Laser-induced fluorescence (LIF) spectra of a 1:1 complex between 7-azaindole (7AI) and five-member cyclic amide 2-pyrrolidinone (2-PDN) have been measured in a supersonic free jet expansion. The bands in the excitation spectrum appear doublet, which has been attributed to splitting of the zero-point level in the ground state due to puckering of 2-PDN moiety of the complex in a symmetric double minimum potential. This feature is consistent with low puckering barrier (similar to 260 cm (1)) predicted by electronic structure calculation. The complex emits only UV fluorescence from locally excited state in the jet, but visible tautomer fluorescence is observed in hydrocarbon solution. (C) 2011 Published by Elsevier B.V.