Boron Subphthalocyanine Dyes: 3 ... - American Chemical Society

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Boron Subphthalocyanine Dyes: 3-Pentadecylphenol as a Solubilizing Molecular Fragment Emma R. L. Brisson,† Andrew S. Paton,† Graham E. Morse,† and Timothy P. Bender*,†,‡,§ †

Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario, M5S 3E5, Canada ‡ Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada, M5S 3H6 § Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada

bS Supporting Information ABSTRACT: We report the synthesis and characterization of a series of boronsubphthalocyanine (BsubPc) dyes which have organic solubility >10 2 M while being amenable to doping into polymeric films. To achieve high solubility we have placed the 3-pentadecylphenoxy molecular fragment in a variety of positions within the BsubPc chemical structure including around the periphery of the BsubPc ligand and in the axial position to the boron atom. We have found that placement of the 3-pentadecylphenoxy molecular fragment around the periphery adversely affects the photostability of the resulting BsubPc whereas placement in the axial position has little effect. We also confirm that the presence of fluorine atoms around the periphery improves the photostability. Overall we present a systematic study of the 3-pentadecylphenoxy fragment as a solubilizing moiety for BsubPc. The nature of the substituents and their position does not affect the nearly pure magenta color characteristic of BsubPc derivatives.

1. INTRODUCTION Boron subphthalocyanines (BsubPcs) are unique phthalocyanine (Pc) analogues wherein boron templates the formation of its cone-shaped macrocyclic aromatic ligand.1 Meller and Ossko first reported the isolation and single crystal X-ray diffraction of chloroboronsubphthalocyanine (Cl-BsubPc) in 1972.2 The chemistry of BsubPcs was extensively revisited during the 1990s when Kobayashi expanded their chemistry by using them as precursors to asymmetric Pcs via a ring-expansion insertion reaction.3 Because of their distinctive optical and electrical properties, BsubPcs derivatives have shown to be useful as a functional material in a variety of applications including nonlinear optics,4 photodynamic therapy,5 biological tagging,6 and organic electronics such as organic solar cells7 and organic light emitting diodes.8 Additionally, the nearly perfect magenta color of BsubPcs has led to investigation of these compounds as possible colorants;9,10 however, a systematic study has shown that various chloro-BsubPc and phenoxy-BsubPc derivatives possess relatively poor photo-oxidative stability.9 The stability tests were performed in dilute solutions (10 5 M) under a variety of conditions including the presence of water and illuminated using standard indoor fluorescent lighting. The dilute conditions, near the saturation points, were no doubt necessitated by the known low solubility of common BsubPc derivatives (Cl-BsubPc 1.8 10 4 M or 77 mg/L; phenoxy-BsubPc derivatives 5.1 10 3 M or 2480 mg/L).11 While this test provides a systematic look at the stability of BsubPcs in dilute solutions, it does not provide a realistic measure of the functional limits of these compounds in real applications. Consequently, it remains unclear whether doping into a polymeric film (a more practical assumption of what a functional environment would resemble) would result in improved photooxidative stability. Unfortunately, because of the low solubility of common BsubPc derivatives, doping polymeric films at high or r 2011 American Chemical Society

practical concentrations using solvent dissolution and coating methods is not practical. Therefore, we present the design and synthesis of a systematic series of oil soluble BsubPc derivatives obtained through the use of the 3-pentadecylphenoxy molecular fragment. This fragment has been placed in both peripheral (bound around the BsubPc ligand) and axial (bound to the boron atom) positions, resulting in derivatives with >10 2 M solubility. At this level of solubility the practical application of BsubPc derivatives becomes realistic, because they are soluble enough to use solution processing methods. Accordingly, we have dissolved each of our five novel BsubPcs in two different polymer matrixes: polystyrene (PS) and polymethylmethyacrylate (PMMA).12 Each sample was coated onto printing ink drawdown paper and the doped film was exposed to light and oxygen by hanging all samples concurrently in the windows of our laboratory, and we have observed the degradation of the BsubPc derivatives over time. Neat samples of each dye were also coated onto printing ink drawdown paper for reference. Because of the systematic variation, we have formed a structure property relationship for the stability of our series of BsubPc derivatives. Furthermore, we have determined which substituent group, in terms of their nature and position, are necessary to achieve the best stability concurrent with having >10 2 M solubility.

