Synthesis, photophysical and electrochemical properties of water–soluble phthalocyanines bearing 8-hydroxyquinoline-5-sulfonicacid derivatives

Author’s Accepted Manuscript Synthesis, Photophysical and Electrochemical Properties of Water–Soluble Phthalocyanines Bearing 8-hydroxyquinoline-5-sulfonicacid Derivatives Armağan Günsel, Sibel Kocabaş, Ahmet T. Bilgiçli, Sevgi Güney, Mehmet Kandaz www.elsevier.com/locate/jlumin

PII: DOI: Reference:

S0022-2313(15)30224-6 http://dx.doi.org/10.1016/j.jlumin.2016.03.036 LUMIN13914

To appear in: Journal of Luminescence Received date: 9 July 2015 Revised date: 11 March 2016 Accepted date: 28 March 2016 Cite this article as: Armağan Günsel, Sibel Kocabaş, Ahmet T. Bilgiçli, Sevgi Güney and Mehmet Kandaz, Synthesis, Photophysical and Electrochemical Properties of Water–Soluble Phthalocyanines Bearing 8-hydroxyquinoline-5sulfonicacid Derivatives, Journal of Luminescence, http://dx.doi.org/10.1016/j.jlumin.2016.03.036 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis, Photophysical and Electrochemical Properties of Water–Soluble Phthalocyanines Bearing 8-hydroxyquinoline-5-sulfonicacid Derivatives

Armağan Günsela, Sibel Kocabaşa, Ahmet T. Bilgiçlia, Sevgi Güneyb, Mehmet Kandaza* a b

Department of Chemistry, Sakarya University, 54140, Esentepe, Sakarya, Turkey.

Department of Chemistry, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey.

___________________________________________________________________________ Abstract: We have presented in this paper, the synthesis, characterization, photophysical properties and electrochemical characterization of water soluble phthalocyanines (Pcs) bearing 8-hydroxyquinoline-5-sulfonicacid conjugates and their cationic quaternized counterpart that play important roles their application in photodynamic therapy (PDT). The periphery and non-periphery substituted phthalocyanines show high solubility and low aggregation tendency due to bulky 8-hydroxyquinoline-5-sulfonicacid steric hindrance moieties and axially bound counter chlorine anion. Singlet oxygen quantum yields, photodegradation quantum yields, photophysical properties and also the nature of the substituent and solvent effect on the photophysical and photochemical parameters of α-ZnPc and β-ZnPc are reported. In electrovalent cobalt (II) and manganese (III) compounds, metal based electron transfer reactions have been observed in addition to the common phthalocyanine ring-based electron transfer processes. The effect of point of substitution on the electrochemical properties of newly synthesized phthalocyanines substituted with 8hydroxyquinoline-5-sulfonicacid group were evaluated.

Keywords : Phthalocyanine, Hydroxyquinoline-5-sulfonicacid, Water soluble, Fluorescence Quenching, Electrochemistry *Authors to whom correspondence should be addressed [Tel./Fax; + 90 (264) 295 60 42; + 90 (264) 295 59 50; E-mail address: [email protected] (M. Kandaz)

1

1. Introduction Molecular materials and their application fields have great importance [1-3]. In recent years, there are many efforts to be devoted the construction of well-defined molecular materials for some technological applications, such as chemical sensors [4-6], semiconductors [7], electrochromic display devices [8-10], liquid crystals [11-12], solar cells [13], photovoltaics [14] various catalytic processes [15-16] and especially, photosensitizers for photodynamic cancer therapy (PDT) [17,18]. Phthalocyanines (Pc) have been proved as highly promising photosensitizers for PDT (photodynamic therapy) due to their intense absorption in the red region of the visible light [19]. PDT technique based on the administration of a photosensitiser that must be condense more tumour tissues than regular tissues. This is followed by illumination of the tumour with visible light in a wavelength range matching the absorption spectrum of the photosensitizer [20]. The resulting photodynamic reactions give rise to singlet oxygen (1O2) and to other active oxygen species that lead to tumour destruction. The PDT efficiency can be improved with the use of photosensitisers that absorb strongly red light above 700 nm, where tissue exhibits optimal transparency. Up to now, several new generation of potential sensitisers for PDT have been developed and investigated; among these phthalocyanines have been found to be as highly promising due to high absorbance coefficient in the region of 650–680 nm [17]. Phthalocyanine compounds exhibit a tendency to aggregate (by attractive π-π stacking interactions) in solution to form the dimer and higher oligomeric species because of the extended π-system. Thus, many phthalocyanines have been restricted in application areas as a result of lower solubility in common organic solvents and water due to aggregation. Therefore, our main synthetic aims is that soluble phthalocyanines, with bulky groups in common organic solvents and their cationic derivatives in water have been of great scientific and technological importance such as PDT. It is vitally important to control the aggregation 2

types in order to realize the Pc’s function [2, 15]. 8-hydroxyquinoline-5-sulfonic acid derivatives which biologically, fluorophore and electroactive compounds are widely used in some applications such as, synthesizing laser dyes, chemosensors for metal detections, pH sensors, due to their characteristics of high emission yield, excellent photostability, and extended spectral range. Understanding of the redox behavior of metal phthalocyanines (MPcs) synthesized with redox-active metal center is very important and closely related to their applicability in various technological areas, such as electrocatalysis [21-22] and electrochromism [23]. In this paper, we have reported the synthesis, characterization and photophysical properties of a novel water soluble phthalocyanines bearing 8-hydroxyquinoline-5-sulfonicacid (HQSA) [MPc-α-HQSA(2a, 3a, 4a, 5a and 6a) and MPc- β-HQSA(2b, 3b, 4b, 5b and 6b); (M=2H, Zn(II), Cu(II), Co(II) and Mn(III); X:Cl)] conjugates and their cationic quarternized counterpart that play important roles their application in PDT. Aggregation formations of these Pcs in the presence of solution were investigated by UV-vis spectroscopy and fluorescence measurements. In addition, the redox behavior of these newly synthesized complexes was studied by voltammetry.

