Spectroscopic and TDDFT studies on the charge-transfer properties of metallated Octa(carbazolyl)phthalocyanines

Dyes and Pigments 170 (2019) 107593

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Spectroscopic and TDDFT studies on the charge-transfer properties of metallated Octa(carbazolyl)phthalocyanines

T

Shereen A. Majeeda, Basma Ghazala, Dustin E. Nevonenb, Victor N. Nemykinb,∗∗, Saad Makhseeda,∗ a b

Department of Chemistry, Kuwait University, P. O. Box 5969, Safat, 13060, Kuwait Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada

A B S T R A C T

Four novel phthalocyanine complexes containing carbazole moieties were synthesized and characterized by 1H & 13C NMR, IR, and UV–visible spectroscopies, magnetic circular dichroism (MCD), elemental analysis, matrix-assisted laser desorption ionization mass spectrometry (MALDI), and X-ray crystallography. In all new compounds, characteristic interligand charge transfer transitions were observed in the 400–600 nm range and are indicative of interligand charge transfer transitions. The electrochemical and spectroelectrochemical methods used to probe the redox properties of 2–5 suggested phthalocyanine-centered first oxidation and reduction processes. Photophysical measurements of the prepared complexes in different solvents exhibited interesting properties due to the charge transfer effect and consequently prolonged excited state lifetime (5.00 ns) with high singlet oxygen quantum yield (ФΔ = 0.825) were acquired. Due to their remarkable solvatochromism phenomena and enhanced photo-related properties, the presented compounds have high potential in chemo-sensors and optical limiting material applications.

1. Introduction Phthalocyanine (Pc) compounds possess excellent photosensitizing ability due to their delocalized π-systems which can easily be tuned to the desirable 650–750 nm optical spectrum range making them good candidates for many applications such as photodynamic therapy (PDT) [1–3] of cancer, organic light emitting diodes (OLED) [4,5], and solar cells [6,7]. The nature of the central metal atom effects photophysical and spectroscopic properties of the Pc. Complexation of phthalocyanines with transition metals affords dyes with short triplet lifetimes; however, closed shell diamagnetic ions, such as Ga3+ and In3+ give phthalocyanine complexes both high triplet yields and long lifetimes due to their heavy atom effect [8,9]. In addition, the small-sized metals with high charge density like Mg2+, are used for phthalocyanine metallation due to their strong electrostatic interactions and in turn, a variation in the charge density of the ligands attached to them [9]. Singlet oxygen (1O2) is a highly reactive form of reactive oxygen species (ROS) which interacts with most biomolecules such as lipids, proteins, and DNA/RNA, with a preference for electron-rich regions which impart a form of selectivity to its interaction. Phthalocyanines are known to have long enough triplet lifetimes which allow them to generate singlet oxygen, making Pcs good candidates to be used in green chemistry as photocatalysts [10] where they are used to photodegrade pollutants in water such as pesticides, petroleum

∗

hydrocarbons, phenols, plasticizers, chlorinated biphenyls, or detergents [11]. Phthalocyanines are also used to develop antibacterial, antiviral biomolecular degradation, and cancer treatment in photodynamic therapy (PDT) [3]. The aggregation behavior exhibited by the large and planar Pc macrocycles results in a drastic change of their optical properties, thus limiting their use in many applications [12,13]. Organic solvents are known to reduce aggregation whereas an aqueous medium results in a highly aggregated, biphasic solution [14]. Aromatic solvents such as benzene or toluene are known to give narrow Q-bands in the absorption spectra of phthalocyanine complexes whereas broadening is observed in non-aromatic solvents [9]. Carbazole derivatives are an interesting class of aromatic heterocyclic compounds because of their excellent photophysical and electrochemical properties. They have been widely used in medicine as active components in antitumor, antimicrobial, antihistaminic, antioxidative, anti-inflammatory, and psychotropic drugs [15,16]. There are only few reports on the synthesis of carbazole-containing phthalocyanine complexes by direct [17,18] or indirect [19,20] annulation of carbazole entities onto the Pc core. To the best of our knowledge, this is the first work to show the effect of different metal centers of octa (carbazolyl) phthalocyanine complexes. In this study, we report the effects of different metals and solvents on their photophysical and photochemical properties.

Corresponding author. Corresponding author. E-mail addresses: [email protected] (V.N. Nemykin), [email protected] (S. Makhseed).

∗∗

https://doi.org/10.1016/j.dyepig.2019.107593 Received 8 April 2019; Received in revised form 19 May 2019; Accepted 28 May 2019 Available online 31 May 2019 0143-7208/ Crown Copyright © 2019 Published by Elsevier Ltd. All rights reserved.

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Scheme 1. Synthetic route to Pc compounds 2–5(i) CsF, DMF, 75 °C, 24 h; (ii) Li, pentanol, 115 °C, 24 h; (iii) Mg, I2, BuOH; 145 °C, 3 h; (iv) MCl3, quinoline, 180 °C, 24 h, inert atmosphere.

