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The new zinc(II) phthalocyanine directly conjugated with 4-butylmorpholine units: Synthesis, characterization, thermal, spectroscopic and photophysical properties
Journal Pre-proof The new zinc(II) phthalocyanine directly conjugated with 4-butylmorpholine units: Synthesis, characterization, thermal, spectroscopic and photophysical properties Fatih Mutlu, Mehmet Pişkin, Erdal Canpolat, Ömer Faruk Öztürk PII:
S0022-2860(19)31278-5
DOI:
https://doi.org/10.1016/j.molstruc.2019.127169
Reference:
MOLSTR 127169
To appear in:
Journal of Molecular Structure
Received Date: 31 July 2019 Revised Date:
20 September 2019
Accepted Date: 1 October 2019
Please cite this article as: F. Mutlu, M. Pişkin, E. Canpolat, Ö.Faruk. Öztürk, The new zinc(II) phthalocyanine directly conjugated with 4-butylmorpholine units: Synthesis, characterization, thermal, spectroscopic and photophysical properties, Journal of Molecular Structure (2019), doi: https:// doi.org/10.1016/j.molstruc.2019.127169. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier B.V.
The new zinc(II) phthalocyanine directly conjugated with 4-butylmorpholine units: Synthesis, characterization, thermal, spectroscopic and photophysical properties
Fatih Mutlua, Mehmet Pişkinb*, Erdal Canpolatc, Ömer Faruk Öztürka
a b
Department of Chemistry, Faculty of Science, Çanakkale Onsekiz Mart University, Çanakkale, Turkey
Department of Food Processing, Canakkale Technical Sciences Vocational School, Çanakkale Onsekiz Mart University, Çanakkale, Turkey c
Department of Science Education, Faculty of Education, Fırat University, Elazığ, Turkey
ABSTRACT In this study, new peripheral tetra-4-butylmorpholine substituted zinc(II) phthalocyanine was synthesized through C-C bond formation using the palladium catalyzed Suzuki-Miyaura coupling reaction. Its structure was characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, UV-vis, fluorescence, and MALDI-TOF-mass spectroscopic techniques. Its thermal property were evaluated by thermogravimetric analysis and differential scanning calorimetry. In addition, the photophysical properties of the zinc(II) phthalocyanine were also investigated in DMSO. Keywords: Phthalocyanine, 4-butylmorpholine, Suzuki-Miyaura coupling reaction, spectroscopic, photophysical
* Corresponding Author Department of Food Processing, Çanakkale Technical Sciences Vocational School, Çanakkale Onsekiz Mart University, 17020, Çanakkale, Turkey. Tel:+90 286 218 00 18/ 5522. Fax: +90 286 218 05 49. E-mail addresses: [email protected] (Mehmet Pişkin)
1. Introduction Phthalocyanine (Pc) is a macrocyclic and tetramer molecule, which is a planar conjugated system of 18π electrons exhibiting aromatic behavior, formed of four isoindoline units. Pcs have great attention due to characteristic 18π-electron delocalization, outstanding electronic and unconventional physical properties, high chemical and thermal stability and various applications in different technological and medical area such as chemical sensors [1], electrochromic displaying systems [2], non-linear optics [3], solar cells [4], molecular electronics [5], semiconductors [6], liquid crystals [7], optical storage devices [8], catalyst [9] and photodynamic therapy (PDT) [10]. Applications of phthalocyanines are restricted owing to their insolubility in common organic solvents and water. It has been found that suitable functional groups in the peripheral benzene rings of the phthalocyanine structure can improve the solubility in protic or non-protic solvents [11-13]. The intermolecular interaction of phthalocyanines is also one of the main problems for their technological applications. This interaction results in aggregation that decreases the solubility of phthalocyanine. The tendency of phthalocyanines to aggregate in solution reduces both their luminescence ability and their photo-sensing ability. The bulky peripheral substituents particularly decrease the aggregation, preventing the π-π stacking between planar phthalocyanine rings [14,15]. Many different substituents and over seventy metals used to modify the properties of phthalocyanines and to enhance their potential application areas [16]. For this, many methods have been applied in the synthesis of phthalocyanine. Palladium-catalyzed Suzuki reaction provides an interesting way to synthesize targeted new phthalocyanine derivatives [17,18]. Suzuki cross-linking reaction using palladium catalyst is one of the most widely used methods for the formation of carbon-carbon bonds [19-21]. In order to be able to use it in different fields of application, we have prepared a new directly substituted zinc(II) phthalocyanine capable of absorbing at long wavelength. New peripheral tetra-4-butyl morpholine substituted
zinc (II) phthalocyanine (ZnPc) 3 was synthesized by substituting the 4-butylmorpholine units directly to the phthalocyanine skeleton by C-C bonding via the Suzuki-Miyaura coupling reaction (Scheme 1). To further extend the absorption wavelength of the targeted phthalocyanine, 4-butylmorpholine units were substituted directly from the peripheral positions of the phthalocyanine skeleton instead of any binding heteroatoms such as oxygen, sulfur or nitrogen. The Q band of the new ZnPc 3 shifted red at 22 nm compared to unsubstituted zinc (II) phthalocyanine in DMSO. I I N
NC
N
I
DMAE, 135oC
N Zn
N
N
ZnCl2, 4 hour N
NC
N
1
N
2
I
I O
N O
O N
N
N
Pd(PPh 3)4/Cs2CO3,
2
1,4-dioxane/water (4:1),
N
101oC, 6 hour O
N Zn
N
N
B N
N
O N
3 O
N
O
N
Scheme 1. Synthesis of peripheral tetra-iodo substituted zinc(II) phthalocyanine 2 and tetra-4-butyl morpholine substituted zinc(II) phthalocyanine 3.
