Fluorescent RET-Based Chemosensor Bearing 1,8-Naphthalimide and Styrylpyridine Chromophores for Ratiometric Detection of Hg2+ and Its Bio-Application

Abstract

Dyad compound NI-SP bearing 1,8-naphthalimide (NI) and styrylpyridine (SP) photoactive units, in which the N-phenylazadithia-15-crown-5 ether receptor is linked with the energy donor naphthalimide chromophore, has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In an aqueous solution, NI-SP selectively responds to the presence of Hg2+ via the enhancement in the emission intensity of NI due to the inhibition of the photoinduced electron transfer from the receptor to the NI fragment. At the same time, the long wavelength fluorescence band of SP, arising as a result of resonance energy transfer from the excited NI unit, appears to be virtually unchanged upon Hg2+ binding. This allows self-calibration of the optical response. The observed spectral behavior is consistent with the formation of the (NI‑SP)·Hg2+ complex (dissociation constant 0.13 ± 0.04 µM). Bio-imaging studies showed that the ratio of fluorescence intensity in the 440–510 nm spectral region to that in the 590–650 nm region increases from 1.1 to 2.8 when cells are exposed to an increasing concentration of mercury (II) ions, thus enabling the detection of intracellular Hg2+ ions and their quantitative analysis in the 0.04–1.65 μM concentration range.

1,8‐Naphthalimide‐Based Chemosensors: A Promising Strategy for Detection of Metal Ions in Environmental and Biological Systems

“…Thus, the sensing mechanism of 40 was based on the interplay between PET and RET upon excitation. Further, the quantitative detection of Hg 2+ inside A549 cells with 40 was possible in the 0.04–1.65 μM concentration range with strong binding affinity of 4.04×10 4 M −1 [90] …”

“…In the first step, 6bromo-1,8-naphthalic anhydride (1) was reacted with n-butyl- Reproduced from reference. [90] amine for introducing a non-polar tail on moiety forming compound 41 which on further reaction under basic conditions in the presence of methanol at high temperature produced compound 42. Deprotection of 42 in strongly acidic conditions yielded 43 which was converted to formyl derivative (44) under oxidizing conditions.…”

“…Further, the quantitative detection of Hg 2 + inside A549 cells with 40 was possible in the 0.04-1.65 μM concentration range with strong binding affinity of 4.04×10 4 M À 1 . [90] Tian et al, (2020) synthesized and reported a fluorescent marker (45) for the detection of Hg 2 + ions. In the first step, 6bromo-1,8-naphthalic anhydride (1) was reacted with n-butyl- Reproduced from reference.…”

“…Figure 5. Selectivity of probe 40 in the presence of other metal ions.Reproduced from reference [90]. …”

Dual and Panchromatic Emission from N-Aryl-phenanthridinones: Extension of the Seesaw Photophysical Model with a Slight Twist

“…Therefore, the LW fluorescence of N -aryl-naphthalimides could be attributed to intramolecular charge transfer (ICT) from a π-orbital of the N -aryl group to a π* orbital of the naphthalene skeleton, whereas the SW emission should be attributed to the π–π* transition on the naphthalene component. Recently, this model was successfully applied by other researchers for the predictive luminescence outcomes of 2,3-naphthalimide derivatives bearing extended π-substituents. − As illustrated in Figure , the structural similarities between NAN and NAP dyes prompted the investigation into the generality of the model for dual color emission.…”