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Synthesis, characterization, photophysical, and photochemical properties of novel zinc(II) and indium(III) phthalocyanines containing 2-phenylphenoxy units
Author’s Accepted Manuscript Synthesis, characterization, photophysical, and photochemical properties of novel zinc(II) and indium(III) phthalocyanines containing 2phenylphenoxy units Haytham Elzien Alamin Ali, Mehmet Pişkin, Selçuk Altun, Mahmut Durmuş, Zafer Odabaş www.elsevier.com/locate/jlumin
PII: DOI: Reference:
S0022-2313(15)30354-9 http://dx.doi.org/10.1016/j.jlumin.2015.12.010 LUMIN13754
To appear in: Journal of Luminescence Received date: 5 August 2015 Revised date: 23 November 2015 Accepted date: 9 December 2015 Cite this article as: Haytham Elzien Alamin Ali, Mehmet Pişkin, Selçuk Altun, Mahmut Durmuş and Zafer Odabaş, Synthesis, characterization, photophysical, and photochemical properties of novel zinc(II) and indium(III) phthalocyanines containing 2-phenylphenoxy units, Journal of Luminescence, http://dx.doi.org/10.1016/j.jlumin.2015.12.010 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, characterization, photophysical, and photochemical properties of novel zinc(II) and indium(III) phthalocyanines containing 2-phenylphenoxy units Haytham Elzien Alamin Alia,b, Mehmet Pişkinc, Selçuk Altuna, Mahmut Durmuşd*, Zafer Odabaşa** a
Department of Chemistry, Marmara University, Istanbul, 34722, Turkey.
b
University Of Khartoum, Department of Chemistry, Faculty of Science, P.O. Box 321, Khartoum, 11115, Sudan
c
ÇanakkaleOnsekiz Mart University, Vocational School of Technical Sciences, Department of Food Technology, Çanakkale, 17100, Turkey
d
Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze, Kocaeli, 41400, Turkey
ABSTRACT
The synthesis of highly soluble and non-aggregated peripherally/non-peripherally Zn and In(OAc) phthalocyanines was achieved by 3-/ and 4-(2-phenylphenoxy)phthalonitrile as starting materials. The novel compounds were characterized by elemental analyses, FTIR,
UV–vis
and
MALDI-TOF
mass
spectroscopic
techniques.
Additionally,
photophysical, photochemical and spectral properties of the phthalocyanines were reported. Especially, the indium(OAc) phthalocyanines showed good singlet oxygen quantum yields in DMSO and they can be appropriate candidates as Type II photosensitizers in photodynamic therapy (PDT) applications. Keywords: Phthalocyanine; 2-Phenylphenol; Photochemical; Photophysical; fluorescence; singlet-oxygen *Corresponding author, address: Department of Chemistry, Marmara University, 34722 Goztepe, Istanbul, Turkey. Tel.: +90 216 347 96 41/1368; Fax: +90 216 347 87 83. E-mail address: [email protected]. (Z. Odabaş)
1. INTRODUCTION Phthalocyanine (Pc) is a macrocyclic and tetramer molecule, which is a planar conjugated system of 18 electrons exhibiting aromatic behavior, formed of four isoindoline units. The particular electronic delocalization of the 18π system gives rise to outstanding electronic and unconventional physical properties, and high chemical and thermal stability. Due to the 1
excellent stabilities, these conjugated compounds have attracted much research interest in the fabrication of electronic molecular devices, such as opto-electronic devices [1], gas sensors [2,3], static induction transistors [4], photoreceptor devices in laser beam printers and photocopiers
[5-7],
liquid
crystals
[8],
as
Langmuir-Blodgett
films
[9,10],
in
electrophotographic applications [11,12], optical data storage [13], in fuel cells [14], electrochemical sensors [15,16], and in nonlinear optics (NLO) [17,18]. A particular area of Pc application is as photosensitizers (PS) in photodynamic therapy (PDT), e.g. of certain forms of cancer [19-24]. The biomedical function of a PS depends on its ability to absorb visible light (optimal range of 650–800 nm) and highly red-shifted analogs of Pcs are preferred as PS [25,26]. However, some Pcs with additional benzo groups attached to the Pc skeleton such as naphthalocyanines and anthracocyanines [27] have been usually difficult to prepare, highly insoluble, and prone to decomposition [28]. Hence we tried to synthesize Pcs which are easy to prepare, and are highly soluble, non-aggregated, chemically stable and structurally similar to naphthalocyanines (Scheme 1). In this study, newly 3- or 4-(2phenylphenoxy)phthalonitrile and Zn and In(OAc) phthalocyanines were achieved and characterized using
1
H-NMR, FT-IR,
UV-vis spectroscopy and MALDI-TOF-mass
spectrometry. The synthesized novel Pcs are highly soluble and non-aggregated in common organic solvents unlike naphthalocyanines. In addition, the photophysical (fluorescence quantum
yields
and
lifetimes),
photochemical
(singlet
oxygen
generation
and
photodegradation under light irradiation), and spectral properties of the Pcs (3-6) and unsubstituted In(OAc)Pc were investigated in dimethylsulfoxide (DMSO). Especially, the In(OAc)Pcs showed good singlet oxygen quantum yields in DMSO and they can be appropriate candidates as Type II photosensitizers in photodynamic therapy (PDT) applications. The effects of the substituent position and the nature of the central metal in the Pc cavity were also studied.
2
2. EXPERIMENTAL The used materials, equipment, and photophysical and photochemical formulas and parameters were supplied as supplementary information.
2.1. SYNTHESIS 2.1.1. Synthesis of the nitrile compounds (1 and 2) 3-/ or 4-nitrophthalonitrile (2.30 g, 13.30 mmol), 2-phenylphenol (2.50 g, 14.70 mmol) anhydrous K2CO3 (2.60 g, 18.80 mmol) and 20 mL dimethylformamide (DMF) were added in a flask. The reaction mixture was stirred at 50ο C for 72 hours under inert atmosphere and monitored by thin layer chromatography (TLC). Then the mixture was poured into 200 mL ice-water and the formed precipitate was filtered off, washed with water, and dried in vacuum at 50ο C. The crude product was purified by column chromatography with silica gel eluting with chloroform. 3-(2-phenylphenoxy)phthalonitrile (1): Yield: 2.10 g (53.85%). This compound is soluble in CH2Cl2, CHCl3, DMF, dimethylsulfoxide (DMSO), tetrahydrofuran (THF), and hot acetic acid (AcOH). Mp: 128-131° C. IR (ATR) max/cm-1: 3096.62(=CH str.), 3062.50(=CH str.),
3031.25(=CH str.),
2230.75(C≡N str.),
1572.36(C=C str.), 1451.51(CH bend.), 1430.09(CH bend.), 1196.72(CN str.),
1169.22(CN str.),
1117.99(CN str.),
1051.02(CC str.), 1011.30(CC str.), 986.11, 915.66, 871.30, 770.32, 759.74, 745.20, 728.75, 697.61.
