Self-agglomerated crystalline needles harnessing ESIPT and AIEE features for the ‘turn-on’ fluorescence detection of Al 3+ ions

We report the synthesis of probe 2 for the fluorescence “turn-on” detection of Al 3+ ions in CH 3 OH. Probe 2 has been designed via utilizing the aggregation-induced emission properties of the tetraphenylethylene unit, with further enhancement from Schiff base units for the ESIPT phenomenon. Probe 2 exhibits emission at 548 nm ( λ ex = 360 nm), with a large Stokes shift of 188 nm, indicating the ESIPT phenomenon. Probe 2 also exhibits emission enhancement via increasing the H 2 O ratio up to 70–90% H 2 O/THF (v/v) and altering the spherical morphology to needle shapes. Probe 2 has been found to be highly selective and sensitive towards Al 3+ ions over other metal ions in pure CH 3 OH using absorption and emission spectroscopy. FESEM analysis revealed that the size of probe 2 increases upon the addition of Al 3+ ions. Thus, the fluorescence “ turn-on ” behaviour of probe 2 ·Al 3+ is due to metal-induced aggregation.