2. Experimental The used materials, equipment, photophysical formulas and parameters were provided as supplementary information. The peripheral tetra-iodo substituted zinc(II) phthalocyanine (ZnI4Pc) 2 was synthesized and purified according to the literature [22]. 2.1.Synthesis of peripheral tetra-4-butylmorpholine substituted zinc(II) phthalocyanine (3)
75 mg (6.934.10-2 mmol) of the ZnI4Pc 2 and 142.88 mg (5.599.10-1 mmol) of 3-(4morpholinyl)propyl-1-boronic acid pinacol ester were added to 50 mL schlenk tube. The mixture was dissolved in 12 mL of 1,4-dioxane and 3 mL of water mixture and the mixture was stirred. To the mixture in the argon gas atmosphere was added 2.36 mg (6.8 mmol) of Pd(PPh3)4 and 1.142 mg (3.5 mmol) of Cs2CO3. The reaction mixture was stirred at 101 °C in reflux for 6 hour under an argon gas atmosphere. This reaction mixture was stirred at reflux temperature until complete conversion of the starting material to the product. After cooling to room temperature, this mixture was extracted with chloroform /water. The chloroform phase was dried by anhydrous Mg2SO4 and then filtered off. The bluish-green product was purified by column chromatography with silica gel as the stationary phase, eluting with a solvent system of chloroform / methanol (10: 1) as mobile phase. Yield: 84.55 mg (58%). M.p. >300 o
C. IR (ATR) λmax/cm-1: 1035 (C‒H str.), 1189(C‒N str.), 1324 (C‒O str.), 1484 (C‒H bend.),
1609(C=C str.), 1664(C=N str.), 2952 (>CH2 str.), 3038(=C‒H str.). 1H NMR [500 MHz, DMSO-d6, δ (ppm)]: 7.90-6.53 (m, Ar-H, 12H), 3.30 (DMSO-d6), 2.46-1.29 (m, N-CH2, 24H), 2.30-1.26 (m, O-CH2, 16H), 1.26-0.80 (m, N-(CH2)3, 16H).
13
C NMR [500 MHz,
DMSO-d6, δ (ppm)]: 179, 172, 166, 159, 151,142, 139, 132, 128, 124, 120,109,105,101, 66, 62, 58, 55. UV–vis (DMSO, 1x10-5 M): λmax(nm), (log ε): 352 (4.07), 644 (3.71), 684(4.00). Calc. for C60H68N12O4Zn: C, 66.32; H, 6.31; N, 15.47%; Found C, 66.45; H, 6.10, N 15.75%. MALDI-TOF MS m/z: calc. 1086.66; found 1087.950 [M]+.
3. Results and Discussions 3.1. Synthesis and characterization The synthesis and purification of the ZnI4Pc 2 were carried out according to the literature [22]. The results obtained for its characterization are consistent with the literature [22]. The ZnPc 3 which the 4-butylmorpholine units were directly conjugated to Pc skeleton from
peripheral positions was synthesized by means of Suzuki-Miyaura cross-coupling reaction between the ZnI4Pc 2 and 3-(4-morpholinyl)propyl-1-boronic acid pinacol ester (Scheme 1). After purification of ZnPc 3, it was characterized by general spectroscopic methods such as FT-IR, 1H NMR,
13
C NMR, MALDI-TOF mass, UV-vis, and elemental analysis, and the
results obtained supported the proposed structure. In the FT-IR spectrum, the ZnPc 3 demonstrated vibrational peak at 3038 cm-1 for aromatic C-H stretching. Aliphatic CH stretching vibrations were observed at 2952 cm-1 for the ZnPc 3. Furthermore, its C = N stretching vibration in the IR spectrum was observed at 1664 cm-1. The 1H NMR and
13
C NMR spectra of the ZnPc 3 was recorded in deuterated DMSO
(DMSO-d6) . The 1H-NMR and
13
C-NMR spectra of the new phthalocyanine also
confirmed the target structure of this phthalocyanine. The resonances of aromatic CH protons for the 3 were observed in the range 7.90-6.53 ppm (Fig.1 in ESI). The characteristic signals of -N-CH2, -O-CH2 and -N-(CH2)3 protons for the ZnPc 3 were observed in the range of 2.46-1.29, 2.30-1.26 and 1.26-0.80 ppm, respectively (Fig.1 in ESI). For the 1H-NMR spectrum of ZnPc 3, all aromatic and aliphatic protons were observed at their expected regions and integration of the peaks were found to be consistent with the expected numbers of the protons (Fig.1 in ESI). 13C NMR spectrum of the ZnPc 3 showed 14 aromatic carbon atoms signals and 8 aliphatic carbon atoms signals. The
13
C-
NMR spectrum of the ZnPc 3 confirmed that all aliphatic and aromatic carbon atoms appeared at their expected regions. The MALDI-TOF mass spectrum of the ZnPc 3 verified the proposed structure (Fig.2). 2,5-Dihydroxybenzoicacid (DHB) was used as a MALDI matrix. The molecular ion peak as a [M+H]+ for the ZnPc 3 was readily defined at m/z: 1087.950 (Fig.2). The elemental analysis of ZnPc 3 also confirmed the proposed structure.