1582.80(C=C str.),
1279.86(ArOAr str.), 1073.06(CC str.), 854.24, 815.24, 799.94,
Anal.Calc. for C20H12N2O: C, 81.07; H, 4.08; N,
9.45. Found: C, 80.91; H, 4.19; N, 9.58 %. 1H-NMR (CDCl3) , ppm: 6.83 (d, J = 8.50 Hz, 1H), 7.24 (d, J = 7.88 Hz, 1H), 7.30 (t, J = 7.41 Hz, J = 7.10 Hz, 2H), 7.37 (t, J = 8.20 Hz, J = 7.88 Hz, 1H), 7.37 (t, J = 8.20 Hz, J = 7.88 Hz, 1H),7.40 (d, J = 8.20 Hz, 1H), 7.46 (dd, J = 7.88 Hz, J = 7.25 Hz, 2H), 7.51 (d, J = 7.72 Hz, 2H), 7.60 (d, J = 7.10 Hz, 1H). 3
4-(2-phenylphenoxy)phthalonitrile (2): Yield: 2.50 g (64.00%). This compound is soluble in CH2Cl2, CHCl3, THF, DMF, DMSO, and hot AcOH. Mp: 78-81° C. IR (ATR)max/cm-1:
3106.25(=CH
str.),
3068.84(=CH
str.),
3056.25(=CH
str.),
2234.82(C≡N str.), 1599.92(C=C str.), 1578.82(C=C str.), 1561.07(C=C str.), 1454.10(CH bend.), 1427.62(CH bend.), 1274.01(ArOAr str.), 1243.81(ArOAr str.), 1201.92(CN str.), 1157.09(CN str.), 1109.03(CN str.), 1089.23(CC str.), 1045.93(CC str.), 972.24, 948.50,
919.26,
901.10, 843.72,
827.81,
772.82,
740.87,
698.93. Anal.Calc. for
C20H12N2O: C, 81.07; H, 4.08; N, 9.45. Found: C, 81.20; H, 4.21; N, 9.32 %. 1H-NMR (CDCl3) , ppm: 7.08 (dd, J = 8.67 Hz, J = 2.52 Hz, 1H), 7.12 (d, J = 2.52 Hz, 1H), 7.18 (dd, J = 7.72 Hz, J = 1.42 Hz, 1H), 7.30 (d, J = 7.25 Hz, 2H), 7.35 (t, J = 7.40 Hz, J = 7.09 Hz, 1H), 7.42 (t, J = 8.20 Hz, J = 7.10 Hz, 2H), 7.46 (ddd, J = 7.72 Hz, J = 7.57 Hz, 2.05 Hz 1H), 7.46 (ddd, J = 7.72 Hz, J = 7.57 Hz, 1.42 Hz 1H), 7.55 (dd, J = 7.41 Hz, J = 2.05 Hz, 1H), 7.58 (d, J = 8.83 Hz, 1H),
2.1.2. General procedure for the synthesis of metallo-phthalocyanines(MPcs) A mixture of 1.50 mmol (200 mg) 3-/or 4-(2-phenylphenoxy)phthalonitrile (1 or 2) and 0.35 mmol metal salts (75 mg Zn(OAc)2.2H2O or 100 mg anhydrous indium(III)acetate) was taken in a reaction tube. 0.30 mL of DMF was added to this reaction mixture, and then the mixture was heated in a sealed glass tube for 20 minutes under inert atmosphere at 350o C. The reaction mixture was precipitated by adding acetic acid. The precipitate was filtered, washed with hot acetic acid-water solution 7/3 by volume, water, ethanol and acetonitrile for 12 hrs, respectively in a Soxhlet apparatus. The crude product was purified by column chromatography with silica gel eluting with chloroform. 1(4),8(11),15(18),22(25)-Tetra-(2-phenylphenoxy)phthalocyaninatozinc (3): Solubility: CH2Cl2, CHCl3, THF, DMF, DMSO, toluene Mp>300ο C. Yield: 40.00 mg (25.30%). IR
4
(ATR) max / cm-1: 3056.98(=CH str.), 3032.91(=CH str.), 1656.26(C=N str.), 1600.56(C=C str.)1578.34(C=C str.), 1502.31, 1474.17, 1430.77(CH bend.), 1328.82(CO str.), 1235.00(CO str.), 1198.46, 1107.52(CN str.), 1076.65(CC str.), 1047.27(CC str.), 1002.89(CC str.), 973.03, 878.01, 829.92, 802.68, 735.72, 696.66. Anal. Calc. for C80H48N8O4Zn : C, 76.83; H, 3.87; N, 8.96 %. Found: C, 76.65; H, 4.02; N, 10.10 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 699 (5.02), 670 (4.47), 632 (4.30), 381(4.40), 333 (4.44). M/z: 1249.822 (M+). 2(3),9(10),16(17),23(24)-Tetra-(2-phenylphenoxy)phthalocyaninatozinc
(4):
Solubility:CH2Cl2, CHCl3, DMF, DMSO, THF, toluene. Mp>300ο C. Yield: 42.00 mg (26.60%). IR (ATR) max / cm-1: 3061.97(=CH str.), 3022.78(=CH str.), 1654.38(C=N str.), 1610.58(C=C str.), 1582.11(C=C str.), 1473.02, 1431.20(CH bend.), 1393.97, 1333.69(CO str.), 1251.25(CO str.), 1220.47, 1113.32(CN str.), 1081.07, 1045.39(CC str.), 1010.04(CC str.), 944.47, 890.30, 869.96, 823.92, 765.76, 736.28, 696.86, 669.25. Anal. Calc. for C80H48N8O4Zn : C, 76.83; H, 3.87; N, 8.96 %. Found: C, 77.01; H, 4.05; N, 10.12 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 682 (5.16), 654 (4.48), 616 (4.43) 357 (4.78). M/z: 1249.584 (M+). 1(4),8(11),15(18),22(25)-Tetrakis-([1,1'-biphenyl]-2-yloxy)phthalocyaninatoindium(III)acetate (5): Solubility:CH2Cl2, CHCl3, THF, DMF, DMSO, toluene Mp>300ο C. Yield: 35.00 mg (21.20%). IR (ATR) max / cm-1: 3058.05(=CH str.), 2922.97(>CH2 str.), 2851.63(>CH2 str.), 1721.92(C=O str.), 1656.86(C=N str.), 1578.58(C=O str.), 1502.58, 1473.97, 1430.78(CH bend.), 1331.34(CO str.), 1231.53(CO str.), 1198.22, 1107.12(CN str.), 1079.52(CC str.), 1046.85(CC str.), 1000.95(CC str.), 963.37, 879.33, 829.69, 802.12, 736.35, 696.66. Anal. Calc. for C82H51N8O4In : C, 72.46; H, 3.78; N, 8.24; %. Found: C, 72.29; H, 3.92; N, 8.11 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 713 (4.90), 684
5
(4.34), 643 (4.19), 378 (4.36), 329 (4.43). M/z: 1452.953 (M-OAc+DHB)+. DHB (2,5dihydroxybenzoicacid) was used a MALDI matrix 2(3),9(10),16(17),23(24)-Tetra-(-2phenylphenoxy)phthalocyaninatoindium (III)acetate (6): Solubility:CH2Cl2, CHCl3, DMF, DMSO, THF, toluene. Mp>300ο C. Yield: 39.00 mg (23.60%). IR (ATR) max/cm-1 : 3056.93(=CH str.), 3022.78(=CH str.), 2924.29(>CH2 str.), 1716.97(C=O str.), 1659.48(C=N str.), 1609.83(C=C str.), 1581.98(C=C str.), 1470.37, 1430.45(CH bend.), 1392.67, 1335.46(CO str.), 1251.15(CO str.), 1217.79, 1114.51(CN str.), 1084.49(CC str.), 1043.01(CC str.), 1009.68(CC str.), 943.32, 891.09 867.95, 823.80, 769.62, 734.26, 695.65. Anal. Calc. for C82H51N8O4In : C, 72.46; H, 3.78; N, 8.24; %. Found: C, 72.58; H, 3.94; N, 8.07 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 695 (4.98), 668 (4.45), 625 (4.30), 360 (4.67). M/z: 1299.374 (M)+, 1453.689 (M-OAc+DHB)+, 2598.611 (M2)+, 2752.673 (M2+DHB)+.
3. RESULTS AND DISCUSSION 3.1. Synthesis and characterization The synthetic routes for novel starting materials (1 and 2) and Pcs (3, 4, 5 and 6) are shown in scheme 1. When the IR spectra of 3-/or 4-nitrophthalonitriles and starting compounds 1 and 2 were compared with each other, the disappearance of the NO2 band of 3 or 4nitrophthalonitrile nearby 1350 cm-1 and the appearance of new absorption at 1279.86 and 1274.01 cm-1 belonging to ArOAr indicated the formation of 1 and 2. The extra C≡N band also appeared at 2230.75 and 2234.82 cm-1 in the IR spectrum of 1 and 2 and they disappeared after conversion to Pcs (3-6). The spectrum of 1 and 2 also showed aromatic rings C=C peaks at 1582.80;1572.36 and 1599.92;1578.82 cm-1, and ArH stretching frequencies peaks at 3096.62;3058.22;3027.84 and 3103.79;3068.84;3048.10, respectively.