2. Experimental 2.1.

Materials

All solvents used, metal salts, 8-hydroxyquinoline-5-sulfonic acid, CoCl2, MnCl2 Zn(CH3COO)2, CuCl2, 3-nitrophthalonitrile, 4-nitrophthalonitrile and, anhydrous K2CO3 were purchased from Merck and Sigma-Aldrich and used without purification. 8-(3,4dicyanophenoxy) quinoline-5-sulfonic acid (1b) and 1(4),8(11),15(18),22(25)-Tetrakis-α-(8(2,3-dicyanophenoxy) quinoline-5-sulfonic acid)-zinc(II) phthalocyanine (3a)

3

compounds

were synthesized according to literature procedure[15]. All reactions were carried out under dry condition and N2 atmosphere. n-hexanol and tetrahydrofuran (THF) were distilled from anhydrous CaCl2 and acetophenon. FT-IR spectra were recorded on Shimatzu IR-prestige-2 spectrophotometer. Routine UV-Vis spectra were recorded on Agillent Model 8453 diode array spectrophotometer. 1H and

13

C-NMR spectra were recorded on a Bruker 300 MHz

spectrometer instruments. Multiplities are given as s (singlet), d (dublet), t (triplet). Elemental analysis (C, H and N) were performed at the Instrumental Analysis Laboratory of Marmara University. Fluorescence excitation and emission spectra were recorded on a HITACHI F7000 fluorescence spectrophotometer using 1cm path length cuvettes at room temperatures in Marmara University. Chromatography was performed with silica gel (Merck grade 60 and sephadex) from Aldrich. Matrix-assisted laser desorption/ionisation time of-flight (MALDITOF) mass spectra (MS) were measured by Bruker Autoflex III mass spectrometer equipped with a nitrogen UV-Laser operating at 337 nm. Dihydroxy benzoic acid (DHBA) was chosen as the best MALDI matrice. Finally 1 μL of this mixture was deposited on the sample plate, dried at room temperature and then analyzed.

2.2. Electrochemical Measurements The cyclic (CV) and differential pulse voltammetry (DPV) measurements were investigated by PARSTAT 2273 potentiostat/galvanostat (Ametek, USA) driven by the PowerSuite data processing software (version 1.07). DPV parameters were applied as pulse time 50 ms, pulse size 100 mV, step size 5 mV, sample period 100ms. A conventional three-electrode configuration was used at 25 ˚C. Ag/AgCl/3MKCl was served as the reference electrode (PAR-K0265) and separated from the bulk of the solution by a double bridge. A platinum wire was employed as the counter electrode (PAR-K0266). The working electrode (PARG0228) was a platinum (Pt) disc with surface area of 0.03 cm2. The surface of the platinum 4

electrode was polished with a diamond suspension before each run. The reference electrode tip was moved as close as possible to the working electrode so that uncompensated resistance of the solution was a smaller fraction of the total resistance, and therefore the potential control error was low. IR compensation was applied to the CV runs to further minimizing the potential control error. Electrochemical grade tetrabutylammonium perchlorate (TBAP) in extra pure dimethyl sulphoxide (DMSO) was employed as the supporting electrolyte at a concentration of 0.10 mol L-1. High purity N2 was used for deoxygenating for at least 10 min prior to each run and to maintain a nitrogen blanket during the measurements.

2.3. Photophysical and Photochemical Studies 2.3.1. Fluorescence quantum yields Fluorescence quantum yields (ΦF) were determined by the comparative method (Eq. 1) [24],

ΦF  ΦF(Std)

F . AStd . n 2 2 FStd . A . nStd

(1)

where F and FStd are the areas under the fluorescence emission curves of the samples (3a and 3b) and the standard, respectively. A and AStd are the respective absorbances of the samples 2

2 and standard at the excitation wavelengths, respectively. n and n Std are the refractive

indices of solvents used for the sample and standard, respectively. Unsubstituted ZnPc (in DMSO) (ΦF = 0.20) [25], was employed as the standard. The absorbance of the solutions at the excitation wavelength ranged between 0.04 and 0.05.

2.3.2. Singlet oxygen quantum yields Singlet oxygen quantum yield () determinations were investigated by using the experimental set-up described in literature [26-28]. Photogeneration quantum yields of singlet 5

oxygen were performed in air (no oxygen bubbled) using the relative method with ZnPc as reference and DPBF and ADMA as chemical quencher for singlet oxygen, using formula 2

R . I Std abs ΦΔ  Φ R Std . Iabs Std Δ

(2)

Std Std where Φ Δ is the singlet oxygen quantum yields for the standard ZnPc ( Φ Δ = 0.67 in DMSO

[29], R and RStd are the DPBF or ADMA photo bleaching rates in the presence of the Std

respective samples (3a and 3b) and standard, respectively. Iabs and I abs are the rates of light absorption by the samples (3a and 3b) and standard, respectively. To avoid chain reactions induced by DPBF or ADMA in the presence of singlet oxygen [30], the concentration of quencher (DPBF or ADMA) was lowered to ~3 x 10-5 mol.dm-3 Solutions of sensitizer (containing DPBF or ADMA)) were prepared in the dark and irradiated in the Q band region using the setup described above. DPBF degradation at 417 nm (in DMSO) and ADMA degradation at 380 nm (in water) were monitored. The light intensity of 7.05 x 1015 photons s1

cm-2 was used for  determinations.

