- Email: [email protected]
Fluorescent chemosensor for Ag(I) based on amplified fluorescence quenching of a new phthalocyanine bearing derivative of benzofuran
Polyhedron 28 (2009) 3110–3114
Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
Fluorescent chemosensor for Ag(I) based on amplified fluorescence quenching of a new phthalocyanine bearing derivative of benzofuran Mehmet Kandaz a,*, Orhan Güney b,*, Filiz B. Senkal b a
Sakarya University, Department of Chemistry, 54140 Esentepe, Sakarya, Turkey Istanbul Technical University, Department of Chemistry, 34469 Maslak, Istanbul, Turkey
b_
a r t i c l e
i n f o
Article history: Received 23 March 2009 Accepted 24 June 2009 Available online 27 June 2009 Keywords: Phthalocyanine Zinc aggregation Optical metal sensor Silver ion Fluorescence quenching
a b s t r a c t A fluorescent chemosensor for Ag(I) as a new family of peripherally functionalized zinc-phthalocyanine, 2(3),9(10),16(17),23(24)-tetrakis-{6-(-benzofuran-2-carboxylate)-hexylthio} phthalocyaninatozinc(II) {Zn[Pc(b-S(CH2)6OCOBz-furan)4], (ZnPcBzF), (3), which was derivated from 6-(3,4-dicyanophenylthio)hexyl–2-benzofuranate (BzF), (2), has been synthesized and fully characterized by elemental analysis, FT-IR, 1H and 13C NMR, MS (ESI and Maldi-TOF). An optical silver ion (Ag(I)) sensor based on the fluorescence quenching of benzofuran moiety and ZnPc core was developed. Both absorbance and fluorescence spectra of ZnPcBzF, (3) exhibit distinct changes in visible region in response to treatment with Ag(I) ion in solution. Such properties make compound ZnPcBzF, (3) intriguing candidates for incorporation into the transducer layer in optically based chemical sensors. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction An understanding of the electronic communication between chromophores is of great significance in designing organic materials for applications in optoelectronic technologies [1]. Therefore, much interest is devoted the construction of precisely defined molecular materials designed to perform specific functions such as chemical sensors [2,3], semiconductivity [4], fibrous assemblies [5], photovoltaics [6], optical data storage [7]. Phthalocyanines (Pcs) are highly versatile and stable chromophores with unique physicochemical properties that make them, alone or in combination with many other functional structures for the construction of molecular materials or electro and photoactive moieties [8,9]. Therefore, the synthesis of precursors bearing one/or more functionality is vital in the preparation of new photoactive phthalocyanines and the design of Pcs linked to strong fluoroprobe moieties appears particularly promising [9,10]. Optochemical sensor can be prepared based on fluorescence quenching depends on metal ion concentration by immobilizing a fluorophore on a solid substrate and monitoring the change in optical properties of the sensing layer upon interaction with the analyte [10]. When the changes of fluorescence caused by chelation of metal ions are significant and detectable, the chromophore can be used as a fluorescent chemosensor. The majority of fluorescence chemosensors reported
* Corresponding authors. Tel.: +90 264 295 60 42; fax: +90 264 295 59 50 (M. Kandaz), tel.: +90 212 285 31 62; fax: +90 212 285 63 86 (O. Güney). E-mail addresses: [email protected] (M. Kandaz), [email protected] (O. Güney). 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2009.06.058
to date for the detection of metal ions are either crown ether or their analogs [11–14]. In order to extend the scope of the metal ion chemosensor from crown ether-based systems to other sensory units [12–16], we have designed new phthalocyanine derivatives which bear four peripheral derivatives of benzofuran substituents as antennae. We previously reported on preparation of peripheral functional macrocycle phthalocyanines and demonstrated changes in the optical spectra brought about by peripheral metal ion binding as part of a development of functionalized phthalocyanines (Pc) with multiple metal ion binding sites [17,18]. In present work, we have synthesized a new benzofuran derivative, BzF (2), and designed a zinc phthalocyanine,2(3),9(10), 16(17),23(24)-tetrakis-{6-(-benzofuran-2-carboxylate)-hexylthio}phthalocyaninatozinc(II), ZnPcBzF (3), as a fluorescent chemosensor for the purpose of quantitative detecting of Ag(I) ion based on fluorescence quenching. A comparative study on silver ion recognition property of ZnPcBzF (3) and BzF (2) has been carried out to elucidate the substitution effect on sensing ability of fluoroprobe. 2. Experimental All solvent used in this study, Zn(O2CMe)2, were purchased from Merck and used as received. THF (Tetrahydrofuran) were distilled from anhydrous CaCl2 and acetophenon. 4-Nitrophthalonitrile, 4-(6-hydroxyhexylthio)-1,2-dicyanobenzene was prepared according to literature [19,20]. Chromatography was performed with silica gel (Merck grade 60 and sephadex) from Aldrich. 1H
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
NMR and 13C NMR spectra were recorded on a Bruker 300 spectrometer instruments. Multiplities are given as s (singlet), d (dublet), t (triplet). FT-IR was recorded on SHIMADZU IR-PRESTIGE-2 Spectrophotometer. Elemental analysis (C, H and N) was performed at the instrumental Analysis Laboratory. Routine UV–Vis spectra were obtained in a quartz cuvette on an Agilelt 8453 UV– Vis spectrophotometer. Mass spectra were performed on a Bruker Autoflex III mass spectrometer. Spectra were recorded both in linear and reflectron modes with average of 50 and 100 shots for linear and reflectron modes. 2,5-Dihydroxy benzoic acid (DHB) MALDI matrix for 3 was prepared. MALDI samples were prepared by mixing complexes (2 mg/mL in acetonitrile) with the matrix solution (1:10 v/v) in a 0.5 mL eppendorfÒ micro tube. Finally 1 lL of this mixture was deposited on the sample plate, dried at room temperature and then analyzed. Fluorescence spectra were measured by a JASCO FP-777 W spectrophotometer (Japan Spectroscopic Co. Ltd.) at 25 °C; the slits for the excitation and emission monochrometers were 5 nm; and the spectral scan rate was 50.0 nm/min. The concentration of compound 3 was 5 lM and that of 2 was 20 lM since four derivative of benzofuran groups were bounded to one ZnPc core. 2.1. Synthesis 2.1.1. 