A Redox-Driven Fluorescence Off-On Molecular Switch Based on a 1,1'-Unsymmetrically Substituted Ferrocenyl Coumarin System: Mimicking Combinational Logic Operation

A unique electrochemical- and fluorescence active molecular switch based on a 1;1'-unsynimetrically substituted ferrocenyl-coumarin system has been developed. Upon chemical oxidation of the ferrocene moiety with Fe(ClO4)(3), the present system displays high fluorescence output through an inhibited photoinduced electron transfer (PET) process and also exhibits slight diminution of emission intensity upon the addition of Hg2+. The feasibility of the PET process was further verified by the Weller equation and DFT studies, which indicate that oxidation of ferrocene units in 5 depletes electron population from the HOMO of central: ferrocene, and thus the PET process is forbidden and reemergence of fluorescence is observed. Theoretical studies further revealed that charge. transfer in the excited state from coumarin-centered orbitals (LUMO+1) to mercury-centered empty orbitals (LUMO) may be attributed to fluorescence quenching upon addition of Hg' ion. The unprecedented combination of Fe2+ ion, Hg2+ ion, and sodium L-ascorbate (LAS) has been used to generate a molecular system exhibiting combinational INHIBIT logic operation.