2.3.3. Photodegradation quantum yields Photodegradation quantum yield (Φd) determinations were investigated by using the experimental set-up described in literature [31-33]. Photodegradation quantum yields were determined using formula 3,

Φd 

(C0  Ct) . V . NA Iabs .S . t

(3)

where “C0” and “Ct” are the sample (3a and 3b) concentrations before and after irradiation respectively, “V” is the reaction volume, “NA” the Avogadro’s constant, “S” the irradiated 6

cell area and “t” the irradiation time, “Iabs” is the overlap integral of the radiation source light intensity and the absorption of the samples (3a and 3b). A light intensity of 2.50x1016 photons s-1 cm-2 was employed for Φd determinations.

3. Results and discussion 3.1. Syntheses and characterization 3.1.1. 8-(2,3-dicyanophenoxy) quinoline-5-sulfonic acid (1a)

8-hydroxyquinoline-5-sulfonic acid (1.30 g, 5.78 mmol) was dissolved in dry DMF (8,00 mL) at 45 oC and anhydrous K2CO3 (1.50 g, 11.56 mmol) was added. After stirring for 15 min, 3nitrophthalonitrile or 4-nitrophthalonitrile dissolved in DMF (1,00 g, 5.78 mmol) was added dropwise in 2h with efficient stirring. The reaction mixture was stirred under N2 at 45 oC for 4 days. After the mixture cooled to room temperature, this product was poured into ca. 200 mL ice-water media and 1M HCl (50 mL) was added in it. After completion of the precipitation approximately in 0.5 h, the creamy precipitate that formed was filtered and then washed with ca. 100 mL water until the washings became neutral. Column chromatography with methanol/dichloromethane (5:1) eluent on silica gel was employed to obtain the pure product. As expected, the yellow products were soluble in DMF and DMSO.

Yield of 1a: 1.36 g (67 %); m.p.: Anal. Calc. for C17H9N3O4S (Mw: 351.34): C, 58.12; H, 2.58; N, 11.96. Found: C, 57.90; H, 2.56; N, 11.81 %. FT-IR (KBr disc) ν/cm-1: 3082, 3027, 2980 (Ar H), 2240 (-CN), 1590, 1574, 1550 (Ar), 1273 (Ar-O-Ar), 1191, 1154 (SO2), 789, 774, 674. UV/Vis (DMSO): λmax = 299, 259.

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3.1.2. 1(4),8(11),15(18),22(25)-Tetrakis(8-(2,3-dicyanophenoxy) quinoline-5-sulfonic acid)phthalocyaninato metal free (2a); 2(3),9(10),16(17),23(24)-Tetrakis(8-(3,4-dicyanophenoxy) quinoline-5-sulfonic acid)-phthalocyaninato metal free (2b)

A mixture of 8-(2,3-dicyanophenoxy)quinoline-5-sulfonic acid (1a) (Scheme 1) or 8-(3,4dicyano phenoxy) quinoline-5-sulfonic acid (1b) (Scheme 2) (0.30 g, 0.85 mmol) in the presence

of

N,N-dimethylaminoethanol

(NNDMAE,

0.50

mL)

and

1.8-

diazabicyclo[5.4.0]undec-7-ene (DBU) (0.10 mL) were heated reflux temperature in a tube under N2 atmosphere for 10h. The color of the mixture was turned green within 1-2h. After the heating was continued for an additional 7-8 h, the green blue product was cooled to room temperature. Hexane (50 mL) was added into the reaction mixture to completely precipitate the crude product, which was then filtered off and washed with i-PrOH and acetone. The crude product, taken into 50 mL of EtOH, was refluxed for 0.5 h, then the hot mixture was filtered off. The same procedure was repeated several times. The obtained product was purified by column chromatography (silica gel, MeOH:CH2Cl2, 5:2). These compounds are soluble in H2O, MeOH, DMF and DMSO.

Yield of 2a: 0.20 g (16 %). Anal. Calc. for C68H38N12O16S4 (Mw: 1407,36): C, 58.03; H, 2.72; N, 11.94. Found: C, 57.90; H, 2.82; N, 11.78%. FT-IR (KBr disc) ν/cm-1: 3035, 2934 (Ar H), 1607, 1590, 1567, 1495 (Ar), 1240 (Ar-O-Ar), 1180, 1153, (SO2), 970, 886, 813, 790. UV/Vis (DMSO): λmax = 334, 426, 611, Qx: 680, Qy: 711.