intermolecular π-π interactions among neighboring Pcs. The presence of highly coordinating pyridine solvent molecules favored this tendency by coordinating to the zinc atom from both axial positions. In the present work, the single crystal X-ray diffraction technique was employed to generate structural features of carbazole substituted magnesium-phthalocyanine (3) and its packing characteristics. From the crystal data it is observed that the Pc macrocycle of 3 is planar in geometry and the magnesium ion fits exactly within the cavity due to its small size (Fig. 1). This planar geometry enables efficient intermolecular carbazole-carbazole π-interactions in the case of pyridine coordinated ZnPc-carbazoles. It is also observed that two methanol molecules are coordinated from both axial positions on the magnesium atom thereby making it a hexa-coordinated compound. As in the case of its zinc analogues, the plane of peripheral carbazole moieties in 3 are about 60° twisted with respect to the Pc plane. Due to this twisted orientation of the carbazole moieties, the face-to-face aggregation of the moieties on 3 are efficiently blocked in this crystal and it is observed that the Pc-Pc core distance is greater than 8 Å which is too far away to cause any appreciable π-interactions which cause Jtype aggregation. As pointed out earlier, four out of eight peripheral carbazole groups in this phthalocyanine are capable of forming intermolecular π-π interactions with suitably oriented carbazoles of adjacent Pcs. Fig. 2 shows such lateral orientations of neighboring carbazole moieties in adjacent Pcs, which are less than 4 Å in range and are well sufficient for intermolecular π-π interactions. The same features of carbazole-carbazole intermolecular π-interactions were observed in the case of planar 2 having pyridine coordination which is more efficient when compared to the dome-shaped analogue. The intermolecular π-π bonding among carbazole units provides sufficient stability to the bulky 3 moieties in their crystal network. As expected, the possible H-bonding and nonbonding van der Waal's interactions which involve adjacent 3 molecules as well as other solvent molecules present in the system are also providing additional stability to these crystals. More discussion about the crystal data are provided in the supporting information. UV–vis and MCD spectroscopy. The UV–vis and MCD spectra of 2–5 in DCM are presented in Fig. 3. In the cases of 3–5, the classical B- and Q-bands dominate their UV–vis spectra. Due to the anticipated twofold effective symmetry of metal-free compound 2, its Qx- and Qy-bands should have different energies and this behavior was experimentally observed using chloroform (Fig. S2); however, in the case of DCM solution, observation of strong aggregation was confirmed by the UV–vis and MCD spectra of Fig. 3. The solubility of 2 was notably worse than that of the metallated octacarbazoles 3–5 in DCM. The Q-band of 3 (701 nm), 4 (732 nm), and 5 (733 nm) are slightly shifted to lower energy compared to unsubstituted ZnPc (678 nm) [22,23]. In addition, the effect of the group III, p-block metal-

2. Results and discussion 2.1. Synthesis The synthetic route for the target Pc macrocycles (2–5) bearing eight sterically hindered peripherally bulky carbazole substituents is shown in Scheme 1. The phthalonitrile precursor 4,5-di(9H-carbazol-9yl)phthalonitrile was prepared according to the reported procedure [20]. Metal-free compound 2 was synthesized using lithium as an initiator in pentanol (i.e. Linstead method) [21]. Magnesium butoxideinduced cyclotetramerization gave complexes 3. Complexes 4 and 5 were synthesized by base-promoted cyclization reaction of the corresponding precursors 1 in quinoline in the presence of GaCl3 and InCl3, respectively, with a catalytic amount of 1,8-diazabicyclo-[5.4.0]un dec7-ene (DBU). Complexes 2 and 3 are partially soluble in common organic solvents (e.g. CHCl3, THF, benzene, acetone, and DCM) but have a high solubility in DMSO and DMF. The presence of large-sized ions in phthalocyanines 4 and 5 facilitates their improved solubility in most organic solvents since both of the metal atoms will be located out of the Pc plane. Structural identification of the new phthalocyanines 2–5 was achieved by 1H and 13C NMR, IR, and UV–vis spectroscopies as well as MALDI spectrometry. The purity of each compound was verified by elemental analysis. Thermal gravimetric analysis confirms high thermal stability of all the Pcs as their decomposition occurs above 300 °C. The compounds are stable in the solid state and in solution for a prolonged time. The electronic absorption spectra of all compounds showed monomeric behavior evidenced by a single (narrow) Q-band, typical of metallated phthalocyanine compounds (Fig. 4 and S1), except compound 2 (discussed below). Moreover, the 1H NMR spectrum of the synthesized complexes in DMSO gave sharp and well-resolved peaks at room temperature (Figures S4, S6, S8 and S10) showing the effect of bulky carbazole in decreasing the undesired common aggregation of the phthalocyanine complexes. X-Ray Single-Crystal Structures. We have earlier reported crystal structures of carbazole- substituted zinc phthalocyanines in two different morphologies [20]. When these crystals were grown from acetone solution, the ZnPc-octacarbazole molecules have a domed shape with the Zn atom projected a little outward from the Pc-cavity and a water molecule is coordinated at the axial position. When these crystals are simultaneously grown from pyridine, the zinc-phthalocyanine is planar in shape with two pyridine molecules coordinated to the central zinc atom. Such a planar morphology in octacarbazole-substituted ZnPc is quite uncommon and we presumed that this tendency to adapt planar geometry is to effectively engage carbazole-based

2

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Fig. 1. Crystal structure of 3 obtained from diffraction data ((A) top view and (B) side view) showing planar Pc with Mg ion positioned exactly in the middle of the cavity and two methanol ligands coordinated to the magnesium from both top and bottom directions. All other solvent molecules and hydrogen atoms except at the coordinated methanol have been hid for clarity. Color code: red-oxygen; blue-nitrogen; gray-carbon; brown- magnesium, and black-hydrogen. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

assigned as ILCT transitions. MCD spectroscopy on compounds 2–5 was used to support these tentative assignments (Fig. 3). The MCD spectra of metallated compounds 3–5 exhibited Q-band region domination by an intense, Faraday MCD A-term which was centered at 699 (3) or 733 nm (4,5). The A-terms of compounds 3–5 feature two positive MCD signals which line up with the vibronic satellites of the Q-band, and these spectroscopic features are common for closed-shell Pc systems [22–24,26]. The Q-band region of 2–5 is approximately an order of magnitude more intense than the B-band region which agrees well with previously reported [22–24,26] MCD spectra of phthalocyanines. Additionally, in the case of compound 3, the MCD Faraday A-term in the Bband region is clearly defined and supports fourfold effective symmetry of this chromophoric phthalocyanine. The very low intensity of the broad MCD signals in the 400–600 nm region of 3–5 are in agreement with the tentative ILCT transitions assignment and similar cases have been previously described [26,27] in porphyrino- and phthalocyaninoclathrochelate systems. Contrary to the monomeric complexes 3–5 in DCM solution, the metal-free phthalocyanine 2 was highly aggregated as was suggested by its UV–vis and MCD spectra. In particular, the MCD intensities were about an order of magnitude lower than 3–5 in the Qband region. The negative MCD signal around 732 nm and the positive MCD signal around 705 nm are close to the Qx- and Qy-band position for metal-free compound 2 in chloroform (Fig S2); however, the UV–vis spectrum of 2 in DCM is dominated by a strong absorption at 770 nm, followed by a prominent shoulder in the NIR region which is indicative of J-aggregate formation. The spectral signal at 791 nm, observed in the MCD, can be associated with the J-aggregate of metal-free compound 2. Complexes 2 has a green color in DMF as well as pyridine and a purple color in other studied solvents as well as in the solid state. Complex 3 has a green color in all studied solvents and in the solid state. Complex 4 and 5 have a green color in DMF, DMSO, pyridine, acetone, and THF and a purple color in CHCl3, DCM, benzene, toluene, p-xylene, 1-CN (1-Chloronaphthalene), and in the solid state (Figure S12). This color change can be related to the transparency shift region of Pcs in the 400–600 nm region which is responsible for the common green color of Pcs [23]. As expected, solvatochromic properties in the prepared complexes are more prominent in the interligand charge transfer (ILCT) band region (Fig. 3 and S1). Although the broad nature and presence of several ILCT bands in the complexes precludes accurate determination of the solvatochromic effect, ILCT solvent dependence spans over 2,000 cm−1, confirming its charge-transfer nature. The intensity of this band was also found to decrease as the dipole moment of the solvent increased (i.e. negative solvatochromism) as it was reported previously for our carbazole containing zinc phthalocyanine complexes

