Photophysical, photochemical and aggregation behavior of novel peripherally tetra-substituted phthalocyanine derivatives

Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

Contents lists available at SciVerse ScienceDirect

Journal of Photochemistry and Photobiology A: Chemistry journal homepage: www.elsevier.com/locate/jphotochem

Photophysical, photochemical and aggregation behavior of novel peripherally tetra-substituted phthalocyanine derivatives Ece Tu˘gba Saka a , Cem Göl b , Mahmut Durmus¸ b , Halit Kantekin a,∗ , Zekeriya Bıyıklıo˘glu a a b

Department of Chemistry, Faculty of Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey Gebze Institute of Technology, Department of Chemistry, PO Box 141, Gebze 41400, Kocaeli, Turkey

a r t i c l e

i n f o

Article history: Received 27 February 2012 Received in revised form 26 April 2012 Accepted 23 May 2012 Available online 1 June 2012 Keywords: Phthalocyanine Zinc J-aggregation Photophysical Photochemical Singlet oxygen

a b s t r a c t In this study, the novel metal-free (4) and zinc (II) (5) phthalocyanine compounds substituted with four 1(2-oxyethyl)-4-piperidone ethylene ketal functional groups at peripheral positions have been prepared. These new phthalocyanine compounds have been characterized by IR, 1 H NMR, 13 C NMR spectroscopy, MS spectral data and elemental analysis. The synthesized phthalocyanine compounds exhibited excellent solubility in common organic solvents and the zinc (II) phthalocyanine complex (5) showed J-type aggregation in chloroform. The photophysical and photochemical properties of metal-free (4) and zinc (II) (5) phthalocyanine complexes were also investigated in DMSO. The investigation of the photophysical and photochemical properties of photosensitizers is very useful for photodynamic therapy (PDT) applications. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Metallophthalocyanine (MPc) complexes are being extensively researched because of their diverse applications. These include their uses in electronic devices, non-linear optics, electrochromic devices, Langmuir–Blodgett films, as gas sensors and photosensitizers in photodynamic therapy (PDT) of cancer [1,2]. The exceptional chemical and physical properties of phthalocyanines can be because of various substituents on the phthalocyanine framework. Over 70 elements can be included into the phthalocyanine core and its chemical versatility allows the introduction of many different substituents at peripheral positions [3,4]. Metallophthalocyanines are known to have low solubility in most organic solvents. The solubility of these compounds can be improved via substitution of different groups on the phthalocyanine skeleton. It has been documented that tetra-substituted phthalocyanines are more soluble than their octa-substituted counterparts due to formation of constitutional isomers and their high dipole moments [5,6]. Aggregation of the phthalocyanine compounds is an important phenomenon. The substituted metallophthalocyanines could be form two types of aggregations which affect on electronic and optical properties, namely face-to-face H-aggregation and

∗ Corresponding author at: Department of Chemistry, Karadeniz Technical University, 61080 Trabzon, Turkey. Tel.: +90 462 3772599; fax: +90 462 3253196. E-mail address: [email protected] (H. Kantekin). 1010-6030/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jphotochem.2012.05.023

side-to-side J-aggregation [1,2]. Typically, phthalocyanine aggregation results in a decrease in intensity of the Q band corresponding to the monomeric species, meanwhile a new, broader and blueshifted band is seen to increase in intensity. This shift to lower wavelengths indicates to H-type aggregation among the phthalocyanine molecules. Rare cases red-shifted bands have been observed corresponding to J-type aggregation of the phthalocyanine molecules. Generally, J-aggregates of Pc occurred by utilizing the coordination of the side substituent from one Pc molecule to the central metal ion in a neighbor [7–11]. The substituted zinc Pcs in non-coordinated organic solvents, e.g. chloroform and dichloromethane exhibit J-aggregation [12,13]. The addition of coordinating solvents such as methanol or ethanol caused dissociation of the dimers, which implies that the absence of coordinating solvents is essential for J-aggregation of Pc [14]. UV–vis and MALDITOF-MS spectra could be used for determination presence of J-aggregation for Pc compounds [15]. Furthermore, owing to their extensively planar aromatic ␲ system, phthalocyanines exhibit a high aggregation tendency which leads to insolubility in the case of unsubstituted parent derivatives or hinders purification and characterization of compounds in many respects together with a lower efficiency in their use in PDT [16,17]. PDT is a binary therapy that involves the combination of visible light and a photosensitizer [18]. Diamagnetic ions such as Zn2+ , Al3+ , Ga3+ and Ti4+ give phthalocyanine complexes comprising both high triplet yields and long triplet lifetimes which are suitable for photodynamic therapy (PDT) applications [19]. Due to the intense absorption in the visible region, high efficiency to generate

68

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

reactive oxygen species (such as singlet oxygen), and low dark toxicity, phthalocyanines have been used in this avenue for the treatment of various cancers and photoinactivation of viruses [18,20]. Our previous studies have already reported synthesis, photophysical and photochemical properties of various substituted phthalocyanines [21–25]. These phthalocyanine complexes show interesting photophysical and photochemical properties especially high singlet oxygen quantum yields which are very important for PDT of cancer. In this work, we have been synthesized new metal-free (4) and zinc (5) phthalocyanines substituted with four 1(2-oxyethyl)-4-piperidone ethylene ketal groups as potential PDT agents. Aggregation behavior, photophysical (fluorescence lifetime and quantum yields) and photochemical (singlet oxygen and photodegradation quantum yields) properties were investigated. This work has also been reported the effects of the substituents and the nature of the metal on the photophysical and photochemical parameters of 1-(2-oxyethyl)-4-piperidone ethylene ketal substituted phthalocyanine derivatives in DMSO. This work also explores the effects of substituents and nature of the central metal ions on the fluorescence properties of the phthalocyanines and on the quenching of the phthalocyanines by 1,4-benzoquinone (BQ) using the Stern–Volmer relationship.

2.3. Photophysical parameters 2.3.1. Fluorescence quantum yields and lifetimes Fluorescence quantum yields (˚F ) were determined in DMSO by the comparative method using equation 1 [29,30]. ˚F = ˚F (Std)

F · AStd · n2 FStd · A · n2Std

,

(1)

where F and FStd are the areas under the fluorescence emission curves of the samples (4 and 5) and the standard, respectively. A and AStd are the respective absorbances of the samples and standard at the excitation wavelengths, respectively. n2 and n2Std are the refractive indices of solvents used for the sample and standard, respectively. Unsubstituted ZnPc (in DMSO) (˚F = 0.20) [31] was employed as the standard. The absorbance of the solutions at the excitation wavelength ranged between 0.04 and 0.05. Natural radiative life times ( 0 ) were determined using PhotochemCAD program [32] which uses the Strickler–Berg equation. The fluorescence lifetimes ( F ) were evaluated using Eq. (2). ˚F =

F . 0

(2)

2.4. Photochemical parameters 2. Experimental 2.1. Materials phthalocyanine reactions were carried out All under nitrogen atmosphere using standard Schlenk techniques. 1,3-Diphenylisobenzofuran (DPBF) and 1,8diazabicyclo[5.4.0]undec-7-ene (DBU) were purchased from Fluka. All solvents were dried and purified as described by reported procedure [26]. 1-(2-Hydroxyethyl)4-piperidone ethylene ketal (1) [27], 4-nitrophthalonitrile (2) [28] were prepared according to the literature procedure.