Yield of 2b: 0.27 g (22 %). Anal. Calc. for C68H38N12O16S4 (Mw: 1407.36): C, 58.03; H, 2.72; N, 11.94. Found: C, 59.01; H, 2.79; N, 11.96 %. FT-IR (KBr disc) ν/cm-1: 3052, 2988 (Ar H), 1670, 1670, 1548, 1489 (Ar), 1288 (Ar-O-Ar), 1160 (SO2), 809, 780, 745. UV/Vis (DMSO): λmax = 259, 287, 341, 611, Qx: 673, Qy: 701. 8

3.1.3. 1(4),8(11),15(18),22(25)-Tetrakis(8-(2,3-dicyanophenoxy) quinoline-5-sulfonic acid)zinc(II)phthalocyanine (3a)

A mixture of 8-(2,3-dicyanophenoxy) quinoline-5-sulfonic acid (1a) (0.30 g, 0.85 mmol) and anhydrous Zn(CH3COO)2 (0.03 g, 0.25 mmol) in the presence of N,N-dimethylaminoethanol (NNDMAE, 0.50 mL) and 1.8-diazabicyclo[5.4.0]undec-7-ene (DBU) (0.70 mL) was heated reflux temperature in a tube under a N2 atmosphere for 5h. The color of the mixture was turned green within 1-1.5h. After the heating was continued for an additional 5h, the green blue product was cooled to room temperature. Hexane (50 mL) was added into the reaction mixture to completely precipitate the crude product, which was then filtered off and washed with i-PrOH and acetone. The crude product was taken into 50 mL of ethanol, was refluxed for 20 min, then the hot mixture was filtered off. The same procedure was repeated for three or more times. The obtained product was purified by column chromatography (silicagel, MeOH:CH2Cl2, 5:1). These compounds are soluble in H2O, MeOH, DMF and DMSO.

Yield of 3a: 0.40 g (33 %). Anal. Calc. for C68H36N12O16S4Zn (Mw: 1470.75): C, 55.53; H, 2.47; N, 11.43. Found: C, 53.07; H, 2.50; N, 11.45 %. FT-IR (KBr disc) ν/cm-1]: 3015, 2937 (Ar H), 1606, 1590, 1581, 1567 (Ar), 1270 (Ar-O-Ar), 1190, 1170 (SO2), 791, 738, 697. UV/Vis (DMSO): λmax = 254, 318, 627, 698.

3.1.4. 1(4),8(11),15(18),22(25)-Tetrakis(8-(2,3-dicyanophenoxy) quinoline-5-sulfonic acid)copper (II) phthalocyanine (4a); 2(3),9(10),16(17),23(24)-Tetrakis(8-(3,4-dicyanophenoxy) quinoline-5-sulfonic acid)-copper (II) phthalocyanine (4b)

9

The same procedure as for 3a and 3b were used to prepare compounds 4a and 4b, starting with 1a and 1b (0.30 g, 0.85 mmol) respectively and CuCl2 (0.03 g, 0.25 mmol). These compounds are soluble in H2O, MeOH, DMF and DMSO.

Yield of 4a: 0.49 g (40 %). Anal. Calc. for C68H36N12O16S4Cu (Mw:1468,89): C, 55.60; H, 2.47; N, 11.44. Found: C, 54.90; H, 2.55; N, 11.30 %. FT-IR (KBr disc) ν/cm-1]: 2938 (Ar H), 1645, 1606, 1567, 1462 (Ar), 1220 (Ar-O-Ar), 1180, (SO2), 815, 792, 747, 648. UV/Vis (DMSO): λmax = 254, 311, 628, 698.

Yield of 4b: 0.60 g (50 %). Anal. Calc. for C68H36N12O16S4Cu (Mw:1468,89): C, 55.60; H, 2.47; N, 11.44. Found: C, 56.11; H, 2.75; N, 11.60 %. FT-IR (KBr disc) ν/cm-1]: 2925 (Ar H), 1644, 1591, 1567, 1498 (Ar), 1225 (Ar-O-Ar), 1176, 1154 (SO2), 889, 811, 790, 738. UV/Vis (DMSO): λmax = 252, 283, 352, 612, 684.

3.1.5. 1(4),8(11),15(18),22(25)-Tetrakis(8-(2,3-dicyanophenoxy) quinoline-5-sulfonic acid)cobalt (II) phthalocyanine (5a); 2(3),9(10),16(17),23(24)-Tetrakis(8-(3,4-dicyanophenoxy) quinoline-5-sulfonic acid)-cobalt (II) phthalocyanine (5b)

The same procedure as for 4a and 4b was used to prepare compounds 5a and 5b, starting with 1a and 1b (0.30 g, 0.85 mmol) respectively and CoCl2 (0.03 g, 0.25 mmol). These compounds are soluble in H2O, MeOH, DMF and DMSO.

Yield of 5a: 0.36 g (30 %). Anal. Calc. for C68H36N12O16S4Co (Mw: 1464.28): C, 55.78; H, 2.48; N, 11.48. Found: C, 55.07; H, 2.55; N, 11.51 %. FT-IR (KBr disc) ν/cm-1: 3089, (Ar H), 1589, 1555, 1500 (Ar), 1267 (Ar-O-Ar), 1179 (SO2), 751, 645. UV/Vis (DMSO): λmax = 262, 296, 614, 683.

10

Yield of 5b: 0.53 g (44 %). Anal. Calc. for C68H36N12O16S4Co (Mw: 1464.28): C, 55.78; H, 2.48; N, 11.48. Found: C, 55.23; H, 2.41; N, 11.54%. FT-IR (KBr disc) ν/cm-1: 2963 (Ar H), 1601, 1512, 1501 (Ar), 1250 (Ar-O-Ar), 1179, 1155 (SO2), 814, 751, 645. UV/Vis (DMSO): λmax = 260, 303, 602, 659.

3.1.6. 1(4),8(11),15(18),22(25)-Tetrakis(8-(2,3-dicyanophenoxy) quinoline-5-sulfonic acid)phthalocyaninatomanganese (III) chloride (6a); 2(3),9(10),16(17),23(24)-Tetrakis(8-(3,4dicyanophenoxy) quinoline-5-sulfonic acid)-phthalocyaninato manganese (III) chloride (6b)

The same procedure as for 5a and 5b was used to prepare compounds 6a and 6b, starting with 1a and 1b (0.30 g, 0.85 mmol) respectively and MnCl2 (0.05 g, 0.24 mmol). These compounds are soluble in H2O, MeOH, DMF and DMSO.