Fig. 2. Pattern of 3 molecules in their crystal network showing the possibilities of intermolecular π-π interactions through carbazole moieties.

centers in 4 (Ga) and 5 (In) was clearly noticeable via red-shifting of the Q-band when compared to their analogous compound 3. The Q-bands of 3–5 each featured two vibronic satellites at higher energy in their UV–vis spectra. The B-band region for 2–5 features a dominant series of overlapping transitions which are centered at ∼350 nm and is quite common for phthalocyanine systems [24]. The UV–vis spectra of featured compounds 2–5 al l exhibited a low-intensity, broad band between 400 and 600 nm which is absent in the case of unsubstituted or alkyl group-substituted ZnPcs [25]. The carbazole substituents of 2–5 are electron-donating in nature; therefore, the energies of the carbazole-centered molecular orbitals (MOs) are expected to be close in energy to the Pc-centered highest occupied molecular orbital (HOMO) πorbital. Due to the carbazole substituents, low-energy carbazole-tophthalocyanine interligand charge-transfer (ILCT) bands are expected at higher than Q-band energies. Therefore, the broad bands observed in the UV–vis spectra of 2–5 in the 400–600 nm region are tentatively 3

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Fig. 3. UV–Vis and MCD spectra of phthalocyanines 2–5 in DCM.

This broadening, which appears in the UV–vis spectra of 2 in some basic solvents like DMSO and acetone (Figure S1 (A1)), suggests the presence of more than one species in solution. Our previous study on carbazole containing zinc phthalocyanine complexes [20] demonstrated facile protonation of the meso-nitrogen compounds. The presence of two hydrogen atoms bound to the pyrrole-nitrogen (H2(p)) in the metal-free phthalocyanine 2 make the complex act as an inner salt and leads to the protonation of the meso-nitrogen (H(m)) and hence, having more than one possible species in the solution as illustrated in Scheme 2. Addition of a few drops of trifluoroacetic acid (TFA) to basic solvents or dissolving the complex in acidic solvents like CHCl3 results in the protonation of the meso-nitrogen and release of the hydrogen on the core and consequently, splitting of the Q-band. A small peak appears in these acidic media at around 770 nm, confirming the presence of the protonated form of the metal-free complex [H2(p)Pc.H+ (m)]. This also explains the small absorption of complex 3 in CHCl3 (Figure S2 (A2)) where the absorption band around 750 nm corresponds to the presence of MgPc.H+. Using strong, basic coordinating solvents (B) like DMF to dissolve complex 2, allows solvent molecules to coordinate to the two hydrogens of the core, resulting in one peak in the UV spectrum (Figure S3 (c)). In this solution, there are no recorded peaks corresponding to protonation of the meso-nitrogen of compound 2 indicating the existence of only the coordinated form of 2 [H2(B)Pc]. The equilibrium between species is confirmed by adding TFA to acidic solvents and tetrabutylammonium hydroxide (TBAH) to basic solvents, as demonstrated in (Figure S3). The color change of this complex is not affected by the polarity of the solvents like the cases of compounds 4 and 5. For example, acetone (μ = 2.85) solution of 2 gives the same purple color of the benzene (μ = 0) solution of the same complex (Figure S12). The green color was only noticed in coordinating solvents such as DMF and pyridine with an unsplit Q-band. Fluorescence spectra. Fluorescence emission and excitation spectra of studied phthalocyanine complexes (2–5) were carried out in DMF, pyridine and benzene (Table 1 and Figure S18). Small Stokes shifts were recorded and are typical for closed-shell Pcs. Fig. 6A shows the absorption, fluorescence emission and excitation spectra of the phthalocyanine complexes in benzene. The profiles of the excitation spectra

[20]. Solvatochromism can be correlated with the different solvent parameters such as chemical structure, polarity, coordinating power and refractive index [28]. The Q-band shift to longer wavelength could be due to either the destabilization of the highest occupied molecular orbital (HOMO) and/or the stabilization of the lowest unoccupied molecular orbital (LUMO) [29]. Table S1 shows that as the refractive index of the solvent increased, the red shift of the Q-band increased as was published previously [20,30]. The electronic absorption spectra of 3–6 in the examined solvents were analyzed using the method described originally by Bayliss [31]. The plot of F = (n2-1)/(2n2+1), (where n is the refractive index of the solvent), versus λmax (i.e. Q-band) is shown in Fig. 5. Compound ZnPc (octacarbazolyl zinc phthalocyanine) [20] is added for the comparison. The solvent-based relationship for the solvents evaluated can be expressed by Eqn. (1) – (4):

υ = −4995.4F + 15262

(1)

2

with R = 0.9125 for 3

υ = −5430.8F + 15369

(2)

2

with R = 0.9102 for ZnPc

υ = −8792F + 15476

(3)

2

with R = 0.9076 for 4

υ = −9603.4F + 15676

(4)

2

with R = 0.9165 for 5 The pair of complexes (ZnPc and 3) with small-sized zinc and magnesium centers and (4 and 5) with large-sized gallium and indium centers, show the same color and similar variation upon changing the solvents (Fig. 5 and S12). The UV–vis spectra of compound 2 (Fig. 4 (B1) and S1 (B1)), do not show a significant shift in ILCT bands. The Qband of this complex is broad in some solvents like DMSO (Figure S1 (B1)). Primarily thinking, such phenomena can be attributed to the intrinsic aggregation of phthalocyanine molecules; however, sharp and well resolved peaks of the 1H NMR spectrum of this complex in DMSO at room temperature (Figure S4) ensures the absence of aggregation. 4

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Fig. 4. Normalized UV–vis spectra of 2-HH (A1), 3-Mg (A2), 4-Ga (A3) and 5-In (A4) in the Q-band region, and ILCT-band region 2 (B1), 3 (B2), 4 (B3) and 5 (B4) in DMF, benzene, acetone and 1-CN.