2. EXPERIMENTAL SECTION 2.1. Materials.Tetrahydrofuran (THF; 99%), toluene (99.5%), cyclohexanone (99%), acetone (99.5%), 1,2-dichlorobenzene (o-DCB; 98%), dimethyl sulphoxide (DMSO; 99.9%), cyclohexane (99%), dichloromethane (DCM; 98%), ethyl ether (98%), Received: March 10, 2011 Accepted: August 20, 2011 Revised: July 11, 2011 Published: August 20, 2011 10910

dx.doi.org/10.1021/ie200480x | Ind. Eng. Chem. Res. 2011, 50, 10910–10917

Industrial & Engineering Chemistry Research methanol (99.8%), acetonitrile-190 (AcCN; HPLC grade, 99.9%), N,N-dimethylformamide (DMF, distilled in glass, 99.9%), potassium carbonate, and magnesium sulfate (anhydrous) were purchased from Caledon Laboratories (Caledon, Ontario, Canada) and used as received. Dibutylphthalate was purchased from Acros Organics (Geel, Belgium) and used as received. 3-pentadecylphenol (PDPh; 90%), poly(styrene) (PS; Mn 170,000, Mw 350,000), poly(methylmethacrylate) (PMMA Mw 120,000), boron trichloride (100 mL, 1.0 M in heptane), boron tribromide (99%), and phenol (99%) were purchased from Sigma-Aldrich Chemical Co. (Mississauga, Ontario, Canada) and used as received. Phthalonitrile, tetrafluorophthalonitrile, 3,4-dimethylphenol, and 4-nitrophthalonitrile were purchased from TCI America (Portland, Oregon, USA) and used as received. Soxhlet extractions were performed with Whatman single thickness cellulose extraction thimbles (33 118 mm). 50 200 μm Alumina Standard Activity - pH = 10, and 15 25 μm silica gel were purchased from Caledon Laboratories (Caledon, Ontario, Canada), and were both used as received. Thin-film Liquid Chromatography (TLC) was performed, depending on the compound, on Alugram 20 80 mm 200 μm thick silica gel on an aluminum substrate, or on Analtech Uniplate Alumina GF 250 μm alumina on a scored glass substrate, with a UV fluorescence indicator, (Machery-Nagel). Printing Ink Drawdown Sheets (3NT-32; neutral white with a horizontal jet black stripe across the page) were purchased from R. B Atlas (Toronto, Ontario, Canada). Lacquers were mixed overnight by slow rotation on a LAB QUAKE Shaker Rotisserie from ThermoScientific (Dubuque, Iowa, U.S.A.). Polymer films were coated onto the Printing Ink Drawdown Sheets with a No. 2 Standard K Hand Coater Bar from R K Print Coat Instruments Ltd. (U.K.), which consists of a 0.15 mm stainless steel precision pulled wire wound around a stainless steel rod, producing a film with an estimated 12 μm thickness (Litlington, Royson, Herts, U.K.). 2.2. Characterization Details. Reactions were monitored by HPLC with a SunFire C18 3.5 μm 4 300 mm column in a Waters 2695 Separations Module with a Waters UV vis 2998 Photodiode Array by one of two methods: (1) AcCN HPLC grade was used as the mobile phase at a flow rate of 0.6 mL/min or (2) in the same column, an isocratic mixture of 20% DMF and 80% AcCN as used. Purities were determined by HPLC or low molecular weight GPC analysis. GPC could be used to monitor reactions on BsubPc derivatives peripherally bound pentadecylphenoxy groups. For GPC analysis, a Waters Styragel HR0.5 and a Waters Styragel HR1 placed in series each having a column size of 4.6 300 mm columns. GPC was operated with THF as the mobile phase at a rate of 0.75 mL/min. All 1H NMR were acquired on a Varian Mercury 400 MHz system in either deuterated chloroform (CDCl3) or deuterated dichloromethane (CCl2D2) with an internal standard of 0.05% TMS purchased from Cambridge Isotope Laboratories which was used as received. The absorbencies of the coatings were taken from the λmax (normalized for λmax at t = 0) measured using a PerkinElmer Lambda 1050 UV/vis/NIR Spectrometer equipped with a Labshere 150 mm InGaAs Integrating Sphere. 2.3. Synthesis. 2.3.1. Synthesis of Chloroboronsubphthalocyanine (Cl-BsubPc, 1). Cl-BsubPc (1) was synthesized as previously reported by this group with a modified procedure based on the report of Zyskowski et al.13 2.3.2. Synthesis of 3-Pentadecylphenoxyboronsubphthalocyanine (PDPh-BsubPc, 2). In a procedure adapted from Torres et al.,14 Cl-BsubPc (1) (1.0 g, 2.3 mmol) was mixed with 3-pentadecylphenol (3.813 g, 12.5 mmol) in toluene (20 mL)

