The absorption spectra of ethyl 1-naphthoate in hexane and in water demonstrate normal dependences upon solvent hydrogen bonding and polarity properties while the absorption spectra of 1-naphthoic acid do not. This is attributed to inhibition of conjugation by steric interference between the carbethoxy group of the ester or the hydrated carboxyl group of the acid and the peri-hydrogen atom of the naphthalene ring in the 5-position, in the ground electronic state. The anomalous fluorimetric titration characteristics of the 1- and 2- naphthoic esters and of 1-naphthoic acid are attributed to hydrogen bonded exciplex formation in the lowest excited singlet state.