2.2. Photophysical studies, fluorescence quantum yield, and fluorescence lifetime

were similar to the absorption spectra for all complexes and these spectra were mirror images of the fluorescence emission spectra, except complex 2, suggesting that the nuclear configurations of the ground and excited states are similar and not affected by excitation; however, the emission spectra of the complex 2 (Fig. 6A (A)) are not split, since metal free phthalocyanines are known to fluoresce with only one main peak, assigned as the 0–0 transition of the fluorescence in organic media [32].

The fluorescence quantum yields (ΦF) of Pc complexes (2–5) were studied in DMF, pyridine and benzene (Table 1, Fig. 6B and S18). Fluoresence is influenced by factors such as solvent polarity, viscosity, refractive index, temperature and fluorophore molecular stucture [33]. The magnesium phthalocyanine complex is more fluorescent than other 5

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existence of free excited molecules [36]. Corresponding fluorescence rate constants (kf = ΦF / τF ) and nonradiative rate constants (κnr = (1 − ΦF )/ τF ) were calculated from these lifetime data and listed in Table 1. Singlet oxygen quantum yields ΦΔ. A good photosensitizer equates to an efficient singlet oxygen generator. Singlet oxygen is produced by the energy transfer between the triplet state of the photosensitizer and the ground state of molecular oxygen. The generation of singlet oxygen is affected by many factors such as triplet excited state energy, ability of substituents and solvents to quench the generated singlet oxygen, the triplet excited state lifetime and the efficiency of the energy transfer between the triplet excited state and the ground state of oxygen [37]. The singlet oxygen quantum yield can be measured by optical, chemical and calorimetric methods. Optical determination of 1O2 can be performed by two main methods: (1) direct monitoring of 1O2 phosphorescence at 1270–1280 nm [38] or, (2) indirect measurements based on the use of a chemical quencher [31]. In this study, the direct detection of the luminescence peak of 1O2 at 1276 nm of the phthalocyanine complexes (2–5) in DMF, pyridine and benzene were monitored, and the corresponding singlet oxygen quantum yields ΦΔ were calculated using unsubstituted ZnPc as a reference (ΦΔ = 0.56 in DMF) [39] (Table 1, Fig. 6C and S20). The data shows that the order of ΦΔ values for the studied complexes among the studied solvents are as follows: 3 < 2 ZnPc < 4 < 5. The experimentally observed singlet oxygen generation yields follow the general trend of increasing spinorbit coupling in complexes 4 and 5 which is not surprising since increased spin-orbit coupling will facilitate singlet oxygen production in phthalocyanines through intersystem crossing. 2.3. Redox properties of phthalocyanines 2-5 The electrochemical properties of phthalocyanines 2, 3, 4, and 5 were analyzed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques with a DCM/0.1 M tetrabutylammonium perchlorate (TBAP) system (Fig. 7). Observed within the electrochemical window for all compounds were one single-electron oxidation and one single-electron reduction processes. Additionally, one irreversible multielectron oxidation process was observed for 3, 4, and 5 at higher potential. Both of the first reduction and oxidation processes are attributed to the oxidation and reduction of the phthalocyanine core, while the irreversible multielectron oxidation was assigned to a simultaneous oxidation of the carbazole moities [20,40,41]. For the metal-free compound 2, no multielectron oxidation process was observed at higher potential. In order to explore spectroscopic signatures of the singly oxidized phthalocyanines 2–5, spectroelectrochemical oxidations were conducted using a DCM/0.3 M TBAP system and are shown in Fig. 8. Compounds 3, 4, and 5 undergo similar transformations of their UV–vis spectra under the conditions of spectroelectrochemical oxidation. Specifically, the intensity of the Q-band of 3, 4, and 5 decreases while new bands of lower intensity at 758, 860, and 1045 nm (3), 909 and 1290 nm (4), or 895 and ∼1200 nm (5) appear in their UV–vis–NIR

Fig. 5. Variation of 3–5 and ZnPc: Q-band with F (A) and ILCT-band with solvent's dipole moment (μ) (B).

studied phthalocyanine compounds due to the diamagnetic, small magnesium atom. The (ΦF) values of complexes 4 and 5 were very low due to the heavy atom effect of gallium and indium in these compounds, respectively. No clear trend was observed for the fluorescence quantum yields values among the different solvents (Figure S20 and Table S). The metallated complexes showed mono-exponential decay (Table 1) which falls within the same range typical for most monomeric metallated phthalocyanines [34,35] however, biexponential decay was observed for complex 3 in DMF and pyridine which suggests the presence of two forms in the solution: the coordinated Pc to the solvent and the deprotonated one as reported previously [9]. It has been shown that exhibition of fluorescence bi-exponential decay in some molecules can be attributable to the possibility of a percentage of the sample exhibiting reversible, complex formation of the excited molecule with the solvent molecules, while the other sample percentage contributes to the

Scheme 2. Suggested structures of complex 2 in solution, B represents the basic coordinating solvent or TBAH. 6

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Table 1 Photophysical parameters of complexes (2–5) in different solvents. (λQ): Q-band absorption maximum wavelength, (λex): excitation maximum wavelength, (λem): emission maximum wavelength, (Δλstoks): Stoke's shift, (ΦF): fluorescence quantum yield, (τF): fluorescence lifetime, (κf): fluorescence rate constant, (κnr): nonradiative rate constant, (ΦΔ): singlet oxygen quantum yield, ZnPc is the reported octacarbazole-substituted [20]. Comp.