6-(3,4-Dicyanophenylthio)-hexyl–2-chloroacetate (1) About 1.0 g (3.84 mmol) of 40 -(1-hydroxyhexylthio)-1,2-dicyanobenzene (1) and ca. 0.32 mL (excess) of triethylamine were dissolved in 20 mL of THF at room temperature. The mixture was placed in an ice-bath. About 0.45 mL (4.2 mmol, excess 10%) of 2-chloroethylchloride was added dropwise to a stirred solution at 5 °C. The mixture was stirred at 0 °C for 3 h and at room temperature for 12 h and finally was heated for 1 h at 30 °C. The reaction mixture was poured into water and the resulting precipitates was filtered and washed with lots of water. It was dried under vacuum for 12 h at room temperature. It was chromatographed over silica gel column using a mixture of CHCl3:MeOH 100/5 as eluent, giving yellow 6-(3,4-dicyanophenylthio)-hexyl-2-chloroacetate finally pure powder was dried in vacuum. Yield: 1.04 g (80.47%) m.p.: 80 °C, Anal. Calc. for C16H17ClN2O2S (336.5 g/mol): C, 57.05; H, 5.09; N, 8.32; S, 9.52. Found: C, 56.77; H, 5.11; N, 8.08; S, 9.36%. FT-IR (KBr thin film) m/cm1: 3020 (w), 2956, 2928, (Aliph-CH2), 2226 (CN, st), 1755, 1721 (–COOR, strong), 1476 (w), 1450, 1389, 1370, 1311, 1244 (Ar–S–CH2), 1145 (st), 1048, 960, 873, 931, 879, 748, 699.; 1H NMR ([D6]DMSO) d: 7.68 (dd, 1H, ortho to Ar–S–), 7.64 (s, isomer, 1H, ortho to CN and Ar–H), 7.60 (dd, 1H, ortho to CN and Ar–H, Phenyl H6), 4.35 (s, br, –COCH2Cl Aliph., 4.10 (t, 2H, CH2CH2–OCO), 2.78 (t, 2H, –S–CH2–CH2–) 1.54–1.63 (multiplet, superimposed 4H, –O–CH2CH2–CH2– and –S–CH2–CH2–CH2), 1.27–1.31 (multiplet, 4H, –OCH2 CH2CH2–CH2– and –S–CH2–CH2–CH2). 13C NMR ([300 MHz, d, D6]-DMSO): 167.2 (C@O), 143,2 (isomer, Ar–C–S), 132,6 (Bz), 132.1, 129.9, 116.8 112.7(Bz), 64.7 (CH2OCO), 40.9(CO–CH2Cl) 40.4 (DMSO), 36.8 (S–CH2), 30.9 (SCH2CH2), 28.6 (OCH2 CH2), 28.2 (SCH2CH2CH2), 25.4 (CH2CH2CH2CH2O) ppm. MS (ESI-MS): m/z (%): 370, 0 [M]+. 2.1.2. 6-(3,4-Dicyanophenylthio)-hexyl–2-benzofuranate, BzF (2) About 0.49 g (3.56 mmol) of K2CO3 in 50 mL of CH3CN (Acetonitrile) was added to 0.38 mL (3.56 mmol) of salicylaldehyde. The mixture was stirred at room temperature for 1 h and heated at 40 °C for 1 h. About 1.00 g (2.96 mmol) of 6-(3,4-dicyanophenylthio)-hexyl-2-chloroacetate was added to this mixture at room temperature. The reaction was continued at room temperature for 1 h and refluxed for 6 h. The product formed was poured into water (100 mL). The precipitated product was filtered and washed
3111
with excess of water and was dried at 40 °C under vacuum. The product was crystallized from EtOH. Yield: 1.04 g (86.96%) m.p.: 80 °C, Anal. Calc. for C23H20N2O3S (404 g/mol): C, 68.32; H, 4.95; N, 6.93; S, 7.92. Found: C, 67.89; H, 4.90; N, 6.48; S, 7.46%. FT-IR (KBr thin film) m/cm1: 3093 (w), 3057 (w), 2953, 2906, 2874 (Aliph-CH2, st), 2231 (CN, st), 1732 (COOR, strong), 1685, 1599 (w), 1489, 1460, 1396, 1354, 1280 (Ar–S–CH2), 1195, 1145, 1165, 977, 933, 871, 833, 759(st), 640, 532.; 1H NMR ([D6]-DMSO) d: 7.96 (dd, 1H, ortho to Ar–S–), 7.72–7.58 (s, isomer, 1H, ortho to CN and dd, 1H, ortho to CN and Ar–H, Phenyl H6), 7.10–7.22 (multiplet, superimposed benzofuran 5 H), 4.15 (t, 2H, CH2CH2–OCO), 3.30 (DMSO, CH3), 2.96 (t, 2H, –S– CH2–), 2.52 (DMSO, H2O), 1.70–1.62 (multiplet, superimposed 4H, –O–CH2CH2– and –S–CH2–CH2), 1.40–1.20 (multiplet, 4H, – OCH2CH2CH2– and –S–CH2–CH2–CH2). 13C NMR ([300 MHz, d, D6]-DMSO): 169.7 (C@O, ester), 160.7 (O–C–Ar–H (Bz), 147,4 (O–C2 (furan), 137.0 (Bz1, Ar–S), 134.4, 131.1, 130.9 (Bz1), 130.9 (Benzofuran C4), 128.3, 125.2, 122.2 (Bz, Benzofuran C4, C5, C6), 116.8 (Ar–C, ortho Ar–S), 116.4 (–CN), 115.8 (CN), 114.6 (Bz1, Ar– C–CN), 113.3 (Furan C3), 110.1 (Benzofuran C7), 65.3 (CH2OCO), 40.99 (DMSO, CH3), 39.31(S–CH2), 30.99 (SCH2CH2), 28.5 (OCH2CH2), 28.3 (SCH2CH2), 25.3 (CH2CH2CH2O) ppm. MS (MaldiTOF): m/z (%): 405, 2 [M+1]+. 2.1.3. 2,9,16,23-Tetrakis-{6-(-benzofuran-2-carboxylate)-hexylthio}phthalocyaninato zinc (II) ZnPcBzF (3) A mixture of 2 (0.150 g, 0.405 mmol), anhydrous Zn (O2CMe)2 (0.019 g, 0.107 mmol), DBU (one drop) and hexan-1-ol (0,2 mL) in a sealed tube was heated 6 h with efficient stirring at 150– 160 °C under N2 atmosphere. After cooling to room temperature, resulting solid was washed successively with MeOH, MeCN, and i-PrOH (2-propanol) and filtered to remove impurities until the filtrate was clear. The green–blue product was isolated by silica gel column chromatography with CHCl3/MeOH (9,1 v/v) as eluent. Pure 3 was obtained as viscous green oil after column chromatography over sephadex (THF/CHCl3, 1:2 v/v eluent) and then dried in vacuum. This product exhibited moderate solubility in CHCl3 and excellent solubility in THF, DMF, DMSO and pyridine. Yield: 0.036 g (23.0%). Anal. Calc. for C92H80N8O12S4Zn (1681 g/mol): C, 67.68; H, 4.76; N, 6.66; S, 7.61. Found: C, 67.14; H, 4.80; N, 6.45; S, 7.37%. FT-IR (KBr thin film) m/cm1: 3085 (w), 3057 (w), 2954, 2906, 2874 (Aliph-CH2, st), 2231 (CN, st), 1735 (COOR, strong),1685 1595 (w), 1482, 1456, 1395, 1350, 1282 (Ar–S–CH2), 1186, 1140, 986, 927, 852, 750, 544.; 1H NMR ([D6]-DMSO) d: 8.05–7.90 (dd, 4H, ortho to Ar–S–), 7.75–7.43 (m, 8H, ortho to CN and Ar–H, Phenyl H6), 7.35–6.96 (m, superimposed 20 H (Benzofuran)), 4.20 (t, 8H, CH2CH2–OCO), 3.35 (DMSO, CH3), 2.98 (t, 8H, –S– CH2–), 2.53 (DMSO, H2O), 1.74–1.60 (multiplet, superimposed 16H, –O–CH2CH2– and –S–CH2–CH2), 1.43–1.20 (multiplet, 16H, –OCH2CH2CH2– and –S–CH2–CH2–CH2). 13C NMR ([300 MHz, d, D6]-DMSO): 170.2 (C@O, ester), 148,5 (O–C2 (furan), 136.8 (Bz1, Ar–S), 135.0, 132.4, 131.0 (Bz1), 130.2 (Benzofuran C4), 128.6, 124.5, 123.6 (Bz, Benzofuran C4, C5, C6), 116.2 (Ar–C, ortho Ar–S), 115.4 (–CN), 115.0 (CN), 114.7 (Bz1, Ar–C–CN), 114.0 (furan C3), 111.4 (Benzofuran C7), 64.6 (CH2OCO), 40.9 (DMSO, CH3), 38.2 (S– CH2), 29.7 (SCH2CH2), 28.2 (OCH2CH2), 28.0 (SCH2CH2), 25.5 (CH2CH2CH2O) ppm. UV–Vis (THF, kmax/nm: 688 (Q), 662 (agg), 620, 355 (B); MS (Maldi-TOF): m/z (%): 1682, 4 [M+1]+ and the peaks at 1683, 16584, 1685 and 1686 show the isotopic peak distributions of protonated molecular peak of the complex.