Fig. 2. MALDI-TOF mass spectrum of the ZnPc 3 Solvents such as dichloromethane (DCM), dimethylformamide (DMF), tetrahydrofuran (THF), dimethylsulfoxide (DMSO) are known as polar aprotic solvents, while solvents such as ethanol (EtOH) and water are known as polar protic solvents. On the other hand, toluene is known as a non-polar solvent. The ZnPc 3 dissolves quite well in each of the aforementioned types of solvents, whereas in hexane, a non-polar solvent, it dissolves very little (Fig.3).
Fig. 3. Electronic absorption spectra of the ZnPc 3 in different solvents at 1x10-5 M.
The electronic spectrum of the ZnPc 3 demonstrated characteristic absorption with Q band at 684 nm up to 1x10-5 mol dm-3 in DMSO as typical of metallo phthalocyanine (Fig.4). The B-band of the ZnPc 3 was observed at λmax =352 nm (Fig.3). The substitution of the 4butylmorpholine units to Pc skeleton induced 22 nm more red-shifted than Q band absorption of unsubstituted zinc(II) phthalocyanine in DMSO [23]. This may be due to direct binding from 4-butylmorpholine units as the substituent type and / or from the binding types of the substituents which bind to the phthalocyanine ring [24]. The aggregation behavior of the ZnPc was examined in DCM, DMF, DMSO, EtOH, hexane, THF, toluene, water (Fig.1). The ZnPc 3 formed highly aggregated species in EtOH and water. Its resolution in hexane was quite low. The aggregation behavior of the ZnPc 3 was also explored at different concentrations in DMSO (Fig.4). In DMSO solution, the BeerLambert law was obeyed for the ZnPc 3 at concentrations ranging from 1.20 x10-5 to 2 x10-6 M. As the concentration was increased, the intensity of the absorption of the Q band also increased and no new bands (normally blue shifted) due to aggregated species appeared, evidencing that the ZnPc 3 was aggregated in DMSO at these concentrations.
Fig.4. Electronic absorption spectra of the ZnPc 3 in DMSO at different concentrations (inset: plot of absorbance vs. concentration).
3.2. Fluorescence spectra Fig. 5 shows fluorescence emission, absorption and excitation spectra of the ZnPc in DMSO. Fluorescence emission and excitation maximum peaks of the ZnPc 3 were observed at 698 nm and 685 nm in DMSO, respectively. The observed Stokes shift of the ZnPc 3 in DMSO was 14 nm and this value was longer than unsubstituted zinc(II) Pc [23]. In this case, again, as mentioned above, it can be due to the substituent type and / or direct substitution of the substituent with phthalocyanine [24]. In DMSO, the shape of the excitation spectrum of the ZnPc 3 was observed to be slightly different from that of its absorption spectrum. This situation is due to the following reasons. The intensity of peaks seen in the excitation spectrum is directly proportional to the number of photons absorbed. On the other hand; in absorption spectroscopy, one usually measures the absorbance, which is log of incident light intensity over transmitted light intensity. For this reason, although the peaks in the excitation spectrum need to appear at the same wavelengths, they will not have the same relative intensities as the peaks in the absorption spectrum. However, in a highly diluted sample, the relative intensities in the two spectra can approach the same value.
Fig. 5. Absorption, excitation and emission spectra of the ZnPc 3 in DMSO. Excitation wavelength = 642 nm.
3.4. Fluorescence quantum yields and lifetimes The fluorescence quantum yield (ΦF) value of the ZnPc 3 was typical for MPcs and 0.15 in DMSO. This value was lower compared to unsubstituted zinc(II) phthalocyanine in DMSO [23] due to the higher quenching of fluorescence by the substituents. In DMSO, the fluorescence lifetime (τF) of the ZnPc 3 was determined using a time-correlated single photon counting (TCSPC) (Fig. 6). The τF value of ZnPc 3 was characteristic for MPcs and was 2.78 ns in DMSO.
The fluorescence decay of the ZnPc 3 ended up the
monoexponential curve with lifetime 2.78 ns. This value was observed within the range expected for MPc [25] and was shorter than unsubstituted zinc(II) Pc in DMSO [26]. The fluorescence rate constant (kF) is directly proportional to the ΦF of the Pc. The kF value of the ZnPc 3 was 5.40 x107 s-1 in DMSO and was higher than unsubstituted zinc(II) Pc [27]. This may be related to the substitution of 4-butylmorpholine units directly from peripheral positions on the skeleton of phthalocyanine. The natural radiation life (τ0) value of the ZnPc 3 in DMSO solvent was determined to be 18.53 ns. This value was shorter than unsubstituted zinc(II) Pc in DMSO [27].