Yield of 6a: 0.41 g (34 %). Anal. Calc. for C68H36N12O16S4MnCl (Mw: 1495.74): C, 54.60; H, 2.43; N, 11.24. Found: C, 56.01; H, 2.55; N, 11.20 %. FT-IR (KBr disc) ν/cm-1]: 3042, 2934 (Ar H), 1645, 1603, 1567, 1496 (Ar), 1280 (Ar-O-Ar), 1167, 1151, (SO2), 883, 790, 749, 648. UV/Vis (DMSO): λmax = 260, 290, 515, 676, 757.

Yield of 6b: 0.58 g (48%). Anal. Calc. for C68H36N12O16S4MnCl (Mw: 1495.74): C, 54.60; H, 2.43; N, 11.24. Found: C, 56.01; H, 2.55; N, 11.20 %. FT-IR (KBr disc) ν/cm-1]: 3050, 2960 (Ar H), 1601, 1590, 1512, 1483 (Ar), 1267 (Ar-O-Ar), 1149 (SO2), 805, 790, 730. UV/Vis (DMSO): λmax = 258, 286, 371, 503, 657, 734.

3.2. Spectroscopic characterization of free and metal based phthalocyanine Phthalocyanines show characteristic Q and B bands in UV-vis spectra. Two principle π–π * transitions are known for phthalocyanines: a Q-band which is a π– π* transition from the highest occupied molecular orbital (HOMO, a1u) to the lowest unoccupied molecular orbital 11

(LUMO, eg) of the complexes. The B bands (B1 and B2), are observed in the 300 to 350 nm region [34, 35]. A new type of soluble free and metallophthalocyanine derivatives are coherent (Fig. 1). Characteristic Q and B bands for α (Fig. 1A) and β (Fig. 1B) substituted novel phthalocyanines can be seen. In this study the Q-band absorptions in the UV-vis absorption spectra of the phthalocyanines (3a and 3b) were observed as a single high intensity band due to a π– π * transition at, 697, 682 nm in DMSO; 696, 682 nm in water (Table 1 and Fig. 2). Aggregation tendency of phthalocyanines are depicted as a coplanar association of rings progressing from monomer to dimer and higher order complexes and it is dependent on concentration, nature of solvent and kind of substituents, type of metal ions and temperature [36]. The aggregation properties of the ZnPc and CuPc derivatives (3b and 4b) were investigated in water and DMSO at different concentrations. When concentration was increased, the intensity of the Q band also increased and new band was observed due to the aggregated species about 640 nm for 3b in water (Fig. 3). In water, the UV/vis absorption spectra of quaternized phthalocyanines (Fig. 3B for 3b and Fig. 3A for 4b) showed cofacial aggregation (Haggregation), as evidenced by the presence of two non-vibrational peaks in the Q band region. The lower energy (red-shifted) band at 646 nm for 3b is due to monomeric species, while the higher energy (blue-shifted) band at 682 nm for is due to aggregated species. Addition of triton X-100 (0.1mL) which is a surfactant used to prevent aggregation to a water solution of quaternized phthalocyanines (3b) resulted in a considerable increase in intensity of the low energy side of the Q band suggesting that the molecules were aggregated and that the addition of triton X-100 broke up the aggregates between the Pc molecules.

12

3.3. Fluorescence spectra and quantum yields Fluorescence properties of 3a and 3b were investigated in two different solvent (DMSO and water). Fig. 4 shows the absorption, fluorescence excitation and emission spectra of 3a and 3b in DMSO and water. Fluorescence emission peaks were observed at 728 nm for 3a, 714 nm for 3b in DMSO; 743 nm for 3a, 696 nm for 3b in water (Table 1). The Stokes’s shifts range from 7 to 11 nm in DMSO and water, which is usual for ZnPc derivatives [37]. As has been observed before, there is a increase F on going from ZnPc (F = 0.20 [38], in DMSO) to derivatives F = 0,075 (3a), and 0,115 (3b) with complex 3b showing the largest value; ZnPc (F = 0.02 [39] in water) to derivatives F = 0,017 (3a), and 0,095 (3b) with complex 3b showing the largest value. This comparison yields a slight increase in fluorescence was not observed.

3.4. Photochemical properties

3.4.1. Singlet oxygen quantum yields

Singlet oxygen quantum yields Φ∆ are a measure of singlet oxygen generation which is important for PDT study. The Φ∆ values were obtained using eq. (2). Singlet oxygen quantum yields were studied in DMSO and Water as a chemical method by using 1,3diphenylisobenzofuran,

(DPBF)

and

9,10-antracenediyl-bis(methylene)dimalonoicacid

(ADMA) as a singlet oxygen quenches. Fig. 5 shows spectral changes observed during photolysis of complex 3a in DMSO in the presence of DPBF and ADMA. The disappearance of DPBF and ADMA were monitored using UV-vis spectroscopy. The rate at which the DPBF and ADMA degrades is related to the production of singlet oxygen. There were no changes in the Q band intensities during the Φ∆ determinations, confirming that complexes are 13

not degraded during singlet oxygen studies [37]. The Φ∆ values for 3a and 3b (Φ∆ = 0,0005, 0,0008, in DMSO ; 0,0008, 0,0105 in Water). When compared to Φ∆ was of ZnPc to higher than expect in DMSO (0.67 [40]) and in Water +Triton X-100 (0.56 [39])

3.4.2. Photodegradation (photobleaching) quantum yields Photobleaching is a process where phthalocyanine as photosensitizer is degraded under light irradiation owing to singlet oxygen attack which also important for photocatalitic studies. MPcs stability is especially important in the body at a suitable under light. The photo bleaching stabilities of complexes 3a and 3b were determined in DMSO and water by monitoring the decrease in the intensity of the Q band under irradiation with increasing time (Fig. 6 as a sample for 3a in DMSO). The photodegradation quantum yield (Φd) values for the complexes were listed in Table 2 are of the order of 10-4. Stable ZnPc molecules show values as low as 10-6 and for unstable molecules, values of the order 10-3 have been reported [41].

