A calixarene–BODIPY fluorescent sensor for selective Fe³⁺ detection in environmental water samples: insights into static and dynamic quenching mechanisms

Abstract

A calix[4]arene-functionalized BODIPY fluorescent probe (Calix-BODIPY) was developed for the selective detection of Fe³⁺ ions in aqueous media for the first time. The integration of a calixarene recognition unit with a BODIPY fluorophore enabled efficient fluorescence signal transduction, resulting in a rapid “turn-off” response (∼10 s) toward Fe³⁺ ions with high selectivity over competing species. The sensor platform exhibited a linear response in the concentration range of 332–3537 µM, with a limit of detection (LOD) of 87.65 µM. Spectroscopic studies revealed that the sensing mechanism is governed by combined static and dynamic quenching processes. The applicability of the proposed system was validated through the determination of Fe³⁺ ions in tap and well water samples, yielding satisfactory recovery values (75.17–121.12%) without the need for complex sample pretreatment. Compared to nanomaterial-based sensors, the Calix-BODIPY probe offers advantages such as a well-defined molecular structure, operational simplicity, and high selectivity. These findings demonstrate that calixarene–BODIPY hybrid systems represent a promising platform for the development of practical fluorescent sensors for metal ion detection.

A calix[4]arene-functionalized BODIPY fluorescent probe (Calix-BODIPY) was developed for the selective detection of Fe³⁺ ions in aqueous media for the first time.

Introduction

The development of selective and sensitive fluorescent sensors for metal ion detection has attracted considerable attention due to their critical roles in environmental monitoring, biological systems, and industrial processes. Metal ions are essential for many physiological functions; however, their imbalance can lead to serious environmental and health-related issues. In particular, iron(iii) (Fe³⁺) plays a key role in biological systems, but excessive accumulation may cause oxidative stress and related disorders, highlighting the need for reliable detection methods.^1,2

Fluorescence-based sensing techniques have emerged as powerful analytical tools due to their high sensitivity, rapid response, operational simplicity, and capability for real-time monitoring. Compared to conventional analytical methods, fluorescent probes offer significant advantages in detecting trace amounts of analytes in complex systems. In this regard, the design of efficient fluorophores is crucial for improving sensing performance.^1,3

Among various fluorophores, boron–dipyrromethene (BODIPY) dyes have gained considerable interest owing to their outstanding photophysical properties, including high molar absorptivity, narrow emission bands, high fluorescence quantum yields, and excellent photochemical stability.⁴ These features make BODIPY derivatives highly attractive platforms for the development of fluorescent chemosensors. Recent studies have demonstrated that BODIPY-based probes can selectively detect metal ions through mechanisms such as photoinduced electron transfer (PET), intramolecular charge transfer (ICT), and fluorescence resonance energy transfer (FRET), resulting in “turn-on” or “turn-off” responses.⁵

Calixarenes are versatile macrocyclic hosts widely utilized in supramolecular chemistry due to their preorganized cavity structures and strong host–guest interaction capabilities.^6,7 Owing to these well-defined cavities, they can form stable inclusion complexes with a diverse range of guest species such as pesticides,^8,9 azo dyes,^10,11 amino acids,¹² and metal ions.^13,14 Furthermore, the structural tunability of calixarenes via functionalization at the upper and lower rims allows precise modulation of their binding affinity and selectivity toward specific analytes.¹⁵ As a result, calixarene-based systems have been extensively employed in the design of selective receptors and fluorescent sensors for environmental and biological applications.

Recent studies have demonstrated that the incorporation of fluorophoric units into calixarene scaffolds significantly enhances their sensing performance by improving both recognition ability and signal transduction efficiency. In particular, fluorescent calixarene derivatives have shown remarkable potential in supramolecular sensing systems, where their integration with organic fluorophores enables efficient optical responses through mechanisms such as photoinduced electron transfer (PET) and intramolecular charge transfer (ICT).^16–18 These features make calixarene-based platforms highly attractive for the development of advanced fluorescent sensors for the selective detection of metal ions such as Fe³⁺.