3. Results and discussion Benzofuran attached zinc phthalocyanine, ZnPcBzF, (3), was synthesized by heating pulverized compound 2 with anhydrous
3112
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
Zn(O2CMe)2 salt at ca. 150–160 °C under N2 atmosphere in the presence of 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) as a strong base (Scheme 1). The yield of ZnPcBzF (3) was low (23.0%). Final product was obtained as pure sample after purifications via column chromatography over silica gel. Purification steps were tedious because of peripheral reactive end-group. The blue–green ZnPcBzF (3) was isolated as a mixture of isomers as expected. The structures of newly synthesized compounds were verified by FT-IR, 1H NMR, UV–Vis and MALDI-TOF MS spectroscopic methods, as well as by elemental analysis. All the analytical and spectral data are consistent with the predicted structures. While the major strong –CN band appeared at 2231 in the IR spectrum of BzF (2) disappeared after conversion to ZnPcBzF (3), the strong COOR band in the compound ZnPcBzF (3), at around 1700 cm–1 came out with small shift. The aliphatic and aromatic peaks at above and below 3000 cm–1 and the rest of the spectra is closely similar to that of compound 2 and diagnosed easily. The 1H NMR spectra of ZnPcBzF (3), was almost identical with starting compound 1 and BzF (2) except small shifts and broadening. The aromatic, aliphatic protons in the lower and higher field region of the 1H NMR spectrum on the periphery and sixteen different aromatic carbon atoms between 110 and 170 ppm in addition to the aliphatic ones (30–65 ppm) in 13C APT spectrum are the most instinctive indicator signals for (1), BzF (2) and ZnPcBzF (3). UV–Vis spectra of the ZnPcBzF (3), exhibit characteristic Q and B bands, one in the visible region at ca. 600–700 nm (Q-band) attributed to the p–p* transition from HOMO (Highest occupied molecular orbital) to the LUMO (Lowest unoccupied molecular orbital) of
the Pc2 ring, and the other in the UV region at ca. 300–400 nm (B-band) arising from the deeper p–p* transitions [21]. The Q-band absorptions in the UV–Vis absorption spectra of ZnPcBzF (3), was observed as a single band with high intensity due to a single p–p* transition at 688, with shoulder at slightly higher energy side of the Q-band of ZnPcBzF (3). The absorption positions of spectrum are dependent on the ionic radii of the metal center and peripheral substitutions. The effect of S-substitution on the periphery for the ZnPcBzF (3) was a shift in these intense Q-bands to longer wavelengths as a result of the electron-donating thioether substituents when compared with those of unsubstituted and alklyl or O-substituted derivatives[19,20,22,23]. Maldi-MS spectroscopy has been extensively used to characterize metal-base phthalocyaninates. Therefore, the mass spectra of 1, BzF (2) and ZnPcBzF (3), confirmed the proposed structures. The protonated mono isotopic molecular ion peaks were easily identified at m/z: 1682 [M+H]+ for ZnPcBzF (3). Protonated molecular ion peak was observed at 1682 Da that was exactly overlapped with the mass of the lowest mass of the isotopic mass distribution of complex ZnPcBzF (3), calculated theoretically from the elemental composition of the zinc complex. Isotopic peaks resulted from isotopic distribution of the protonated molecular ion of the ZnPcBzF (3) was observed in between 1682 and 1690 Da with 1 Da increment in the high mass range. Following the protonated molecular ion peak, a peak group was observed at 38 Da mass higher than the protonated molecular ion peak group resulting almost same pattern. This peak is resulted from the potassium adduct of the neutral ZnPcBzF (3).
Scheme 1. Synthetic route of 2,9,16,23-tetrakis-{6-(-thiophene-2-carboxylate)-hexylthio}-metallophthalocyanine {Zn [Pc(S-C6H12OH)4]2}. (i) Choloroacetylchloride, TEA, THF, 5 °C, (ii) K2CO3, CH3CN, salicylaldehyde, (iii) Zn(O2CMe)2, dbu, hexanol.
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
3.1. Peripheral silver ion binding 3.1.1. UV-measurement Sulfur donor atoms on the periphery of the tetra or octa substituted phthalocyanines act as heavy metal ionophore and impart a preference for coordination with soft heavy metal ions with different size [3,17,18,23]. Soft-acid and soft-base coordination on peripheral side of ZnPcBzF (3) was carried out with Ag+ ion as acceptor and readily monitored by UV–Vis spectroscopy. Addition of Ag+ ion to the solution of ZnPcBzF (3) caused a gradual color change, from blue–green to intractable black–darkgreen, suggesting the complex formation of ZnPcBzF (3), with Ag+ (Fig. 1). As seen from Fig. 1, binding of Ag+ to the donor atoms of ZnPcBzF (3) resulted in pronounced effects in the Q and B bands, and in the n–p* transitions. As shown in the Fig. 1, while addition of small increment of Ag+ to ZnPcBzF (3) leads to gradual disappearance of monomeric species at which show absorption at 688, simultaneously enhancing the intensity of the oligomeric aggregated species around 642 nm (inset figure in Fig. 1). B-band of the ZnPcBzF (3) shifts to higher energy sides about 10 nm, such as from 362 to 352 nm together with change in intensity. These spectroscopic changes indicate the coordination of Ag+ by the donor atoms of the phthalocyanines to form less soluble oligomeric aggregated species [3,18,23].
3113
A bathochromic shift was observed from k ¼ 425 nm to k ¼ 470 nm along with a steady quenching of the fluorescence intensity on addition of silver ion (Fig. 4). Red shifts in spectra can be explained by a lowering of the LUMO energy level upon binding of benzofuran moiety to Pc core because formation of dimmer spicies
Fig. 2. Excitation spectra of 5 lM 3 in THF as function of Ag+ ion titration. Inset: excitation spectra of 20 lM 2 upon titration with Ag+ ion. Arrow shows the increase in Ag+ ion concentration. (kem ¼ 425 nm).
3.1.2. Fluorescence measurements Excitation spectra of BzF (2) and ZnPcBzF (3) in THF were obtained upon titration with Ag+ ion (Fig. 2). As seen from Fig. 2, BzF (2) displays three distinct peaks centered near 252 nm, 298 nm and 336 nm. When substituted on Pc ring, the peaks of benzofuran derivative at shorter and longer wavelengths regions are 9 nm red shifted. Both of the excitation intensities of BzF (2) and ZnPcBzF (3) were diminished by addition of silver ion and there was no spectral shift in maxima of the peaks. When excited at 345 nm of wavelength, BzF (2) and ZnPcBzF (3) exhibit maximum emission at 402 and 425 nm, respectively (Fig. 3). The maximum fluorescence emission of ZnPcBzF (3) gradually reduced and shifted to red region upon addition of Ag+ ion. Silver ion titration also influenced the emission spectra of BzF (2) causing to quenching of fluorescence intensity but spectral shift in maximum was not observed (Fig. 3, inset). Two possibilities must be considered for the reason of the fluorescence quenching effect: The first is attributed to electron density variations on benzofuran moiety, caused by introducing positively charged ions. The second is that the decreased fluorescence is the result of benzofuran substituted Pc aggregations [24].