2.4.1. Singlet oxygen quantum yields Singlet oxygen quantum yield (˚ ) determinations were carried out using the experimental set-up described in the literature [33–35]. Typically, a 3 ml portion of the respective unsubstituted, metal-free Pc (4) and zinc Pc complex (5) solutions (C = 1 × 10−5 M) containing the singlet oxygen quencher was irradiated in the Q band region with the photo-irradiation set-up described in references [33–35]. Singlet oxygen quantum yields (˚ ) were determined in DMSO using the relative method with unsubstituted ZnPc as reference. DPBF was used as chemical quencher for singlet oxygen in DMSO. Eq. (3) was employed for the calculations: ˚ = ˚Std 

2.2. Equipment FT-IR spectra were obtained on a Perkin Elmer 1600 FTIR spectrophotometer with the samples prepared as KBr pellets. NMR spectra were recorded on a Varian Mercury 200 MHz spectrometer in CDCl3 , and chemical shifts were reported (ı) relative to TMS as an internal standard. Mass spectra were recorded on a Micromass Quatro LC/ULTIMA LC–MS/MS spectrometer. The elemental analyses were performed on a Costech ECS 4010 instrument. The formation of J-aggregation for zinc (II) Pc complex (5) was determined by positive ion and linear mode MALDI-MS in dihydroxybenzoic acid as MALDI matrix using nitrogen laser accumulating 50 laser shots using Bruker Microflex LT MALDI-TOF mass spectrometer. Melting points were measured on an electrothermal apparatus. Domestic microwave oven was used synthesis of zinc (II) Pc complex (5). Absorption spectra in the UV–vis region were recorded with a Shimadzu 2001 UV spectrophotometer. Fluorescence excitation and emission spectra were recorded on a Varian Eclipse spectrofluorometer using 1 cm pathlength cuvettes at room temperature. Photo-irradiations were done using a General Electric quartz line lamp (300 W). A 600 nm glass cut off filter (Schott) and a water filter were used to filter off ultraviolet and infrared radiations, respectively. An interference filter (Intor, 670 nm with a band width of 40 nm) was additionally placed in the light path before the sample. Light intensities were measured with a POWER MAX5100 (Molelectron detector incorporated) power meter.

Std R · Iabs

RStd · Iabs

,

(3)

where ˚Std is the singlet oxygen quantum yield for the stan

= 0.67 in DMSO)[36]. R and RStd dard unsubstituted ZnPc (˚Std  are the DPBF photobleaching rates in the presence of the samStd are the ples (4 and 5) and standard, respectively. Iabs and Iabs rates of light absorption by the samples (4 and 5) and standard, respectively. To avoid chain reactions induced by DPBF in the presence of singlet oxygen, the concentration of quenchers (DPBF) was lowered to ∼3 × 10−5 mol dm−3 [37]. Solutions of sensitizer (C = 1 × 10−5 M) containing DPBF were prepared in the dark and irradiated in the Q band region using the photoirradiation setup. DPBF degradation at 417 nm was monitored. The light intensity 7.3 × 1015 photons s−1 cm−2 was used for ˚ determinations. 2.4.2. Photodegradation quantum yields Photodegradation quantum yield (˚d ) determinations were carried out using the experimental set-up described in the literature [33–35]. Photodegradation quantum yields were determined using Eq. (4), ˚d =

(C0 − Ct ) · V · NA , Iabs · S · t

(4)

where C0 and Ct are the samples (4 and 5) concentrations before and after irradiation respectively, V is the reaction volume, NA is the Avogadro’s constant, S is the irradiated cell area and t is the irradiation time. Iabs is the overlap integral of the radiation source light intensity and the absorption of the samples (4 and 5). A

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

light intensity of 2.19 × 1016 photons s−1 cm−2 was employed for ˚d determinations. 2.5. Fluorescence quenching by 1,4-benzoquinone (BQ) Fluorescence quenching experiments on the metal-free (4) and zinc (II) (5) Pc compounds were carried out by the addition of different concentrations of BQ to a fixed concentration of the compounds, and the concentrations of BQ in the resulting mixtures were 0, 0.008, 0.016, 0.024, 0.032 and 0.040 M. The fluorescence spectra of the substituted metal-free (4) and zinc (II) (5) Pc compounds at each BQ concentration were recorded, and the changes in fluorescence intensity related to BQ concentration by the Stern–Volmer (SV) equation [38] using Eq. (5): I0 = 1 + KSV [BQ ], I

(5)

where I0 and I are the fluorescence intensities of samples in the absence and presence of BQ, respectively. KSV is the Stern–Volmer constant; and this is the product of the bimolecular quenching constant (kq ) and the fluorescence lifetime  F (Eq. (6)): KSV = kq F .

(6)

The ratios I0 /I were calculated and plotted against [BQ] according to Eq. (5), and KSV determined from the slope. 2.6. Synthesis 2.6.1. 4-[2-(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy]phthalonitrile (3) 1-(2-Hydroxyethyl)4-piperidone ethylene ketal (1) (2 g, 0.010 mol) was dissolved in dry DMF (0.04 L) under N2 atmosphere and 4-nitrophthalonitrile (2) (2.13 g, 0.010 mol) was added to the solution. After stirring 10 min, finely ground anhydrous K2 CO3 (4.64 g, 0.032 mol) was added portion wise within 2 h with efficient stirring. The reaction mixture was stirred under N2 at 50 ◦ C for 2 days. Then the solution was poured into ice-water (0.1 L). The precipitate formed was filtered off, washed with water firstly until the filtrate was neutral and then diethyl ether and dried in vacuum over P2 O5 . The crude product was recrystallized from methanol. Yield: 2.67 g (80%), mp: 85–86 ◦ C. IR (KBr tablet) max /cm−1 : 3082 (Ar H), 2956–2888 (Aliph. C H), 2231 (C N), 1598, 1561, 1493, 1470, 1424, 1366, 1311, 1255, 1212, 1147 (C O C), 1097, 1039, 964, 946, 912, 839, 762. 1 H-NMR. (CDCl3 ), (ı:ppm): 7.72 (d, 1H, ArH), 7.28 (s, 1H, ArH), 7.22 (d, 1H, ArH), 4.16 (t, 2H, CH2 O), 3.95 (t, 4H, CH2 O), 2.86 (t, 2H, CH2 N), 2.65 (t, 4H, CH2 N), 1.75 (t, 4H, CH2 N). 13 C-NMR. (CDCl3 ), (ı:ppm): 162.12, 135.47, 119.99, 119.67, 117.59, 115.95, 115.51, 107.00, 67.58, 64.51, 56.44, 52.11, 34.96. MS (ES+ ), (m/z): 314 [M+H]+ . C17 H19 N3 O3 : calcd. C 65.14, H 6.06, N 13.40%; found: C 65.42, H 6.35, N 13.20. 2.6.2. Tetrakis[2-(1,4-dioxa-8-azaspiro[4.5]dec-8yl)ethoxy]phthalocyanine (4) 4-[2-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy]phthalonitrile (3) (0.3 g, 0.96 × 10−3 mol), n-pentanol (0.003 L) and 1,8diazabicyclo[5.4.0] undec-7-ene (DBU) (0.07 × 10−3 L, −3 0.48 × 10 mol) was placed in a standard Schlenk tube under nitrogen atmosphere and degassed three times. Then temperature was increased up to 160 ◦ C. The reaction system was stirred at 160 ◦ C for 16 h. After the reaction mixture was cooled to room temperature, 0.06 L n-hexane was added and mixed for half an hour. Precipitate was filtered and washed with diethyl ether. The crude product was purified by column chromatography which is placed aluminum oxide using CHCl3 :CH3 OH (9:1) as solvent system and gave pure green solid product. This product was dried under vacuum over P2 O5 . Yield: 0.12 g (40%), mp >300 ◦ C.