The integration of BODIPY fluorophores with calixarene frameworks represents a promising strategy for constructing advanced fluorescent sensing systems. Such hybrid systems combine the superior optical properties of BODIPY with the molecular recognition ability of calixarenes, enabling efficient and selective detection of metal ions. Recent reports have highlighted that BODIPY-based sensors can exhibit strong fluorescence quenching responses toward Fe³⁺ ions, making them suitable candidates for selective detection in aqueous environments.¹⁹

Recent studies have reported various fluorescence-based systems for Fe³⁺ detection employing nanomaterials, supramolecular receptors, and organic fluorophores. For example, nitrogen-doped carbon dots exhibited a very low detection limit of 0.07 µM for Fe³⁺ sensing in biological samples,²⁰ while UiO-66-Ph-based fluorescent systems demonstrated highly sensitive detection in environmental water samples with detection limits in the sub-micromolar range.²¹ In addition, BODIPY-based fluorescent probes have been widely investigated due to their excellent photophysical properties and high fluorescence efficiency. For instance, a BODIPY-based fluorescence turn-on probe was reported for Fe³⁺ detection and bioimaging applications in living cells,²² demonstrating high sensitivity toward Fe³⁺ ions. Similarly, a bis-calix[4]arene-based molecular probe exhibiting colorimetric, ratiometric, and fluorescence enhancement responses toward Fe³⁺ ions was also reported.²³ Similarly, calixarene-based molecular probes have also been developed for colorimetric, ratiometric, and fluorescence sensing of Fe³⁺ ions. Despite these advances, many nanomaterial-based sensing systems still suffer from drawbacks such as heterogeneous structures, multistep synthesis procedures, and reproducibility limitations. Moreover, previously reported BODIPY- or calixarene-based Fe³⁺ probes were generally designed either for bioimaging applications or individual sensing mechanisms. In contrast, structurally well-defined calixarene–BODIPY hybrid systems for rapid and selective Fe³⁺ detection in tap and well water samples remain relatively limited. In this context, the present Calix-BODIPY probe combines the supramolecular recognition capability of a calix[4]arene platform with the favorable photophysical properties of BODIPY fluorophores, providing rapid fluorescence response (∼10 s), selective Fe³⁺ recognition, successful applicability in tap and well water samples, and mechanistic insight through combined static and dynamic quenching analysis.

In this study, the design, synthesis, and characterization of a novel calix[4]arene-functionalized BODIPY derivative (Calix-BODIPY) were reported. Its photophysical and sensing properties toward various metal ions were also evaluated. The developed sensor exhibits a highly selective fluorescence “turn-off” response toward Fe³⁺ ions. Detailed analytical investigations, including selectivity, sensitivity, binding stoichiometry, and quenching mechanism were carried out to elucidate the sensing behavior. Furthermore, the applicability of the proposed sensor was demonstrated through successful detection of Fe³⁺ in tap and well water samples.

Experimental section

Materials and instruments

The used materials, equipment, photophysical and photochemical parameters are given in the SI.

Experimental

The synthetic pathway for Calix-BODIPY, was given in Scheme 1. The p-tert-butylcalix[4]arene (4), compounds 1 and 5 were synthesized according to procedures given in the literature.^24–26

Scheme 1. Synthesis of Calix-BODIPY derivative.

