Substitution effects on the excited state intramolecular proton transfer (ESIPT) in the salicylic acid (SA) frame were studied by electronic and infrared spectroscopy of jet-cooled 5-methoxylsalicylic acid (5-MeOSA), 5-methylsalicylic acid (5-MeSA), 5-fluorosalicylic acid (5-FSA), 6-fluorosalicylic acid (6-FSA), and methyl salicylate (MS). Infrared spectra were measured in the 3 μm region for both the electronic ground (S₀) and first excited (S₁) states. The electronic excitation/emission spectra of 5-MeSA and 6-FSA showed the typical spectral features of ESIPT, which have been found in the spectra of SA. On the other hand, 5-MeOSA and 5-FSA exhibit a mirror-image relation between their excitation and emission spectra, which has been regarded as a result of the suppression of ESIPT. Despite such a remarkable difference among the electronic spectra, IR spectroscopy shows that a drastic change of the phenolic OH stretching vibration does occur upon electronic excitation of all substituted SAs, that is, the phenolic OH band of all the SAs disappears from the 3 μm region, indicating a large elongation of the phenolic O–H bond (over 0.1 Å) in S₁. This result means that the intramolecular hydrogen bond strength is remarkably enhanced by electronic excitation in all the substituted SAs. Substitution effects on ESIPT in dimers are also discussed.