69

(KBr tablet) max /cm−1 : 3290 (N H), 3065 (Ar H), 2926–2875 (Aliph. C H), 1611, 1468, 1425, 1389, 1365, 1341, 1310, 1240, 1146 (C O C), 1096, 1010, 962, 944, 911, 822, 745, 716. 1 H NMR (CDCl3 ) (ı:ppm): 7.90–7.71 (m, 4H, ArH), 7.09–6.98 (m, 4H, ArH), 6.79 (m, 4H, ArH), 4.10 (m, 24H, CH2 O), 3.06 (bs, 8H, CH2 N), 2.91 (bs, 16H, CH2 N), 1.99 (bs, 16H, CH2 N), −5.34 (s, 2H, NH). 13 C-NMR. (CDCl ), (ı:ppm): 160.04, 136.99, 129.04, 128.18, 122.89, 3 118.28, 107.47, 104.54, 66.51, 64.61, 57.41, 52.41, 35.25. MS (ES+ ), (m/z): 1255 [M]+ . C68 H78 N12 O12 : calcd. C 65.07, H 6.21, N 13.39%; found: C 65.40, H 6.39, N 13.18. 2.6.3. Tetrakis-[2-(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy] phthalocyaninato zinc(II) (5) A mixture of 4-[2-(1,4-dioxa-8-azaspiro[4.5]dec-8yl)ethoxy]phthalonitrile (3) (0.6 g, 1.91 × 10−3 mol), Zn(CH3 COO)2 (0.086 g, 0.47 × 10−3 mol) and 2-(dimethylamino)ethanol (0.006 L) was irradiated in a microwave oven at 175 ◦ C, 350 W for 12 min. After the mixture being cooled to the room temperature, it was stirred by EtOH (0.025 L) addition for overnight, and then filtered off. The product was refluxed by EtOH (0.04 L) for 4 h. The green product was filtered off, washed with hot EtOH–MeOH. The crude product was purified by column chromatography which is placed aluminum oxide using CHCl3 :CH3 OH (9:1) as solvent system and gave pure green solid product. This product was dried under vacuum over P2 O5 . Yield: 0.264 g (42%), mp >300 ◦ C. IR (KBr tablet) ␯max /cm−1 : 3060 (Ar H), 2950–2884 (Aliph. C H), 1717, 1606, 1489, 1390, 1365, 1337, 1282, 1237, 1096, 1054, 963, 946, 913, 855, 827, 748, 665. 1 H NMR (CDCl3 ) (ı:ppm): 8.87 (bs, 4H, ArH), 8.42 (bs, 4H, ArH), 7.44 (bs, 4H, ArH), 4.49 (bs, 8H, CH2 O), 3.98 (bs, 16H, CH2 O), 3.09 (bs, 8H, ArH), 2.83 (m, 16H, CH2 N), 1.88 (m, 16H, CH2 N). 13 C-NMR. (CDCl3 ), (ı:ppm): 160.80, 141.07, 132.09, 125.46, 124.21, 120.98, 108.86, 106.18, 67.35, 64.47, 56.58, 52.05, 34.95. MS (ES+ ), (m/z): 1318 [M]+ . C68 H76 N12 O12 Zn: calcd. C 61.90, H 5.77, N 12.75%; found: C 62.14, H 6.09, N 12.88. 3. Results and discussion 3.1. Synthesis and characterization The general synthetic route was used for the new substituted phthalonitrile compound (3) starting from 1-(2-hydroxyethyl)4piperidone ethylene ketal (1) and 4-nitrophthalonitrile (2) in the presence of dry K2 CO3 as a base at 50 ◦ C in dry DMF (Scheme 1). The tetramerization of the substituted phthalonitrile compound (3) in a high-boiling solvent in the presence of a few drops DBU as a strong base at reflux temperature under a nitrogen atmosphere afforded the metal-free phthalocyanine (4) as a green solid after purification by column chromatography which is placed aluminum oxide using CHCl3 :CH3 OH (9:1) as solvent system. Zinc (II) phthalocyanine complex (5) was obtained using microwave irradiation in the presence of the anhydrous Zn(CH3 COO)2 in 2-(dimethylamino)ethanol as a green solid after purification by column chromatography which is placed aluminum oxide using CHCl3 :CH3 OH (9:1) as solvent system. In the IR spectrum, the formation of phthalonitrile compound (3) was clearly confirmed by the disappearance of the–OH and–NO2 bands and appearance of C N band at 2231 cm−1 . In the 1 H NMR spectrum of compound 3, OH group of compound 1 disappeared as expected. The signals were observed at ı = 7.72 ppm, 7.28 ppm and 7.22 ppm for the aromatic protons and 4.16 ppm, 3.95 ppm, 2.86 ppm, 2.65 ppm, 1.75 ppm for aliphatic CH2 protons. The 13 CNMR spectrum of 3 showed signals at ı = 162.12, 135.47, 119.99, 119.67, 117.59, 115.95, 115.51, 107.00, 67.58, 64.51, 56.44, 52.11, 34.96 ppm. The MS spectrum of compound 3, which showed a peak

70

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

CN O

OH

N

O

O 2N

1

CN

2

i CN O

N

O

O 3

ii

RO

CN

iii

RO

OR

OR

N N

N

HN

RO

4

N

N

N

N

Zn

N

N

NH

N

N N

N

N OR

RO O

R=

5

OR

N

O Scheme 1. The synthetic route of the phthalonitrile, metal-free and zinc phthalocyanines. Reagents and conditions: (i) dry DMF, K2 CO3 , 50 ◦ C, 48 h; (ii) n-pentanol, DBU, 160 ◦ C, (iii) Zn(CH3 COO)2 , DMAE, 175 ◦ C, 350 W.