3.5. Electrochemical characterization Electrochemical characterizations of the compounds (2-6) were investigated in an electrolyte solution to elucidate possible applications of the compounds in electrochemical fields. For this purpose, CV’s and DPV’s of the compounds (2-6) were obtained in a deaerated DMSO/TBAP electrolyte system on platinum working electrode. The assignments of the redox couples and electrochemical parameters estimated were listed in Table 3, including the half wave peak potentials (E1/2), peak to peak potential separations (ΔEp), ratio of anodic to cathodic peak currents (Ip,a/Ip,c), and the difference between the first oxidation and reduction processes (ΔE1/2). Compound 2b exhibits three reduction labeled as R1 (E1/2= -0.39 V), R2 (E1/2= -0.82 V) and R3 (E1/2= -1.17 V) and one oxidation processes labeled as O1 (E1/2= 1.10 V) in DMSO/TBAP 14

electrolyte system (Fig. 7). While the first (R1) and second (R2) reductions are both electrochemically and chemically reversible, the oxidation (O1) and third reduction (R3) reactions are irreversible with respect to ∆Ep and Ip,a/Ip,c values. DPVs also clearly show the reversibility of the R1 and R2 redox processes (Fig. 7, inset). The potential difference between the first and second reduction processes of 2b is 0.43 V, which refers to an average separation for the first and second reduction processes of 2a and 2b on the phthalocyanine ring system [42,43]. One of the important electrochemical parameters, ΔE1/2 shows HOMOLUMO gap for metal free-base Pcs and is associated with HOMO-LUMO gap in MPc species containing redox-inactive metal center. ΔE1/2 value was obtained for 2a and 2b as ca. 1.49 V which is good agreement with the metal-free phthalocyanine complexes in the literature [4446]. Redox processes of 3a gives three reduction reductions (R1 at -0.70 V, R2 at -1.12 V, R3 at 1.38 V), and one oxidation processes (O1 at 0.79 V) at various scan rates (Fig 8). Since compound 3a involves electro-inactive metal center, Zn(II), all of these processes are ligand based. The reversibility of redox processes are shown by DPV’s (Fig. 8, inset). The first, second reductions and oxidation reaction of 3a show reversible to quasi-reversible behavior with respect to peak separation (ΔEp), and cathodic to anodic peak currents (Ip,a/Ip,c) values. The third reduction couple of 3a shows irreversible character because of the considerably higher value of ΔEp and Ip,a/Ip,c. Compound 3b exhibit three reductions (R1 at -0.67 V, R2 at -1.08 V, R3 at -1.24 V), and one oxidation processes (O1 at 0.81 V) at various scan rates. When the redox potentials of 3b are compared with that of 2b, it is seen that the reduction half-peak potential of 3b shifts to more negative values (Table 3). This result can be explained by difference in the polarizing effects of 2b and 3b. In addition, electrochemical properties of compound 3b were slightly different from that of complex 3a. Non-peripheral positions are sterically crowded positions that may

15

impose some conformational stress on MPc complexes [47]. Therefore, the effect of the position of substituent on the electrochemical properties of 3b was obvious when compared to that of 3a. Compound 4a has four reductions (R1 at -0.59 V, R2 at -0.85 V, R3 at -1.19 V, R4 at -1.54), and two oxidation processes (O1 at 0.28 V, O2 at 0.93 V) (Fig. 9a). All of these processes are successive removal of electrons from, or addition of electrons to the macrocycle orbitals due to the electro-inactive metal center of the compounds. Differential pulse voltammetry of 4a confirms the recorded redox processes clearly (Fig. 9a, inset). Compound 4b also gives four reductions and two oxidation reactions. However, the redox potentials of 4a and 4b are completely different from each other, indicating a various effect of the substituents at α- and β- positions to the electronic nature of the Pc ring (Table 3). When considered for reduction potentials, 4a is more difficult to be reduced than 4b. This result clearly defines the impact of point of substitution on the voltammetric properties of these compounds. Besides, the first oxidation potential of 4b shifted to less positive value (0.30 V) which is compatible with common copper phthalocyanine [42,43,46,48]. Therefore, potential difference between the first oxidation and first reduction redox processes (HOMO-LUMO gap) of 4b decreased, which is in agreement with the previous phthalocyanine studies [48-50]. The effect of switching potential on the redox processes of 4b was also examined (Fig. 9b). As seen from Fig. 9b, compound 4b gives a clear reversible oxidation couple at +0.34 V and irreversible oxidation peak at +0.06 V during CV scan when the potential is switched from -0.54 V. The couple at +0.34V decreased and the oxidation peak at +0.06 V almost disappeared when the switching potential is shifted to more negative potentials and repetitive CV scans are performed. In addition, two reduction couples at -0.78 and -1.39 V and an oxidation peak at 0.82 V are also recorded. After the repetitive CV scans, the peak at +0.06V did not observed on CV and DPV upon switched from -0.54 V. The reason of decrease in couple at +0.34V and