The synthesis of compound 2

Compound 1 (2.94 mmol, 1.00 g) was dissolved in 60 mL of dry acetone, and 1,2-dibromoethane (58.79 mmol, 5.10 mL) and potassium carbonate (K₂CO₃, 2.94 mmol, 0.41 g) were added to the reaction mixture. The mixture was heated under reflux conditions for 48 hours, and the progress of the reaction was monitored by Thin Layer Chromatography (TLC). After completion, the reaction mixture was extracted three times with 20 mL of dichloromethane (CH₂Cl₂). The combined organic layers were dried over anhydrous sodium sulfate (Na₂SO₄), and the solvent was evaporated under reduced pressure to yield a crude solid. The crude product was further purified by silica gel column chromatography using a mixture of dichloromethane : hexane (1 : 2) as the eluent, affording the desired compound with an R_f value of 0.56. FT-IR: 3018 (aromatic. C–H), 2970–2860 (aliph. C–H), 1609 (C N), 1540 (C C). ¹H NMR (500 MHz; DMSO-d₆): δ_H, ppm: 1.43 (s, 6H, CH₃), 2.46 (s, 6H, CH₃), 3.82 (t, 2H, J: 8.5 Hz, CH₂–Br), 4.41 (t, 2H, J: 8.5 Hz, OCH₂), 6.21 (s, 2H, Ar-H), 7.16 (d, 2H, J: 8.5 Hz, Ar-H), 7.31 (d, J: 8.5 Hz, 2H, Ar-H). MS (ES+), (m/z): cal. for: C₂₁H₂₂BF₂N₂OBr, 447.12; found: 447.024 [M]⁺.

The synthesis of compound 3

Compound 2 (2.24 mmol, 1.00 g) was dissolved in 15 mL of dimethyl sulfoxide (DMSO), followed by the addition of sodium azide (4.47 mmol, 0.29 g) to the reaction mixture. The resulting mixture was heated to 65 °C for 12 hours. The progress of the reaction was monitored using Thin Layer Chromatography (TLC). After completion of the reaction, the mixture was extracted three times with 20 mL of dichloromethane (CH₂Cl₂). The combined organic layers were dried over anhydrous sodium sulfate (Na₂SO₄), and the solvent was removed under reduced pressure using a rotary evaporator. The crude product was purified to afford compound 3 in pure form. FT-IR: 2950 (aromatic. C–H), 2915 (aliph. C–H), 2120 (C–N₃). ¹H NMR (500 MHz; DMSO-d₆): δ_H, ppm: 1.38 (s, 6H, CH₃), 2.40 (s, 6H, CH₃), 3.65 (t, J: 6 Hz, 2H, CH₂–N₃), 4.20 (t, J: 6 Hz, 2H, OCH₂), 6.16 (s, 2H, Ar-H), 7.14 (d, J: 8 Hz, 2H, Ar-H), 7.26 (d, J: 8.5 Hz, 2H, Ar-H). MS (ES+), (m/z): cal. for: C₂₁H₂₂ON₅BF₂, 409.24; found: 409.147 [M]⁺.

The synthesis of compound 6 (Calix-BODIPY)

Compound 5 (1.25 mmol, 1 g) was dissolved in 20 mL of dry toluene. To this solution, a mixture of compound 3 (5.00 mmol, 2.04 g), copper(i) iodide (CuI, 1.25 mmol, 0.24 g), and triethylamine (2.0 mmol, 0.20 g) dissolved in 20 mL of dimethylformamide (DMF) was added. The reaction mixture was then heated under reflux conditions for 24 hours. Upon completion of the reaction, the mixture was extracted three times with a water–dichloromethane (CH₂Cl₂) system. The combined organic layers were dried over anhydrous sodium sulfate (Na₂SO₄), and the solvent was evaporated under reduced pressure using a rotary evaporator. The crude product was purified by silica gel column chromatography using an ethyl acetate/hexane (1 : 2) solvent system as an eluent to afford the desired compound. FT-IR: 3000 (aromatic. C–H), 2900 (aliph. C–H), 2126 cm⁻¹ (C–N₃). ¹H NMR (500 MHz; DMSO-d₆): δ_H, ppm: 1.16 (s, 36H, tert-butyl), 1.41 (s, 24H, CH₃), 2.46 (s, 24H, CH₃), 3.23 (d, J: 12.5, 4H, Ar-CH₂-Ar), 3.73(t, J: 8 Hz, N–CH₂), 4.02 (s, 8H, Calix-O-CH₂), 4.39 (t, J: 8 Hz, O–CH₂), 4.62 (d, J: 12.5 Hz, 4H, Ar-CH₂-Ar), 6.20 (s, 8H, Ar-H, pyrrole), 7.08 (s, 8H, Ar-H, calix), 7.18 (d, J: 8 Hz, 8H, Ar-H), 7.22 (d, J: 8 Hz, 8H, Ar-H), 7.30 (d, J: 8 Hz, 4H, Ar-H). MS (ES+), (m/z): cal. for: C₁₃₉H₁₅₂N₂₀O₈B₄F₈, 2426.05; found: 2427.431 [M]⁺.