at m/z = 314 [M+H]+ support the proposed formula for this compound. The sharp peak in the IR spectrum for the C≡N vibration of phthalonitrile compound (3) at 2231 cm−1 disappeared after conversion into metal-free phthalocyanine, indicative of phthalocyanine formation. The characteristic IR band for the inner N H stretching of metal-free phthalocyanine (4) was observed at 3290 cm−1 . The IR spectra of metal-free (4) and zinc (II) (5) phthalocyanine compounds are very similar, except these  (NH) vibrations of the inner phthalocyanine core in the metal-free molecule. The N H protons of metal-free phthalocyanine (4) were also identified in the 1 H NMR spectrum (Fig. 1) with a singlet peak at ı = −5.34 ppm, and the signals disappeared after the addition of D2 O [39,40]. The 1 H NMR spectrum of compound 4 indicated signals were observed at ı = 7.79–7.71 ppm, 7.09–6.98 ppm and 6.79 ppm for the aromatic protons and 4.10 ppm, 3.06 ppm, 2.91 ppm, 1.99 ppm for aliphatic CH2 protons. The 13 C-NMR spectrum of 4 showed signals at ı = 160.04, 136.99, 129.04, 128.18, 122.89, 118.28, 107.47, 104.54, 66.51, 64.61, 57.41, 52.41, 35.25 ppm. In the mass spectrum of compound 4, the presence of the characteristic molecular ion peak at m/z = 1255 [M]+ confirmed the proposed structure. In the IR spectrum of zinc(II) phthalocyanine compound (5) the sharp vibration for the C N groups in the IR spectrum of phthalonitrile compound (3) at 2231 cm−1 disappeared after conversion into zinc (II) phthalocyanine. The 1 H NMR spectrum of zinc (II) phthalocyanine showed aromatic ring protons at 8.87 ppm, 8.42 ppm and 7.44 ppm as broad peaks, and the aliphatic protons were observed at 4.49 ppm, 3.98 ppm and 3.09 ppm as broad peaks

and 2.83 ppm, 1.88 ppm as multiplets. The 13 C-NMR spectrum of 5 showed signals at ı = 160.80, 141.07, 132.09, 125.46, 124.21, 120.98, 108.86, 106.18, 67.35, 64.47, 56.58, 52.05, 34.95 ppm. In the mass spectrum of compound 5, the presence of molecular ion peaks at m/z = 1318 [M]+ confirmed the proposed structure.

3.2. Ground state electronic absorption spectra Phthalocyanine compounds exhibit typical electronic spectra with two strong absorption regions, one around ca. 300 nm is called as the “B” or Soret band because of electronic transitions from deeper ␲-HOMO to n*-LUMO energy levels, while the other one at 600–750 nm is called as the “Q” band, due to electronic transitions from ␲-HOMO to ␲*-LUMO energy levels [41]. One of the best indicators of the formation of phthalocyanines is their UV–vis spectra in dilute solution. The UV–vis spectra of the studied metal-free (4) and zinc (II) (5) phthalocyanine compounds in DMSO were given in Fig. 2. The Q band of the metal-free phthalocyanine was observed as splitted two bands due to D2h symmetry [42]. The splitting Q band was observed at max 704 and 676 nm in DMSO (Table 1), indicating the structure with non-degenerate D2h symmetry [42]. The ground state electronic absorption spectrum of zinc (II) phthalocyanine compound (5) showed monomeric behavior evidenced by a single (narrow) Q band, typical of metallated phthalocyanine complexes, Fig. 2 [43]. The Q band of this complex was observed at 684 nm in DMSO, Table 1. The B bands of studied phthalocyanine compounds (4 and 5) were observed at around 340–360 nm in DMSO (Fig. 2).

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

Fig. 1.

1

H-NMR spectrum of metal-free phthalocyanine 4.

1.8

Absorbance

1.5 1.2

4

0.9

5

0.6 0.3 0 300

400

500

600

71

700

800

Wavelenght (nm) Fig. 2. Absorption spectra of compounds 4 and 5 in DMSO. Concentration = 1 × 10−5 M.

3.3. Aggregation studies High aggregation tendency of phthalocyanine compounds due to the interactions between their 18 ␲-electron systems often cause weak solubility or insolubility in many solvents. It also affects seriously their spectroscopic, photophysical, photochemical and electrochemical properties. It has been established that phthalocyanines can form H- and J-type aggregates depending on the orientation of the induced transition dipoles of their constituent monomers [44–46]. In H-aggregates, the component monomers are arranged into a face-to-face conformation, and transition dipoles

are perpendicular to the line connecting their centers. In contrast, in J-aggregates, the component monomers adopt a side-by-side conformation, and their transition dipoles are parallel to the line connecting their centers [47]. Aggregation is highly depends on some parameters such as concentration, temperature, nature of the substituents, nature of solvents and complexed metal ions [48]. Aggregation behavior of metal-free (4) and zinc (II) (5) Pc compounds was investigated in different solvents (Fig. 3). Compound 4 did not show any aggregation in chloroform, dichloromethane and THF, but this compound showed a little bit H-type aggregation (Fig. 3a) in both DMF and DMSO due to coordinating ability of these solvents. On the other hand the zinc (II) Pc compound (5) did not show aggregation in DMSO, DMF and THF, but this compound showed splitting Q bands at 678 and 698 nm in both chloroform and dichloromethane (Fig. 3b). The observed red-shifted splitting band at 698 nm could be due to protonation of nitrogen atoms on phthalocyanine skeleton or formation of Jaggregates between phthalocyanine molecules in these solvents. Chloroform (or dichloromethane) in fact usually contains traces of acids which are probably protonating the Pcs giving rise to the peak at 698 nm which would be the result of a protonation process. Trifluoroacetic acid (TFA) was added to chloroform solution of complex 5 for understanding the reason of the formation of splitting Q band (protonation or formation of J-aggregates). A new band was observed at 713 nm instead of 698 nm by addition of TFA (Fig. 4). It is suggesting that the splitting of Q band in chloroform (or dichloromethane) is not due to protonation of complex 5. The phthalocyanine compounds can be form J-aggregates in non-coordinating solvents such as chloroform or dichloromethane and J-aggregation can be deducible exhibition of red-shifted

Table 1 Absorption, excitation and emission spectral data for unsubstituted zinc (ZnPc), substituted metal-free (4) and substituted zinc (II) (5) phthalocyanine compounds in DMSO. Compound 4 5 ZnPca a

Data from Ref. [54].

Q band max , (nm) 676,704 684 672

log ε 4.65,4.54 5.17 5.14

Excitation Ex , (nm) 675,710 687 672

Emission Em , (nm)

Stokes shift Stokes , (nm)

714 695 682

10 11 10

72

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

1,2

(a)

Absorbance

0,9

DMSO DMF THF

0,6

DCM Chloroform

0,3

0 300

400

500

600

700

800

Wavelength (nm)

1,8

(b)

Absorbance

1,5 1,2

DMSO DMF

0,9

THF DCM

0,6

Chloroform

0,3 0 300

400

500

600

700

800

Wavelength (nm) Fig. 3. Absorption spectra of metal-free Pc compound 4(a) and zinc (II) Pc compound 5(b) in different solvents.