Solvent

λQ

λex

λem

Δλstoks

ΦF

τF (ns)

κf (s−1) (x107)

κnr (s−1) (x107)

ΦΔ

(2) H2

DMF Pyridine Benzene DMF Pyridine Benzene DMF Pyridine Benzene DMF Pyridine Benzene DMF Pyridine Benzene

691 707 740 700 705 711 698 704 712 715 719 744 715 721 742

691 692 639 696 705 709 698 710 710 704 718 744 714 720 740

702 722 748 707 716 721 711 721 722 727 739 756 730 734 752

11 15 8 7 11 10 13 17 10 12 20 12 15 13 10

0.256 0.181 0.308 0.375 0.494 0.486 0.189 0.221 0.151 0.008 0.043 0.074 0.004 0.011 0.009

3.23(76.33%), 5.43(23.67%) 2.52(74.98%), 4.82(25.02%) 4.58 5.03 4.73 4.96 2.33 2.35 2.36 – – 2.1 – – –

7.93, 4.71 7.18, 3.76 6.72 7.46 10.44 9.86 8.11 9.40 6.40 – – 3.52 – – –

23.03, 13.70 46.87, 16.99 15.11 12.43 10.70 10.36 34.81 33.15 35.97 – – 44.09 – – –

0.292 0.288 0.458 0.01 0.136 0.034 0.222 0.332 0.482 0.104 0.34 0.706 0.292 0.431 0.825

(3) Mg

ZnPc [20] (4) GaCl

(5) InCl

a

: (κf = ΦF / τF ) , b: (κnr = (1 − ΦF )/ τF )

Fig. 6A. Normalized absorption, fluorescence excitation and emission spectra of 2-HH (A), 3-Mg (B), ZnPc (C), 4-Ga (D) and 5-In (E) in benzene. 7

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macrocycle. Consistent with previously established literature findings on the oxidation of Pc systems, the NIR band present at 860, 909, and 895 nm for [3].+, [4].+, and [5].+, respectively, can be assigned as monomeric species, while the transitions present at 758 and 1045 nm for [3].+, 1290 nm for [4].+, and ∼1200 nm for [5].+ indicate some degree of aggregation of the cation-radical species [20]. Generally, the aggregation properties of phthalocyanines 3 and 4 are sterically hindered by the bulky carbazole groups and are proven by the aggregation experiment discussed above. Nonetheless, the spectroelectrochemical data suggests that aggregation of [3].+ and [4].+ species can be achieved. The reversibility of the macrocyclic phthalocyanine oxidation was proven with the reduction of species [3].+ and [4].+ into the neutral initial Pcs 3 and 4, under spectroelectrochemical conditions (Figure S31). Because of strong aggregation observed for metal-free compound 2, its oxidation under spectroelectrochemical conditions were not conclusive and will not be discussed further.

Fig. 6B. Fluorescence emission spectra of complex 3 in different solvents at concentration of 2 μM.

2.4. DFT and TDDFT calculations. Computational insight into the electronic structures and vertical excitation energies of phthalocyanines 2–5 were gained on the basis of density functional theory (DFT) and time dependence density functional theory (TDDFT) calculations. The polarized continuum model (PCM) approach with chloroform as a solvent was used to correlate between DFT and TDDFT data with experimental UV–vis spectra and redox properties in all calculations. DFT-PCM predicted frontier molecular orbitals are depicted in Fig. 10A–D and S32, in addition to the selected molecular orbital energy diagrams for complexes 2–5 are shown in Fig. 9 and selected molecular orbital (MO) profiles are depicted in Fig. 10A–D and S32 For all tested complexes 2–5, the HOMO has Gouterman's a1u orbital character [46,47] with a large contribution from pyrrolic α- and βpyrrolic carbons in the studied complexes. In agreement with our finding on ZnPc [20], the DFT predicts that the HOMO-1 to higher HOMOs (HOMO-17-HOMO-24) should be centered at carbazole fragments, while HOMO-25 should resemble Gouterman's a2u orbital with large contributions from inner- and meso-nitrogen atoms of the phthalocyanine core. Indeed, the energy difference between Gouterman's a1u and a2u orbitals is typical for phthalocyanines (∼2.3 eV), and all carbazole-centered HOMO-1 to higher HOMOs (HOMO-17-HOMO-24) orbitals are also closely spaced (∼2 eV) in energy (Fig. 9a). The LUMO and LUMO+1 in the studied complexes 2–5 were also resemble the classic Gouterman's eg pair which is dominated by contributions not only from the α- and β-pyrrolic carbon atoms, but also from meso- and inner-nitrogen atoms and the benzene ring in the phthalocyanine core (Fig. 7A–D). Based on these results and from the DFT calculations, the data can be explained in a similar manner of ZnPc [20] as the first oxidation and reduction will be centered at the phthalocyanine core, while a second oxidation should be multi-electron in nature and centered at carbazole fragments. This prediction correlates well with the electrochemical and spectroelectrochemical data on Pcs 2–5. Based on the DFT-predicted electronic structures of 2–5, a large number of ILCT transitions between the Q- and B-bands of the phthalocyanine core are expected. Fig. 11 showed the TDDFT-predicted UV–Vis spectra of compounds 2–5, while the expansion coefficients for the relevant excited states are presented starting on Supporting Information Pg. 67. The experimental UV–Vis spectra for compounds 2–5 along with their electronic structures were in good agreement with their TDDFT results. The first excited state in metal-free compound 2 is non-degenerate and primarily composed of a HOMO → LUMO excitation which is consistent with its twofold effective symmetry and matches with the previously reported examples of metal-free phthalocyanines [48,49]. TDDFT also predicted the first excited state in compounds 3–5 to be doubly degenerate and dominated by single electron HOMO → LUMO, LUMO+1 excitations which is consistent with previous reports [22,50]

Fig. 6C. Luminescence of singlet oxygen of complexes (2–5 and octacarbazole substituted ZnPc) in benzene (OD∼0.15; λex (ZnPc, 2, 3) = 620 nm while λex(4,5) = 650 nm).

Fig. 7. CV (blue) and DPV (red) data for compounds 2, 3, 4, and 5. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

spectra. Additionally, a broad interligand charge transfer (ILCT) band in 3, 4, and 5 is converted into higher-intensity transitions which are centered at 487, 506, and ∼422 nm, respectively. These transitions are typical for the formation of a phthalocyanine-centered cation-radical species [42–45] and confirm the first oxidation being centered on the 8

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Fig. 8. Oxidation of compounds 2, 3, 4, and 5 under spectroelectrochemical conditions in a DCM/0.3 M TBAP system.

of standard ZnPc compounds. Several ILCT transitions were predicted by TDDFT and are primarily compounds of single electron excitations originating at the cabazole-centered HOMO-1 to HOMO-24 and going to the higher-energy carbazole centered and unoccupied Pc (LUMO and LUMO+1) orbitals. Lastly, the TDDFT data indicates significant HOMO-25 → LUMO, LUMO+1 contributions, represented by the Bregion transitions of greatest intensity. In general, the TDDFT calculations indicate and accurately model the phthalocyanine-centered excited states of low energy and the expected ILCT transitions.

