The sole existence of a t-bone-shaped naphthalimide derivative [2-(2-aminoethyl)-1H-benzo[de]isoquinoline-1,3(2H)dione] (NAP), which gives rise to a photoinduced electron transfer (PET) mechanism, has been established using a combination of experimental and theoretical studies. In parallel an in vitro-in cell PET mechanism has also been shown. To understand the photophysics of NAP, solvent studies have been carried out in different solvents. In addition, theoretical calculations have been conducted to explain the spectroscopic properties through optimized structures. A "turn off" PET mechanism has also been observed in the presence of specific metal ions, namely, Cr , Fe and Hg among a series of metal ions. Theoretical studies reveal that NAP-Cr , NAP-Fe and NAP-Hg have their HOMO energy states lying in between a HOMO-LUMO energy state of the t-bone-type NAP molecule. On the contrary, the HOMO state of the other metal ion-NAP conjugate (NAP-M ) does not lie in between the HOMO-LUMO energy gap of the t-bone-type NAP molecule. Coupled with in vitro studies, in cell investigations reveal an enhancement of fluorescence intensity of NAP upon cytosolic metal sensing. Furthermore, a very high cell viability of NAP treated cells as tested by MTT assay and a fast permeation of the said compound as revealed by flow cytometry suggest NAP to be a potential candidate in metal sensing and bioimaging applications.
Many reports on metal ion sensing applications are available in literature but the mechanism of selectivity is not clear. Here the synthesis and characterization of a Schiff base Furan‐2‐carboxylic acid pyren‐1‐ylmethylene‐hydrazide (PYFH) has been described with selective detection of copper(II) metal ion among different metal ions by UV–vis, fluorescence and HRMS spectroscopic methods. The S2− ion (Na2S) was added to the PYFH:Cu2+ complex for checking reversibility of PYFH by fluorescence, fluorescence microscopic imaging and molecular logic gate construction (combination of NOT and OR gate). From the experimental findings the reason for selectivity of Cu2+ metal ion among a series of metal ions is not clear. So, to explore the causes of selectivity of Cu2+ metal ion by PYFH, Density Functional Theory (DFT) calculation was conducted for free PYFH and various sets of metal ions individually with PYFH. From DFT calculation it was understandable that selectivity of PYFH towards Cu2+ ions occurred due to lowering of HOMO‐LUMO energy of PYFH:Cu2+ composites (‐8.46 & −5.80 eV) compared to free PYFH (‐5.56 & −2.15 eV). Whereas energy of HOMO and LUMO with other metals ions (PYFH:Mn+) are ∼‐5.50 and ∼‐2.24 eV respectively, as a result PYFH does not get any extra stability.
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