splitting Q band in these solvents. It is suggesting that the zinc (II) Pc complex (5) exhibits J-type aggregates instead of protonation in these solvents as evidenced by the appearance of a redshifted band at 698 nm due to non-coordinating behavior of these

solvents. It is suggesting that complementary coordination between the nitrogen atoms on the substituted groups in one phthalocyanine molecule and zinc (II) metal ion of another phthalocyanine molecule could be responsible for the formation of J-aggregation. On the other hand, the linker oxygen atoms may also interact with the central zinc (II) metal ion. Generally, oxygen atoms can be coordinated with zinc (II) when they attached to phthalocyanine framework at non-peripheral position (not peripheral position as in this study). It could not be possible interaction of the oxygen atoms on the substituents with zinc (II) metal ion due to distance between these oxygen atoms and zinc (II) metal ion. As a result, the J-aggregation was formed among the zinc (II) phthalocyanine molecules due to interaction between nitrogen atoms on the substituents and zinc (II) metal ions in the phthalocyanine cavity in this study. Fig. 5 shows the slipped-cofacial structure of J-aggregates of zinc (II) phthalocyanine compound (5). The studied tetra-substituted phthalocyanine compounds were obtained as a mixture of four regioisomers of C4h , D2h , C2v and Cs symmetry, but only the C4h symmetrical structure is shown in Fig. 5 for complex 5. It should be noted that unfortunately, we were not able to separate the isomeric mixtures of studied tetra-substituted phthalocyanines. On the other hand, only monomer band at 678 nm was appeared and J-aggregation band at 698 nm disappeared by the addition of methanol to the J-aggregated solution (Fig. 6). Thus, the addition of a coordinating solvent breaks J-aggregation completely as a result of the competitive coordination of MeOH molecules to central Zn atoms [10,15,49]. The formation of J-aggregation among the zinc (II) phthalocyanine molecules instead of protonation was also confirmed by the appearance of peaks in its MALDI-TOF mass spectrum (Fig. 7) at 2636.717 Da for dimer formation, 3954.802 Da for trimer formation and 5272.496 Da for tetramer formation of the molecules. Beer–Lambert law could be obeyed for studied metal free (4) and zinc (II) (5) Pc compounds in non-aggregated solvents in the concentrations ranging from 1.2 × 10−5 to 2 × 10−6 M (Fig. 8 for compound 5 in DMSO). 3.4. Fluorescence studies The fluorescence behavior of the metal-free (4) and zinc (II) (5) phthalocyanine compounds was studied in DMSO. Fig. 9 shows

0.8

5 in CHCl 3

Absorbance

0.6

0.4 5 in CHCl3+TFA

0.2

0 300

400

500

600

700

800

Wavelength (nm) Fig. 4. Absorption spectra of zinc Pc compound 5 in chloroform and changing by addition of trifluoroacetic acid (TFA).

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

73

O O O

N

O

O

N O

N N N

N Zn

N

N N

N

O N

O

O

O

N

O

N

O

O

O

O

N

O O

O

N N N

N Zn

N

N N

N

O N

O

O

N

O

O O Fig. 5. The slipped-cofacial structure of J-aggregates of substituted zinc (II) Pc compound (5). This figure only shows the C4h isomer of zinc (II) Pc compound (5).

fluorescence emission, absorption and excitation spectra of compound 5 in DMSO as an example. Metal-free Pc 4 and zinc Pc complex 5 showed similar fluorescence behavior in DMSO. The excitation spectra were similar to absorption spectra and both were mirror images of the fluorescent spectra for phthalocyanine compounds 4 and 5 in DMSO. The proximity of the wavelength

1.2

3.5. Fluorescence quantum yields and lifetimes

Absorbance

0.9

0.6 Chloroform Chloroform+Methanol

0.3

0 300

of each component of the Q-band absorption to the Q band maxima of the excitation spectra for all studied compound suggested that the nuclear configurations of the ground and excited states are similar and not affected by excitation. The observed Stokes shifts were within the region (∼10–20 nm) observed for Pc complexes (Table 1).

400

500

600

700

800

Wavelength (nm) Fig. 6. Absorption spectra of compound 5 in chloroform and changing by addition of methanol.

The fluorescence quantum yields (˚F ) of metal-free (4) and zinc (II) (5) phthalocyanine compounds in DMSO are given in Table 2. The ˚F values of the studied phthalocyanine compounds (4 and 5) are slightly higher than unsubstituted zinc Pc in DMSO. The increasing in the (˚F ) value for substituted phthalocyanine complexes in the presence of the ring substituents suggests that the substituents less quench the excited singlet state then the fluorescence. Fluorescence lifetime ( F ) refers to the average time a molecule stays in its excited state before emission, and its value is directly related to that of ˚F . Any factor that shortens the fluorescence lifetime of a fluorophore indirectly reduces the value of ˚F . Such factors include internal conversion and intersystem crossing. As a result, the nature and the environment of a fluorophore determine its fluorescence lifetime. Lifetimes of fluorescence were calculated using the Strickler–Berg equation. Using this equation, a good correlation has been found [50] between experimentally and the theoretically determined lifetimes for the unaggregated molecules

74

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

Fig. 7. MALDI-TOF mass spectrum of zinc (II) phthalocyanine compound (5) with dihydroxybenzoic acid matrix.

as is the case for DMSO in this work. While the  F values of metal-free Pc (4) and zinc (II) Pc (5) compounds are higher than unsubstituted zinc Pc, compound 4 has also the highest value in DMSO. The natural radiative lifetime ( 0 ) and the rate constants for

fluorescence (kF ) values are also given in Table 2. The  0 values of metal-free Pc (4) and zinc Pc (5) compounds are higher while the kF values of these compounds (4 and 5) are lower than unsubstituted zinc Pc complex in DMSO.

Table 2 Photophysical and photochemical parameters of unsubstituted zinc (ZnPc), substituted metal-free (4) and substituted zinc (II) (5) phthalocyanine compounds in DMSO. Compound

˚F

 F (ns)

kF a (s−1 ) (× 108 )

 0 (ns)

˚d (× 10−5 )

˚

4 5 ZnPc

0.21 0.23 0.20b

3.38 1.78 1.22c

0.62 1.29 1.47c

16.32 7.72 6.80c

2.16 2.01 2.61c

0.49 0.71 0.67c

a b c

kF is the rate constant for fluorescence. Values calculated using kF = ˚F / F . Data from Ref. [32]. Data from Ref. [54].

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

Absorbance

1.6

Absorbance

2.0 1.5

y = 146801x + 0.030 R = 0.999

1.0

2.00E-06

0.5

1.2

4.00E-06 0.0 0.00E+00

3.00E-06

6.00E-06

9.00E-06

6.00E-06

1.20E-05

8.00E-06

Concentration

0.8

1.00E-05 1.20E-05

0.4

0 300

400

500

600

700

800

Wavelength (nm) Fig. 8. Absorption spectra of compound 5 in DMSO at different concentrations. (Inset: Plot of absorbance versus concentration.)

3.6. Singlet oxygen quantum yields

Intensity a.u.

Energy transfer from the triplet state of a photosensitizer to ground state molecular oxygen leads to the production of singlet oxygen. There is a necessity of high efficiency of transfer of

energy between excited triplet state of photosensitizer and ground state of oxygen to generate large amounts of singlet oxygen, essential for PDT. The singlet oxygen quantum yield (˚ ) value gives the amount of the singlet oxygen generation and this value is an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required. The ˚ values were determined using a chemical method (using DPBF in DMSO as quenchers). The disappearance of DPBF was monitored using UV–vis spectrophotometer (Fig. 10 as an example for compound 5 in DMSO) Many factors are responsible for the magnitude of the determined quantum yield of singlet oxygen including such as triplet excited state energy, ability of substituents and solvents to quench the singlet oxygen, the triplet excited state lifetime and the efficiency of the energy transfer between the triplet excited state and the ground state of oxygen. There was no decrease in the Q band of formation of the studied metal-free (4) and zinc (II) (5) phthalocyanine derivatives during ˚ determinations (Fig. 10 as an example for compound 5 in DMSO). Table 2 gives the ˚ values of substituted metal-free (4), substituted zinc (II) (5) phthalocyanines and unsubstituted zinc phthalocyanine which is used as standard for singlet oxygen studies of phthalocyanine compounds. While the ˚ value of substituted zinc (II) phthalocyanine compound (5) is higher, the ˚ value of substituted metal-free (4) phthalocyanine compound is lower than unsubstitued zinc (II) phthalocyanine in DMSO. The ˚ value of

1000

1,6

750

1,2 Excitation Emission Absorbance

500

0,8

250

0 500

Absorbance

2

75

0,4

550

600

650

700

750

800

0 850

Wavelength (nm) Fig. 9. Absorption, excitation and emission spectra of 5 in DMSO. Excitation wavelength: 650 nm.