3. Conclusions 2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyanine (2), 2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato magnesium(II) (3), 2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato gallium(III) (4), and 2,3,9,10,16,17,23·24-Octakis(9H-carbazol-9-yl) phthalocyaninato indium(III) (5) compounds were synthesized using various methods. The studied compounds 2–5 were characterized with X-ray crystallography, MALDI-TOF spectrometry, magnetic circular dichroism, in addition to NMR and UV–vis spectroscopies. The broad bands present between 400 and 550 nm in the UV–vis and MCD spectra of 2–5 were indicative of interligand chargetransfer transitions. Photophysical and photochemical analysis for the studied complexes were performed, and the results confirms the significant influence of In and Ga as a heavy metal effect in case of 4 and 5, resulting in high singlet oxygen quantum yield (ФΔ = 0.825) specially in aromatic solvent. Electrochemical and spectroelectrochemical approaches were used to probe the redox properties of 2–5 which suggested reversible phthalocyanine-centered oxidation and reduction processes and an irreversible second oxidation process, determined to be carbazole-centered. DFT and TDDFT calculations were employed to correlate with spectroscopic results. The DFT data suggested the

Fig. 9. DFT–PCM predicted orbital energy diagram for target compounds. (a) Frontier orbital energies; (b) selected Gouterman's molecular orbital energies.

9

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fluoride (CsF), anhydrous salts of zinc acetate, indium chloride, gallium chloride and unsubstituted zinc phthalocyanine (ZnPc) were purchased from Sigma-Aldrich. 5,6-Dichlorophthalonitrile was obtained from TCI (Toshima, Japan). TLC was performed using Polygram sil G/UV 254 TLC plates and visualization was carried out by ultraviolet light at 254 nm and 350 nm. Column chromatography was performed using Merck silica gel 60 of mesh size 0.040–0.063 mm. Anhydrous solvents were either supplied from Sigma-Aldrich and used as they were received or dried as described by Perrin [51]. 3.2. Instrumentation. 1

H and 13C NMR spectra were recorded using Bruker DPX 600 at 600 MHz and 150 MHz, respectively, and IR spectra were obtained using JASCO 6300 FTIR. UV–Vis spectra were recorded with a Varian Cary 5 or Shimadzu UV-2600 spectrophotometer. Elemental analyses were carried out using an ElementarVario Micro Cube. High resolution mass analyses (HRMS) were measured on Xevo G2-S QTof (Waters). In addition, clusters of peaks that correspond to the calculated isotope composition of the molecular ion were observed by matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF) via ultrafleXtreme (Bruker). The MALDI-TOF mass data for Pcs are presented as the mass of the most intense peak in the cluster instead of exact mass. Melting points were determined via differential scanning calorimetry (DSC) analyses on Shimadzu DSC-50. Single crystal data collections were made on a Rigaku R-Axis Rapid diffractometer using Mo-Kα radiation. The diffraction data were collected at a temperature of −123 °C (Oxford cryosystems). X-ray structures of 3 were solved using CrystalStructure 4.0″ analysis package from Rigaku. CrystalStructure crystallographic software and refined using SHELXL97 software [52]. The fluorescence spectra were collected on an FLS980 (Edinburgh Instruments) for complexes 2–5 in DMF, pyridine and benzene. The absolute fluorescence quantum yield was determined by an absolute method using an integrating sphere (Edinburgh Instruments FLS-980 fluorimeter) with a 150 W Xenon lamp [53,54] The fluorescence lifetimes were recorded on an Edinburgh Analytical Instruments FLS980 spectrometer, equipped with a supercontinuum ultrafast fiber lasers (Fianium), using the time correlated singlephoton-counting (TCSPC) method. Typically, 10,000 counts were collected at the peak channel, and the decay curves were fit by least-squares deconvolution with original Edinburgh Instrument software; the quality of the parameters were judged by the reduced χ2 values and the randomness of the weighted residuals. Electrochemical data were collected using CH-620 instrument with platinum working and auxiliary electrodes and Ag/AgCl pseudo-reference electrode. Decamethylferrocene was used as an internal standard for all the studied complexes and the reported potentials were corrected for FcH/FcH+ couple. Spectroelectrochemical experiments were conducted in custom-made 1 mm cell with platinum mesh working electrode, platinum auxiliary electrode, and Ag/AgCl pseudoreference electrode. All electrochemical experiments were conducted in a DCM/0.1 M TBAP system, while a DCM/0.3 M TBAP system was used in all spectroelectrochemical experiments. 4. Photophysical parameters Fig. 10. Gouterman's molecular orbitals of 2–5 calculated at the CAM-B3LYP/ LANL2DZ level of theory.

4.1. Fluorescence quantum yields

presence of phthalocyanine-centered HOMO and LUMO orbitals and carbazole-centered HOMO-1 to higher HOMOs (HOMO-17- HOMO-24) orbitals.

Fluorescence quantum yields (ΦF) were determined by the Direct Excitation method which compares the ratio of the number of photons emitted to the number of photons absorbed using the equation:

ΦF = 3.1. Experimental section. Reagents.