Fig. 6. Time correlated single photon counting (TCSPC) fluorescence decay curve with mono-exponential fitting of the ZnPcs 3 in DMSO. Excitation wavelength: 642 nm Bottom: fitting residues. 3.5. DTG/TGA and DSC measurements Thermogravimetric analysis (TGA) is one of the characterization techniques that quantitatively give the weight changes caused by increasing temperature in the mass of material. It is possible to observe changes in material' weight during dehydration or degradation of a material depending on time or temperature. The weight change of the material occurs as a result of the material's physical or chemical bonds breaking at high temperatures. Two-step weight reduction was observed in the TGA of the ZnPc 3 (Fig.7 in ESI). It was observed that the ZnPc 3 thermally began to decompose after a temperature range of 120-130 oC and that the ZnPc 3 degradation continued up to 320 °C. A 45% mass loss of the ZnPc 3 was determined in the first decay interval, which is considered to be the degradation of the phthalocyanine ring. In the second decomposition range, a 10% mass loss of the ZnPc 3 was determined between 450-700 oC as a result of oxygen combustion. The ZnPc 3 was completely degraded after 700 °C. The ZnPc 3 had high thermal stability. Differential scanning calorimetry (DSC) thermal analysis measures the amount of energy that is absorbed or released when heated or cooled by a sample, and provides quantitative and qualitative data on the endothermic (heat absorption) and exothermic (heat generation) processes. The DSC spectrum of the ZnPc 3 (2.42 mg) obtained with a heating and cooling rate of 5 oC / min is quite wide and diffuse (Fig.8 in ESI). This can be caused by 4butylmorpholine units which are substituted directly to the peripheral positions of the phthalocyanine ring [28]. The glass transition value (Tg) of the ZnPc 3 was 47.48 oC, which is acceptable for a molecular weight of 1086.66 g / mol. This decrease in the Tg value of the
ZnPc 3 was attributed to the plasticizing effect of the ZnPc 3 substituted with bulky groups [29].
3. Conclusions The new zinc(II) Pc 3 directly conjugated with four 4-butylmorpholine units was synthesized via C-C bond formation using the palladium-catalyzed Suzuki-Miyaura coupling reaction. The new zinc(II) Pc 3 was characterized by elemental analysis, FT-IR, 1H NMR,
13
C NMR,
UV-vis, fluorescence, TGA, DSC and MALDI-TOF mass spectroscopic methods. The new zinc(II) Pc 3 showed good solubility in non-polar solvent, polar aprotic and protic solvents. However, the new ZnPc 3 showed little solubility in hexane, one of the non-polar solvents. It was found the aggregated state in polar protic solvent solutions (ethanol, water). The directly conjugated with 4-butylmorpholine substituent shifted the absorption band to red region. The shape of excitation spectrum was different from the absorption spectrum for the ZnPc 3 in DMSO. This is due to a decrease in the intensity of the excitation caused by the concentration difference. The new ZnPc 3 showed typical thermal stabilities under air atmosphere. In order to determine the photophysical properties of the new ZnPc 3 in DMSO solvent, its fluorescence quantum yield, fluorescence lifetime, fluorescence rate constant and natural radiative lifetime values were determined.. According to the spectral data and results obtained, it was reported that the presence of a substituent directly conjugated to the phthalocyanine ring from peripheral positions greatly influenced the fluorescence properties.
Acknowledgements This study was supported by Çanakkale Onsekiz Mart University Scientific Research Projects Coordination Unit. Project number: FYL-2018-2538. References
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1.244 1.162 1.149 1.057
2.486 2.294 2.074
3.325
7.648
38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6
16.08
16.06
24.09
12.19
4 2 0 8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0 f1 (ppm)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Fig. 1. 1H NMR spectrum of the ZnPc 3 in Dimethyl sulfoxide-d6
Fig. 2. MALDI-TOF mass spectrum of the ZnPc 3
0.0
Fig. 3. Electronic absorption spectra of the ZnPc 3 in different solvents at 1x10-5 M.
Fig.4. Electronic absorption spectra of the ZnPc 3 in DMSO at different concentrations (inset: plot of absorbance vs. concentration).
Fig. 5. Absorption, excitation and emission spectra of the ZnPc 3 in DMSO. Excitation wavelength = 642 nm.
Fig. 6. Time correlated single photon counting (TCSPC) fluorescence decay curve with mono-exponential fitting of the ZnPcs 3 in DMSO. Excitation wavelength: 642 nm Bottom: fitting residues.
Fig. 7. TGA thermogram of the ZnPc 3
Fig. 8. DSC thermogram of the ZnPc 3
Highlights (for review) • The new zinc(II) phthalocyanine substituted directly with 4-butylmorpholine was synthesized and characterized by widely known spectroscopic methods. • Thermal properties of new zinc(II) phthalocyanine were determined. • Photophysical properties of the new zinc(II) phthalocyanine were reported in dimethylsulfoxide. • The new zinc(II) phthalocyanine has good solubility in non-polar solvent, polar aprotic and protic solvents. • The new zinc(II) phthalocyanine has the ability to absorb at long wavelengths.
