A study on the vibrational dynamics of the NH stretching mode of pyrrole base complexes in carbon tetrachloride, using subpicosecond infrared pump-probe (PP) spectroscopy, is reported. The time evolution of the PP signal of the NH stretching mode for all the complexes was frequency-dependent; the signal decay time increased with the frequency. This frequency dependence was thought to originate from the relationship between vibrational energy relaxation (VER) and spectral diffusion. For hydrogen-bonded systems, spectral diffusion corresponds to the reorganization of the solvent environment. Qualitative analysis of the frequency dependence of the PP signal decay time indicated that a simple energy gap law could not be applied to all the pyrrole base complexes. This conclusion was supported by spectral simulation of the PP signal using the modified Smoluchowski equation to clarify the frequency dependence of the VER and the spectral diffusion.