Fig. 3. Emission intensity responses of 5 lM 3 and 20 lM 2 (inset figure) in THF upon addition of 1.0, 2.5, 5.0, 7.5, 10, 25 and 50 lM Ag+ ion. Arrow shows the increase in Ag+ ion concentration. (kex ¼ 345 nm).
Fig. 1. UV–Visible spectra of 10 lM 3 in THF upon addition of 10, 20, 30, 40, 50, 60, 70, 90 lM Ag+ ion. Inset: spectroscopic changes in Q-band (a), B-band (b) and nonbonding band (c) of 3 during Ag+ ion titration.
Fig. 4. Change in the maximum emission wavelength of 3 (1) and F/Fo values for 2 (2) and 3 (3) in THF with regard to Ag+ concentration. (kex ¼ 345 nm).
3114
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
phthalocyanine bearing benzofuran derivative which can be used as a new fluorescent chemosensor for Ag(I). Fluoroprobe bounded Pc; ZnPcBzF (3), exhibits distinct changes in both spectra of absorbance and fluorescence upon titration with Ag+ ion where as derivative of benzofuran, BzF (2), does not exhibit a definite affinity for Ag+ ion. Q-band absortion peak of ZnPcBzF (3) gradually disappeared and dimeric peak increased in response to treatment with Ag+ in solution. Fluorescence emission intensities at shorter and longer wavelength regions were quenched but there was only spectral shift at shorter wavelength region which belongs to BzF (2). This indicates the complex formation between Ag+ and ZnPcBzF (3), and also shows that Ag+-induced Pc aggregation plays a major role in the amplified fluorescence quenching.
Acknowledgements Fig. 5. Excitation spectra of 3 recorded for emission at 730 nm as a function of Ag+ concentration. Inset: emission obtained for excitation at 616 nm. Arrow indicates decrease in intensity.
of ZnPcBzF (3) in solution effects p-electron conjugation on molecule causing to lowered LUMO energy level [25,26]. The variation of the electron density of the benzofuran backbone caused by Ag+ ion plays a minor role both in the quenching of fluorescence and bathochromic effect on the emission spectra of ZnPcBzF (3). From the above analysis, it is reasonably deduced that the amplified fluorescence quenching effect of benzofuran moiety results mainly from the Ag+-induced Pc core aggregation. These facts allow us to conclude that the emission band shift of BzF (2) on silver-cation addition is due to cation-p electron interactions [27]. The fluorescence intensity of BzF (2) is solely quenched without an accompanying band shift showing that the association between the sulfur atom on BzF (2) molecule and the silver-cation is rather weak (Fig. 4). This observation indicates that the electron transfer from the sulfur atom to the photoexcited Pc unit should be weakly depressed by the complexation of sulfur with silver ion. Fig. 5 depicts the plots of excitation spectra belonging to Pc core [28] of ZnPcBzF (3) in long wavelength region with regard to titration with Ag+ ion. As seen from Fig. 5, the excitation intensity of ZnPcBzF (3) was decreased by the addition of silver ion. When excited at wavelength of 616 nm, which is the isobestic point of Pc core, the fluorescence emission of ZnPcBzF (3) was also decreased with the increase in the silver ion concentration. This demonstrates that formation of the silver ion complex via sulfur atom on BzF (2) influences the fluorescence emission of Pc core. This effect is probably due to the intermolecular aggregation induced by silver ion, which brings Pc unit close each other and interacts with the p-electrons of the Pc core, causes to quenching of fluorescence emission. 4. Conclusion In conclusion, we described the complete synthesis and characterization of a new family of peripherally functionalized zinc
_ We thank the Research Funds of TUBITAK (TBAG: Project No: 108T094) and ITU (BAP: Project No: 31472).
References [1] C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines: Properties and Applications, VCH, Weinheim, 1989 (vol. 1), 1993 (vols. 2 and 3), 1996 (vol. 4). [2] L. Valli, Adv. Colloid Interf. Sci. 116 (2005) 13. [3] S.L.J. Michel, A.G.M. Barrett, B.M. Hoffman, Inorg. Chem. 42 (2003) 814. [4] J.J. Simon, H.J. Andre, Molecular Semiconductors, Springer, Berlin, 1985. [5] X. Li, L.E. Sinks, B. Rybtchinski, M.R. Wasielewski, J. Am. Chem. Soc. 126 (2004) 10810. [6] M. Brumbach, D. Placencia, N.R. Armstrong, J. Phys. Chem. C 112 (2008) 3142. [7] Z. Ou, J. Shen, K.M. Kadish, Inorg. Chem. 45 (2006) 9569. [8] J.R. Siqueira Jr., L.H.S. Gasparotto, O.N. Oliveira Jr., V. Zucolotto, J. Phys. Chem. C 11 (2008) 9050. [9] M. Kimura, T. Hamakawa, K. Hanabusa, H. Shirai, N. Kobayashi, Inorg. Chem. 40 (2001) 4775. [10] Z. Zhao, K.I. Ozoemena, D.M. Maree, T. Nyokong, J. Chem. Soc., Dalton Trans. 7 (2005) 1241. [11] A. Muranaka, K. Yoshida, T. Shoji, N. Moriichi, S. Masumoto, T. Kanda, Y. Ohtake, N. Kobayashi, Org. Lett. 12 (2006) 2447. [12] O. Güney, Y. Yılmaz, Ö. Pekcan, Sens. Actuators B 85 (2002) 86. [13] X.B. Zhang, C.C. Guo, Z.Z. Li, G.L. Shen, R.Q. Yu, Anal. Chem. 74 (2002) 821. [14] R. Ostuni, M.C. Larciprete, G. Leahu, A. Belardini, C. Sibilia, M. Bertolotti, J. Appl. Phys. 101 (2007) 33116. [15] A.P. De Silva, H.Q.N. Gunaratne, A.J.M. Huxley, C.P. Mc Coy, J.T. Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515. [16] A. Ehrlich, P.J. Skrdla, W.K. Jarrell, J.W. Sibert, N.R. Armstrong, S.S. Saavedra, A.G.M. Barrett, B.M. Hoffman, Inorg. Chem. 39 (2000) 3963. [17] M.N. Yarasir, M. Kandaz, B.F. Senkal, A. Koca, Polyhedron 26 (2007) 5235. [18] M.N. Yarasir, M. Kandaz, B.F. Senkal, A. Koca, B. Salih, Dyes Pigments 77 (2008) 7. [19] J.G. Young, W. Onyebuagu, J. Org. Chem. 55 (7) (1990) 2155. [20] M.N. Yarasir, M. Kandaz, A. Koca, B. Salih, Polyhedron 26 (2007) 1139. [21] M. Gouterman, in: D. Dolphin (Ed.), The Porphyrins, vol. 3, Academic Press, New York, 1978, p. 1. [22] M. Kandaz, I. Yılmaz, Ö. Bekarog˘lu, Polyhedron 19 (2000) 115. [23] S.J. Lange, J.W. Sibert, A.G.M. Barrett, B.M. Hoffman, Tetrahedron 56 (2000) 7371. [24] B. Valeur, Molecular Fluorescence Principles and Applications, Wiley-VCH, Weinheim, Germany, 2002. [25] M. Schmittel, H. Lin, Inorg. Chem. 46 (2007) 9139. [26] J.I. Kim, I.S. Shin, H. Kim, J.K. Lee, J. Am. Chem. Soc. 127 (2005) 1614. [27] J. Kang, M. Choi, J.Y. Kwon, E.Y. Lee, J. Yoon, J. Org. Chem. 67 (12) (2002) 4384. [28] J.C. Swarts, M.D. Maree, J. Porphyrins Phthalocyanins 11 (8) (2007) 613.
Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
Fluorescent chemosensor for Ag(I) based on amplified fluorescence quenching of a new phthalocyanine bearing derivative of benzofuran Mehmet Kandaz a,*, Orhan Güney b,*, Filiz B. Senkal b a
Sakarya University, Department of Chemistry, 54140 Esentepe, Sakarya, Turkey Istanbul Technical University, Department of Chemistry, 34469 Maslak, Istanbul, Turkey
b_
a r t i c l e
i n f o
Article history: Received 23 March 2009 Accepted 24 June 2009 Available online 27 June 2009 Keywords: Phthalocyanine Zinc aggregation Optical metal sensor Silver ion Fluorescence quenching
a b s t r a c t A fluorescent chemosensor for Ag(I) as a new family of peripherally functionalized zinc-phthalocyanine, 2(3),9(10),16(17),23(24)-tetrakis-{6-(-benzofuran-2-carboxylate)-hexylthio} phthalocyaninatozinc(II) {Zn[Pc(b-S(CH2)6OCOBz-furan)4], (ZnPcBzF), (3), which was derivated from 6-(3,4-dicyanophenylthio)hexyl–2-benzofuranate (BzF), (2), has been synthesized and fully characterized by elemental analysis, FT-IR, 1H and 13C NMR, MS (ESI and Maldi-TOF). An optical silver ion (Ag(I)) sensor based on the fluorescence quenching of benzofuran moiety and ZnPc core was developed. Both absorbance and fluorescence spectra of ZnPcBzF, (3) exhibit distinct changes in visible region in response to treatment with Ag(I) ion in solution. Such properties make compound ZnPcBzF, (3) intriguing candidates for incorporation into the transducer layer in optically based chemical sensors. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction An understanding of the electronic communication between chromophores is of great significance in designing organic materials for applications in optoelectronic technologies [1]. Therefore, much interest is devoted the construction of precisely defined molecular materials designed to perform specific functions such as chemical sensors [2,3], semiconductivity [4], fibrous assemblies [5], photovoltaics [6], optical data storage [7]. Phthalocyanines (Pcs) are highly versatile and stable chromophores with unique physicochemical properties that make them, alone or in combination with many other functional structures for the construction of molecular materials or electro and photoactive moieties [8,9]. Therefore, the synthesis of precursors bearing one/or more functionality is vital in the preparation of new photoactive phthalocyanines and the design of Pcs linked to strong fluoroprobe moieties appears particularly promising [9,10]. Optochemical sensor can be prepared based on fluorescence quenching depends on metal ion concentration by immobilizing a fluorophore on a solid substrate and monitoring the change in optical properties of the sensing layer upon interaction with the analyte [10]. When the changes of fluorescence caused by chelation of metal ions are significant and detectable, the chromophore can be used as a fluorescent chemosensor. The majority of fluorescence chemosensors reported
* Corresponding authors. Tel.: +90 264 295 60 42; fax: +90 264 295 59 50 (M. Kandaz), tel.: +90 212 285 31 62; fax: +90 212 285 63 86 (O. Güney). E-mail addresses: [email protected] (M. Kandaz), [email protected] (O. Güney). 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2009.06.058
to date for the detection of metal ions are either crown ether or their analogs [11–14]. In order to extend the scope of the metal ion chemosensor from crown ether-based systems to other sensory units [12–16], we have designed new phthalocyanine derivatives which bear four peripheral derivatives of benzofuran substituents as antennae. We previously reported on preparation of peripheral functional macrocycle phthalocyanines and demonstrated changes in the optical spectra brought about by peripheral metal ion binding as part of a development of functionalized phthalocyanines (Pc) with multiple metal ion binding sites [17,18]. In present work, we have synthesized a new benzofuran derivative, BzF (2), and designed a zinc phthalocyanine,2(3),9(10), 16(17),23(24)-tetrakis-{6-(-benzofuran-2-carboxylate)-hexylthio}phthalocyaninatozinc(II), ZnPcBzF (3), as a fluorescent chemosensor for the purpose of quantitative detecting of Ag(I) ion based on fluorescence quenching. A comparative study on silver ion recognition property of ZnPcBzF (3) and BzF (2) has been carried out to elucidate the substitution effect on sensing ability of fluoroprobe. 2. Experimental All solvent used in this study, Zn(O2CMe)2, were purchased from Merck and used as received. THF (Tetrahydrofuran) were distilled from anhydrous CaCl2 and acetophenon. 4-Nitrophthalonitrile, 4-(6-hydroxyhexylthio)-1,2-dicyanobenzene was prepared according to literature [19,20]. Chromatography was performed with silica gel (Merck grade 60 and sephadex) from Aldrich. 1H
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
NMR and 13C NMR spectra were recorded on a Bruker 300 spectrometer instruments. Multiplities are given as s (singlet), d (dublet), t (triplet). FT-IR was recorded on SHIMADZU IR-PRESTIGE-2 Spectrophotometer. Elemental analysis (C, H and N) was performed at the instrumental Analysis Laboratory. Routine UV–Vis spectra were obtained in a quartz cuvette on an Agilelt 8453 UV– Vis spectrophotometer. Mass spectra were performed on a Bruker Autoflex III mass spectrometer. Spectra were recorded both in linear and reflectron modes with average of 50 and 100 shots for linear and reflectron modes. 2,5-Dihydroxy benzoic acid (DHB) MALDI matrix for 3 was prepared. MALDI samples were prepared by mixing complexes (2 mg/mL in acetonitrile) with the matrix solution (1:10 v/v) in a 0.5 mL eppendorfÒ micro tube. Finally 1 lL of this mixture was deposited on the sample plate, dried at room temperature and then analyzed. Fluorescence spectra were measured by a JASCO FP-777 W spectrophotometer (Japan Spectroscopic Co. Ltd.) at 25 °C; the slits for the excitation and emission monochrometers were 5 nm; and the spectral scan rate was 50.0 nm/min. The concentration of compound 3 was 5 lM and that of 2 was 20 lM since four derivative of benzofuran groups were bounded to one ZnPc core. 2.1. Synthesis 2.1.1. 