S0022-2860(19)31278-5
DOI:
https://doi.org/10.1016/j.molstruc.2019.127169
Reference:
MOLSTR 127169
To appear in:
Journal of Molecular Structure
Received Date: 31 July 2019 Revised Date:
20 September 2019
Accepted Date: 1 October 2019
Please cite this article as: F. Mutlu, M. Pişkin, E. Canpolat, Ö.Faruk. Öztürk, The new zinc(II) phthalocyanine directly conjugated with 4-butylmorpholine units: Synthesis, characterization, thermal, spectroscopic and photophysical properties, Journal of Molecular Structure (2019), doi: https:// doi.org/10.1016/j.molstruc.2019.127169. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier B.V.
The new zinc(II) phthalocyanine directly conjugated with 4-butylmorpholine units: Synthesis, characterization, thermal, spectroscopic and photophysical properties
Fatih Mutlua, Mehmet Pişkinb*, Erdal Canpolatc, Ömer Faruk Öztürka
a b
Department of Chemistry, Faculty of Science, Çanakkale Onsekiz Mart University, Çanakkale, Turkey
Department of Food Processing, Canakkale Technical Sciences Vocational School, Çanakkale Onsekiz Mart University, Çanakkale, Turkey c
Department of Science Education, Faculty of Education, Fırat University, Elazığ, Turkey
ABSTRACT In this study, new peripheral tetra-4-butylmorpholine substituted zinc(II) phthalocyanine was synthesized through C-C bond formation using the palladium catalyzed Suzuki-Miyaura coupling reaction. Its structure was characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, UV-vis, fluorescence, and MALDI-TOF-mass spectroscopic techniques. Its thermal property were evaluated by thermogravimetric analysis and differential scanning calorimetry. In addition, the photophysical properties of the zinc(II) phthalocyanine were also investigated in DMSO. Keywords: Phthalocyanine, 4-butylmorpholine, Suzuki-Miyaura coupling reaction, spectroscopic, photophysical
* Corresponding Author Department of Food Processing, Çanakkale Technical Sciences Vocational School, Çanakkale Onsekiz Mart University, 17020, Çanakkale, Turkey. Tel:+90 286 218 00 18/ 5522. Fax: +90 286 218 05 49. E-mail addresses: [email protected] (Mehmet Pişkin)
1. Introduction Phthalocyanine (Pc) is a macrocyclic and tetramer molecule, which is a planar conjugated system of 18π electrons exhibiting aromatic behavior, formed of four isoindoline units. Pcs have great attention due to characteristic 18π-electron delocalization, outstanding electronic and unconventional physical properties, high chemical and thermal stability and various applications in different technological and medical area such as chemical sensors [1], electrochromic displaying systems [2], non-linear optics [3], solar cells [4], molecular electronics [5], semiconductors [6], liquid crystals [7], optical storage devices [8], catalyst [9] and photodynamic therapy (PDT) [10]. Applications of phthalocyanines are restricted owing to their insolubility in common organic solvents and water. It has been found that suitable functional groups in the peripheral benzene rings of the phthalocyanine structure can improve the solubility in protic or non-protic solvents [11-13]. The intermolecular interaction of phthalocyanines is also one of the main problems for their technological applications. This interaction results in aggregation that decreases the solubility of phthalocyanine. The tendency of phthalocyanines to aggregate in solution reduces both their luminescence ability and their photo-sensing ability. The bulky peripheral substituents particularly decrease the aggregation, preventing the π-π stacking between planar phthalocyanine rings [14,15]. Many different substituents and over seventy metals used to modify the properties of phthalocyanines and to enhance their potential application areas [16]. For this, many methods have been applied in the synthesis of phthalocyanine. Palladium-catalyzed Suzuki reaction provides an interesting way to synthesize targeted new phthalocyanine derivatives [17,18]. Suzuki cross-linking reaction using palladium catalyst is one of the most widely used methods for the formation of carbon-carbon bonds [19-21]. In order to be able to use it in different fields of application, we have prepared a new directly substituted zinc(II) phthalocyanine capable of absorbing at long wavelength. New peripheral tetra-4-butyl morpholine substituted
zinc (II) phthalocyanine (ZnPc) 3 was synthesized by substituting the 4-butylmorpholine units directly to the phthalocyanine skeleton by C-C bonding via the Suzuki-Miyaura coupling reaction (Scheme 1). To further extend the absorption wavelength of the targeted phthalocyanine, 4-butylmorpholine units were substituted directly from the peripheral positions of the phthalocyanine skeleton instead of any binding heteroatoms such as oxygen, sulfur or nitrogen. The Q band of the new ZnPc 3 shifted red at 22 nm compared to unsubstituted zinc (II) phthalocyanine in DMSO. I I N
NC
N
I
DMAE, 135oC
N Zn
N
N
ZnCl2, 4 hour N
NC
N
1
N
2
I
I O
N O
O N
N
N
Pd(PPh 3)4/Cs2CO3,
2
1,4-dioxane/water (4:1),
N
101oC, 6 hour O
N Zn
N
N
B N
N
O N
3 O
N
O
N
Scheme 1. Synthesis of peripheral tetra-iodo substituted zinc(II) phthalocyanine 2 and tetra-4-butyl morpholine substituted zinc(II) phthalocyanine 3.