6
The IR spectra of the all Pcs are similar in most peaks, indicating that central metal has small influence on the vibrations (Table S1). The 1H-NMR spectra of 1 and 2 exhibited characteristic signals for the aromatic protons at 6.83-7.60 and 7.08-7.58 ppm, respectively (Fig. S1 and S2 in supporting information). In MALDI-TOF mass spectra, the molecular ion peaks [M]+ of the Pcs 3 and 4, the [M–OAc+DHB]+ peaks of the Pcs 5, and [M–OAc]+, (M-OAc+DHB)+, dimmer (M2)+ and (M2+DHB)+peaks of the Pcs 4 were found easily with DHB MALDI matrix at 1249.822, 1249.584, 1452.953, 1299.374, 1453.689, 2598.611, and 2752.673 Da, respectively (Fig. S3S6 in supporting information). Figure 1 Generally, the electronic spectra of the Pcs showed a monomeric behaviour evidenced by a single and narrow Q band for ZnPcs, In(OAc)Pcs (3–6) and unsubstituted In(OAc)Pc in DMSO, typical of Pcs [29,30]. UV-vis spectra of the Pcs (3–6) were measured in DMSO, DMF, THF, toluene, chloroform, and DCM due to their high solubility, and the UV-vis spectrum of 3 in the solvents is shown as an example in Figure 1. The Q bands of the complexes (3–6 and unsubstituted In(OAc)Pc) were observed at 699, 682, 713, 695, and 687 nm with shoulders at 632, 616, 643, 625 and 620 nm in DMSO, respectively. Moreover, the extinction coefficients (Ԑ ) of the complexes (3–6 and unsubstituted In(OAc)Pc) were calculated as 105524, 143246, 79629, 93734, and 176976 M-1cm-1, respectively (Fig. 2a and 2b). The low absorption coefficients of In(OAc)Pcs (5-6) may be of concern with a decrease in molecular symmetry [31]. In DMSO, Soret bands (B bands) of the peripherally substituted Pcs (4 and 6) and unsubstituted In(OAc)Pc were observed at 357, 360 and 358 nm, respectively. The shoulder between 370 and 380 nm may be due to the charge transfer from the electron-rich ring to the electron-poor metal. The B bands for non-peripherally substituted
7
Pcs were observed at 333 and 381 nm for 3 and at 329 and 378 nm for 5 as broad due to the superimposition of the B1 and B2 bands. Figure 2 The Q bands of the non-peripherally substituted Pcs 3 and 5 were red-shifted when compared to the corresponding peripherally substituted Pcs 4 and 6 in DMSO (Fig. 2a-2b). The red-shifts were 17 nm between 3 and 4, and 8 nm between 5 and 6. The observed red spectral shifts were typical of Pcs with substituents at the non-peripheral positions due to the linear combination of the atomic orbitals (LCAO) coefficients at the non-peripheral positions of the highest occupied molecular orbital (HOMO) being greater than those at the peripheral positions as explained in the literature [32,33]. The Q bands of the In(OAc)Pcs 5 and 6 were red-shifted when compared to the corresponding ZnPcs 3 and 4 in DMSO, suggesting that the non-planar effect of the bigger central indium atom (Fig. 2a-2b).
3.2. Aggregation studies In this study, the aggregation behaviors of the Pcs were examined in DMSO, DMF, THF, toluene, chloroform and DCM solutions to select the suitable solvent for the investigation of photophysical and photochemical properties of the complexes. Absorption spectrum of the Pc 3 in the above solvents is shown as an example in Figure 1. Not all Pcs (3-6) showed aggregation in all the studied solvents. However, DMSO was preferred as the solvent among the studied solvents for further photophysical and photochemical studies because DMSO occurs the non-aggregated solutions with the Pcs and can be used for biological applications without any toxic effect. The aggregation behaviors of the Pcs (3-6 and InAcPc) in DMSO were also studied in concentrations ranging from 1.2×10−5 to 2×10−6 M. When the concentration was increased, the intensity of absorption of the Q band also increased and no new band was observed, which is an evidence for the formation of non-aggregated species (Fig. 3 given as an example for complex 5 in the substituted complexes and Fig. S7 for 8
unsubstituted In(OAc)Pc. Lambert–Beer law was obeyed and no aggregated species was shown in the concentration range in DMSO. The non-peripherally substituted ZnPc 3 showed an extra peak at 747 nm in DCM and chloroform solutions (Fig. 2). The extra peak may be due to the J-type aggregated species or the protonated nitrogen atoms of the Pc core. Because DCM and chloroform solvents contain small amounts of acid (generally HCl) and acidic impurities may protonate the inner nitrogen atoms, so the symmetry of the Pc core can turn into D4h symmetry. To understand cause of the formation of the extra peak (J-type aggregation or protonation), an organic (pyridine) and inorganic base (anhydrous K2CO3) were added to neutralize into DCM and the chloroform solutions of ZnPc 3, respectively. During the neutralization process, the absorption intensity of this extra peak at 747 nm decreased and then the peak disappeared. These results suggested that the extra peak is related to the protonation of nitrogen atoms of the Pc core instead of the formation of J-type aggregates (Fig. S8 and S9).
Figure 3
3.3. Fluorescence spectra The maximum emission intensities of the Pcs 3, 4, 5, 6 and unsubstituted In(OAc)Pc in DMSO were observed at Em 702, 692, 718, 703 and 696 nm when the solutions were excited at Ex 699, 684, 712, 697 and 687 nm, respectively. The fluorescence behaviours of the Pcs (3 and 5) and unsubstituted In(OAc)Pc in DMSO at room temperature were given in Fig. 4 as examples. As seen in Fig. 4, the excitation spectra and absorption spectra of the Pcs were similar and the fluorescence spectra were mirror images of the excitation spectra for the Pcs (3–6 and unsubstituted In(OAc)Pc) in DMSO. The ZnPcs (3 and 4) showed strong fluorescence signal after excitation with a shape of the fluorescence emission spectra while
9
the In(OAc)Pcs (5, 6, and unsubstituted In(OAc)Pc) showed very low fluorescence emission due to the heavy metal atom effect.
Figure 4
3.4. Fluorescence quantum yields (ΦF) and lifetimes (τF) The fluorescence quantum yields of the ZnPcs (3 and 4), In(OAc)Pcs (5 and 6) substituted with 2-phenylphenoxy groups and unsubstituted In(OAc)Pc in DMSO were found as 0.148, 0.218, 0.014, 0.019, and 0.017, respectively. The ΦF values of In(OAc)Pcs were much lower than ZnPcs (3 and 4). It is known that the heavy metal atom increases the number of the triplet state species and causes quenching of the fluorescence [34,35]. Furthermore, the singlet oxygen quantum yield () values of In(OAc)Pcs 5 and 6 have very high. When the ΦF values of the Pcs compared with each other in DMSO, it was observed that the ΦF values of the unsubstituted ZnPc and In(OAc)Pc were higher than those of the non-peripherally Pcs (3 and 5) and lower than those of the peripherally Pcs (4 and 6). The results showed clearly that the substituents and their positions on the Pc unit effect their ΦF values.
The fluorescence lifetimes for the complexes 3 (3.51 ns), 4 (3.98 ns) and unsubstituted In(OAc)Pc (0.32 ns) were obtained by the Time Correlated Single Photon Counting (TCSPC) technique by fitting the fluorescence decay data to a monoexponential function, following excitation at the emission maxima in DMSO (Fig. 5). This technique showed that Pc samples were pure and not aggregate. The τF values for the InPcs 5 and 6 were not found because of their very low fluorescence emission. The lifetimes of ZnPcs were measured within the expected range [36]. In addition, the τF values of the unsubstituted ZnPc and In(OAc)Pc were higher than those of the non-peripherally Pcs (3 and 5) and lower than those of the
10
peripherally Pcs (4 and 6). These results indicated that the substituents and their positions on the Pc unit also affect their fluorescence properties.
