Sensors and Actuators B 237 (2016) 621–627
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Diamidonaphthalenodipyrrole-derived ﬂuorescent sensors for anions Janusz Jurczak ∗ , Pawel Dydio 1 , Pawel Stepniak, Tomasz Zielinski 2 Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw, Poland
a r t i c l e
i n f o
Article history: Received 26 January 2016 Received in revised form 23 June 2016 Accepted 24 June 2016 Keywords: Fluorescence (Benzo)pyrroles Anions Complexation Molecular recognition
a b s t r a c t We describe the synthesis and properties of bisamide derivatives of naphthalenedipyrrole, which represent a convenient platform for the construction of ﬂuorescent anion sensors. As we show, the spectroscopic properties of such sensors can be ﬁne-tuned through small modiﬁcations of the structure at the sensor periphery. The strong ﬂuorescence of these compounds is perturbed through the binding of anionic species in the binding pocket through four hydrogen bonds. Importantly, these effects depend on the nature of the anionic guest, its concentration, and the speciﬁc structure of the receptor host. For instance, in the case of one derivative (2a) the ﬂuorescence is selectively quenched upon addition of PhCO2 − , while other anions do not have an effect on its spectral properties. In another case (2b), only H2 PO4 − triggers a spectacular enhancement of ﬂuorescence (more than ﬁve times higher intensity), while other anions do not change its spectral properties. Such selective responses are related to the selectivity of the anionic species binding, which can be controlled with the structure of the binding pocket. Overall, the study demonstrates that a diamidonaphthalenedipyrrole platform can be used to construct selective sensors for anions that allow for fast and efﬁcient identiﬁcation of the desired anion present in the analytical samples. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Fluorescent sensors for anions that respond selectively to the presence of desired anionic species are attractive for the development of fast and efﬁcient analytical methods, suitable for high-throughput applications, such as: monitoring against environmental pollution, controlling industrial processes, as well as, medical diagnostic methods . While myriads of highly selective anion receptors have been reported , there is only a limited number of ﬂuorescent sensors, which properties change upon anion binding, hence offering limited potential for such applications . The common issue is the separation of the binding site from the reporting site – the ﬂuorescent moiety, which results in weak responses of the sensor upon anion binding . We envisioned that the construction of sensors with the ﬂuorescent moiety incorporated directly into the binding site would allow to overcome such limitations.
∗ Corresponding author. E-mail address: jurczak [email protected]
(J. Jurczak). 1 Present address: Department of Chemistry, University of California, Berkeley, California 94720, United States. 2 Present address: SynthSys and School of Biological Sciences, University of Edinburgh, C.H. Waddington Building, Edinburgh EH9 3JD, UK. http://dx.doi.org/10.1016/j.snb.2016.06.142 0925-4005/© 2016 Elsevier B.V. All rights reserved.
Pyrrole and benzopyrroles bearing amide functions have been used to construct effective anion receptors . For instance, diamide derivatives of benzodipyrrole (1) can bind hydrogenpyrophosphate in aqueous solution (acetone with 5% water), as reported by Curiel et al. . Inspired by these results and taking into account the absorption-emission properties of the naphthalene moiety, we designed the diamidonaphthalenodipyrrole platform that combines the ﬂuorescent unit with the binding pocket. We synthesized receptors, equipped with two amide groups and both n-butyl (2a) or phenyl (2b) residue. Here we report the synthesis and properties of these compounds as the sensors for anions.