16

disappearance of the peak at +0.06 V might be due to the aggregation of the monomeric species which forms upon reorganization of the species during the reduction and re-oxidation processes of the repetitive cycles. Compound 5b displays three reduction (R1 at -0.28 V, R2 at -0.76 V and R3 at -1.26 V) and two oxidation (O1 at 0.52 V and O2 at 1.14 V) couples at various scan rates. The redox couples of O1 and R1 are assigned to the metal based oxidation and reduction processes while R2 and O2 are ring-based reduction and oxidation process, and R3 is further ring reduction [51]. The second reduction couple (R2) is electrochemically reversible whereas R1, R3 and O1 are in quasi-reversible behavior with respect to ∆Ep of the couples. However, the couples are not chemically reversible with respect to the Ip,a/Ip,c ratio (Table 3). Compound 5a shows three reduction (R1 at -0.36 V, R2 at -1.01 V and R3 at -1.38 V) and two oxidation (O1 at 0.41 V and O2 at 0.93V) couples in DMSO/TBAP electrolyte system (Data were not shown). The comparison of the reduction potentials of 5a and 5b indicate that peripheral substitution (5b) results in easier reduction than non-peripheral substitution (5a), while oxidation is easier for non-peripheral derivative (5a) as shown Table 3. The ease of oxidation of 5a could be a result of conformational distortion, induced by non-peripheral substitution [52]. Compound 6b gives one oxidation (O1 at 0.57 V) and three reversible reductions (R1 at -0.13 V, R2 at -0.52 V and R3 at -1.39 V) at various scan rates (Fig. 10). While the first two reductions and oxidation processes of the compound are metal-based, the third reduction is ligand-based process [53]. For the first and second reduction couples of 6b, anodic to cathodic peak separations (∆Ep) changed from 57 to 120 mV with the scan rates from 25 to 500 mV s-1, indicating electrochemical reversibility of the electron transfer (Ep’s, 60 to 110 mV, were obtained for ferrocene reference). The effect of coupled chemical reactions on electron transfer reactions is illustrated with Ip,a/Ip,c ratio change as a function of the scan rate. Unity of

17

Ip,a/Ip,c ratios at all scan rates indicates purely diffusion controlled and chemically reversible behavior of R1 and R2 processes. However, the processes of R3 and O1 are not chemically reversible with respect to ratio of Ip,a/Ip,c. Chemical and electrochemical reversibility are clarified by the similarity of the peak currents and symmetry of the peaks in the forward and reverse DPV scans (Fig. 10, inset). The first reduction potential of 5b and 6b are highly different from those of 2b, 3b, and 4b in the same media (Table 3). As compared with compound 2b, 3b and 4b, the first reductions of 5b and 6b occur at less negative potentials (0.28 V and -0.13 V vs.Ag/AgCl, respectively). The reason of that some of MPcs, such as CoPc, MnPc and FePc containing a metal ion that has energy levels lying between the HOMO and LUMO of the Pc ligand, in most cases shows the metal ion-centered redox processes [49,50,54-56]. Similarly, compound 6a gives one oxidation (O1 at 0.55 V) and three reversible reduction (R1 at -0.24 V, R2 at -0.57 V and R3 at -1.44 V) couples in DMSO/TBAP electrolyte system. When compared the reduction potentials of 6a and 6b, it could be realized that 6a was reduced more difficult than 6b. This is due to the different effect of the substituents at α- and βpositions to the electronic nature of the Pc ring.

4. Conclusion In this study, phthalocyanines bearing 8-hydroxyquinoline-5-sulfonicacid (HQSA) [MPc-αHQSAand MPc- β-HQSA]; (M=2H, Zn(II), Cu(II), Co(II) and Mn(III); X:Cl)] conjugates and their cationic quaternized counterpart that play important roles in PDT were synthesized and characterized. The singlet oxygen quantum, which give indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II 18

mechanism). Thus, these new zinc phthalocyanines complexes can’t exhibit Type II photosensitizer properties on PDT applications. The reduction potentials of α- substitued compounds that were observed have more negative values than that of β- substitued compounds. Since non-peripheral positions are sterically crowded positions that could impose some conformational stress on MPc complexes, peripheral substitution results in easier reduction than non-peripheral substitution, while oxidation is easier for non-peripheral derivative. The ease of oxidation in non-peripheral positions could be a result of conformational distortion, induced by non-peripheral substitution. Non-peripheral substitutied compounds exhibited more susceptibility to oxidation than peripheral ones because of the electron-donating tendency of the substituent.

Acknowledgements

We thanks, The Research Fund of Sakarya University (Project no: BAP-2014-02-04-011).

19

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22

Figure Caption

Scheme 1

Synthetic route of 1(4), 8(11), 15(18), 22(25)-tetrakis 8-hydroxyquinoline-5sulfonicacid (HQSA) phthalocyanine [(MPc-α-HQSA and MPc- β-HQSA); (M=2H, Zn(II), Cu(II), Co(II) and Mn(III)]

Scheme 2

Synthetic route of 2(3), 9(10), 16(17), 23(24)-tetrakis 8-hydroxyquinoline-5sulfonicacid (HQSA) phthalocyanine [(MPc-α-HQSA and MPc- β-HQSA); (M=2H, Zn(II), Cu(II), Co(II) and Mn(III)]

Fig. 1.