Determination of the fluorescence quantum yield

The fluorescence quantum yield (Φ_F) is determined by using rhodamine 6G in water (Φ_F = 0.95) as a standard.²⁷ Through testing, the absorption and fluorescence spectra of Calix-BODIPY and rhodamine 6G were recorded and the quantum yield is determined by the comparative method using the following equation:^27–29

1

where Φ_F and Φ_Fstd are quantum yield of the sample and the standard, A and A_std are the values of the sample and standard at the excitation wavelength, respectively. I and I_std are the areas under the fluorescence emission peaks of the sample and standard. The ‘η’ refers to refractive index of the sample and ‘η_std’ refers to refractive index of the standard, respectively.

General procedure of spectroscopic experiments

Stock solutions of nitrate salts of metal ions and the Calix-BODIPY derivative were prepared in ultra-pure water and EtOH, respectively. All spectral measurements were carried out using a micropipette in a 3 mL spectroscopic quartz cuvette at 25 °C. In order to identify the selectivity of the developed fluorescence sensor, the impact of interfering species including different metal cations (Na⁺, Ca²⁺, K⁺, Ag⁺, Cu²⁺, Al³⁺, Zn²⁺, Pb²⁺, Cd²⁺, Co²⁺, Ni²⁺, Fe³⁺, NH₄⁺) and anions (S₂O₃²⁻, CO₃²⁻, HSO₃⁻, NO₃⁻, NO₂⁻, HPO₄²⁻, H₂PO₄⁻) on the fluorescence intensity of the Calix-BODIPY were measured. All ions were measured at the same concentration (0.1 M) and under the same condition.

Real sample analysis

To investigate the real sample application of the Calix-BODIPY sensor to determination of Fe³⁺ ions was evaluated by analyzing tap water and well water samples using fluorescence emission spectroscopy. Tap water and well water samples were collected and filtered through 0.22 µm pore size membrane filter and centrifuged at 12 000 rpm for 10 min, and the clean water samples were used to prepare the Fe³⁺ solution to be tested.

Results and discussion

Photophysical properties of Calix-BODIPY derivative

The excitation and emission behavior of the synthesized Calix-BODIPY was tested in ten different solvents with varying polarities, including toluene, chloroform, DMF, THF, ethyl acetate, DMSO, DCM, acetone, ethanol and methanol (Fig. 1). In accordance with this purpose, the absorbance and fluorescence emission spectra of the compound were measured in various solvents using 1 × 10⁻⁵ M and 1 × 10⁻⁶ M Calix-BODIPY solutions. The absorbance and fluorescence spectra were recorded directly without normalization, and the values are presented in their original scales as absorbance units and arbitrary units (a.u.), respectively, corresponding to the detector responses. Compared to other solvents, ethanol was found to have better intensity peaks for excitation and emission. Thus, ethanol was used as the solvent for Calix-BODIPY in further studies.

Fig. 1. (a) UV-vis absorption spectra for 1 × 10⁻⁵ M Calix-BODIPY in different solvents. (b) Fluorescence spectra for 1 × 10⁻⁶ M Calix-BODIPY in different solvents.

The calculation results of the absorption and fluorescence emission spectra of Calix-BODIPY indicated that the optimal absorption, emission and excitation wavelengths were observed at 496, 508 and 460 nm, respectively (Fig. 2). Stokes shift was calculated 12 nm for this compound. This relatively small Stokes shift showed minimal structural relaxation between the ground and excitation states. The quantum yield (Φ_F) of the Calix-BODIPY was found to be 0.235. Molar absorptivity (ε) was found as 125.5 × 10³ M⁻¹ cm⁻¹ (Table 1).