6-(3,4-Dicyanophenylthio)-hexyl–2-chloroacetate (1) About 1.0 g (3.84 mmol) of 40 -(1-hydroxyhexylthio)-1,2-dicyanobenzene (1) and ca. 0.32 mL (excess) of triethylamine were dissolved in 20 mL of THF at room temperature. The mixture was placed in an ice-bath. About 0.45 mL (4.2 mmol, excess 10%) of 2-chloroethylchloride was added dropwise to a stirred solution at 5 °C. The mixture was stirred at 0 °C for 3 h and at room temperature for 12 h and finally was heated for 1 h at 30 °C. The reaction mixture was poured into water and the resulting precipitates was filtered and washed with lots of water. It was dried under vacuum for 12 h at room temperature. It was chromatographed over silica gel column using a mixture of CHCl3:MeOH 100/5 as eluent, giving yellow 6-(3,4-dicyanophenylthio)-hexyl-2-chloroacetate finally pure powder was dried in vacuum. Yield: 1.04 g (80.47%) m.p.: 80 °C, Anal. Calc. for C16H17ClN2O2S (336.5 g/mol): C, 57.05; H, 5.09; N, 8.32; S, 9.52. Found: C, 56.77; H, 5.11; N, 8.08; S, 9.36%. FT-IR (KBr thin film) m/cm1: 3020 (w), 2956, 2928, (Aliph-CH2), 2226 (CN, st), 1755, 1721 (–COOR, strong), 1476 (w), 1450, 1389, 1370, 1311, 1244 (Ar–S–CH2), 1145 (st), 1048, 960, 873, 931, 879, 748, 699.; 1H NMR ([D6]DMSO) d: 7.68 (dd, 1H, ortho to Ar–S–), 7.64 (s, isomer, 1H, ortho to CN and Ar–H), 7.60 (dd, 1H, ortho to CN and Ar–H, Phenyl H6), 4.35 (s, br, –COCH2Cl Aliph., 4.10 (t, 2H, CH2CH2–OCO), 2.78 (t, 2H, –S–CH2–CH2–) 1.54–1.63 (multiplet, superimposed 4H, –O–CH2CH2–CH2– and –S–CH2–CH2–CH2), 1.27–1.31 (multiplet, 4H, –OCH2 CH2CH2–CH2– and –S–CH2–CH2–CH2). 13C NMR ([300 MHz, d, D6]-DMSO): 167.2 (C@O), 143,2 (isomer, Ar–C–S), 132,6 (Bz), 132.1, 129.9, 116.8 112.7(Bz), 64.7 (CH2OCO), 40.9(CO–CH2Cl) 40.4 (DMSO), 36.8 (S–CH2), 30.9 (SCH2CH2), 28.6 (OCH2 CH2), 28.2 (SCH2CH2CH2), 25.4 (CH2CH2CH2CH2O) ppm. MS (ESI-MS): m/z (%): 370, 0 [M]+. 2.1.2. 6-(3,4-Dicyanophenylthio)-hexyl–2-benzofuranate, BzF (2) About 0.49 g (3.56 mmol) of K2CO3 in 50 mL of CH3CN (Acetonitrile) was added to 0.38 mL (3.56 mmol) of salicylaldehyde. The mixture was stirred at room temperature for 1 h and heated at 40 °C for 1 h. About 1.00 g (2.96 mmol) of 6-(3,4-dicyanophenylthio)-hexyl-2-chloroacetate was added to this mixture at room temperature. The reaction was continued at room temperature for 1 h and refluxed for 6 h. The product formed was poured into water (100 mL). The precipitated product was filtered and washed
3111
with excess of water and was dried at 40 °C under vacuum. The product was crystallized from EtOH. Yield: 1.04 g (86.96%) m.p.: 80 °C, Anal. Calc. for C23H20N2O3S (404 g/mol): C, 68.32; H, 4.95; N, 6.93; S, 7.92. Found: C, 67.89; H, 4.90; N, 6.48; S, 7.46%. FT-IR (KBr thin film) m/cm1: 3093 (w), 3057 (w), 2953, 2906, 2874 (Aliph-CH2, st), 2231 (CN, st), 1732 (COOR, strong), 1685, 1599 (w), 1489, 1460, 1396, 1354, 1280 (Ar–S–CH2), 1195, 1145, 1165, 977, 933, 871, 833, 759(st), 640, 532.; 1H NMR ([D6]-DMSO) d: 7.96 (dd, 1H, ortho to Ar–S–), 7.72–7.58 (s, isomer, 1H, ortho to CN and dd, 1H, ortho to CN and Ar–H, Phenyl H6), 7.10–7.22 (multiplet, superimposed benzofuran 5 H), 4.15 (t, 2H, CH2CH2–OCO), 3.30 (DMSO, CH3), 2.96 (t, 2H, –S– CH2–), 2.52 (DMSO, H2O), 1.70–1.62 (multiplet, superimposed 4H, –O–CH2CH2– and –S–CH2–CH2), 1.40–1.20 (multiplet, 4H, – OCH2CH2CH2– and –S–CH2–CH2–CH2). 13C NMR ([300 MHz, d, D6]-DMSO): 169.7 (C@O, ester), 160.7 (O–C–Ar–H (Bz), 147,4 (O–C2 (furan), 137.0 (Bz1, Ar–S), 134.4, 131.1, 130.9 (Bz1), 130.9 (Benzofuran C4), 128.3, 125.2, 122.2 (Bz, Benzofuran C4, C5, C6), 116.8 (Ar–C, ortho Ar–S), 116.4 (–CN), 115.8 (CN), 114.6 (Bz1, Ar– C–CN), 113.3 (Furan C3), 110.1 (Benzofuran C7), 65.3 (CH2OCO), 40.99 (DMSO, CH3), 39.31(S–CH2), 30.99 (SCH2CH2), 28.5 (OCH2CH2), 28.3 (SCH2CH2), 25.3 (CH2CH2CH2O) ppm. MS (MaldiTOF): m/z (%): 405, 2 [M+1]+. 2.1.3. 2,9,16,23-Tetrakis-{6-(-benzofuran-2-carboxylate)-hexylthio}phthalocyaninato zinc (II) ZnPcBzF (3) A mixture of 2 (0.150 g, 0.405 mmol), anhydrous Zn (O2CMe)2 (0.019 g, 0.107 mmol), DBU (one drop) and hexan-1-ol (0,2 mL) in a sealed tube was heated 6 h with efficient stirring at 150– 160 °C under N2 atmosphere. After cooling to room temperature, resulting solid was washed successively with MeOH, MeCN, and i-PrOH (2-propanol) and filtered to remove impurities until the filtrate was clear. The green–blue product was isolated by silica gel column chromatography with CHCl3/MeOH (9,1 v/v) as eluent. Pure 3 was obtained as viscous green oil after column chromatography over sephadex (THF/CHCl3, 1:2 v/v eluent) and then dried in vacuum. This product exhibited moderate solubility in CHCl3 and excellent solubility in THF, DMF, DMSO and pyridine. Yield: 0.036 g (23.0%). Anal. Calc. for C92H80N8O12S4Zn (1681 g/mol): C, 67.68; H, 4.76; N, 6.66; S, 7.61. Found: C, 67.14; H, 4.80; N, 6.45; S, 7.37%. FT-IR (KBr thin film) m/cm1: 3085 (w), 3057 (w), 2954, 2906, 2874 (Aliph-CH2, st), 2231 (CN, st), 1735 (COOR, strong),1685 1595 (w), 1482, 1456, 1395, 1350, 1282 (Ar–S–CH2), 1186, 1140, 986, 927, 852, 750, 544.; 1H NMR ([D6]-DMSO) d: 8.05–7.90 (dd, 4H, ortho to Ar–S–), 7.75–7.43 (m, 8H, ortho to CN and Ar–H, Phenyl H6), 7.35–6.96 (m, superimposed 20 H (Benzofuran)), 4.20 (t, 8H, CH2CH2–OCO), 3.35 (DMSO, CH3), 2.98 (t, 8H, –S– CH2–), 2.53 (DMSO, H2O), 1.74–1.60 (multiplet, superimposed 16H, –O–CH2CH2– and –S–CH2–CH2), 1.43–1.20 (multiplet, 16H, –OCH2CH2CH2– and –S–CH2–CH2–CH2). 13C NMR ([300 MHz, d, D6]-DMSO): 170.2 (C@O, ester), 148,5 (O–C2 (furan), 136.8 (Bz1, Ar–S), 135.0, 132.4, 131.0 (Bz1), 130.2 (Benzofuran C4), 128.6, 124.5, 123.6 (Bz, Benzofuran C4, C5, C6), 116.2 (Ar–C, ortho Ar–S), 115.4 (–CN), 115.0 (CN), 114.7 (Bz1, Ar–C–CN), 114.0 (furan C3), 111.4 (Benzofuran C7), 64.6 (CH2OCO), 40.9 (DMSO, CH3), 38.2 (S– CH2), 29.7 (SCH2CH2), 28.2 (OCH2CH2), 28.0 (SCH2CH2), 25.5 (CH2CH2CH2O) ppm. UV–Vis (THF, kmax/nm: 688 (Q), 662 (agg), 620, 355 (B); MS (Maldi-TOF): m/z (%): 1682, 4 [M+1]+ and the peaks at 1683, 16584, 1685 and 1686 show the isotopic peak distributions of protonated molecular peak of the complex.