Figure 5 The fluorescence rate constant (kF) is directly proportional to the ΦF of the Pcs and the kF values of the ZnPcs 3, 4, unsubstituted ZnPc and In(OAc)Pc were found 4.30x10-7 s-1, 5.53x10-7 s-1, 5.01x10-7 s-1 and 5.31x10-7 s-1 in DMSO, respectively. The kF of ZnPc 3 has relatively lower than that of ZnPc 4 due to non-peripherally substitutent' effect. The natural radiative life time (τ0) values for ZnPcs 3, 4, unsubstituted ZnPc and In(OAc)Pc in DMSO were also determined 23.40 ns, 18.09 ns, 19.95 ns and 18.83 ns, respectively. Similarly, the τ0 value of non-peripherally substituted ZnPc 3 were longer than the peripherally substituted ZnPc 4 in DMSO.
3.5. Singlet oxygen quantum yields (ΦΔ) Singlet oxygen quantum yields were determined using the decomposition of its chemical scavenger 1,3-diphenylisobenzofuran (DPBF) in DMSO. The disappearance of the absorption maximum of DPBF at 417 nm was monitored using the UV–vis spectral changes. We did not observe any changes in the Q band intensities of the Pcs during the ΦΔ determination, confirming that complexes are not degraded during the singlet oxygen measuraments (Fig. 6 (a) for 3, (b) 5 and (c) InAcPc as examples). The ΦΔ values of Pcs (3-6 and unsubstituted In(OAc)Pcs) were 0.81, 0.75, 0.89, 0.85, and 0.61 in DMSO, respectively. The values of the substituted Pcs were higher than those of counterpart unsubstituted Pcs in DMSO confirms that 2-phenylphenoxy moieties on the Pc rings increases the efficiency of singlet oxygen creation for Pc complexes.
11
The values of In(OAc)Pcs 5 and 6 were higher than those of the ZnPcs 3 and 4 in DMSO, indicated that the coordination of large atoms in the Pc cavity remarkably enhances the efficiency of singlet oxygen formation.
Figure 6 The values of the non-peripherally Pcs 3 and 5 were higher than those of the peripherally counterparts 4 and 6 in DMSO, can be explained with the effect of substituent’s position.
3.6. Photodegradation studies Photodegradation of a compound depends on its molecular structure, concentration, nature of the solvent and light intensity, and its stability is especially important for using as a photocatalysts [37]. The photodegradation degree can be determined by the photodegradation quantum yield (Φd). In this study, the photobleaching stabilities of the Pcs were evaluated in DMSO and UV-vis spectral changes of 3, 5, and unsubstituted In(OAc)Pc during light irradiation were given in Fig. 7. as examples. The Φd values were found to be 0.70x10-5, 0.94x10-5 0.99x10-5, 2.53x10-5 and 4.10x10-5 for Pcs 3, 4, 5, 6 and unsubstituted In(OAc)Pc, respectively. These values demonstrated that MPcs were moderately stable in DMSO. Moreover, it seems that indium, zinc metals in the Pc cavity and 2-phenylphenoxy groups on the Pc skeleton decrease their Φd values and increase their stability under light irradiation during the photodegradation studies. Figure 7 The ZnPcs showed same stability compared to In(OAc)Pcs with Φd of the order of 10-5. The stable ZnPc molecules show values as low as 10-6 and for unstable molecules, values of the order 10-3 have been reported [38]. The Φd values of the In(OAc)Pcs were higher than counterpart the ZnPcs in DMSO. It seems that indium metal increases the Φd values and 12
decreases the stability of the Pcs. Because the diameter of indium metal ion is larger than the Pc cavity leading to the loss of molecular symmetry [34]. The Φd values of Pcs 3 and 5 were lower than Pcs 4 and 6. Hence the non-peripherally substituted Pcs were more stable than the peripherally counterparts and it could be a consequence of the initial partial oxidation [39]. The absence of significant spectral changes during the irradiation of the Pcs confirms that no significant phototransformation occurred during the measurements.
4. CONCLUSIONS In the present work, the syntheses of new non-peripherally and peripherally tetra 2phenylphenoxy substituted Zn(II) and In(III)Pc and characterization by elemental analysis, 1
H-NMR, MALDI-TOF, IR, UV-vis, and fluorescence spectral data were described. The
novel Pcs showed excellent solubility and non-aggregated species in chloroform, DCM, toluene, THF, DMF and DMSO. The excitation, absorption and fluorescence emission spectra, fluorescence quantum yields ΦF, fluorescence lifetimes τF, fluorescence rate constants kF and natural radiative lifetime of the Pcs were not determined. These spectral measuraments indicated that the nature of central metal (Zn2+ as d10 configuration and closed shell and indium3+ as the coordination of large metal atoms) in the Pc cavity, peripheral or nonperipheral position effect of substituent on the Pc skeleton and the presence or absence of substituents on the macrocycle considerably affect their fluorescence properties. The 2-phenylphenoxy substituted ZnPcs and InPcs (3-6) gave good singlet oxygen quantum yields (), especially the substituted InPcs (5 and 6) showed the highest values in DMSO. Moreover, ZnPcs 3 and 4 also demonstrated well values due to the d10 configuration of the central Zn2+. The for the Pcs indicate the potential of these complexes
13
as photosensitizers for the PDT of cancer where singlet oxygen is required (Type II mechanism).
ACKNOWLEDGMENTS We are thankful to The Foundation of Marmara University, The Commission of Scientific Research (BAPKO) (Project No: FEN-C-DRP-140115-0011).
14
FIGURE CAPTIONS Scheme 1. Synthetic route of 3-(2-phenylphenoxy)phthalonitrile (1), 4-(2-phenylphenoxy)phthalonitrile (2)
and Pcs 3, 4, 5, and 6 (i) K2CO3, DMF, 50o C 3 days. (ii) N2,
Zn(OAc)2.2H2O or In(OAc)3, DMF, DBU, 350o C, 10 min. Fig. 1. Absorption spectra of the ZnPc 3 in different solvents Fig. 2. Absorption spectra of (a) ZnPc 3 and 4, and (b) In(OAc)Pcs 5 and 6, and unsubstituted In(OAc)Pc in DMSO at 1.0x10−5 M. Fig. 3. Absorption spectra of the In(OAc)Pc 5 in DMSO at different concentrations. (Inset: plot of absorbance vs. concentration) Fig. 4. Absorption, excitation and emission spectra of the ZnPc 4 (a), the In(OAc)Pc 6 (b), and the unsubstituted In(OAc)Pc (c) in DMSO. Excitation wavelength = 650 nm for 4, 665 nm for 6, and 656 nm for the unsubstituted In(OAc)Pc. Fig.5. Time correlated single photon counting (TCSPC) fluorescence decay curves with mono -exponential fitting of the ZnPcs 3 and 4, and unsubstituted In(OAc)Pc in DMSO. Excitation wavelength = 670 nm for 3, 650 nm for 4 and 656 nm for unsubstituted In(OAc)Pc. Bottom: fitting residues for 4. Fig. 6. A typical spectrum for the determination of singlet oxygen quantum yield of (a) ZnPc 3, (b) In(OAc)Pc 5, and (c) unsubstituted In(OAc)Pc in DMSO at = 1x10−5 M (inset: plots of DPBF absorbance versus time) Fig. 7. The photodegradation of (a) ZnPc 4, (b) Pc In(OAc)Pc 6, and (c) unsubstituted In(OAc)Pc in DMSO plot of Q band absorbance versus time in DMF at= 1×10−5 M .