Fig. 2. Absorption, excitation and emission spectra of Calix-BODIPY.

Table 1. The photophysical parameters of Calix-BODIPY derivative.

λ ex (max, nm)	λ em (max, nm)	λ ab (max, nm)	Quantum yield	Molar absorptivity (M−1 cm−1)
496	508	496	0.235	125.5 × 103

Selectivity

To assess the selectivity of the Calix-BODIPY sensor, different cations and anions were added to the Calix-BODIPY solution at 10 µL each and fluorescence measurements were performed. The results of the fluorescence spectra of the Calix-BODIPY solution (Fig. 3) showed significant fluorescence quenching upon the addition of Fe³⁺ ions. In contrast, the addition of other metal cations and anions, including Na⁺, Ca²⁺, K⁺, Ag⁺, Cu²⁺, Al³⁺, Zn²⁺, Pb²⁺, Cd²⁺, Co²⁺, Ni²⁺, NH₄⁺, S₂O₃²⁻, CO₃²⁻, HSO₃⁻, NO₃⁻, NO₂⁻, HPO₄²⁻ and H₂PO₄⁻ did not lead to significant changes in the fluorescence intensity of the Calix-BODIPY solution. These results showed further that Calix-BODIPY could be used for selective detection of Fe³⁺. Therefore, Calix-BODIPY can be used as a fluorescent turn-off sensor for the detection of Fe³⁺ ions.

Fig. 3. Fluorescence spectra of the Calix-BODIPY upon addition of different cations and anions.

Time response of Calix-BODIPY towards Fe³⁺ ions

The effect of reaction time on the fluorescence intensity of Calix-BODIPY after Fe³⁺ addition was investigated. The findings are presented in Fig. 4. Calix-BODIPY reached its maximum fluorescence intensity in 10 seconds, after which the fluorescence intensity remained a steady state for up to 10 minutes. Furthermore, a waiting time of 10 s before the measurement was observed for the interaction between the Calix-BODIPY–Fe³⁺ complex.

Fig. 4. Fluorescence spectra of the Calix-BODIPY (1 × 10⁻⁶ M) after adding Fe³⁺ (0.1 M) over time.

Binding stoichiometry and fluorescent quenching mechanisms of Calix-BODIPY–Fe³⁺ complex

To study the binding of Calix-BODIPY with Fe³⁺, the Job's plot method was employed. The overall concentration of Calix-BODIPY and Fe³⁺ maintained at 1 µM and the mole fraction of Fe³⁺ was changed from 0 to 1. The Job's plot indicates that the mole fraction of Fe³⁺ is 0.33, revealing a 1 : 2 binding stoichiometry between Calix-BODIPY and Fe³⁺ (Fig. 5a).

Fig. 5. (a) Job's plot (b) Stern–Volmer plot for the Calix-BODIPY with the addition of different concentrations of Fe³⁺ (332–3537 µM) (λ_ex = 460 nm and slit width = 5 nm).

The fluorescence quenching mechanism is determined by the Stern–Volmer equation:I₀/I = 1 + K_sv[M]where K_sv is the Stern–Volmer quenching constant, [M] is the molar concentration of the Fe³⁺, I₀ and I represent the fluorescence intensities of the Calix-BODIPY in the absence and presence of Fe³⁺, respectively. As depicted in Fig. 5b, a linear fluorescence response is observed with increasing Fe³⁺ concentration up to 2913 µM, and beyond this value, a positive divergence becomes apparent for the Calix-BODIPY–Fe³⁺ system. This indicates that the fluorescence quenching of Calix-BODIPY involves a combination of both static and dynamic quenching mechanisms.