DPBF Absorbance

1

Absorbance

0,8

0,9 0,6 0,3 0 0

10

20

30

Time (sec)

0,6

0 sec 10 sec 20 sec

0,4

30 sec

0,2

0 300

400

500

600

700

800

Wavelength (nm) Fig. 10. Absorbance changes during the determination of singlet oxygen quantum yield of 5 in DMSO at a concentration of 1.0 × 10−5 M. (Inset: plots of DPBF absorbance versus time.)

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

substituted zinc (II) phthalocyanine compound (5) is also higher than the ˚ value of substituted metal-free (4) phthalocyanine compound in DMSO. Generally, zinc phthalocyanine compounds possess high triplet yields and they can be generated highly singlet oxygen since the d10 configuration of the central Zn2+ ion, which make them more appropriate photosensitizers for PDT applications. ˚ value of employed metal-free (4) phthalocyanine compound higher than the metal-free phthalocyanine derivatives having different substituents on the phthalocyanine ring ranging from 0.01 to 0.27 in the literature [51]. Generally, the ˚ value of studied zinc (II) phthalocyanine compound (5) is also higher than zinc (II) phthalocyanines having different substituents on the phthalocyanine ring ranging from 0.07 to 0.88 in the literature [52]. Only a few zinc (II) phthalocyanine complexes have higher ˚ yields than studied zinc (II) phthalocyanine complex (5) in this study [52]. Although, the ˚ value of standard unsubstituted zinc (II) phthalocyanine (ZnPc) is quite good, its cell penetration is low and unsufficient for PDT applications. The possible use of phthalocyanine derivatives in PDT can not be overemphasized; considering the fact that the effectiveness of photodynamic action is chiefly based on the generation of singlet oxygen, suffice is it to conclude that phthalocyanine derivatives studied in this work are potential candidates as regards consideration in PDT. Singlet oxygen quantum yields of studied

(a)

1,6 Absorbance

76

Absorbance

1,2

1,6 1,2 0,8 0,4 0

y = -8.73E-05x + 1.47 R =0.995 0

600

1200 1800 2400

0 min

3000 3600

10 min

Time (sec)

20 min

0,8

30 min 40 min 50 min 60 min

0,4

0 300

400

500

600

700

800

Wavelenght (nm) Fig. 11. Absorbance changes during the photodegradation study of 5 in DMSO showing the disappearance of the Q-band at 10 min intervals. (Inset: plot of Q band absorbance versus time.)

800 2,2

700

2,0 1,8 Io/I

[BQ]=0

Intensity (a.u.)

600

1,6 1,4

y = 21.66x +0.97 R = 0.993

1,2

500

1,0 0,000

400

0,010

0,020

0,030

0,040

0,050

[BQ]

300 [BQ]=saturated

200 100 0 650

700

750

800

850

Wavelength (nm)

(b)

600 [BQ]=0

Intensity (a.u.)

Io/I

500

400

2,2 2,0 1,8 1,6 1,4 1,2 1,0 0,000

y = 24.81x + 1 R = 0.997

0,010

300

0,020

0,030

0,040

0,050

[BQ]

200

[BQ]=saturated

100

0 650

700

750

800

850

Wavelength (nm) Fig. 12. Fluorescence emission spectral changes of: (a) compound 4 and (b) compound 5 (C = 1.00 × 10−5 M) on addition of different concentrations of BQ in DMSO. [BQ] = 0, 0.008, 0.016, 0.024, 0.032, 0.040 M and saturated with BQ. (Insets: Stern–Volmer plots for benzoquinone (BQ) quenching compounds 4 and 5 in DMSO.)

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78 Table 3 Fluorescence quenching data for unsubstituted zinc (ZnPc), substituted metal-free (4) and substituted zinc (II) (5) phthalocyanine compounds in DMSO. Compound

BQ KSV /(M−1 )

kq /1010 (M−1 s−1 )

4 5 ZnPca

21.66 24.81 31.90

0.64 1.39 2.61

a

Data from Ref. [54].

phthalocyanine derivatives ranged from 0.49 to 0.71 in DMSO. Photosens® , which has been in use for PDT has a singlet oxygen quantum yield of 0.42, which is about the least value obtained for the studied phthalocyanine derivatives studied. 3.7. Photodegradation studies Degradation of the molecules under irradiation can be used to study their stability and this is especially important for those molecules intended for use in photocatalysis. The collapse of the absorption spectra without any distortion of the shape confirms photodegradation not associated with phototransformation into different forms of photosensitizers absorbing in the visible region. The spectral changes observed for metal-free (4) and zinc (II) (5) Pc complexes during confirmed photodegradation occurred without phototransformation (Fig. 11 as an example for compound 5). The photodegradation quantum yield (˚d ) values of metal-free (4) and zinc (II) (5) Pc complexes as well as unsubstituted zinc (II) phthalocyanine in DMSO are given in Table 2. All the studied complexes showed about the same stability with ˚d of the order of 10−5 . The ˚d values, found in this study, are similar with zinc Pc complexes having different substituents on the phthalocyanine ring in literature [52]. Stable zinc phthalocyanine complexes show ˚d values as low as 10−6 and for unstable molecules, values of the order of 10−3 have been reported [52]. The metal-free (4) and zinc (II) (5) Pc complexes showed slightly lower ˚d values when compared to the unsubstituted ZnPc in DMSO. The substitution of the phthalocyanine framework with 1-(2-oxyethyl)-4-piperidone ethylene ketal groups slightly increased the stability of studies phthalocyanine compounds. The substituted zinc (II) phthalocyanine compound (5) is a little bit more stable than metal-free phthalocyanine (4) compound in DMSO. 3.8. Fluorescence quenching studies by 1,4-benzoquinone [BQ] The fluorescence quenching of metal-free (4) and zinc (II) (5) phthalocyanine compounds by BQ in DMSO was found to obey Stern–Volmer kinetics, which is consistent with diffusioncontrolled bimolecular reactions. Fig. 12 shows the quenching of metal-free (4) (Fig. 12a) and zinc (II) (5) (Fig. 12b) Pc compounds by BQ in DMSO. The slopes of the plots were given as insets in Fig. 12a and b. These plots gave Stern–Volmer constants (KSV ) values and listed in Table 3. The linearity of these plots indicates that fluorescence quenching is reasonably described by a collisional quenching mechanism. The KSV values of the substituted phthalocyanine complexes (4 and 5) are lower than unsubstituted ZnPc in DMSO. KSV value the studied zinc Pc complex (5) was higher than metal free Pc complex (4) in DMSO. The bimolecular quenching rate constant (kq ) values of the substituted phthalocyanine complexes (4 and 5) are also lower than unsubstituted ZnPc in DMSO, thus substitution of phthalocyanine framework with 1-(2-oxyethyl)-4-piperidone ethylene ketal groups seems to decrease the kq values of the compounds. The kq values are near 1010 M−1 s−1 and in agreement with the theoretical Smoluchowski–Stokes–Einstein approximation at 298 K [53].