2. Material and methods Fluorescence measurements were conducted in DMSO dried over molecular sieves (4 Å). Solutions of 6 × 10−6 M of ligands were
J. Jurczak et al. / Sensors and Actuators B 237 (2016) 621–627
used. The slit width was 0.5 m/0.3 m (ex/em). Compounds 2a and 2b were excited by 320 and 350 nm, respectively, spectra were registered with 1 nm interval and 0.5 s acquisition time. NMR titration experiments were conducted in DMSO-d6 (with 0.5% H2 O). In a typical, experiment 0.55 ml of receptor solution (12–17 mM) was titrated with TBA salt dissolved in a receptor solution (to avoid receptor dilution). 12–16 titration points were taken. Ka ’s were calculated using HypNMR software , taking all N H protons into account. In most cases, 1:1 stoichiometry allowed good reﬁnement. In case of 2b:H2 PO4 − complex sequential binding model was used in reﬁnement. Mass spectra were recorded using EI BE sector mass spectrometer. All measurements of crystals were performed on a KM4CCD -axis diffractometer with graphite-monochromated MoK␣ radiation. The crystal was positioned at 65 mm from the CCD camera. 1500 frames were measured at 0.5◦ intervals with a counting time of 12 s. The data was corrected for Lorentz and polarization effects. Empirical correction for absorption was applied . Data reduction and analysis were carried out with the Oxford Diffraction programs . The structure was solved by direct methods  and reﬁned using SHELXL . The reﬁnement was based on F2 for all reﬂections except those with very negative F2 . Weighted R factors and all goodness-of-ﬁt S values are based on F2 . Conventional R factors are based on F with F set to zero for negative F2 . The Fo 2 > 2(Fo 2 ) criterion was used only for calculating R factors and is not relevant to the choice of reﬂections for the reﬁnement. The R factors based on F2 are about twice as large as those based on F. All hydrogen atoms were located geometrically and their position and temperature factors were not reﬁned. Scattering factors were taken from Tables 220.127.116.11 and 18.104.22.168 in Ref. . 2.1. Diethyl 2,2 -(2,2 -(naphthalene-2,3-diyl)bis(hydrazin-2-yl1-ylidene))dipropanoate 5 Double-necked ﬂask, equipped with funnel, was charged with Na2 SO3 (60 g) and dissolved in boiling water. H2 SO4 (40 ml) was dropped into the solution. Evolved SO2 (15 g) was coldtrapped, and cooled hydrazine monohydrate (55 ml) was slowly added. The mixture was diluted with ethanol (35 ml) and 2,3dihydroxynaphtalene (170 mmol, 27 g) was added. It was then reﬂuxed for 6 h and left for 12 h to cool down. Resulting precipitate was ﬁltered off, washed with ethanol (250 ml), affording 21 g (65%) of 4 which was subjected to next reaction step without further puriﬁcation. Methyl pyruvate (22 ml) was added into vigorously stirred solution of hydrazine 4 (11 g, 58 mmol) in ethanol (15 ml). After a few minutes a yellow solid precipitated. Stirring was continued for 2 h, and the precipitate was ﬁltered off and washed with cold ethanol (250 ml). After recrystallization from ethanol yellow crystals of 5 (13.4 g, 70%) were obtained. mp. 123–124◦ C (lit . 123−125◦ C); 1 H NMR (200 MHz, CDCl ) ı = 9.18 (bs, 2H), 7.64 (m, 2H), 7.60 3 (s, 2H), 7.28 (m, 2H), 4.32 (q, 4H, J1 = 7 Hz), 2.18 (s, 6H), 1.37 (t, 6H, J1 = 7 Hz). 13 C NMR (50 MHz, CDCl ) ı = 164.8, 133.9, 131.6, 129.9, 126.5, 3 124.7, 112.6, 61.2, 14.4, 10.8. 2.2. Diethyl 1,10-dihydrobenzo[e]pyrrolo[3,2-g]indole-2,9-dicarboxylate 6 P2 O5 (142 g, 1 mol) was dissolved in diethyl ether (300 ml) and chloroform (150 ml) and reﬂuxed for 4 d under Ar. Resulting solution was decanted from a yellowish precipitate. The clear solution was concentrated and the residual solvents were evaporated under