2. Experimental The used materials, equipment, photophysical formulas and parameters were provided as supplementary information. The peripheral tetra-iodo substituted zinc(II) phthalocyanine (ZnI4Pc) 2 was synthesized and purified according to the literature [22]. 2.1.Synthesis of peripheral tetra-4-butylmorpholine substituted zinc(II) phthalocyanine (3)
75 mg (6.934.10-2 mmol) of the ZnI4Pc 2 and 142.88 mg (5.599.10-1 mmol) of 3-(4morpholinyl)propyl-1-boronic acid pinacol ester were added to 50 mL schlenk tube. The mixture was dissolved in 12 mL of 1,4-dioxane and 3 mL of water mixture and the mixture was stirred. To the mixture in the argon gas atmosphere was added 2.36 mg (6.8 mmol) of Pd(PPh3)4 and 1.142 mg (3.5 mmol) of Cs2CO3. The reaction mixture was stirred at 101 °C in reflux for 6 hour under an argon gas atmosphere. This reaction mixture was stirred at reflux temperature until complete conversion of the starting material to the product. After cooling to room temperature, this mixture was extracted with chloroform /water. The chloroform phase was dried by anhydrous Mg2SO4 and then filtered off. The bluish-green product was purified by column chromatography with silica gel as the stationary phase, eluting with a solvent system of chloroform / methanol (10: 1) as mobile phase. Yield: 84.55 mg (58%). M.p. >300 o
C. IR (ATR) λmax/cm-1: 1035 (C‒H str.), 1189(C‒N str.), 1324 (C‒O str.), 1484 (C‒H bend.),
1609(C=C str.), 1664(C=N str.), 2952 (>CH2 str.), 3038(=C‒H str.). 1H NMR [500 MHz, DMSO-d6, δ (ppm)]: 7.90-6.53 (m, Ar-H, 12H), 3.30 (DMSO-d6), 2.46-1.29 (m, N-CH2, 24H), 2.30-1.26 (m, O-CH2, 16H), 1.26-0.80 (m, N-(CH2)3, 16H).
13
C NMR [500 MHz,
DMSO-d6, δ (ppm)]: 179, 172, 166, 159, 151,142, 139, 132, 128, 124, 120,109,105,101, 66, 62, 58, 55. UV–vis (DMSO, 1x10-5 M): λmax(nm), (log ε): 352 (4.07), 644 (3.71), 684(4.00). Calc. for C60H68N12O4Zn: C, 66.32; H, 6.31; N, 15.47%; Found C, 66.45; H, 6.10, N 15.75%. MALDI-TOF MS m/z: calc. 1086.66; found 1087.950 [M]+.
3. Results and Discussions 3.1. Synthesis and characterization The synthesis and purification of the ZnI4Pc 2 were carried out according to the literature [22]. The results obtained for its characterization are consistent with the literature [22]. The ZnPc 3 which the 4-butylmorpholine units were directly conjugated to Pc skeleton from
peripheral positions was synthesized by means of Suzuki-Miyaura cross-coupling reaction between the ZnI4Pc 2 and 3-(4-morpholinyl)propyl-1-boronic acid pinacol ester (Scheme 1). After purification of ZnPc 3, it was characterized by general spectroscopic methods such as FT-IR, 1H NMR,
13
C NMR, MALDI-TOF mass, UV-vis, and elemental analysis, and the
results obtained supported the proposed structure. In the FT-IR spectrum, the ZnPc 3 demonstrated vibrational peak at 3038 cm-1 for aromatic C-H stretching. Aliphatic CH stretching vibrations were observed at 2952 cm-1 for the ZnPc 3. Furthermore, its C = N stretching vibration in the IR spectrum was observed at 1664 cm-1. The 1H NMR and
13
C NMR spectra of the ZnPc 3 was recorded in deuterated DMSO
(DMSO-d6) . The 1H-NMR and
13
C-NMR spectra of the new phthalocyanine also
confirmed the target structure of this phthalocyanine. The resonances of aromatic CH protons for the 3 were observed in the range 7.90-6.53 ppm (Fig.1 in ESI). The characteristic signals of -N-CH2, -O-CH2 and -N-(CH2)3 protons for the ZnPc 3 were observed in the range of 2.46-1.29, 2.30-1.26 and 1.26-0.80 ppm, respectively (Fig.1 in ESI). For the 1H-NMR spectrum of ZnPc 3, all aromatic and aliphatic protons were observed at their expected regions and integration of the peaks were found to be consistent with the expected numbers of the protons (Fig.1 in ESI). 13C NMR spectrum of the ZnPc 3 showed 14 aromatic carbon atoms signals and 8 aliphatic carbon atoms signals. The
13
C-
NMR spectrum of the ZnPc 3 confirmed that all aliphatic and aromatic carbon atoms appeared at their expected regions. The MALDI-TOF mass spectrum of the ZnPc 3 verified the proposed structure (Fig.2). 2,5-Dihydroxybenzoicacid (DHB) was used as a MALDI matrix. The molecular ion peak as a [M+H]+ for the ZnPc 3 was readily defined at m/z: 1087.950 (Fig.2). The elemental analysis of ZnPc 3 also confirmed the proposed structure.