EB − EA SA − SB

(5)

Where EA and EB are the integral of emissions of the solvent and the sample. SA and SB are the integral of scattering of the solvent and the

Carbazole, deuterated dimethylsulphoxide (DMSO‑d6), cesium 10

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Fig. 11. Experimental (upper graph) and TDDFT-PCM predicted (lower graph) UV–vis spectra of compounds 2–5.

molecular orbital analysis. The phthalocyanines 2–5 were optimized using the CAM-B3LYP exchange-correlation functional [58] coupled with the LANL2DZ basis set [59] for all atoms. Frequencies were calculated for all the optimized geometry in order to confirm to ensure that the final geometry were energy minima on the potential energy surface. Solvation effects were calculated using the polarized continuum model (PCM) [60] using chloroform as a solvent in all the single point DFT-PCM and TDDFT-DCM calculations. PCM-TD-DFT calculations were conducted for the first 100 exited states for each complex. Molecular orbital contributions were assembled from single point calculations using the program QMForge [61].

sample, respectively. 4.2. 1O2 luminescence measurements Luminescence spectra of all samples from 1240 to 1330 nm with 1 nm step were recorded in DMF, pyridine and benzene perpendicularly to the excitation beam on a commercial FLS980 spectrofluorimeter (Edinburgh Instruments Ltd., UK), which was equipped with a 650 nm laser lamp and a NIR-PMT (Hamamatsu, R5509-72) with a two-stage Te- cooled InGaAs detector (Hamamatsu, G8605-23). Higher diffraction orders were filtered by the built-in long wave-pass filters in the FLS980. Luminescence spectra were recorded with excitation and emission bandwidths of 10 nm, and the dwell time was 3.0 s.

4.5. Syntheses

4.3. 1O2 quantum yields (ΦΔ) determination

2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyanine (2). A mixture of lithium (6.94 g, 8.65 mmol) and phthalonitrile 1 (1 g, 2.18 mmol) in dry n-pentanol was refluxed for 24 h. After cooling to room temperature and diluting with MeOH, the reaction mixture was filtered. The crude product was refluxed in methanol then acetone several times. The resultant precipitate was then purified via column chromatography with silica gel (MeOH then eluted gradually with CHCl3) resulting in a purple solid. Yield: 0.333 g (∼33.37%). Anal. Calcd for C128H74N16: C, 82.12, H, 4.20; N, 11.97%. Found: C, 82.68; H, 4.68; N, 11.90%. IR (KBr): υ, cm−1: 1332 (m, C–N). 1H NMR (600 MHz, DMSO‑d6, 95 °C): δ, ppm: 7.06 (s, 16H, H8), 7.14 (d, 16H, H7), 7.57 (s, 16H, H6), 7.94 (s, 16H, H9), 9.60 (s, 8H, H3). 13C NMR (150 MHz, DMSO‑d6, 25 °C): δ, ppm: 110.08 (C6), 119.60 (C2), 119.86 (C1), 122.59 (C9), 123.67 (C7), 125.34 (C10), 133.74 (C8), 140.42 (C3), 140.61 (C4), 154.06 (C5). UV/Vis (CHCl3 0.5 μM): λmax, nm (log ε) = 733 (Qx) (5.12), 705 (Qy) (4.97), 668 sh (4.40), 635 (4.20), 338 (4.88), 324 (4.74), 293 (4.75). MS (MALDI-TOF, α-cyano-4-hydroxycinnamic acid (HCCA) as matrix): m/z = Calcd: 1857.223, found: 1857.600 [M]+.

The determination of the 1O2 quantum yields (ΦΔ) was based on the direct detection of NIR 1O2 luminescence by optical method based on the comparison of singlet molecular oxygen phosphorescence in the near infrared region at 1276 nm generated by the phthalocyanines complexes 2–5 with that generated by the reference ZnPc (ΦΔ = 0.56 in DMF) [37]. 1O2 quantum yields ΦΔ were calculated according to equation (6), [55].

ϕΔs = ϕΔr

ηs2 Ar Is ηr2 As Ir

(6)

In eqn. (6), ΦΔs and ΦΔr are the quantum yields of the sample and reference, ηs and ηr are refractive indexes of the solvents used for the measurements of the sample and reference. As and Ar are the absorbance of the sample and the reference and Is and Ir are the integrated areas under the emission spectra of the sample and the reference, respectively. 4.4. Computational details

4.5.1. 2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato magnesium(II) (3) Magnesium (0.34 g, 13.99 mmol) was added to dry pentanol and refluxed with a small crystal of iodine for 3 h, then phthalonitrile 1 (1 g,

All computations were preformed using the Gaussian 09 software package [56], and the Gaussview program [57] was used for the 11

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doi.org/10.1016/j.dyepig.2019.107593.

2.18 mmol) was added. The reaction was refluxed for 3 h. After cooling to room temperature and diluting with MeOH, the reaction mixture was filtered. The crude product was refluxed in methanol several times. The resultant precipitate was then purified via column chromatography with silica gel (MeOH then eluted gradually with CHCl3) resulting in a dark green solid. The X-ray crystal was achieved by slow evaporation of CHCl3 into air. Yield: 0.467 g (46.09%). Anal. Calcd for C128H72N16Mg + 3H2O: C, 80.39, H, 4.11; N, 11.72%. Found: C, 80.36; H, 3.87; N, 11.63%. IR (KBR): υ, cm−1: 1333 (m, C–N). 1H NMR (600 MHz, DMSO‑d6, 95 °C): δ, ppm: 6.79 (s, 16H, H8), 6.90 (s, 16H, H7), 7.36 (d, 16H, H6), 7.50 (s, 16H, H9), 10.07 (s, 8H, H3). 13C NMR (150 MHz, DMSO‑d6, 25 °C): δ, ppm: 109.65 (C6), 110.24 (C2), 119.82 (C1), 122.66 (C9), 125.16 (C7), 135.39 (C10), 138.65 (C8), 140.10 (C3), 153.39 (C4), 162.23 (C5). UV/Vis (CHCl3 0.5 μM): λmax, nm (log ε) = 709 (5.09), 675 sh (3.88), 637 (3.94), 663 (4.54), 338 (4.57), 325 (4.49), 293 (4.25). MS (MALDI-TOF, α-cyano-4-hydroxycinnamic acid (HCCA) as matrix): m/z = Calcd: 1857.223, found: 1857.600 [M]+.