vacuum in 40◦ C for 2 d. Hydrazide 5 (8.8 g, 23 mmol) and PPE (100 g) was stirred for 1 h in 100◦ C. The mixture was then poured into water (500 ml), and the resulting precipitate was ﬁltered off and washed with water (500 ml) until the ﬁltrate became neutral. The crude product has been recrystallized twice from ethyl acetate, resulting in 6.4 g (80%) of crystals of ester 6. mp > 280◦ C (lit . 315◦ C); 1 H NMR (200 MHz, DMSO) ı = 11.87 (d, 2H, J = 1.8 Hz), 1 8.34–8.29 (m, 2H), 7.82 (d, 2H, J1 = 2.2 Hz), 7.48–7.44 (m, 2H), 4.38 (q, 4H, J1 = 7.2 Hz), 1.38 (t, 6H, J1 = 7.2 Hz); 13 C NMR (50 MHz, DMSO) ı = 161.6, 126.1, 125.5, 124.8, 124.4, 122.2, 109.7, 61.1, 15.1; LR ESI calcd for C20 H18 N2 O4 [M+H]+ : 351.13, found: 351.16. 2.3. 1,10-Dihydrobenzo[e]pyrrolo[3,2-g]indole-2,9-dicarbonyl dichloride 7 Ester 6 (1.5 g, 4.4 mmol) was dissolved in i-PrOH (8 ml) and KOH (6 g, solution in 50 ml of water) was added and the mixture was reﬂuxed for 8 h. Active charcoal was added, reﬂuxed for a few minutes and subsequently ﬁltered on Celite. The ﬁltrate was acidiﬁed and the precipitate was ﬁltered off, washed with water (200 ml) and air-dried. The crude product was then dissolved in THF, triturated with hexanes, yielding 1 g (80%) of diacid (colorless crystals). Diacid (0.7 g, 2.4 mmol) was suspended in CH2 Cl2 (20 ml) and thionyl chloride (1.7 ml, 24 mmol) was added. After addition of two drops of DMF the mixture was reﬂuxed under Ar. During reﬂux SOCl2 (0.85 ml, 12 mmol, in 10 ml of CH2 Cl2 ) was added after 8 and 16 h. After 30 h of continuous reﬂux mixture was cooled down to rt and green precipitate of dichloride 7 was ﬁltered off, washed with CH2 Cl2 , and dried under vacuum, yielding 0.75 g (94%) of green crystals which were used without further puriﬁcation. Mp. 238–240◦ C (lit . 240–241◦ C). 2.4. N2 ,N9 -Dibutyl-1,10-dihydrobenzo[e]pyrrolo[3,2-g]indole2,9-dicarboxamide 2a Ester 6 (0.6 g, 1.6 mmol) and butylamine (4 ml) were placed in a dry vial, sealed and heated at 70◦ C for 12 h. The mixture was then diluted with EtOAc (50 ml) and washed with 2 M HCl (3 × 30 ml) and brine (20 ml), dried over MgSO4 , and evaporated under reduced pressure. The crude product was crystalized from EtOAc (20 ml) with a few drops of THF, yielding 0.52 g (80%) of colorless crystals of amide 2a. Mp. > 280◦ C. 1 H NMR (200 MHz, DMSO) ı = 11.73 (d, 2H, J = 1.6 Hz), 8.48 (t, 1 2H, J1 = 5.7 Hz), 8.13–8.08 (m, 2H), 7.74 (d, 2H, J1 = 2.0 Hz), 7.48–7.44 (m, 2H), 3.34 (dt, 4H, J1 = 6.2 Hz, J2 = 6.4 Hz), 1.56 (m, 4H), 1.35 (m, 4H), 0.93 (t, 6H, J1 = 7.3 Hz); 13 C NMR (50 MHz, DMSO) ı = 161.2, 128.8, 125.9, 124.6, 123.5, 123.0, 120.8, 103.6, 38.9, 32.0, 20.2, 14.3; HR EI calcd for C24 H28 N4 O2 M+ : 404.22123, found: 404.22256; Elemental analysis calcd C24 H28 N4 O2 : C 71.26, H 6.98, N 13.85, found: C 69.66, H 6.86, N 13.19. 2.5. N2 ,N9 -Diphenyl-1,10-dihydrobenzo[e]pyrrolo[3,2-g]indole2,9-dicarboxamide 2b Dichloride 7 (0.74 g, 2.2 mmol) was dissolved in THF (60 ml) and aniline (6 ml, 66 mmol) was added. A white solid precipitated. The mixture was stirred for 6 h and then ﬁltered. The ﬁltrate was poured slowly into HCl solution (3 ml of concentrated acid in 80 ml of water). The precipitate was ﬁltered off, washed with water,
J. Jurczak et al. / Sensors and Actuators B 237 (2016) 621–627
2a 80% (d)
CO2Et N N
80% O OEt
86% O Cl
7 Scheme 1. Synthesis of receptors 2a and 2b. (a): H2 NNH2 , NH2 NH2 SO3 , (b): CH3 COCO2 CH2 CH3 , (c): PPE, (d): PhNH2 , (e): KOHaq , i-PrOH, then SOCl2 ,CH2 Cl2 (f): n-BuNH2 .