Fig. 2. MALDI-TOF mass spectrum of the ZnPc 3 Solvents such as dichloromethane (DCM), dimethylformamide (DMF), tetrahydrofuran (THF), dimethylsulfoxide (DMSO) are known as polar aprotic solvents, while solvents such as ethanol (EtOH) and water are known as polar protic solvents. On the other hand, toluene is known as a non-polar solvent. The ZnPc 3 dissolves quite well in each of the aforementioned types of solvents, whereas in hexane, a non-polar solvent, it dissolves very little (Fig.3).
Fig. 3. Electronic absorption spectra of the ZnPc 3 in different solvents at 1x10-5 M.
The electronic spectrum of the ZnPc 3 demonstrated characteristic absorption with Q band at 684 nm up to 1x10-5 mol dm-3 in DMSO as typical of metallo phthalocyanine (Fig.4). The B-band of the ZnPc 3 was observed at λmax =352 nm (Fig.3). The substitution of the 4butylmorpholine units to Pc skeleton induced 22 nm more red-shifted than Q band absorption of unsubstituted zinc(II) phthalocyanine in DMSO [23]. This may be due to direct binding from 4-butylmorpholine units as the substituent type and / or from the binding types of the substituents which bind to the phthalocyanine ring [24]. The aggregation behavior of the ZnPc was examined in DCM, DMF, DMSO, EtOH, hexane, THF, toluene, water (Fig.1). The ZnPc 3 formed highly aggregated species in EtOH and water. Its resolution in hexane was quite low. The aggregation behavior of the ZnPc 3 was also explored at different concentrations in DMSO (Fig.4). In DMSO solution, the BeerLambert law was obeyed for the ZnPc 3 at concentrations ranging from 1.20 x10-5 to 2 x10-6 M. As the concentration was increased, the intensity of the absorption of the Q band also increased and no new bands (normally blue shifted) due to aggregated species appeared, evidencing that the ZnPc 3 was aggregated in DMSO at these concentrations.
Fig.4. Electronic absorption spectra of the ZnPc 3 in DMSO at different concentrations (inset: plot of absorbance vs. concentration).
3.2. Fluorescence spectra Fig. 5 shows fluorescence emission, absorption and excitation spectra of the ZnPc in DMSO. Fluorescence emission and excitation maximum peaks of the ZnPc 3 were observed at 698 nm and 685 nm in DMSO, respectively. The observed Stokes shift of the ZnPc 3 in DMSO was 14 nm and this value was longer than unsubstituted zinc(II) Pc [23]. In this case, again, as mentioned above, it can be due to the substituent type and / or direct substitution of the substituent with phthalocyanine [24]. In DMSO, the shape of the excitation spectrum of the ZnPc 3 was observed to be slightly different from that of its absorption spectrum. This situation is due to the following reasons. The intensity of peaks seen in the excitation spectrum is directly proportional to the number of photons absorbed. On the other hand; in absorption spectroscopy, one usually measures the absorbance, which is log of incident light intensity over transmitted light intensity. For this reason, although the peaks in the excitation spectrum need to appear at the same wavelengths, they will not have the same relative intensities as the peaks in the absorption spectrum. However, in a highly diluted sample, the relative intensities in the two spectra can approach the same value.
Fig. 5. Absorption, excitation and emission spectra of the ZnPc 3 in DMSO. Excitation wavelength = 642 nm.
3.4. Fluorescence quantum yields and lifetimes The fluorescence quantum yield (ΦF) value of the ZnPc 3 was typical for MPcs and 0.15 in DMSO. This value was lower compared to unsubstituted zinc(II) phthalocyanine in DMSO [23] due to the higher quenching of fluorescence by the substituents. In DMSO, the fluorescence lifetime (τF) of the ZnPc 3 was determined using a time-correlated single photon counting (TCSPC) (Fig. 6). The τF value of ZnPc 3 was characteristic for MPcs and was 2.78 ns in DMSO.
The fluorescence decay of the ZnPc 3 ended up the
monoexponential curve with lifetime 2.78 ns. This value was observed within the range expected for MPc [25] and was shorter than unsubstituted zinc(II) Pc in DMSO [26]. The fluorescence rate constant (kF) is directly proportional to the ΦF of the Pc. The kF value of the ZnPc 3 was 5.40 x107 s-1 in DMSO and was higher than unsubstituted zinc(II) Pc [27]. This may be related to the substitution of 4-butylmorpholine units directly from peripheral positions on the skeleton of phthalocyanine. The natural radiation life (τ0) value of the ZnPc 3 in DMSO solvent was determined to be 18.53 ns. This value was shorter than unsubstituted zinc(II) Pc in DMSO [27].