Sensitivity

In order to investigate the sensitivity of Calix-BODIPY towards Fe³⁺, fluorescence titration experiments were conducted. Fluorescence emission spectra of Calix-BODIPY upon incremental addition of Fe³⁺ ions were measured and the changes in fluorescence intensity with the concentration of Fe³⁺ were plotted (Fig. 6a). The results revealed that the fluorescence intensity of Calix-BODIPY significantly decreased as the Fe³⁺ concentration increased. The fluorescence changes (ΔI = I₀ − I) against the Fe³⁺ concentration display a good linearity in the range of 332 to 3537 µM, according to equations; Y = 0.1949X + 86.1346, R² = 0.9835. Further, the limit of detection (LOD) and limit of quantification (LOQ) were calculated from the equations LoD = 3σ/S and LOQ = 10σ/S, where σ is the standard deviation of the Calix-BODIPY and s is the slope of the calibration curve. The calculated LOD and LOQ were found 87.65 µM and 292.17 µM, respectively. The above results indicating that high sensitivity of Calix-BODIPY for qualitative detection of Fe³⁺.

Fig. 6. (a) Fluorescence titration plot of the Calix-BODIPY with incremental addition of Fe³⁺ ions (332 to 3537 µM). (b) Linearity curve.

Precision

Intra-day and inter-day precisions were identified by conducting three replicates at each concentration in a single day and three times the detection of each concentration in three consecutive days, respectively. Intra-day RSD and inter-day RSD were ranging from 0.07% to 0.23% and 0.10% to 3.13%, respectively (Table 2). The RSD values are within the expected range and the results affirm the method has a satisfactory precision.

Table 2. The precision values of the Calix-BODIPY for fluorescence sensing.

Intra-day (n = 3)				Inter-day (n = 3)
Added (mM)	0.573	2.102	3.274	0.573	2.102	3.274
Found (mM)	0.573	2.110	3.274	0.555	2.122	3.287
	0.571	2.106	3.274	0.584	2.123	3.277
	0.573	2.108	3.278	0.588	2.126	3.280
Mean	572.22	2108.19	3275.17	575.68	2123.79	3281.12
SD	1.29	2.15	2.24	18.04	2.15	4.89
RSD (%)	0.23	0.10	0.07	3.13	0.10	0.15

Real sample

Quantitative detection of Fe³⁺ was performed using environmental water samples, including tap water and well water. Different concentrations (0.573, 1.423 and 2.102 mM) of Fe³⁺ were spiked into each sample, and fluorescence measurements were taken three times for each concentration. The recovery values, shown in Table 3, range from 82.52% to 121.12% for tap water and from 75.17% to 107.65% for well water. The spike and recovery analysis results demonstrate that Calix-BODIPY can be used for Fe³⁺ detection in tap water and well water samples.

Table 3. Measurement of Fe³⁺ in environmental water samples.

Samples	Fe3+ spiked (mM)	Fe3+ found (mM)	Recovery (%)	RSD (%)
Tap water	0	NDa	—	—
	0.573	0.473	82.52	0.18
	1.423	1.723	121.12	0.15
	2.102	2.225	105.84	0.28
Well water	0	NDa	—	—
	0.573	0.431	75.17	0.30
	1.423	1.532	107.65	0.12
	2.102	2.067	98.30	0.19

^aNot detected.

A comparison of the “turn-off” fluorescence methods developed in this study with previously reported fluorescence-based approaches for Fe³⁺ ion detection is presented in Table 4.

Table 4. Comparison of reported spectrofluorimetric methods for Fe³⁺ ion determination.

Materials	Method	Linear range (mM)	LOD (mM)	Application	References
C6&RhB@UiO-66-Ph	Fluorescence	0–0.6	7.1 × 10−4	Tap, lake and river water	21
Naphthoquinone-based chemosensor	Fluorescence	0.5 × 10−2 to 1.0	0.23 × 10−3	Spring, rain, fall, and tap water	30
Carbon dots	Colorimetric	0–0.57	0.18 × 10−3	Lake, farm, and tap water	31
AgNPs	Colorimetric	0.03–0.08	0.45 × 10−2	Tap, drinking water	32
Nitrogen-doped carbon dots	Fluorescence	0–2 × 10−3	0.07	Biological samples	20
PBA@Q[10]	Fluorescence	0–3 × 10−3	0.55	Not reported	33
Lignin–BODIPY probe	Fluorescence	Not reported	0.11–0.21	Not reported	34
Calixarene-based resorcinarene	Fluorescence	Not reported	12.14	Tap and river water	35
Kumarin modified calix[4]arene	Fluorescence	0.033–0.0354	0.30	Tap, well water	36
BODIPY modified calix[4]arene	Fluorescence	0.33–3.53	0.087	Tap, well water	This work