air-dried and crystallized from EtOAc, affording 0.85 g (86%) of amide 2b as colorless crystals. mp. > 280◦ C 1 H NMR (200 MHz, DMSO) ı = 11.96 (s, 2H), 10.30 (s, 2H), 8.24–8.19 (m, 2H), 8.08 (d, 2H, J1 = 2.2 Hz), 7.86 (d, 4H, J1 = 7.6 Hz), 7.56–7.52 (m, 2H), 7.40 (dd, 4H, J1 = J2 = 7.6 Hz), 7.12 (t, 2H, J1 = 7.4 Hz); 13 C NMR (50 MHz, DMSO) ı = 159.8, 139.6, 129.2, 128.6, 126.0, 125.0, 123.9, 123.7, 121.4, 120.5; 105.4; HR EI calcd C28 H20 N4 O2 M+ : 444.15863, found: 444.16023; Elemental analysis calcd for C28 H20 N4 O2 : C 75.66, H 4.54, N 12.60, found: C 75.42, H 4.6, N 12.34.
2.6. Structural analysis Crystallographic data for 2b·TBA Cl : monocrystal was obtained by slow evaporation of DMSO from the solution of salt and receptor and diffusion of H2 O. C150 H210 N16 O7 Cl14 S, M = 2523.20, monoclinic, P2(1)/n, a = 8.4737(7) Å, b = 28.4670(17) Å, c = 58.668(5) Å, ␣ = 90◦ , ␤ = 90.082(7)◦ , = 90◦ , V = 14152.0(18) Å3 , T = 100(2) K, Z = 4, (Mo-K␣) = 0.159 mm−1 , 133156 collected reﬂexes, 34439 unique (Rint = 0.1732). Final R indices [I > 2(I)]: R1(F2 ) = 0.0781 and wR2(F2 ) = 0.1832, R indices (all data) R1(F2 ) = 0.2729 i wR2(F2 ) = 0.2689. All heavy atoms were reﬁned anisotropically. All hydrogen atoms were located geometrically. Crystallographic data for 2b·TBA PhCO2 : monocrystal was obtained by difusive migration of pentane into ethyl acetate solution of salt and receptor. C102 H122 N10 O8 , M = 1616.10, monoclinic, P2(1)/c, a = 30.1716(10) Å, b = 17.5631(8) Å, c = 17.3588(9) Å, ␣ = 90◦ , 103.162(4)◦ , = 90◦ , V = 2330.07(18) Å3 , T = 100(2) K, Z = 4, (Mo-K␣) = 0.076 mm−1 , 137028 collected reﬂexes, 37545 unique (Rint = 0.0607). Final R indices [I > 2(I)]: R1(F2 ) = 0.0710 and wR2(F2 ) = 0.1715, R indices (all data): R1(F2 ) = 0.1566 i wR2(F2 ) = 0.2136. All heavy atoms were reﬁned anisotropically. All hydrogen atoms were located geometrically.
