interestingly, one of the conformers seems to preferentially make complexes with (S)-methyllactate, while the other one shows selective complexation to (R)-methyllactate.