An efficient fluorescent cation chemosensor based on fluorescein L4 was well prepared and identified with spectroscopy analyses. UV–vis and fluorescence measurements examined the analyte complexation of the L4 with various cations, demonstrating a clear tendency to Al3+ ion. In the Job plot study, a stoichiometry ratio of a complex between L4 and Al3+ ion was determined to be 1: 2 (L4: Al3+). A stoichiometry ratio of complex between L4 and Al3+ ion was determined to be 1: 2 (L4: Al3+) using the Job plot. The association constant (Ka) of the L4-Al3+ complex was found 2.8 × 107 M−2. The obtained limit of detection (LOD) value (1.37 × 10−6 M for Al3+) exhibited the considerable sensitivity of the chemosensor L4 to Al3+ ion. DFT/TD-DFT calculations have also been employed to support the binding mode and photophysical properties of the complexation of chemosensor L4 to Al3+ ion and also to investigate the enhancement of L4 fluorescence by Al3+ ion.