15
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Phenoxyl Substituents: A New Cubic Crystal Containing Solvent-Filled, Nanoscale Voids, Chem. Eur. J. 14 (2008) 4810–4815. [22] P. Zimcik, V. Novakova, M. Miletin, K. Kopecky, Azaphthalocyanines Containing Pyrazine Rings with Focus on the Alkylheteroatom, Aryl and Heteroaryl Substitution and Properties Important in Photodynamic Therapy, Macroheterocycles. 1 (2008) 2129. [23] F. Mitzel, S. FitzGerald, A. Beeby, R. Faust, The Synthesis of Arylalkyne-Substituted Tetrapyrazinoporphyrazines and an Evaluation of Their Potential as Photosensitisers for Photodynamic Therapy, Eur. J. Org. Chem. (2004) 1136–1142. [24] M. Kostka, P. Zimcik, M. Miletin, P. Klemera, K. Kopecky, Z. Musil, Comparison of aggregation
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Synthesis, characterization, photophysical and
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19
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Scheme 1
20
Fig. 1
21
Fig. 2
22
Fig. 3
23
Fig. 4
24
Fig. 5
25
Fig. 6
26
Fig. 7
27
PII: DOI: Reference:
S0022-2313(15)30354-9 http://dx.doi.org/10.1016/j.jlumin.2015.12.010 LUMIN13754
To appear in: Journal of Luminescence Received date: 5 August 2015 Revised date: 23 November 2015 Accepted date: 9 December 2015 Cite this article as: Haytham Elzien Alamin Ali, Mehmet Pişkin, Selçuk Altun, Mahmut Durmuş and Zafer Odabaş, Synthesis, characterization, photophysical, and photochemical properties of novel zinc(II) and indium(III) phthalocyanines containing 2-phenylphenoxy units, Journal of Luminescence, http://dx.doi.org/10.1016/j.jlumin.2015.12.010 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, characterization, photophysical, and photochemical properties of novel zinc(II) and indium(III) phthalocyanines containing 2-phenylphenoxy units Haytham Elzien Alamin Alia,b, Mehmet Pişkinc, Selçuk Altuna, Mahmut Durmuşd*, Zafer Odabaşa** a
Department of Chemistry, Marmara University, Istanbul, 34722, Turkey.
b
University Of Khartoum, Department of Chemistry, Faculty of Science, P.O. Box 321, Khartoum, 11115, Sudan
c
ÇanakkaleOnsekiz Mart University, Vocational School of Technical Sciences, Department of Food Technology, Çanakkale, 17100, Turkey
d
Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze, Kocaeli, 41400, Turkey
ABSTRACT
The synthesis of highly soluble and non-aggregated peripherally/non-peripherally Zn and In(OAc) phthalocyanines was achieved by 3-/ and 4-(2-phenylphenoxy)phthalonitrile as starting materials. The novel compounds were characterized by elemental analyses, FTIR,
UV–vis
and
MALDI-TOF
mass
spectroscopic
techniques.
Additionally,
photophysical, photochemical and spectral properties of the phthalocyanines were reported. Especially, the indium(OAc) phthalocyanines showed good singlet oxygen quantum yields in DMSO and they can be appropriate candidates as Type II photosensitizers in photodynamic therapy (PDT) applications. Keywords: Phthalocyanine; 2-Phenylphenol; Photochemical; Photophysical; fluorescence; singlet-oxygen *Corresponding author, address: Department of Chemistry, Marmara University, 34722 Goztepe, Istanbul, Turkey. Tel.: +90 216 347 96 41/1368; Fax: +90 216 347 87 83. E-mail address: [email protected]. (Z. Odabaş)
1. INTRODUCTION Phthalocyanine (Pc) is a macrocyclic and tetramer molecule, which is a planar conjugated system of 18 electrons exhibiting aromatic behavior, formed of four isoindoline units. The particular electronic delocalization of the 18π system gives rise to outstanding electronic and unconventional physical properties, and high chemical and thermal stability. Due to the 1
excellent stabilities, these conjugated compounds have attracted much research interest in the fabrication of electronic molecular devices, such as opto-electronic devices [1], gas sensors [2,3], static induction transistors [4], photoreceptor devices in laser beam printers and photocopiers
[5-7],
liquid
crystals
[8],
as
Langmuir-Blodgett
films
[9,10],
in
electrophotographic applications [11,12], optical data storage [13], in fuel cells [14], electrochemical sensors [15,16], and in nonlinear optics (NLO) [17,18]. A particular area of Pc application is as photosensitizers (PS) in photodynamic therapy (PDT), e.g. of certain forms of cancer [19-24]. The biomedical function of a PS depends on its ability to absorb visible light (optimal range of 650–800 nm) and highly red-shifted analogs of Pcs are preferred as PS [25,26]. However, some Pcs with additional benzo groups attached to the Pc skeleton such as naphthalocyanines and anthracocyanines [27] have been usually difficult to prepare, highly insoluble, and prone to decomposition [28]. Hence we tried to synthesize Pcs which are easy to prepare, and are highly soluble, non-aggregated, chemically stable and structurally similar to naphthalocyanines (Scheme 1). In this study, newly 3- or 4-(2phenylphenoxy)phthalonitrile and Zn and In(OAc) phthalocyanines were achieved and characterized using
1
H-NMR, FT-IR,
UV-vis spectroscopy and MALDI-TOF-mass
spectrometry. The synthesized novel Pcs are highly soluble and non-aggregated in common organic solvents unlike naphthalocyanines. In addition, the photophysical (fluorescence quantum
yields
and
lifetimes),
photochemical
(singlet
oxygen
generation
and
photodegradation under light irradiation), and spectral properties of the Pcs (3-6) and unsubstituted In(OAc)Pc were investigated in dimethylsulfoxide (DMSO). Especially, the In(OAc)Pcs showed good singlet oxygen quantum yields in DMSO and they can be appropriate candidates as Type II photosensitizers in photodynamic therapy (PDT) applications. The effects of the substituent position and the nature of the central metal in the Pc cavity were also studied.
2
2. EXPERIMENTAL The used materials, equipment, and photophysical and photochemical formulas and parameters were supplied as supplementary information.
2.1. SYNTHESIS 2.1.1. Synthesis of the nitrile compounds (1 and 2) 3-/ or 4-nitrophthalonitrile (2.30 g, 13.30 mmol), 2-phenylphenol (2.50 g, 14.70 mmol) anhydrous K2CO3 (2.60 g, 18.80 mmol) and 20 mL dimethylformamide (DMF) were added in a flask. The reaction mixture was stirred at 50ο C for 72 hours under inert atmosphere and monitored by thin layer chromatography (TLC). Then the mixture was poured into 200 mL ice-water and the formed precipitate was filtered off, washed with water, and dried in vacuum at 50ο C. The crude product was purified by column chromatography with silica gel eluting with chloroform. 3-(2-phenylphenoxy)phthalonitrile (1): Yield: 2.10 g (53.85%). This compound is soluble in CH2Cl2, CHCl3, DMF, dimethylsulfoxide (DMSO), tetrahydrofuran (THF), and hot acetic acid (AcOH). Mp: 128-131° C. IR (ATR) max/cm-1: 3096.62(=CH str.), 3062.50(=CH str.),
3031.25(=CH str.),
2230.75(C≡N str.),
1572.36(C=C str.), 1451.51(CH bend.), 1430.09(CH bend.), 1196.72(CN str.),
1169.22(CN str.),
1117.99(CN str.),
1051.02(CC str.), 1011.30(CC str.), 986.11, 915.66, 871.30, 770.32, 759.74, 745.20, 728.75, 697.61.
