As a potential material for use in optical fiber fluorescence sensors for rapid detection of saxitoxin, 9-(monoaza-18-crown-6-methyl)-10-hexadecylanthracene (CAC(16)) was synthesized, and the interfacial and spectroscopic properties of the Langmuir monolayers and Langmuir-Schaefer films of CAC(16) were studied. The surface pressure-area and surface potential-area isotherms of CAC(16) On different subphases were obtained. An increased limiting molecular area was observed on a pH 2 subphase. In situ fluorescence emission spectra (lambda(ex) = 366 nm) of the CAC(16) monolayer showed a broad fluorescence band on a pH 2 subphase hut none on a pure water subphase. Mixed monolayers of CAC(16)/C-20 (arachidic acid) on a pure water subphase showed an increased fluorescence emission intensity of anthracene with an increase in the proportion of C-20. This suggests that the low fluorescence activity of the pure CAC(16) monolayer could be caused by self-quenching due to the high concentration of CAC(16) at the interface. In a mixed monolayer, C-20 acts as a two-dimensional solvent to dilute CAC(16) and diminish the self-quenching, thus recovering the fluorescence activity of CAC(16) When CAC(16) was mixed with C18OH (stearyl alcohol), the monolayers showed no fluorescence signal, regardless of the C18OH content. Analysis of the surface pressure-area isotherms showed that CAC(16) is not miscible with C18OH. Langmuir-Schaefer films of CAC(16)/C-20 showed better anthracene emission spectra than the monolayers at the air-water interface.