3. Results and discussion Receptors 2a and 2b were prepared, as shown in Scheme 1 . 2,3-Dihydroxynaphthalene (3) was reacted with hydrazonium sulfate(IV) to form bishydrazine 4, followed by its condensation with ethyl pyruvate to afford hydrazide 5. Fisher-type condensation of 5, employing polyphosphoric ester, afforded ester 6. Facile hydrolysis of 6 and its chlorination to 7, followed by reaction with
n-butylamine, gave desired compound 2a. Derivative 2b was obtained by direct amidation of ester 6 with aniline. With both putative sensors in hand, we ﬁrst investigated the absorption and emission properties of compounds 2a and 2b (Fig. 1). As expected, 2a and 2b are strongly ﬂuorescent, when irradiated with UV or visible light (Figs. 1 and 2). Compound 2a has two absorption maxima, at 326 and 343 nm, and two ﬂuorescence maxima, at 357 and 372 nm (Fig. 1a). In the case of phenyl derivative 2b, all absorption and emission maxima were about 25 nm redshifted, with the intensity of the ﬂuorescence of 2b about ﬁve times lower than that of 2a, showing that the spectroscopic properties of such naphthalenodipyrrole derivatives can be conveniently controlled with simple modiﬁcations to the structure at the molecule periphery. In the case of both derivatives 2a and 2b, the vibronic structure of the spectra was simpler than that for unsubstituted naphthalene . Similar Stokes shifts and analogous curve shape of absorption and emission spectra suggest that the ﬂuorescence of both receptors is triggered by S1 → S0 transition. We next evaluated the possibility of using 2a and 2b as ﬂuorimetric receptors for anions. We investigated the inﬂuence of the addition of model anions, H2 PO4 − , Cl− , PhCO2 − , on the ﬂuorescent properties of 2a and 2b (Fig. 2). In the case of derivative 2a, addition of Cl- or H2 PO4 − did not cause any signiﬁcant change in emission spectrum, while the addition of benzoate triggered spectacular ﬂuorescence quenching (Figs. 2a and S6). The latter effect was observed only after addition of two equivs of anion into the concentrated receptor solution (10−2 M). Studies with diluted solution of 2a (10−6 M) did not detect ﬂuorescence quenching after addition of benzoate, revealing rather poor afﬁnity of the anion to 2a. Such concentration depended response can be utilized to construct sensors that signal the presence of the desired analyte only above signiﬁcant threshold of its concentration. Interestingly, receptor 2b behaved differently, namely the addition of PhCOO− or Cl− did not have any effect on the spectra, whereas the addition of dihydrogen phosphate caused a spectacular increase in ﬂuorescence (Fig. 2b). In this case, the addition of one equiv. of the anion provided a 50% enhancement of the emission bands even at very low concentration (10−6 M; Fig. 3). The spectra reveal that H2 PO4 − does not change the electron transition character, yet it changes its efﬁciency presumably through affecting the life-time of the excited state. In control experiments, we checked that the inﬂuence of H2 PO4 − is not related to pH change, e.g. through deprotonation of the receptor’s amide or pyrrole moieties, etc. . The addition of TBA hydroxide caused only a slight increase of intensity in the 370–430 nm region, while it triggers
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Fig. 1. Absorption (green) and emission (blue) spectra of compounds 2a and 2b, respectively. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.)
Fig. 2. Fluorescence of receptors 2a (a) and 2b (b) in DMSO. From the left: free receptor, + 2 equivs H2 PO4 − , + 2 equivs Cl− , + 2 equivs PhCOO− (all added as TBA salts).
Fig. 3. Fluorescence spectra of 2a and 2b upon addition of H2 PO4 − and OH− .
evolution of a new band at 450 nm, related to another electron transition for deprotonated 2b. It conﬁrms that the speciﬁc interaction of receptor 2b with H2 PO4 − is responsible for the observed ﬂuorescence enhancement. We postulated that the change of the emission of sensors 2a and 2b triggered by the presence of anions is correlated with the conformational changes upon binding to anions. Such conformational changes depend on the size and geometry of a speciﬁc anion, as well as, on the afﬁnity of that particular anion to the binding site of that receptor. To get a better insight in this correlation we performed detailed conformational studies for 2a and 2b and their afﬁnity towards the model anions.