Fig. 6. Time correlated single photon counting (TCSPC) fluorescence decay curve with mono-exponential fitting of the ZnPcs 3 in DMSO. Excitation wavelength: 642 nm Bottom: fitting residues. 3.5. DTG/TGA and DSC measurements Thermogravimetric analysis (TGA) is one of the characterization techniques that quantitatively give the weight changes caused by increasing temperature in the mass of material. It is possible to observe changes in material' weight during dehydration or degradation of a material depending on time or temperature. The weight change of the material occurs as a result of the material's physical or chemical bonds breaking at high temperatures. Two-step weight reduction was observed in the TGA of the ZnPc 3 (Fig.7 in ESI). It was observed that the ZnPc 3 thermally began to decompose after a temperature range of 120-130 oC and that the ZnPc 3 degradation continued up to 320 °C. A 45% mass loss of the ZnPc 3 was determined in the first decay interval, which is considered to be the degradation of the phthalocyanine ring. In the second decomposition range, a 10% mass loss of the ZnPc 3 was determined between 450-700 oC as a result of oxygen combustion. The ZnPc 3 was completely degraded after 700 °C. The ZnPc 3 had high thermal stability. Differential scanning calorimetry (DSC) thermal analysis measures the amount of energy that is absorbed or released when heated or cooled by a sample, and provides quantitative and qualitative data on the endothermic (heat absorption) and exothermic (heat generation) processes. The DSC spectrum of the ZnPc 3 (2.42 mg) obtained with a heating and cooling rate of 5 oC / min is quite wide and diffuse (Fig.8 in ESI). This can be caused by 4butylmorpholine units which are substituted directly to the peripheral positions of the phthalocyanine ring [28]. The glass transition value (Tg) of the ZnPc 3 was 47.48 oC, which is acceptable for a molecular weight of 1086.66 g / mol. This decrease in the Tg value of the
ZnPc 3 was attributed to the plasticizing effect of the ZnPc 3 substituted with bulky groups [29].
3. Conclusions The new zinc(II) Pc 3 directly conjugated with four 4-butylmorpholine units was synthesized via C-C bond formation using the palladium-catalyzed Suzuki-Miyaura coupling reaction. The new zinc(II) Pc 3 was characterized by elemental analysis, FT-IR, 1H NMR,
13
C NMR,
UV-vis, fluorescence, TGA, DSC and MALDI-TOF mass spectroscopic methods. The new zinc(II) Pc 3 showed good solubility in non-polar solvent, polar aprotic and protic solvents. However, the new ZnPc 3 showed little solubility in hexane, one of the non-polar solvents. It was found the aggregated state in polar protic solvent solutions (ethanol, water). The directly conjugated with 4-butylmorpholine substituent shifted the absorption band to red region. The shape of excitation spectrum was different from the absorption spectrum for the ZnPc 3 in DMSO. This is due to a decrease in the intensity of the excitation caused by the concentration difference. The new ZnPc 3 showed typical thermal stabilities under air atmosphere. In order to determine the photophysical properties of the new ZnPc 3 in DMSO solvent, its fluorescence quantum yield, fluorescence lifetime, fluorescence rate constant and natural radiative lifetime values were determined.. According to the spectral data and results obtained, it was reported that the presence of a substituent directly conjugated to the phthalocyanine ring from peripheral positions greatly influenced the fluorescence properties.
Acknowledgements This study was supported by Çanakkale Onsekiz Mart University Scientific Research Projects Coordination Unit. Project number: FYL-2018-2538. References
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1.244 1.162 1.149 1.057
2.486 2.294 2.074
3.325
7.648
38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6
16.08
16.06
24.09
12.19
4 2 0 8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0 f1 (ppm)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Fig. 1. 1H NMR spectrum of the ZnPc 3 in Dimethyl sulfoxide-d6
Fig. 2. MALDI-TOF mass spectrum of the ZnPc 3
0.0
Fig. 3. Electronic absorption spectra of the ZnPc 3 in different solvents at 1x10-5 M.
Fig.4. Electronic absorption spectra of the ZnPc 3 in DMSO at different concentrations (inset: plot of absorbance vs. concentration).
Fig. 5. Absorption, excitation and emission spectra of the ZnPc 3 in DMSO. Excitation wavelength = 642 nm.
Fig. 6. Time correlated single photon counting (TCSPC) fluorescence decay curve with mono-exponential fitting of the ZnPcs 3 in DMSO. Excitation wavelength: 642 nm Bottom: fitting residues.
Fig. 7. TGA thermogram of the ZnPc 3
Fig. 8. DSC thermogram of the ZnPc 3
Highlights (for review) • The new zinc(II) phthalocyanine substituted directly with 4-butylmorpholine was synthesized and characterized by widely known spectroscopic methods. • Thermal properties of new zinc(II) phthalocyanine were determined. • Photophysical properties of the new zinc(II) phthalocyanine were reported in dimethylsulfoxide. • The new zinc(II) phthalocyanine has good solubility in non-polar solvent, polar aprotic and protic solvents. • The new zinc(II) phthalocyanine has the ability to absorb at long wavelengths.