A new window towards multidimensional sensing of transition metal cations through dual mode sensing ability of N-benzyl-(3-hydoxy-2-naphthalene): Emission enhancement coupled remarkable spectral shift

A structurally simple Schiff base N-benzyl-(3-hydroxy-2-naphthalene) (NBHN32) has been synthesized and characterized by 1H NMR, 13C NMR, and DEPT spectroscopy. The photophysical behaviour of NBHN32 in response to the presence of various transition metal cations has been explored by means of steady-state absorption, emission and time-resolved emission spectroscopy techniques. Efficient through space intramolecular photoinduced electron transfer (PET) between the naphthalene fluorophore and the imine group has been argued for extremely low fluorescence yield of NBHN32 compared to the parent molecule 3-hydroxy-2-naphthaldehyde (HN32) containing the same fluorophore but lacking the receptor moiety. Transition metal ion-induced emission enhancement is thus addressed on the lexicon of perturbation of the PET by the metal ions. Apart from fluorescence enhancement, transition metal ion imparts remarkable shift of the emission maxima of NBHN32, which is another unique aspect on the proposed ability of NBHN32 to function as a fluorescence chemosensor.

The figure provides differential ratiometric chemosensory response of NBHN32 towards various transition metal ions based on emission and absorption spectral changes and expressed as the ratio of (a) I525nm/I425nm (λex ∼ 320 nm), Here 1 → Zn2+, 2 → Cu2+, 3 → Ni2+, 4 → Mn2+, 5 → Co2+, 6 → Cr3+, 7 → Fe2+.Figure optionsDownload as PowerPoint slideResearch highlights
► Multidimensional fluorosensing of transition metal ions.
► N-benzyl-(3-hydoxy-2-naphthalene).
► Dual mode sensing.
► Fluorescence enhancement coupled with remarkable spectral shift.