pH dependent fluorescence switching in salicylideneaniline: 'off-on-off' operation controlled by surfactant micelles

Salaniline, a condensation product of salicylaldehyde and aniline, shows “off-on” fluorescent behaviour with pH in 1:1 (v/v) CH3CN:H2O and when 3% (w/v) anionic sodium dodecylsulphate (SDS) surfactant is present. The fluorescent switch behaviour of salaniline is forced to “off-on-off” type by 3% (w/v) neutral triton X-100 (TX-100) and 3% (w/v) cationic cetyltrimethylammonium bromide (CTAB) surfactant. The fluorescent “on” window is observed in the pH range 8.0-12.5 for TX-100 and 7.0-11.0 for CTAB. Different charge nature of the surfactants affects the protonation/deprotonation behaviour of salaniline differently, hence the photoinduced electron transfer (PET) processes and the fluorescent switch behaviour.