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Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes. Nanoscale Res Lett 2012;7(1):650. [6] Ince M, Yum J-H, Kim Y, Mathew S, Grätzel M, Torres T, et al. Molecular engineering of phthalocyanine sensitizers for dye-sensitized solar cells. J Phys Chem C 2014;118(30):17166–70. [7] Yuen AP, Jovanovic SM, Hor AM, Klenkler RA, Devenyi GA, Loutfy RO, et al. Photovoltaic properties of M-phthalocyanine/fullerene organic solar cells. Sol Energy 2012;86(6):1683–8. [8] Durmuş M, Nyokong T. Synthesis, photophysical and photochemical properties of aryloxy tetra-substituted gallium and indium phthalocyanine derivatives. Tetrahedron 2007;63(6):1385–94. [9] Arslanoğlu Y, Idowu M, Nyokong T. Synthesis and photophysical properties of peripherally and non-peripherally mercaptopyridine substituted metal free, Mg(II) and Al(III) phthalocyanines. Spectrochim Acta Mol Biomol Spectrosc 2012;95:407–13. [10] Fernández L, Esteves VI, Cunha Â, Schneider RJ, Tomé JPC. Photodegradation of organic pollutants in water by immobilized porphyrins and phthalocyanines. J Porphyr Phthalocyanines 2016;20(01n04):150–66. [11] Ali I, Asim M, Khan TA. Low cost adsorbents for the removal of organic pollutants from wastewater. J Environ Manag 2012;113:170–83. [12] Maya EM, Snow AW, Shirk JS, Pong RGS, Flom SR, Roberts GL. Synthesis, aggregation behavior and nonlinear absorption properties of lead phthalocyanines substituted with siloxane chains. J Mater Chem 2003;13(7):1603–13. [13] Martynenko IVO AO, Maslov VG, Fedorov AV, Berwick K, Baranov AV. Beilstein. The influence of phthalocyanine aggregation in complexes with CdSe/ZnS quantum dots on the photophysical properties of the complexes. Beilstein J Nanotechnol 2006;6:1018–27. [14] Saka ET, Durmuş M, Kantekin H. Solvent and central metal effects on the photophysical and photochemical properties of 4-benzyloxybenzoxy substituted phthalocyanines. J Organomet Chem 2011;696(4):913–24. [15] Zhang F-F, Gan L-L, Zhou C-H. Synthesis, antibacterial and antifungal activities of some carbazole derivatives. Bioorg Med Chem Lett 2010;20(6):1881–4. [16] Maneerat W, Phakhodee W, Ritthiwigrom T, Cheenpracha S, Promgool T, Yossathera K, et al. Antibacterial carbazole alkaloids from Clausena harmandiana twigs. Fitoterapia 2012;83(6):1110–4. [17] Bikram CKC, Subbaiyan NK, D'Souza F. Supramolecular donor–acceptor assembly derived from tetracarbazole–zinc phthalocyanine coordinated to fullerene: design, synthesis, photochemical, and photoelectrochemical studies. J Phys Chem C 2012;116(22):11964–72. [18] Göksel M, Sengul IF, Kandemir H, Durmuş M. Novel carbazole containing zinc phthalocyanine photosensitizers: synthesis, characterization, photophysicochemical properties and in vitro study. J Porphyr Phthalocyanines 2016;20(06):708–18. [19] Kimura M, Suzuki H, Tohata Y, Ikeuchi T, Yamamoto S, Kobayashi N. 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4.5.2. 2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato gallium(III) (4) Phthalonitrile 1 (1 g, 2.18 mmol), large excess of flame-dried GaCl3 and 3 drops of DBU were heated for 24 h at 180 °C in dry quinoline under N2. After cooling to room temperature and diluting with MeOH, the reaction mixture was filtered. The crude product was refluxed in methanol several times. The resultant precipitate was then purified via column chromatography with silica gel (MeOH then eluted gradually with CHCl3) resulting in a purple solid. Yield: 0.286 g (27.08%). Anal. Calcd for C128H72N16GaCl + H2O: C, 78.55, H, 3.81; N, 11.45%. Found: C, 78.51; H, 3.93; N, 11.78%. IR (KBr): υ, cm−1: 1333 (m, C–N). 1H NMR (600 MHz, DMSO‑d6, 95 °C): δ, ppm: 7.10 (s, 16H, H8), 7.15 (s, 16H, H7), 7.65 (dd, 16H, H6), 7.97 (s, 16H, H9), 10.15 (s, 8H, H3). 13C NMR (150 MHz, DMSO‑d6, 25 °C): δ, ppm: 110.27 (C6), 120.249 (C2), 122.93 (C1), 125.68 (C9), 126.37 (C7), 136.88 (C10), 137.25 (C8), 140.19 (C3), 150.96 (C4), 152.38 (C5). UV/Vis (CHCl3 0.5 μM): λmax, nm (log ε) = 742 (5.39), 666 sh (4.71), 354 (5.12), 337 (5.13), 292 (5.13). MS (MALDI-TOF, α-cyano-4-hydroxycinnamic acid (HCCA) as matrix): m/z = Calcd: 1902.541, found: 1902.312 [M − Cl]+. 4.5.3. 2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato indium(III) (5) Complex 5 was prepared from phthalonitrile 1 following the same procedure adopted for complex 4 except anhydrous InCl3 was employed instead of GaCl3, resulting in a dark purple solid. Yield: 0.220 g (20.35%). Anal. Calcd for C128H72N16InCl + 4H2O: C, 74.76, H, 3.92; N, 10.90%. Found: C, 74.40; H, 3.85; N, 10.46%. IR (KBr): υ, cm−1: 1333 (m, C–N). 1H NMR (600 MHz, DMSO‑d6, 95 °C): δ, ppm: 6.93, 7.06, 7.37, 7.58, 7.81 (s, 64H, H8, H7, H6, H9), 10.05 (s, 8H, H3). 13C NMR (150 MHz, DMSO‑d6, 25 °C): δ, ppm: 109.81 (C6), 119.98 (C2), 122.67 (C1), 125.28 (C9), 125.53 (C7), 135.87 (C10), 137.59 (C8), 139.94 (C3), 153.88 (C4,5). UV/Vis (CHCl3 0.5 μM): λmax, nm (log ε) = 736 (5.27), 701 sh (4.75), 661 (4.59), 366 (5.64), 336 (4.97). MS (MALDI-TOF, α-cyano-4-hydroxycinnamic acid (HCCA) as matrix): m/z = Calcd: 1902.541, found: 1902.312 [M − Cl]+. Acknowledgments The authors gratefully acknowledge the support of the Kuwait Foundation for the Advancement of Science-KFAS (grant no. P114-14SC0) and the Kuwait University Research administration-RSP unit general facilities of the Faculty of Science GFS (GS 01/01, GS 02/01, GS 03/01, GS 01/03, GS 01/05, GS02/13). This research is also supported by Graduate Studies at Kuwait University for a PhD candidacy 1. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// 12

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