The difference in the NH bond strengths in the L-1(a) and L-1(b) state of 7-azaindole is examined with the fluorescence-detected IR-dip spectroscopy. It has been found that the NE stretch fundamental (3456 cm(-1)) measured by probing the vibronic band at 280 cm(-1) above the zero-point level of L-1(b) is remarkably red-shifted with respect to those (3483-3489 cm(-1)) obtained by probing the other six vibronic bands in the 0-717 cm(-1) region. The electronic state of the band at 280 cm(-1) was assigned to a S-1(L-b)/S-2(L-a) mixing state [Kang et al. J. Chem. Phys. 2005, 123, 094306.]; the prominent red shift of the NH stretch fundamental indicates that the L-1(a) component significantly contributes to weaken the NH bond strength. This finding provides insight into electronic-state dependence of the proton/hydrogen-atom transfer reactions in the hydrogen-bonded 7-azaindole clusters.