1582.80(C=C str.),
1279.86(ArOAr str.), 1073.06(CC str.), 854.24, 815.24, 799.94,
Anal.Calc. for C20H12N2O: C, 81.07; H, 4.08; N,
9.45. Found: C, 80.91; H, 4.19; N, 9.58 %. 1H-NMR (CDCl3) , ppm: 6.83 (d, J = 8.50 Hz, 1H), 7.24 (d, J = 7.88 Hz, 1H), 7.30 (t, J = 7.41 Hz, J = 7.10 Hz, 2H), 7.37 (t, J = 8.20 Hz, J = 7.88 Hz, 1H), 7.37 (t, J = 8.20 Hz, J = 7.88 Hz, 1H),7.40 (d, J = 8.20 Hz, 1H), 7.46 (dd, J = 7.88 Hz, J = 7.25 Hz, 2H), 7.51 (d, J = 7.72 Hz, 2H), 7.60 (d, J = 7.10 Hz, 1H). 3
4-(2-phenylphenoxy)phthalonitrile (2): Yield: 2.50 g (64.00%). This compound is soluble in CH2Cl2, CHCl3, THF, DMF, DMSO, and hot AcOH. Mp: 78-81° C. IR (ATR)max/cm-1:
3106.25(=CH
str.),
3068.84(=CH
str.),
3056.25(=CH
str.),
2234.82(C≡N str.), 1599.92(C=C str.), 1578.82(C=C str.), 1561.07(C=C str.), 1454.10(CH bend.), 1427.62(CH bend.), 1274.01(ArOAr str.), 1243.81(ArOAr str.), 1201.92(CN str.), 1157.09(CN str.), 1109.03(CN str.), 1089.23(CC str.), 1045.93(CC str.), 972.24, 948.50,
919.26,
901.10, 843.72,
827.81,
772.82,
740.87,
698.93. Anal.Calc. for
C20H12N2O: C, 81.07; H, 4.08; N, 9.45. Found: C, 81.20; H, 4.21; N, 9.32 %. 1H-NMR (CDCl3) , ppm: 7.08 (dd, J = 8.67 Hz, J = 2.52 Hz, 1H), 7.12 (d, J = 2.52 Hz, 1H), 7.18 (dd, J = 7.72 Hz, J = 1.42 Hz, 1H), 7.30 (d, J = 7.25 Hz, 2H), 7.35 (t, J = 7.40 Hz, J = 7.09 Hz, 1H), 7.42 (t, J = 8.20 Hz, J = 7.10 Hz, 2H), 7.46 (ddd, J = 7.72 Hz, J = 7.57 Hz, 2.05 Hz 1H), 7.46 (ddd, J = 7.72 Hz, J = 7.57 Hz, 1.42 Hz 1H), 7.55 (dd, J = 7.41 Hz, J = 2.05 Hz, 1H), 7.58 (d, J = 8.83 Hz, 1H),
2.1.2. General procedure for the synthesis of metallo-phthalocyanines(MPcs) A mixture of 1.50 mmol (200 mg) 3-/or 4-(2-phenylphenoxy)phthalonitrile (1 or 2) and 0.35 mmol metal salts (75 mg Zn(OAc)2.2H2O or 100 mg anhydrous indium(III)acetate) was taken in a reaction tube. 0.30 mL of DMF was added to this reaction mixture, and then the mixture was heated in a sealed glass tube for 20 minutes under inert atmosphere at 350o C. The reaction mixture was precipitated by adding acetic acid. The precipitate was filtered, washed with hot acetic acid-water solution 7/3 by volume, water, ethanol and acetonitrile for 12 hrs, respectively in a Soxhlet apparatus. The crude product was purified by column chromatography with silica gel eluting with chloroform. 1(4),8(11),15(18),22(25)-Tetra-(2-phenylphenoxy)phthalocyaninatozinc (3): Solubility: CH2Cl2, CHCl3, THF, DMF, DMSO, toluene Mp>300ο C. Yield: 40.00 mg (25.30%). IR
4
(ATR) max / cm-1: 3056.98(=CH str.), 3032.91(=CH str.), 1656.26(C=N str.), 1600.56(C=C str.)1578.34(C=C str.), 1502.31, 1474.17, 1430.77(CH bend.), 1328.82(CO str.), 1235.00(CO str.), 1198.46, 1107.52(CN str.), 1076.65(CC str.), 1047.27(CC str.), 1002.89(CC str.), 973.03, 878.01, 829.92, 802.68, 735.72, 696.66. Anal. Calc. for C80H48N8O4Zn : C, 76.83; H, 3.87; N, 8.96 %. Found: C, 76.65; H, 4.02; N, 10.10 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 699 (5.02), 670 (4.47), 632 (4.30), 381(4.40), 333 (4.44). M/z: 1249.822 (M+). 2(3),9(10),16(17),23(24)-Tetra-(2-phenylphenoxy)phthalocyaninatozinc
(4):
Solubility:CH2Cl2, CHCl3, DMF, DMSO, THF, toluene. Mp>300ο C. Yield: 42.00 mg (26.60%). IR (ATR) max / cm-1: 3061.97(=CH str.), 3022.78(=CH str.), 1654.38(C=N str.), 1610.58(C=C str.), 1582.11(C=C str.), 1473.02, 1431.20(CH bend.), 1393.97, 1333.69(CO str.), 1251.25(CO str.), 1220.47, 1113.32(CN str.), 1081.07, 1045.39(CC str.), 1010.04(CC str.), 944.47, 890.30, 869.96, 823.92, 765.76, 736.28, 696.86, 669.25. Anal. Calc. for C80H48N8O4Zn : C, 76.83; H, 3.87; N, 8.96 %. Found: C, 77.01; H, 4.05; N, 10.12 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 682 (5.16), 654 (4.48), 616 (4.43) 357 (4.78). M/z: 1249.584 (M+). 1(4),8(11),15(18),22(25)-Tetrakis-([1,1'-biphenyl]-2-yloxy)phthalocyaninatoindium(III)acetate (5): Solubility:CH2Cl2, CHCl3, THF, DMF, DMSO, toluene Mp>300ο C. Yield: 35.00 mg (21.20%). IR (ATR) max / cm-1: 3058.05(=CH str.), 2922.97(>CH2 str.), 2851.63(>CH2 str.), 1721.92(C=O str.), 1656.86(C=N str.), 1578.58(C=O str.), 1502.58, 1473.97, 1430.78(CH bend.), 1331.34(CO str.), 1231.53(CO str.), 1198.22, 1107.12(CN str.), 1079.52(CC str.), 1046.85(CC str.), 1000.95(CC str.), 963.37, 879.33, 829.69, 802.12, 736.35, 696.66. Anal. Calc. for C82H51N8O4In : C, 72.46; H, 3.78; N, 8.24; %. Found: C, 72.29; H, 3.92; N, 8.11 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 713 (4.90), 684
5
(4.34), 643 (4.19), 378 (4.36), 329 (4.43). M/z: 1452.953 (M-OAc+DHB)+. DHB (2,5dihydroxybenzoicacid) was used a MALDI matrix 2(3),9(10),16(17),23(24)-Tetra-(-2phenylphenoxy)phthalocyaninatoindium (III)acetate (6): Solubility:CH2Cl2, CHCl3, DMF, DMSO, THF, toluene. Mp>300ο C. Yield: 39.00 mg (23.60%). IR (ATR) max/cm-1 : 3056.93(=CH str.), 3022.78(=CH str.), 2924.29(>CH2 str.), 1716.97(C=O str.), 1659.48(C=N str.), 1609.83(C=C str.), 1581.98(C=C str.), 1470.37, 1430.45(CH bend.), 1392.67, 1335.46(CO str.), 1251.15(CO str.), 1217.79, 1114.51(CN str.), 1084.49(CC str.), 1043.01(CC str.), 1009.68(CC str.), 943.32, 891.09 867.95, 823.80, 769.62, 734.26, 695.65. Anal. Calc. for C82H51N8O4In : C, 72.46; H, 3.78; N, 8.24; %. Found: C, 72.58; H, 3.94; N, 8.07 %. UV–vis (DMSO, 1×10−5 M): max(nm), (log ): 695 (4.98), 668 (4.45), 625 (4.30), 360 (4.67). M/z: 1299.374 (M)+, 1453.689 (M-OAc+DHB)+, 2598.611 (M2)+, 2752.673 (M2+DHB)+.
3. RESULTS AND DISCUSSION 3.1. Synthesis and characterization The synthetic routes for novel starting materials (1 and 2) and Pcs (3, 4, 5 and 6) are shown in scheme 1. When the IR spectra of 3-/or 4-nitrophthalonitriles and starting compounds 1 and 2 were compared with each other, the disappearance of the NO2 band of 3 or 4nitrophthalonitrile nearby 1350 cm-1 and the appearance of new absorption at 1279.86 and 1274.01 cm-1 belonging to ArOAr indicated the formation of 1 and 2. The extra C≡N band also appeared at 2230.75 and 2234.82 cm-1 in the IR spectrum of 1 and 2 and they disappeared after conversion to Pcs (3-6). The spectrum of 1 and 2 also showed aromatic rings C=C peaks at 1582.80;1572.36 and 1599.92;1578.82 cm-1, and ArH stretching frequencies peaks at 3096.62;3058.22;3027.84 and 3103.79;3068.84;3048.10, respectively.
