The thermodynamics of a variety of 7-azaindole (7AI) hydrogen-bonded complexes in the ground state have been studied on the basis of absorption spectroscopy in combination with ab initio calculations at 6-31G* level. The results indicate that the strength of hydrogen bonding significantly affects the ground-state electronic configuration of 7AI in both normal and tautomer forms. The enthalpy, Delta H, of the association reactions was calculated to be -14.2, -11.3, and -9.2 kcal/mol for the 1:1 acetic acid/7AI complex, 7AI dimer, and methanol/ 7AI complex, respectively. These values are in fair agreement with the experimental results of -12.3, -9.5, and -6.3 kcal/mol. Calculations also show a stronger hydrogen-bonding effect in the tautomer complex forms than in their respective normal forms. Relative energy levels of excited-state double proton transfer are discussed on the basis of ground-state thermodynamics in combination with the spectroscopic data.