3. Results and discussion Benzofuran attached zinc phthalocyanine, ZnPcBzF, (3), was synthesized by heating pulverized compound 2 with anhydrous
3112
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
Zn(O2CMe)2 salt at ca. 150–160 °C under N2 atmosphere in the presence of 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) as a strong base (Scheme 1). The yield of ZnPcBzF (3) was low (23.0%). Final product was obtained as pure sample after purifications via column chromatography over silica gel. Purification steps were tedious because of peripheral reactive end-group. The blue–green ZnPcBzF (3) was isolated as a mixture of isomers as expected. The structures of newly synthesized compounds were verified by FT-IR, 1H NMR, UV–Vis and MALDI-TOF MS spectroscopic methods, as well as by elemental analysis. All the analytical and spectral data are consistent with the predicted structures. While the major strong –CN band appeared at 2231 in the IR spectrum of BzF (2) disappeared after conversion to ZnPcBzF (3), the strong COOR band in the compound ZnPcBzF (3), at around 1700 cm–1 came out with small shift. The aliphatic and aromatic peaks at above and below 3000 cm–1 and the rest of the spectra is closely similar to that of compound 2 and diagnosed easily. The 1H NMR spectra of ZnPcBzF (3), was almost identical with starting compound 1 and BzF (2) except small shifts and broadening. The aromatic, aliphatic protons in the lower and higher field region of the 1H NMR spectrum on the periphery and sixteen different aromatic carbon atoms between 110 and 170 ppm in addition to the aliphatic ones (30–65 ppm) in 13C APT spectrum are the most instinctive indicator signals for (1), BzF (2) and ZnPcBzF (3). UV–Vis spectra of the ZnPcBzF (3), exhibit characteristic Q and B bands, one in the visible region at ca. 600–700 nm (Q-band) attributed to the p–p* transition from HOMO (Highest occupied molecular orbital) to the LUMO (Lowest unoccupied molecular orbital) of
the Pc2 ring, and the other in the UV region at ca. 300–400 nm (B-band) arising from the deeper p–p* transitions [21]. The Q-band absorptions in the UV–Vis absorption spectra of ZnPcBzF (3), was observed as a single band with high intensity due to a single p–p* transition at 688, with shoulder at slightly higher energy side of the Q-band of ZnPcBzF (3). The absorption positions of spectrum are dependent on the ionic radii of the metal center and peripheral substitutions. The effect of S-substitution on the periphery for the ZnPcBzF (3) was a shift in these intense Q-bands to longer wavelengths as a result of the electron-donating thioether substituents when compared with those of unsubstituted and alklyl or O-substituted derivatives[19,20,22,23]. Maldi-MS spectroscopy has been extensively used to characterize metal-base phthalocyaninates. Therefore, the mass spectra of 1, BzF (2) and ZnPcBzF (3), confirmed the proposed structures. The protonated mono isotopic molecular ion peaks were easily identified at m/z: 1682 [M+H]+ for ZnPcBzF (3). Protonated molecular ion peak was observed at 1682 Da that was exactly overlapped with the mass of the lowest mass of the isotopic mass distribution of complex ZnPcBzF (3), calculated theoretically from the elemental composition of the zinc complex. Isotopic peaks resulted from isotopic distribution of the protonated molecular ion of the ZnPcBzF (3) was observed in between 1682 and 1690 Da with 1 Da increment in the high mass range. Following the protonated molecular ion peak, a peak group was observed at 38 Da mass higher than the protonated molecular ion peak group resulting almost same pattern. This peak is resulted from the potassium adduct of the neutral ZnPcBzF (3).
Scheme 1. Synthetic route of 2,9,16,23-tetrakis-{6-(-thiophene-2-carboxylate)-hexylthio}-metallophthalocyanine {Zn [Pc(S-C6H12OH)4]2}. (i) Choloroacetylchloride, TEA, THF, 5 °C, (ii) K2CO3, CH3CN, salicylaldehyde, (iii) Zn(O2CMe)2, dbu, hexanol.
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
3.1. Peripheral silver ion binding 3.1.1. UV-measurement Sulfur donor atoms on the periphery of the tetra or octa substituted phthalocyanines act as heavy metal ionophore and impart a preference for coordination with soft heavy metal ions with different size [3,17,18,23]. Soft-acid and soft-base coordination on peripheral side of ZnPcBzF (3) was carried out with Ag+ ion as acceptor and readily monitored by UV–Vis spectroscopy. Addition of Ag+ ion to the solution of ZnPcBzF (3) caused a gradual color change, from blue–green to intractable black–darkgreen, suggesting the complex formation of ZnPcBzF (3), with Ag+ (Fig. 1). As seen from Fig. 1, binding of Ag+ to the donor atoms of ZnPcBzF (3) resulted in pronounced effects in the Q and B bands, and in the n–p* transitions. As shown in the Fig. 1, while addition of small increment of Ag+ to ZnPcBzF (3) leads to gradual disappearance of monomeric species at which show absorption at 688, simultaneously enhancing the intensity of the oligomeric aggregated species around 642 nm (inset figure in Fig. 1). B-band of the ZnPcBzF (3) shifts to higher energy sides about 10 nm, such as from 362 to 352 nm together with change in intensity. These spectroscopic changes indicate the coordination of Ag+ by the donor atoms of the phthalocyanines to form less soluble oligomeric aggregated species [3,18,23].
3113
A bathochromic shift was observed from k ¼ 425 nm to k ¼ 470 nm along with a steady quenching of the fluorescence intensity on addition of silver ion (Fig. 4). Red shifts in spectra can be explained by a lowering of the LUMO energy level upon binding of benzofuran moiety to Pc core because formation of dimmer spicies
Fig. 2. Excitation spectra of 5 lM 3 in THF as function of Ag+ ion titration. Inset: excitation spectra of 20 lM 2 upon titration with Ag+ ion. Arrow shows the increase in Ag+ ion concentration. (kem ¼ 425 nm).
3.1.2. Fluorescence measurements Excitation spectra of BzF (2) and ZnPcBzF (3) in THF were obtained upon titration with Ag+ ion (Fig. 2). As seen from Fig. 2, BzF (2) displays three distinct peaks centered near 252 nm, 298 nm and 336 nm. When substituted on Pc ring, the peaks of benzofuran derivative at shorter and longer wavelengths regions are 9 nm red shifted. Both of the excitation intensities of BzF (2) and ZnPcBzF (3) were diminished by addition of silver ion and there was no spectral shift in maxima of the peaks. When excited at 345 nm of wavelength, BzF (2) and ZnPcBzF (3) exhibit maximum emission at 402 and 425 nm, respectively (Fig. 3). The maximum fluorescence emission of ZnPcBzF (3) gradually reduced and shifted to red region upon addition of Ag+ ion. Silver ion titration also influenced the emission spectra of BzF (2) causing to quenching of fluorescence intensity but spectral shift in maximum was not observed (Fig. 3, inset). Two possibilities must be considered for the reason of the fluorescence quenching effect: The first is attributed to electron density variations on benzofuran moiety, caused by introducing positively charged ions. The second is that the decreased fluorescence is the result of benzofuran substituted Pc aggregations [24].
