This paper focuses on the examination of the Photoinduced Electron Transfer (PET) and Internal Charge Transfer (ICT) for two coumarin derivatives, namely 7-methoxycoumarin-4-methyl-1-aza-18-crown-6 and di(7-methoxycoumarin-4-methyl)-1,10-diaza-18-crown-6. The spectroscopic properties were investigated by UV-Vis and fluorescence spectroscopies. It was found that a dual mechanism explains the fluorescence enhancement and blue shift in the presence of a cationic species, namely saxitoxin. The ICT was elucidated by the polarity effect of methanol on the fluorescence of di(7-methoxycoumarin-4-methyl)-1,10-diaza-18-crown-6.