Novel 4,4-Fluoresceinoxy Bisphthalonitrile Showing Aggregation-Induced Enhanced Emission and Fluorescence Turn off Behavior to Fe3+ Ions

A novel 4,4-fluoresceinoxy bisphthalonitrile FPN is synthesized from fluorescein and 4-nitrophthalonitrile by aromatic nucleophilic ipso nitro substitution reaction. The structure of FPN constitutes phthalonitrile-fluorescein-phthalonitrile, acceptor-donor-acceptor, A-D-A form and the solvatochromic study of newly synthesized compound FPN was done in hexane, cyclohexane, CHCl3, DCM, DMF, acetonitrile, ethanol and in methanol. The aggregation behavior of FPN was investigated in good-poor solvent mixture DMF-water in various proportions and the molecule was found to be exhibiting Aggregation Induced Emission Enhancement AIEE for volume percentage of water beyond 50% with a significant hypsochromic shift of 70nm in the emission maxima from 458 to 388nm. This phenomenon is termed as Aggregation Induced Blue Shifted Emission Enhancement AIBSEE and was reported in substituted phthalonitrile for the first time. The chemo sensing activity of FPN with various transition metal ions also has been checked by fluorescence spectroscopy where the new molecule FPN exhibited fluorescence turn OFF behaviour towards Fe3+ ion in acetonitrile-methanol ACN-MeOH solution. The binding stoichiometry of FPN with Fe3+ was verified by Job's plot analysis and Density Functional Theory DFT-B3LYP computational methodology by using Gaussian 09 software.