6
The IR spectra of the all Pcs are similar in most peaks, indicating that central metal has small influence on the vibrations (Table S1). The 1H-NMR spectra of 1 and 2 exhibited characteristic signals for the aromatic protons at 6.83-7.60 and 7.08-7.58 ppm, respectively (Fig. S1 and S2 in supporting information). In MALDI-TOF mass spectra, the molecular ion peaks [M]+ of the Pcs 3 and 4, the [M–OAc+DHB]+ peaks of the Pcs 5, and [M–OAc]+, (M-OAc+DHB)+, dimmer (M2)+ and (M2+DHB)+peaks of the Pcs 4 were found easily with DHB MALDI matrix at 1249.822, 1249.584, 1452.953, 1299.374, 1453.689, 2598.611, and 2752.673 Da, respectively (Fig. S3S6 in supporting information). Figure 1 Generally, the electronic spectra of the Pcs showed a monomeric behaviour evidenced by a single and narrow Q band for ZnPcs, In(OAc)Pcs (3–6) and unsubstituted In(OAc)Pc in DMSO, typical of Pcs [29,30]. UV-vis spectra of the Pcs (3–6) were measured in DMSO, DMF, THF, toluene, chloroform, and DCM due to their high solubility, and the UV-vis spectrum of 3 in the solvents is shown as an example in Figure 1. The Q bands of the complexes (3–6 and unsubstituted In(OAc)Pc) were observed at 699, 682, 713, 695, and 687 nm with shoulders at 632, 616, 643, 625 and 620 nm in DMSO, respectively. Moreover, the extinction coefficients (Ԑ ) of the complexes (3–6 and unsubstituted In(OAc)Pc) were calculated as 105524, 143246, 79629, 93734, and 176976 M-1cm-1, respectively (Fig. 2a and 2b). The low absorption coefficients of In(OAc)Pcs (5-6) may be of concern with a decrease in molecular symmetry [31]. In DMSO, Soret bands (B bands) of the peripherally substituted Pcs (4 and 6) and unsubstituted In(OAc)Pc were observed at 357, 360 and 358 nm, respectively. The shoulder between 370 and 380 nm may be due to the charge transfer from the electron-rich ring to the electron-poor metal. The B bands for non-peripherally substituted
7
Pcs were observed at 333 and 381 nm for 3 and at 329 and 378 nm for 5 as broad due to the superimposition of the B1 and B2 bands. Figure 2 The Q bands of the non-peripherally substituted Pcs 3 and 5 were red-shifted when compared to the corresponding peripherally substituted Pcs 4 and 6 in DMSO (Fig. 2a-2b). The red-shifts were 17 nm between 3 and 4, and 8 nm between 5 and 6. The observed red spectral shifts were typical of Pcs with substituents at the non-peripheral positions due to the linear combination of the atomic orbitals (LCAO) coefficients at the non-peripheral positions of the highest occupied molecular orbital (HOMO) being greater than those at the peripheral positions as explained in the literature [32,33]. The Q bands of the In(OAc)Pcs 5 and 6 were red-shifted when compared to the corresponding ZnPcs 3 and 4 in DMSO, suggesting that the non-planar effect of the bigger central indium atom (Fig. 2a-2b).
3.2. Aggregation studies In this study, the aggregation behaviors of the Pcs were examined in DMSO, DMF, THF, toluene, chloroform and DCM solutions to select the suitable solvent for the investigation of photophysical and photochemical properties of the complexes. Absorption spectrum of the Pc 3 in the above solvents is shown as an example in Figure 1. Not all Pcs (3-6) showed aggregation in all the studied solvents. However, DMSO was preferred as the solvent among the studied solvents for further photophysical and photochemical studies because DMSO occurs the non-aggregated solutions with the Pcs and can be used for biological applications without any toxic effect. The aggregation behaviors of the Pcs (3-6 and InAcPc) in DMSO were also studied in concentrations ranging from 1.2×10−5 to 2×10−6 M. When the concentration was increased, the intensity of absorption of the Q band also increased and no new band was observed, which is an evidence for the formation of non-aggregated species (Fig. 3 given as an example for complex 5 in the substituted complexes and Fig. S7 for 8
unsubstituted In(OAc)Pc. Lambert–Beer law was obeyed and no aggregated species was shown in the concentration range in DMSO. The non-peripherally substituted ZnPc 3 showed an extra peak at 747 nm in DCM and chloroform solutions (Fig. 2). The extra peak may be due to the J-type aggregated species or the protonated nitrogen atoms of the Pc core. Because DCM and chloroform solvents contain small amounts of acid (generally HCl) and acidic impurities may protonate the inner nitrogen atoms, so the symmetry of the Pc core can turn into D4h symmetry. To understand cause of the formation of the extra peak (J-type aggregation or protonation), an organic (pyridine) and inorganic base (anhydrous K2CO3) were added to neutralize into DCM and the chloroform solutions of ZnPc 3, respectively. During the neutralization process, the absorption intensity of this extra peak at 747 nm decreased and then the peak disappeared. These results suggested that the extra peak is related to the protonation of nitrogen atoms of the Pc core instead of the formation of J-type aggregates (Fig. S8 and S9).
Figure 3
3.3. Fluorescence spectra The maximum emission intensities of the Pcs 3, 4, 5, 6 and unsubstituted In(OAc)Pc in DMSO were observed at Em 702, 692, 718, 703 and 696 nm when the solutions were excited at Ex 699, 684, 712, 697 and 687 nm, respectively. The fluorescence behaviours of the Pcs (3 and 5) and unsubstituted In(OAc)Pc in DMSO at room temperature were given in Fig. 4 as examples. As seen in Fig. 4, the excitation spectra and absorption spectra of the Pcs were similar and the fluorescence spectra were mirror images of the excitation spectra for the Pcs (3–6 and unsubstituted In(OAc)Pc) in DMSO. The ZnPcs (3 and 4) showed strong fluorescence signal after excitation with a shape of the fluorescence emission spectra while
9
the In(OAc)Pcs (5, 6, and unsubstituted In(OAc)Pc) showed very low fluorescence emission due to the heavy metal atom effect.
Figure 4
3.4. Fluorescence quantum yields (ΦF) and lifetimes (τF) The fluorescence quantum yields of the ZnPcs (3 and 4), In(OAc)Pcs (5 and 6) substituted with 2-phenylphenoxy groups and unsubstituted In(OAc)Pc in DMSO were found as 0.148, 0.218, 0.014, 0.019, and 0.017, respectively. The ΦF values of In(OAc)Pcs were much lower than ZnPcs (3 and 4). It is known that the heavy metal atom increases the number of the triplet state species and causes quenching of the fluorescence [34,35]. Furthermore, the singlet oxygen quantum yield () values of In(OAc)Pcs 5 and 6 have very high. When the ΦF values of the Pcs compared with each other in DMSO, it was observed that the ΦF values of the unsubstituted ZnPc and In(OAc)Pc were higher than those of the non-peripherally Pcs (3 and 5) and lower than those of the peripherally Pcs (4 and 6). The results showed clearly that the substituents and their positions on the Pc unit effect their ΦF values.
The fluorescence lifetimes for the complexes 3 (3.51 ns), 4 (3.98 ns) and unsubstituted In(OAc)Pc (0.32 ns) were obtained by the Time Correlated Single Photon Counting (TCSPC) technique by fitting the fluorescence decay data to a monoexponential function, following excitation at the emission maxima in DMSO (Fig. 5). This technique showed that Pc samples were pure and not aggregate. The τF values for the InPcs 5 and 6 were not found because of their very low fluorescence emission. The lifetimes of ZnPcs were measured within the expected range [36]. In addition, the τF values of the unsubstituted ZnPc and In(OAc)Pc were higher than those of the non-peripherally Pcs (3 and 5) and lower than those of the
10
peripherally Pcs (4 and 6). These results indicated that the substituents and their positions on the Pc unit also affect their fluorescence properties.