77

4. Conclusion The novel metal-free (4) and zinc (II) (5) phthalocyanines bearing four 1-(2-oxyethyl)-4-piperidone ethylene ketal groups at peripheral position have been synthesized for the first time in this study. The studied compounds were characterized by UV–vis, IR, 1 H-NMR, ESI mass spectroscopies and elemental analysis. It was concluded from the investigation of the spectroscopic behavior of these novel compounds in various solvents that the zinc (II) phthalocyanine compound (5) formed J-aggregates in chloroform and DCM as a result of the complementary coordination of the nitrogen atom in the substituents of one molecule to the central zinc metal atom of another molecule through hydrogen bonding. The formation of J-aggregates among the zinc (II) Pc molecules was determined by UV–vis and MALDI-TOF spectroscopic techniques. The J-aggregates among the zinc (II) Pc molecules were broken up by the addition of a coordinating solvent such as methanol. The photophysical (fluorescence quantum yields and lifetimes) and photochemical properties (singlet oxygen and photodegradation quantum yields) of metal-free (4) and zinc (5) phthalocyanine compounds were investigated in DMSO. The substituted zinc Pc compound (5) shows good singlet oxygen generation and gives an indication of the potential of this complex as photosensitizer in photocatalytic applications such as photodynamic therapy of cancer. The fluorescence quenching behavior of the studied phthalocyanine compounds (4 and 5) have also been studied by BQ in DMSO. Acknowledgement This study was supported by the Research Fund of Karadeniz Technical University, Project no: 2010.111.002.5 (Trabzon-Turkey). References [1] K. Kadish, K.M. Smith, R. Guillard (Eds.), The Porphyrin Handbook, vols. 15–20, Academic Press, Boston, 2003. [2] C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines, Properties and Applications, vol. 4, VCH, New York, 1996. [3] F.M. Moser, A.L. Tomas, The Phthalocyanines, CRC, Press, Bocaraton, FL, 1983. [4] N.B. McKeown, Phthalocyanine Materials: Synthesis and Structure and Function, Cambridge University Press, 1998. [5] C.C. Leznoff, S.M. Marcuccio, S. Gringberg, A.B.P. Lever, K.B. Tomer, Metallophthalocyanine dimers incorporating five-atom covalent bridges, Canadian Journal of Chemistry 63 (1985) 623–631. [6] M. Durmus¸, S. Yes¸ilot, V. Ahsen, Separation and mesogenic properties of tetraalkoxy-substituted phthalocyanine isomers, New Journal of Chemistry 30 (2006) 675–678. [7] K. Kameyama, M. Morisue, A. Satake, Y. Kobuke, Highly fluorescent selfcoordinated phthalocyanine dimers, Angewandte Chemie International Edition 44 (2005) 4763–4766. [8] J.L. Sesler, J. Jayawickramarajah, A. Gouloumis, G.D. Patnos, T. Torres, D.M. Guldi, Guanosine and fullerene derived de-aggregation of a new phthalocyanine linked-cytidine derivative, Tetrahedron 62 (2006) 2123–2131. [9] X. Huang, F.Q. Zhao, Z.Y. Li, L. Huang, Y.W. Tang, F. Zhang, C.H. Tung, A novel selfaggregates of phthalocyanine based on Zn–O coordination, Chemistry Letters 36 (2007) 108–115. [10] X. Huang, F.Q. Zhao, Z.Y. Li, Y.W. Tang, F. Zhang, C.H. Tung, Self-assembled nanowire networks of aryloxy zinc phthalocyanines based on Zn–O coordination, Langmuir 23 (2007) 5167–5172. [11] M. Morisue, Y. Kobuke, Tandem cofacial stacks of porphyrin–phthalocyanine dyads through complementary coordination, Chemistry – A European Journal 14 (2008) 4993–5000. [12] F. Cong, B. Ning, X. Yu, B. Cui, S. Chen, C. Cao, The control of phthalocyanine properties through nitro-group electronic effect, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 62 (2005) 394–397. [13] F. Cong, B. Ning, X. Du, C. Ma, H. Yu, B. Chen, Facile synthesis, characterization and property comparisons of tetraaminometallophthylocyanines with and without intramolecular hydrogen bonds, Dyes Pigments 66 (2005) 149–154. [14] F. Würthner, T.E. Kaiser, C.R. Saha-Möller, J-aggregates: from serendipitous discovery to supramolecular engineering of functional dye materials, Angewandte Chemie International Edition 50 (2011) 3376–3410.

78

E.T. Saka et al. / Journal of Photochemistry and Photobiology A: Chemistry 241 (2012) 67–78

[15] F. Conga, J. Li, C. Maa, J. Gaob, W. Duana, X. Dua, Tuning J-type dimers of non-peripherally substituted zinc tetra-4-tert-butylphenophthalocyanine, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 71 (2008) 1397–1401. [16] B.A. Bench, A. Beveridge, W.M. Sharman, G.J. Diebold, J.E. van Lier, S.M. Gorun, Introduction of bulky perfluoroalkyl groups at the periphery of zinc perfluorophthalocyanine: chemical, structural, electronic, and preliminary photophysical and biological effects, Angewandte Chemie International Edition 41 (2002) 748. [17] J. Usuda, S.M. Chiu, E.S. Murphy, M. Lam, A.L. Nieminen, N.L. Oleinic, Domaindependent photodamage to Bcl-2: a membrane anchorage region is needed to form the target of phthalocyanine photosensitization, Journal of Biological Chemistry 278 (2003) 2021–2029. [18] R. Bonnett, Photosensitizers of the porphyrin and phthalocyanine series for photodynamic therapy, Chemical Society Reviews 24 (1995) 19–33. [19] H. Ali, J. van Lier, Metal complexes as photo- and radiosensitizers, Chemical Reviews 99 (1999) 2379–2450. [20] D. Phillips, The photochemistry of sensitisers for photodynamic therapy, Pure and Applied Chemistry 67 (1995) 117–126. [21] D. Atilla, N. Saydan, M. Durmus¸, A.G. Gürek, T. Khan, A. Rück, H. Walt, T. Nyokong, V. Ahsen, Journal of Photochemistry and Photobiology A: Chemistry 186 (2007) 298–307. [22] M. Durmus¸, V. Ahsen, Water-soluble cationic gallium(III) and indium(III) phthalocyanines for photodynamic therapy, Journal of Inorganic Biochemistry 104 (2010) 297–309. [23] M. Durmus¸, T. Nyokong, Synthesis, photophysical and photochemical studies of new water-soluble indium(III) phthalocyanines, Photochemical & Photobiological Sciences 6 (2007) 659–668. [24] N. Saydan, M. Durmus¸, M.G. Dizge, H. Yaman, A.G. Gürek, E. Antunes, T. Nyokong, V. Ahsen, Water soluble phthalocyanines mediated photodynamic effect on mesothelioma cells, Journal of Porphyrins and Phthalocyanines 13 (2009) 681–690. [25] S. Tuncel, F. Dumoulin, J. Gailer, M. Sooriyaarachchi, D. Atilla, M. Durmus¸, D. Bouchu, H. Savoie, R.W. Boyle, V. Ahsen, A set of highly water-soluble tetraethyleneglycol-substituted Zn(II) phthalocyanines: synthesis, photochemical and photophysical properties, binding to plasma proteins and in vitro PDT, Dalton Transactions 40 (2011) 4067–4079. [26] D.D. Perin, W.L.F. Armarego, Purification of Laboratory Chemicals, second ed., Pergamon Press, New York, 1985. [27] A.T. Blizzard, F. DiNinno, J.D. Morgan, I. Jane, Y. Wu, H.Y. Chen, S. Kim, W. Chan, E.T. Birzin, Y.T. Yang, L.Y. Pai, Z. Zhang, E.C. Hayes, C.A. DaSilva, W. Tang, S.P. Rohrer, J.M. Schaeffer, M.L. Hammond, Estrogen receptor ligands. Part 8: DihydrobenzoxathiinSERAMs with heteroatom-substituted side chains, Bioorganic & Medicinal Chemistry Letters 14 (2004) 3865–3868. [28] G.J. Young, W. Onyebuagu, Synthesis and characterization of di-disubstituted phthalocyanines, Journal of Organic Chemistry 55 (1990) 2155–2159. [29] S. Fery-Forgues, D. Lavabre, Are fluorescence quantum yields so tricky to measure? A demonstration using familiar stationery products, Journal of Chemical Education 76 (1999) 1260–1264. [30] M.D. Maree, T. Nyokong, K. Suhling, D. Phillips, Effects of axial ligands on the photophysical properties of silicon octaphenoxyphthalocyanine, Journal of Porphyrins and Phthalocyanines 6 (2002) 373–376. [31] A. Ogunsipe, J.Y. Chen, T. Nyokong, Photophysical and photochemical studies of zinc(II) phthalocyanine derivatives-effects of substituents and solvents, New Journal of Chemistry 28 (2004) 822–827. [32] H. Du, R.A. Fuh, J. Li, A. Corkan, J.S. Lindsey, PhotomC.A.D., A computer aided design and research tool in photochemistry, Photochemistry and Photobiology 68 (1998) 141–142. [33] J.H. Brannon, D. Madge, Picosecond laser photophysics group 3A phthalocyanines, Journal of the American Chemical Society 102 (1980) 62–65. [34] A. Ogunsipe, T. Nyokong, Photophysical and photochemical studies of sulphonated non-transition metal phthalocyanines in aqueous and nonaqueous media, Journal of Photochemistry and Photobiology A: Chemistry 173 (2005) 211–220.