Fig. 3. Emission intensity responses of 5 lM 3 and 20 lM 2 (inset figure) in THF upon addition of 1.0, 2.5, 5.0, 7.5, 10, 25 and 50 lM Ag+ ion. Arrow shows the increase in Ag+ ion concentration. (kex ¼ 345 nm).
Fig. 1. UV–Visible spectra of 10 lM 3 in THF upon addition of 10, 20, 30, 40, 50, 60, 70, 90 lM Ag+ ion. Inset: spectroscopic changes in Q-band (a), B-band (b) and nonbonding band (c) of 3 during Ag+ ion titration.
Fig. 4. Change in the maximum emission wavelength of 3 (1) and F/Fo values for 2 (2) and 3 (3) in THF with regard to Ag+ concentration. (kex ¼ 345 nm).
3114
M. Kandaz et al. / Polyhedron 28 (2009) 3110–3114
phthalocyanine bearing benzofuran derivative which can be used as a new fluorescent chemosensor for Ag(I). Fluoroprobe bounded Pc; ZnPcBzF (3), exhibits distinct changes in both spectra of absorbance and fluorescence upon titration with Ag+ ion where as derivative of benzofuran, BzF (2), does not exhibit a definite affinity for Ag+ ion. Q-band absortion peak of ZnPcBzF (3) gradually disappeared and dimeric peak increased in response to treatment with Ag+ in solution. Fluorescence emission intensities at shorter and longer wavelength regions were quenched but there was only spectral shift at shorter wavelength region which belongs to BzF (2). This indicates the complex formation between Ag+ and ZnPcBzF (3), and also shows that Ag+-induced Pc aggregation plays a major role in the amplified fluorescence quenching.
Acknowledgements Fig. 5. Excitation spectra of 3 recorded for emission at 730 nm as a function of Ag+ concentration. Inset: emission obtained for excitation at 616 nm. Arrow indicates decrease in intensity.
of ZnPcBzF (3) in solution effects p-electron conjugation on molecule causing to lowered LUMO energy level [25,26]. The variation of the electron density of the benzofuran backbone caused by Ag+ ion plays a minor role both in the quenching of fluorescence and bathochromic effect on the emission spectra of ZnPcBzF (3). From the above analysis, it is reasonably deduced that the amplified fluorescence quenching effect of benzofuran moiety results mainly from the Ag+-induced Pc core aggregation. These facts allow us to conclude that the emission band shift of BzF (2) on silver-cation addition is due to cation-p electron interactions [27]. The fluorescence intensity of BzF (2) is solely quenched without an accompanying band shift showing that the association between the sulfur atom on BzF (2) molecule and the silver-cation is rather weak (Fig. 4). This observation indicates that the electron transfer from the sulfur atom to the photoexcited Pc unit should be weakly depressed by the complexation of sulfur with silver ion. Fig. 5 depicts the plots of excitation spectra belonging to Pc core [28] of ZnPcBzF (3) in long wavelength region with regard to titration with Ag+ ion. As seen from Fig. 5, the excitation intensity of ZnPcBzF (3) was decreased by the addition of silver ion. When excited at wavelength of 616 nm, which is the isobestic point of Pc core, the fluorescence emission of ZnPcBzF (3) was also decreased with the increase in the silver ion concentration. This demonstrates that formation of the silver ion complex via sulfur atom on BzF (2) influences the fluorescence emission of Pc core. This effect is probably due to the intermolecular aggregation induced by silver ion, which brings Pc unit close each other and interacts with the p-electrons of the Pc core, causes to quenching of fluorescence emission. 4. Conclusion In conclusion, we described the complete synthesis and characterization of a new family of peripherally functionalized zinc
_ We thank the Research Funds of TUBITAK (TBAG: Project No: 108T094) and ITU (BAP: Project No: 31472).
References [1] C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines: Properties and Applications, VCH, Weinheim, 1989 (vol. 1), 1993 (vols. 2 and 3), 1996 (vol. 4). [2] L. Valli, Adv. Colloid Interf. Sci. 116 (2005) 13. [3] S.L.J. Michel, A.G.M. Barrett, B.M. Hoffman, Inorg. Chem. 42 (2003) 814. [4] J.J. Simon, H.J. Andre, Molecular Semiconductors, Springer, Berlin, 1985. [5] X. Li, L.E. Sinks, B. Rybtchinski, M.R. Wasielewski, J. Am. Chem. Soc. 126 (2004) 10810. [6] M. Brumbach, D. Placencia, N.R. Armstrong, J. Phys. Chem. C 112 (2008) 3142. [7] Z. Ou, J. Shen, K.M. Kadish, Inorg. Chem. 45 (2006) 9569. [8] J.R. Siqueira Jr., L.H.S. Gasparotto, O.N. Oliveira Jr., V. Zucolotto, J. Phys. Chem. C 11 (2008) 9050. [9] M. Kimura, T. Hamakawa, K. Hanabusa, H. Shirai, N. Kobayashi, Inorg. Chem. 40 (2001) 4775. [10] Z. Zhao, K.I. Ozoemena, D.M. Maree, T. Nyokong, J. Chem. Soc., Dalton Trans. 7 (2005) 1241. [11] A. Muranaka, K. Yoshida, T. Shoji, N. Moriichi, S. Masumoto, T. Kanda, Y. Ohtake, N. Kobayashi, Org. Lett. 12 (2006) 2447. [12] O. Güney, Y. Yılmaz, Ö. Pekcan, Sens. Actuators B 85 (2002) 86. [13] X.B. Zhang, C.C. Guo, Z.Z. Li, G.L. Shen, R.Q. Yu, Anal. Chem. 74 (2002) 821. [14] R. Ostuni, M.C. Larciprete, G. Leahu, A. Belardini, C. Sibilia, M. Bertolotti, J. Appl. Phys. 101 (2007) 33116. [15] A.P. De Silva, H.Q.N. Gunaratne, A.J.M. Huxley, C.P. Mc Coy, J.T. Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515. [16] A. Ehrlich, P.J. Skrdla, W.K. Jarrell, J.W. Sibert, N.R. Armstrong, S.S. Saavedra, A.G.M. Barrett, B.M. Hoffman, Inorg. Chem. 39 (2000) 3963. [17] M.N. Yarasir, M. Kandaz, B.F. Senkal, A. Koca, Polyhedron 26 (2007) 5235. [18] M.N. Yarasir, M. Kandaz, B.F. Senkal, A. Koca, B. Salih, Dyes Pigments 77 (2008) 7. [19] J.G. Young, W. Onyebuagu, J. Org. Chem. 55 (7) (1990) 2155. [20] M.N. Yarasir, M. Kandaz, A. Koca, B. Salih, Polyhedron 26 (2007) 1139. [21] M. Gouterman, in: D. Dolphin (Ed.), The Porphyrins, vol. 3, Academic Press, New York, 1978, p. 1. [22] M. Kandaz, I. Yılmaz, Ö. Bekarog˘lu, Polyhedron 19 (2000) 115. [23] S.J. Lange, J.W. Sibert, A.G.M. Barrett, B.M. Hoffman, Tetrahedron 56 (2000) 7371. [24] B. Valeur, Molecular Fluorescence Principles and Applications, Wiley-VCH, Weinheim, Germany, 2002. [25] M. Schmittel, H. Lin, Inorg. Chem. 46 (2007) 9139. [26] J.I. Kim, I.S. Shin, H. Kim, J.K. Lee, J. Am. Chem. Soc. 127 (2005) 1614. [27] J. Kang, M. Choi, J.Y. Kwon, E.Y. Lee, J. Yoon, J. Org. Chem. 67 (12) (2002) 4384. [28] J.C. Swarts, M.D. Maree, J. Porphyrins Phthalocyanins 11 (8) (2007) 613.