UV-vis spectra of 2a-6a(A) and 2b-6b(B)

Fig. 2.

UV-vis absorption spectra of 3b in DMSO (A) and in Water (B) at different concentration

Fig. 3.

UV-vis spectral change of 3b(A) and 4b(B) during water added step by step

Fig. 4

Absorption (

) , excitation (

) and emission (

) spectra of the

compounds 3a in WATER. Fig. 5.

A typical spectrum for the determination of singlet oxygen quantum yield of for complex 3a in DMSO at a concentration 6 x 10-6 mol dm-3.

Fig. 6.

A typical spectrum for the determination of Photodegredation. This figure was for complex 3a in DMSO

Fig. 7.

CVs of 2b (5.0 x 10-4 mol L-1) recorded with various scan rates. Inset: DPVs of 2b in DMSO/TBAP on Pt working electrode.

Fig. 8.

CVs of 5.0 x 10-4 mol L-1 of 3a at various scan rates. Inset: DPVs of 3a on Pt electrode in DMSO/TBAP.

Fig. 9.

(a) CVs of 4a (5.0 x 10-4 mol L-1) recorded with various scan rates. Inset: DPVs of 4a in DMSO/TBAP on Pt working electrode (b) CVs of 4b at different switching potentials.

Fig. 10.

CVs of 5.0 x 10-4 mol L-1 of 6b at various scan rates. Inset: DPVs of 6b in DMSO/TBAP on a Pt working electrode

23

Fig. 1. 24

Fig. 2.

25

Fig. 3

26

27

Fig. 4

Fig. 5

28

Fig. 6

29

Fig. 7

30

Fig. 8

31

Fig. 9

32

Fig. 10

33

Fig. 11

34

Table 1. Spectral parameters of 3a, 3b in WATER, DMSO

Comp.

Q band

inWater

λ max(nm)

3a

696

3b

Excitation

Emission

StokesShift

λ Ex (nm)

λ Em (nm)

Δ Stokes (nm)

5,21

705

713

8

682

5,15

684

696

12

3a

697

5,08

717

728

11

3b

681

5,19

697

714

17

log ε

Comp. in DMSO

35

Table 2.Photophysical and photochemical properties of 3a, 3b in WATER, DMSO

Comp.

Solvent

F

d(10-5)



3a

DMSO

0,08

50,10

0,12

3b

DMSO

0,12

80,40

0,11

Comp.

Solvent

F

d



3a

Water +Triton X-100

0,02

13,20

0,01

3b

Water +Triton X-100

0,10

10,50

0,02

36

Table 3.Voltammetric data of the compounds

Compoun d 2b

O1 a

E1/2 (V)

R4

ΔEp (mV)

b

c

R3 -

R2 -

R1 -

1.1 e

1.17

0.82

0.3

180

110

9

0.93

115

80

Ip,a/Ipc(μA

-

)

O2

ΔE1/

d

2

1.49

1.3

0.8 9 3b

a

E1/2 (V)

-

-

-

0.81

1.24

1.08

0.6

80

e

e

7

110

74

60

-

0.98

1.1

-

-

-

0.79

ΔEp (mV)

1.38

1.12

0.7

60

Ipa/Ipc(μA)

130

35

0

-

0.75

20

ΔEp (mV)

b

c

3a

a

Ipa/Ipc(μA)

0.79

E1/2 (V)

b

c

1.48

e

1.49

0.85

1.0 6 4b

a

E1/2 (V) ΔEp (mV)

b

c

Ipa/Ipc

(μA)

-

-

-

-

0.30

1.04

1.32

1.01

0.61

0.3

63

50

e

e

3 0.93

-

140

100

55

135 -

0.65 37

e

0.63

4a

a

E1/2 (V) ΔEp (mV)

b

c

-

-

e

-

-

-

-

1.54

1.19

e

e

0.85

0.5

30

9

1.10

100

Ipa/Ipc(μA) 60

70

-

0.70

0.28

0.93

0.96

e

130 1.20

110 0.65

0.6 9

5b

a

E1/2 (V)

-

-

-

0.52

1.14

b

1.26

0.76

0.2

e

e

c

70

80

8

110e

80e

0.77

0.65

67

0.55

0.77

e

e

e

e

0.93

ΔEp (mV)

Ipa/Ipc

(μA)

0.5

0.80

5 5a

a

E1/2 (V)

-

-

-

0.41

b

1.38

1.01

0.3

e

c

68

97

6

122e

0.83

0.6e

74

ΔEp (mV)

Ipa/Ipc

(μA)

e

0.7

0.77

63

0.57

0.82 e

e

4 6b

a

E1/2 (V)

-

-

-

0.57 e

b

1.39

0.52

0.1

c

-

94

3

Ipa/Ipc

-

(μA)

-

0.98

71

-

ΔEp (mV)

1.11

1.1 6a

a

E1/2 (V)

-

-

-

0.55

b

1.44

0.57

0.2

70

c

20

125

4

-

0.84

25

ΔEp (mV)

Ipa/Ipc

(μA)

0.81

0.9 1 a

E1/2= (Ep,a + Ep,c)/2 at 0.1 V s-1 ΔEp = Ep,a - Ep,c

b

38

0.79

c

Ip,a/Ip,c for reduction, Ip,c/Ip,afor oxidation processes at 0.1 V s-1 scan rate. ΔE1/2= E1/2 (first oxidation) - E1/2 (first reduction).

d

e

Recorded by DPV

f

Peak potential of the aggregated species were given in parentheses.

39