8-Hydroxyjulolidine aldimine as a fluorescent sensor for the dual detection of Al3+ and Mg2+

A novel series of fluorescent sensors containing julolidine linked with amino benzyl dipicolylamine were successfully synthesized via a simple schiff base reaction to afford J2P, J3P, and J4P in 71%, 76%, and 81% yield, respectively. J2P exhibited strong green fluorescence enhancement upon addition of Al3+ or Mg2+ in different media, i.e. H2O/MeOH (1:9, v/v) and H2O/DMSO (5:95, v/v), respectively. The fluorescence responses were selective over other metal ions with low detection limits of 0.17 and 1.32 μM, respectively. The 1:1 stoichiometric complexation between the sensor and each metal ion was proven by Job's plots and HRMS results. The fluorescence enhancing phenomena of [Al·L]2+ and [Mg·HL]2+ complexes in phenolate and phenolic form, respectively, demonstrated the suppression of ESIPT and CN isomerization through CHEF effect. Furthermore, the application of J2P probe on paper based strip was successfully developed into the array type dual sensing system for Al3+ and Zn2+ ready for use as an on-site-kit.