The NMR titration experiments, performed with TBA salts of the model anions in DMSO-d6 + 0.5% H2 O, revealed the afﬁnity receptors 2a and 2b to anions. To determine the association constants (Ka ) and to identify points of interaction, we analyzed shifts of both pyrrole NH and amide NH proton signals (Table 1). In most cases, we observed the formation of complexes with the 1:1 receptor to anion stoichiometry. Receptors 2a and 2b interact with chloride anions very weakly, with Ka < 5 M−1 . Titration of 2a with PhCOO− showed two different trends of the proton shifting, for both amide and pyrrole NH signals, revealing that carboxylate interacts more strongly with the latter moiety. Interestingly, receptor 2b exhibited higher
J. Jurczak et al. / Sensors and Actuators B 237 (2016) 621–627
Fig. 4. Crystal structure of 2b:Cl− complex.
Table 1 Afﬁnity constants of receptors 2 with anions. 1 H NMR titration in DMSO-d6 + 0.5% H2 O at 296 K. 2a
PhCOO H2 PO4 −
150 ± 10 450 ± 10
260 ± 20 K1 = 12700 ± 2900 K2 = 2000 ± 50 2.3 ± 0.5
Shift change was undistinguishable.
afﬁnity towards PhCOO− than analogue 2a for which the ﬂuorescence quenching was observed (vide infra). The relatively low value of Ka is in agreement with the observation that the efﬁcient ﬂuorescence quenching is observed only for more concentrated solution and requires high number of equivalents of the benzoate anion. In the case of H2 PO4 − , 2a interacts with the anion rather weakly, in contrast to its analogue 2b. In that case, we observed a sigmoidal titration curve, indicative for a sequential binding mechanism. We were able to estimate both association constants with >20% uncertainty: K1 > 10 000 M−1 and K2 > 2000 M−1 . This high afﬁnity is in good agreement with the observation of the ﬂuorescence enhancement of 2b upon H2 PO4 − addition observed even at the very low concentration. To evaluate the conformational changes triggered upon anion binding to sensors 2a and 2b, we carried out a series of structural studies. The molecular modeling (DFT B3LYP)  shows that the diamidonaphthalenodipyrrole unit adopts preferentially the anti-anti conformation over syn-syn one (E = 47.9 kJ/mol), which is required for the anion binding with four convergent hydrogen bonds. The NOESY experiments conﬁrmed that receptor 2a adopts the anti-anti conformation (Fig. S5).
Fig. 5. Crystal structure of 2b: PhCOO− complex.
To investigate the conformation of the receptors upon anion binding, we pursued the structural analysis in the solid state. We were able to analyze two crystal structures of complexes of 2b with Cl− and with PhCOO− . The ﬁrst one has demonstrated that the interaction with Cl− does not change the conformation of the receptor which stays in the anti–anti conformation observed before for the free receptor (Fig. 4). Moreover, Cl− is in fact bound with hydrogen bonds formed by two neighboring receptors which interact with the anion employing either amide or pyrrole NH moieties (Fig. 4). In the second case the receptor adopts different conformation (syn-syn) upon PhCOO− complexation. Such conformation allows the formation of four hydrogen bonds between both pyrrole and amide groups and the centrally located anion (Fig. 5). This also results in the hundred-fold increase in complex stability, as
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conﬁrmed by titration studies (Table 1). The receptor platform in the syn-syn conformation is almost planar, with only phenyl substituents deviated from the plane within 13◦ . These results show that derivatives 2a and 2b can indeed form complexes using four hydrogen bonds, if the interaction is strong enough to induce the conformational change of the receptor. Similar phenomena may be occurring upon H2 PO4 − complexation, yet despite concentrated efforts we were unable to collect the crystallographic data to evaluate the complexes of this anion. The substantial ﬂuorescence enhancement can be also related to the formation of higher ordered species, such as the 1:2 anion to receptor complex, the formation of which was observed during the titration experiments. Undisputedly, the complexation is strong enough to signiﬁcantly change the electron density of the receptor and induce the strong ﬂuorescence enhancement.