As summarized in Table 4, a wide variety of fluorescence- and colorimetric-based systems have been developed for the detection of Fe³⁺ ions, employing diverse platforms such as metal–organic frameworks, carbon-based nanomaterials, nanoparticles, and supramolecular host systems. Many nanomaterial-based sensors, including carbon dots and lignin-derived probes, exhibit very low detection limits in the sub-micromolar range, reflecting their high sensitivity. However, these systems often involve complex synthesis routes, heterogeneous structures, or potential reproducibility issues. In contrast, molecular and supramolecular sensors, such as calixarene-based receptors, generally provide well-defined structures and improved selectivity, although their detection limits are typically in the micromolar range.

In this context, the developed Calix-BODIPY sensor demonstrates competitive performance, offering a broad linear detection range (330–3530 µM), rapid response (∼10 s), and excellent selectivity toward Fe³⁺ ions over various competing species. Notably, the successful application of the sensor in real tap water and well water samples highlights its practical applicability. Furthermore, the integration of a calixarene framework with a BODIPY fluorophore enables a structurally well-defined sensing system with clear signal transduction behavior, governed by both static and dynamic quenching mechanisms. Although the detection limit is higher than that of some nanomaterial-based systems, the overall balance of selectivity, response time, structural precision, and real-sample applicability makes the proposed system a promising candidate for Fe³⁺ detection.

Conclusion

In this study, a novel calix[4]arene-functionalized BODIPY derivative (Calix-BODIPY) was successfully designed, synthesized, and fully characterized as a fluorescent sensor for Fe³⁺ ion detection. The integration of the calixarene platform with the BODIPY fluorophore enabled the construction of a well-defined supramolecular sensing system, combining strong molecular recognition capability with favorable photophysical properties.

The developed sensor exhibited a selective fluorescence “turn-off” response toward Fe³⁺ ions over a wide range of competing cations and anions, demonstrating the effectiveness of the calixarene-based binding sites. Photophysical investigations revealed that the sensing mechanism involves both static and dynamic quenching processes, providing insight into the interaction between the sensor and Fe³⁺ ions. In addition, the system displayed a rapid response time of approximately 10 s, highlighting its suitability for real-time detection.

Although the detection limit of the proposed sensor is higher than that of some recently reported nanomaterial-based systems, it offers several important advantages, including a structurally well-defined molecular framework, operational simplicity, high selectivity, and good reproducibility. Notably, the successful application of the sensor in environmental water samples (tap and well water) without complex sample preparation further demonstrates its practical applicability.

Overall, this work presents a promising strategy for the development of calixarene-based fluorescent sensors through the incorporation of BODIPY fluorophores. The results highlight the potential of such hybrid supramolecular systems as reliable and efficient tools for metal ion detection. Future studies may focus on improving sensitivity through structural modification and expanding the applicability of this platform toward other environmentally and biologically relevant analytes.

Author contributions

Ömer Güngör: senior author/corresponding author: methodology, investigation, supervision, project administration, writing – review & editing, synthesis and characterization. Neşe Taşci: corresponding author, supervision, writing – review & editing, writing – original draft, project administration, conceptualization, formal analysis, visualization, validation. Ayça Şeyma Ünaldi: writing – review & editing, formal analysis, conceptualization. Mahmut Durmuş: corresponding author, supervision, writing – original draft, project administration, conceptualization.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

The data supporting the findings of this study are available within the article and its supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d6ra04073j.