Figure 5 The fluorescence rate constant (kF) is directly proportional to the ΦF of the Pcs and the kF values of the ZnPcs 3, 4, unsubstituted ZnPc and In(OAc)Pc were found 4.30x10-7 s-1, 5.53x10-7 s-1, 5.01x10-7 s-1 and 5.31x10-7 s-1 in DMSO, respectively. The kF of ZnPc 3 has relatively lower than that of ZnPc 4 due to non-peripherally substitutent' effect. The natural radiative life time (τ0) values for ZnPcs 3, 4, unsubstituted ZnPc and In(OAc)Pc in DMSO were also determined 23.40 ns, 18.09 ns, 19.95 ns and 18.83 ns, respectively. Similarly, the τ0 value of non-peripherally substituted ZnPc 3 were longer than the peripherally substituted ZnPc 4 in DMSO.
3.5. Singlet oxygen quantum yields (ΦΔ) Singlet oxygen quantum yields were determined using the decomposition of its chemical scavenger 1,3-diphenylisobenzofuran (DPBF) in DMSO. The disappearance of the absorption maximum of DPBF at 417 nm was monitored using the UV–vis spectral changes. We did not observe any changes in the Q band intensities of the Pcs during the ΦΔ determination, confirming that complexes are not degraded during the singlet oxygen measuraments (Fig. 6 (a) for 3, (b) 5 and (c) InAcPc as examples). The ΦΔ values of Pcs (3-6 and unsubstituted In(OAc)Pcs) were 0.81, 0.75, 0.89, 0.85, and 0.61 in DMSO, respectively. The values of the substituted Pcs were higher than those of counterpart unsubstituted Pcs in DMSO confirms that 2-phenylphenoxy moieties on the Pc rings increases the efficiency of singlet oxygen creation for Pc complexes.
11
The values of In(OAc)Pcs 5 and 6 were higher than those of the ZnPcs 3 and 4 in DMSO, indicated that the coordination of large atoms in the Pc cavity remarkably enhances the efficiency of singlet oxygen formation.
Figure 6 The values of the non-peripherally Pcs 3 and 5 were higher than those of the peripherally counterparts 4 and 6 in DMSO, can be explained with the effect of substituent’s position.
3.6. Photodegradation studies Photodegradation of a compound depends on its molecular structure, concentration, nature of the solvent and light intensity, and its stability is especially important for using as a photocatalysts [37]. The photodegradation degree can be determined by the photodegradation quantum yield (Φd). In this study, the photobleaching stabilities of the Pcs were evaluated in DMSO and UV-vis spectral changes of 3, 5, and unsubstituted In(OAc)Pc during light irradiation were given in Fig. 7. as examples. The Φd values were found to be 0.70x10-5, 0.94x10-5 0.99x10-5, 2.53x10-5 and 4.10x10-5 for Pcs 3, 4, 5, 6 and unsubstituted In(OAc)Pc, respectively. These values demonstrated that MPcs were moderately stable in DMSO. Moreover, it seems that indium, zinc metals in the Pc cavity and 2-phenylphenoxy groups on the Pc skeleton decrease their Φd values and increase their stability under light irradiation during the photodegradation studies. Figure 7 The ZnPcs showed same stability compared to In(OAc)Pcs with Φd of the order of 10-5. The stable ZnPc molecules show values as low as 10-6 and for unstable molecules, values of the order 10-3 have been reported [38]. The Φd values of the In(OAc)Pcs were higher than counterpart the ZnPcs in DMSO. It seems that indium metal increases the Φd values and 12
decreases the stability of the Pcs. Because the diameter of indium metal ion is larger than the Pc cavity leading to the loss of molecular symmetry [34]. The Φd values of Pcs 3 and 5 were lower than Pcs 4 and 6. Hence the non-peripherally substituted Pcs were more stable than the peripherally counterparts and it could be a consequence of the initial partial oxidation [39]. The absence of significant spectral changes during the irradiation of the Pcs confirms that no significant phototransformation occurred during the measurements.
4. CONCLUSIONS In the present work, the syntheses of new non-peripherally and peripherally tetra 2phenylphenoxy substituted Zn(II) and In(III)Pc and characterization by elemental analysis, 1
H-NMR, MALDI-TOF, IR, UV-vis, and fluorescence spectral data were described. The
novel Pcs showed excellent solubility and non-aggregated species in chloroform, DCM, toluene, THF, DMF and DMSO. The excitation, absorption and fluorescence emission spectra, fluorescence quantum yields ΦF, fluorescence lifetimes τF, fluorescence rate constants kF and natural radiative lifetime of the Pcs were not determined. These spectral measuraments indicated that the nature of central metal (Zn2+ as d10 configuration and closed shell and indium3+ as the coordination of large metal atoms) in the Pc cavity, peripheral or nonperipheral position effect of substituent on the Pc skeleton and the presence or absence of substituents on the macrocycle considerably affect their fluorescence properties. The 2-phenylphenoxy substituted ZnPcs and InPcs (3-6) gave good singlet oxygen quantum yields (), especially the substituted InPcs (5 and 6) showed the highest values in DMSO. Moreover, ZnPcs 3 and 4 also demonstrated well values due to the d10 configuration of the central Zn2+. The for the Pcs indicate the potential of these complexes
13
as photosensitizers for the PDT of cancer where singlet oxygen is required (Type II mechanism).
ACKNOWLEDGMENTS We are thankful to The Foundation of Marmara University, The Commission of Scientific Research (BAPKO) (Project No: FEN-C-DRP-140115-0011).
14
FIGURE CAPTIONS Scheme 1. Synthetic route of 3-(2-phenylphenoxy)phthalonitrile (1), 4-(2-phenylphenoxy)phthalonitrile (2)
and Pcs 3, 4, 5, and 6 (i) K2CO3, DMF, 50o C 3 days. (ii) N2,
Zn(OAc)2.2H2O or In(OAc)3, DMF, DBU, 350o C, 10 min. Fig. 1. Absorption spectra of the ZnPc 3 in different solvents Fig. 2. Absorption spectra of (a) ZnPc 3 and 4, and (b) In(OAc)Pcs 5 and 6, and unsubstituted In(OAc)Pc in DMSO at 1.0x10−5 M. Fig. 3. Absorption spectra of the In(OAc)Pc 5 in DMSO at different concentrations. (Inset: plot of absorbance vs. concentration) Fig. 4. Absorption, excitation and emission spectra of the ZnPc 4 (a), the In(OAc)Pc 6 (b), and the unsubstituted In(OAc)Pc (c) in DMSO. Excitation wavelength = 650 nm for 4, 665 nm for 6, and 656 nm for the unsubstituted In(OAc)Pc. Fig.5. Time correlated single photon counting (TCSPC) fluorescence decay curves with mono -exponential fitting of the ZnPcs 3 and 4, and unsubstituted In(OAc)Pc in DMSO. Excitation wavelength = 670 nm for 3, 650 nm for 4 and 656 nm for unsubstituted In(OAc)Pc. Bottom: fitting residues for 4. Fig. 6. A typical spectrum for the determination of singlet oxygen quantum yield of (a) ZnPc 3, (b) In(OAc)Pc 5, and (c) unsubstituted In(OAc)Pc in DMSO at = 1x10−5 M (inset: plots of DPBF absorbance versus time) Fig. 7. The photodegradation of (a) ZnPc 4, (b) Pc In(OAc)Pc 6, and (c) unsubstituted In(OAc)Pc in DMSO plot of Q band absorbance versus time in DMF at= 1×10−5 M .
15
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Scheme 1
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Fig. 1
21
Fig. 2
22
Fig. 3
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Fig. 4
24
Fig. 5
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Fig. 6
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Fig. 7
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