4. Conclusions Easy to prepare bisamide derivatives of naphthalenedipyrrole represent a convenient platform for construction of ﬂuorescent anion sensors. The spectroscopic properties of such sensors can be ﬁne-tuned through small modiﬁcation of the structure at the sensor periphery. As demonstrated, the strong ﬂuorescence of these compounds is perturbed through binding of anionic species in the binding pocket with four hydrogen bonds. Importantly, these effects depend on the nature of the anionic guest, its concentration, and the particular structure of the receptor. For instance, in the case of one derivative (2a) the ﬂuorescence is selectively quenched upon addition of PhCO2 − above the certain concentration threshold, while other anions do not have an effect on its spectral properties. In another case (2b), only H2 PO4 − triggers spectacular enhancement of ﬂuorescence (more than ﬁve times higher intensity), while other anions do not change its spectral properties. Such selective responses are related to the selectivity of the anionic species binding, which can be controlled with the structure of the binding pocket. Overall, the study demonstrates that diamidonaphthalenedipyrrole platform can be used to construct selective sensors for anions that allow for fast and efﬁcient identiﬁcation of the desired anion present in the analytical samples.
Acknowledgment This work was ﬁnanced by Polish National Science Centre grant Maestro UMO-2011/02/A/ST5/00439.
Appendix A. Supplementary data 
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2016.06.142. 
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Biographies Janusz Jurczak (1941) obtained his Ph.D. with Prof. Aleksander Zamojski at the Institute of Organic Chemistry (IOC) of the Polish Academy of Sciences in 1970 and he did his postdoctoral research with Prof. Vladimir Prelog at ETH in Zìrich. He has been at the IOC since 1973, where he became an Assistant Professor in 1979 and he was appointed Full Professor in 1988. In 1992 he accepted an additional position at the University of Warsaw. Currently, a major focus of his research is the supramolecular chemistry of anionic species and of dynamic combinatorial libraries, as well as asymmetric catalysis and application of high pressure in organic synthesis, but his real passions are music and wine. Pawel Dydio was born in 1985 in Sanok, Poland. He studied Natural Sciences and Mathematics at the University of Warsaw, Poland (2004–2009), graduating in Chemistry. While at UW, he did undergraduate research in supramolecular chemistry with Prof. Janusz Jurczak. Subsequently, he joined the group of Prof. Joost Reek at the University of Amsterdam, the Netherlands, where he worked on the discovery and development of new supramolecular strategies in homogeneous transition metal catalysis. After completing his Ph.D. in late 2013, he decided to join the group of Prof. John Hartwig at UC Berkeley, as a postdoctoral fellow, to study the potential of artiﬁcial metal-enzymes and catalytic networks in organic synthesis. In his spare time, Pawel enjoys playing sports and running, reading, cooking and spending time with friends. Pawel Stepniak was born in 1986 in Warsaw, Poland. He studied chemistry and biotechnology at the University of Warsaw, graduating in chemistry in 2009. He continued his academic career in Prof. Janusz Jurczak group at UW, pursuing Ph.D. studies. He was investigating complexing properties of cyclodextrins derivatives towards amino acids. He obtained Ph.D. in 2014 and joined Prof. Jurczak group in the Institute of Organic Chemistry PAS. He is currently investigating new platforms for organic anions receptors. His interests are: organ music, sailing and roman law. Tomasz Zielinski was born in 1976 in Poland. He studied Chemistry and Informatics at the University of Warsaw, Poland (1995–2003), graduating in both disciplines. Then he joined Prof. Janusz Jurczak group in the Institute of Organic Chemistry PAS, where he obtained Ph.D. in 2006. Currently he is a computational resource manager in the School of Biological Sciences, University of Edinburgh, where he is engaged in system biology projects. He is interested in sailing, roller skating and fantasy.