Rhodamine-Based Dual Chemosensor for Al³⁺ and Zn²⁺ Ions with Distinctly Separated Excitation and Emission Wavelengths

Abstract

A rhodamine-based compound, 2-(2-((3-(tert-butyl)-2-hydroxybenzylidene)amino)ethyl)-3′-6′-bis(ethylamino)-2′,7′-dimethylspiro[indoline-1,9′-xanthen]-3-one, (HL-t-Bu), is reported here as a dual chemosensor for Zn 2+ and Al 3+ ions. This compound has been synthesized under mild conditions with high yield and characterized by elemental analysis and different standard spectroscopic methods. Its structure has been confirmed by single-crystal X-ray diffraction analysis. It acts as a fluorescent dual sensor for Zn 2+ and Al 3+ in 10 mM HEPES buffer in the methanol/water mixture (9:1, pH = 7.4) with wellseparated excitation and emission wavelengths. The fluorescence intensity at 457 nm of HL-t-Bu increases by ∼7 folds in the presence of 1 equiv of Zn 2+ when it is excited at 370 nm. With the excitation at 500 nm, the emission intensity of the probe at 550 nm increases massively (∼650 times) in the presence of 1 equiv of Al 3+ . No other metal has any significant effect on the enhancement of the emission intensity of the probe in the detection process for either of the metal ions. The quantum yield of HL-t-Bu enhances significantly in the presence of Zn 2+ and Al 3+ . Rhodamine derivatives are generally colorless and nonfluorescent when the spirolactam ring is closed, and they are pink in color and highly fluorescent when it exists in the ring-open form. In the presence of Al 3+ , the probe is pink and highly fluorescent, indicating that this metal ion is able to the open spirolactam ring of the probe. However, Zn 2+ is not able to open the spirolactam ring, but it is coordinated through phenolic oxygen and imine nitrogen (salicylaldehyde unit) of the Schiff base restricting PET (photoinduced electron transfer) and imposing CHEF (chelation-enhanced fluorescence) to enhance the emission intensity of the probe. 1 H NMR, FT-IR, elemental analysis, and pH-dependent studies support these mechanisms. Limit of detection values are in the nanomolar range for both the metal ions, confirming very high sensitivity of the probe. The probe has been used in cell imaging studies for both of the metal ions.

Zn2+ Recognition for Pathogenesis of Pick's Disease via a Luminescent Test Kit

“…L1 displayed four signals at 220, 250, 325 with a broad signal at 415 nm due to π-π*, n-π* and charge transfer transition within the framework respectively. The absorption spectra of L1 in acetonitrile: HEPES (4 : 1, v/v, conc n : 2 × 10 À 5 M, pH 7.4) [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] (λ max /nm; ε/M À 1 cm À 1 ): 325 (18100) and for L1-Zn 2 + (λ max /nm; ε/M À 1 cm À 1 ): 370 (11100) respectively (Figure S5a-b). Photoexcitation at 400 nm gives fluorescence of L1 (conc n : 5 × 10 À 6 M, pH 7.4) at 495 nm which reveals a Stokes Shift of 80 nm.…”

Anthrone‐spirolactam and quinoline hybrid based sensor for selective fluorescent detection of Fe3+ ions

“…There was an ambiguity about whether the molecule might undergo a ring-opening of lactam in the Fe complex state as the ligand RSD-1 resembles rhodamine derivatives [64][65][66][67] (there are a few reports on rhodamine-based sensors that followed the spirolactam ring closed chelation mechanism). [68][69][70][71][72][73] In the case of spirolactam ring-opened sensors, the complex system showed the formation of a new band over 550 or 600 nm ranges in absorbance and emission. In the present system during complex formation there was no long shift in absorbance and the fluorescence emission was obtained around 420-455 nm.…”

Recent Progress in Small Spirocyclic, Xanthene-Based Fluorescent Probes

“…The final section will summarize recent advances in the synthesis and understanding of their structure including novel computational approaches. Even though a lot of progress has been achieved, pH-sensing [60][61][62][63][64], metal ion detection [65][66][67][68][69][70][71][72], and the use of Spirocyclic, xanthene-based probes usually have a hydroxy-or carboxy-moiety or other intramolecular nucleophiles at the 2 position of a pendant aromatic ring at the C-9 -atom of the xanthene core (Scheme 1) [41,42]. This intramolecular nucleophilic-moiety attacks the sp 2 -hybridized C-9 -atom and forms the colorless spirocyclic form.…”

“…The final section will summarize recent advances in the synthesis and understanding of their structure including novel computational approaches. Even though a lot of progress has been achieved, pH-sensing [ 60 , 61 , 62 , 63 , 64 ], metal ion detection [ 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 ], and the use of nanoparticles [ 21 , 73 , 74 , 75 , 76 , 77 , 78 ] or any other solid support [ 79 , 80 , 81 , 82 ] will be omitted, given the scope of this review.…”