[35] I. Seotsanyana-Mokhosi, N. Kuznetsova, T. Nyokong, Photochemical studies of tetra-2,3-pyridinoporphyrazines, Journal of Photochemistry and Photobiology A: Chemistry 140 (2001) 215–222. [36] N. Kuznetsova, N. Gretsova, E. Kalmkova, E. Makarova, S. Dashkevich, V. Negrimovskii, O. Kaliya, E. Luk’yanets, Relationship between the photochemical properties and structure of porphyrins and related compounds, Russian Journal of General Chemistry 70 (2000) 133–140. [37] W. Spiller, H. Kliesch, D. Wöhrle, S. Hackbarth, B. Roder, G. Schnurpfeil, Singlet oxygen quantum yields of different photosensitizers in polar solvents and micellar solutions, Journal of Porphyrins and Phthalocyanines 2 (1998) 145–158. [38] J. Rose, Advanced Physico-chemical Experiments, Sir Isaac Pitman & Sons Ltd., London, 1964, p. 257. [39] A. Bilgin, C¸. Ya˘gcı, A. Mendi, U. Yıldız, Synthesis and characterization of new metal-free and metallophthalocyanines fused alphamethylferrocenylmethoxy units, Journal of Inclusion Phenomena and Macrocyclic Chemistry 67 (2010) 377–383. [40] H. C¸akıcı, A.A. Esenpınar, M. Bulut, Synthesis and characterization of novel phthalocyanines bearing quaternizable coumarin, Polyhedron 27 (2008) 3625–3630. [41] Y. Gök, H. Kantekin, I˙ . De˘girmencio˘glu, Synthesis and characterization of new metal-free and metallophthalocyanines substituted with tetrathiadiazamacrobicyclic moieties, Supramolecular Chemistry 15 (2003) 335–343. [42] J. Mack, M.J. Stillman, Photochemical formation of the anion-radical of zinc phthalocyanine and analysis of the absorption and magnetic circular-dichroism spectral data-assignment of the optical-spectrum of [ZnPc(-3)](-), Journal of the American Chemical Society 116 (1994) 1292–1304. [43] M.J. Stillman, T. Nyokong, Absorption and magnetic circular dichroism spectral properties of phthalocyanines, in: C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines: Properties and Applications, vol. 1, VCH Publishers, New York, 1989, pp. 133, 289–292. [44] Y.C. Yang, J.R. Ward, R.P. Seiders, dimerization of Cobalt(II) Tetrasulfonated Phthalocyanine In Water and Aqueous Alcoholic Solutions, Inorganic Chemistry 24 (1985) 1765–1769. [45] W.J. Schutte, M.S. Rehbach, J.H. Sluyters, Aggregation of an octasubstituted phthalocyanine in dodecane solution, Journal of Physical Chemistry 97 (1993) 6069–6073. [46] E.J. Osburn, L.K. Chau, S.Y. Chen, N. Collins, D.F. O’Brien, N.R. Armstrong, Novel amphiphilic phthalocyanines: formation of Langmuir-Blodgett and cast thin films, Langmuir 12 (1996) 4784–4796. [47] X.F. Zhang, Q. Xi, J. Zhao, Fluorescent and triplet state photoactive J-type phthalocyanine nano assemblies: controlled formation and photosensitizing properties, Journal of Materials Chemistry 20 (2010) 6726–6733. [48] H. Enkelkamp, R.J.M. Nolte, Molecular materials based on crown ether functionalized phthalocyanines, Journal of Porphyrins and Phthalocyanines 4 (2000) 454–459. [49] L. Niu, C. Zhong, Z. Chen, Z. Zhang, Z. Li, F. Zhang, Y. Tang, Novel azobenzenephthalocyanine dyeds design of photo-modulated J-aggregation, Chinese Science Bulletin 54 (2009) 1169–1175. [50] D. Maree, T. Nyokong, K. Suhling, D. Phillips, Effects of axial ligands on the photophysical properties of silicon octaphenoxyphthalocyanine, Journal of Porphyrins and Phthalocyanines 6 (2002) 373–376. [51] M. Durmus¸, Photochemical, Photophysical characterization, in: T. Nyokong, V. Ahsen (Eds.), Photosensitizers in Medicine, Environment, and Security, Springer, New York, 2012, pp. 135–267. [52] T. Nyokong, Effects of substituents on the photochemical and photophysical properties of main group metal phthalocyanines, Coordination Chemistry Reviews 251 (2007) 1707–1722. [53] S.L. Murov, I. Carmichael, G.L. Hug, Handbook of Photochemistry, 2nd ed., Marcel Decker, New York, 1993, p. 207. [54] I. Gürol, M. Durmus¸, V. Ahsen, T. Nyokong, Synthesis, photophysical and photochemical properties of substituted zinc phthalocyanines, Dalton Transactions 34 (2007) 3782–3791.