Amphiphilic anthracyl crown ether. A Langmuir and Langmuir-Schaefer films study

As a potential material for use in optical fiber fluorescence sensors for r apid detection of saxitoxin, 9-(monoaza-18-crown-6-methyl)-10-hexadecylanth racene (CAC(16)) was synthesized, and the interfacial and spectroscopic pro perties of the Langmuir monolayers and Langmuir-Schaefer films of CAC(16) w ere studied. The surface pressure-area and surface potential-area isotherms of CAC(16) On different subphases were obtained. An increased limiting mol ecular 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 fluor escence band on a pH 2 subphase hut none on a pure water subphase. Mixed mo nolayers of CAC(16)/C-20 (arachidic acid) on a pure water subphase showed a n 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 fluoresc ence signal, regardless of the C18OH content. Analysis of the surface press ure-area isotherms showed that CAC(16) is not miscible with C18OH. Langmuir -Schaefer films of CAC(16)/C-20 showed better anthracene emission spectra t han the monolayers at the air-water interface.