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in a 50 mL three neck round-bottom flask with a reflux condenser and argon inlet. The mixture was stirred and heated at reflux under argon until reaction was determined complete via HPLC, approximately 17 h. Kaufmann chromatography was performed on the crude product with alumina as the stationary phase and DCM as the eluent. Since this purification method did not remove all of the excess phenol, 0.711 g of the crude product that was passed through a Kaufmann column, it was further purified by standard column chromatography and was isolated using alumina as the stationary phase with DCM as the eluent. Removal of the DCM by rotary evaporation yielded a purple waxy powder. Yield 0.53 g (75%). 1H NMR (400 MHz, CDCl3, Me4Si) 8.82 8.88 (m, 6H), 7.88 7.93 (m, 6H), 6.65 (t, 2H), 6.43 (d, 2H), 5.21 (s, 1H), 5.18 (d, 1H), 2.17 (t, 3H), 1.57 (s, 23H), 1.27 (s, 8H), 0.88 (t, 3H); UV vis (CHCl3) λmax = 561 nm; HPLC (20% DMF, 80% AcCN) RT (min) = 16.70 (>99.9%). 2.3.3. Synthesis of Bromododecafluorosubphthalocyanine (Br-F12BsubPc, 3). Br-F12BsubPc (3) was synthesized as previously reported by this group8a using a modified procedure based on the report of Sharman et al.15 2.3.4. Synthesis of 3-Pentadecylphenoxydodecafluoroboronsubphthalocyanine (PDPhO-F12BsubPc, 4). Br-F12BsubPc (3) (2.50 g, 3.62 mmol) was mixed with PDPh (2.20 g, 7.23 mmol) in 30 mL of DCB in a round-bottom flask. The solvent was heated to reflux, and the reaction proceeded under a constant stream of inert argon gas for 2 h. The DCB was removed by rotary evaporation, and some of the crude product (1.8 g) was purified by column chromatography on silica with a 1:1 mixture of DCM and cyclohexane as the eluent. Removal of the solvent by rotary evaporation yielded a purple waxy powder. Yield: 0.87 g (49%). 1 H NMR (400 MHz, CDCl3, SiMe4) 6.70 (t, 1H), 6.52 (d, 1H), 5.19 (s, 1H), 5.14 (d, 1H), 2.22 (t, 2H), 1.23 1.35 (s, 16H), 1.15 1.23 (5H), 1.08 1.16 (3H), 0.88 (t, 3H); UV vis (CHCl3) λmax = 568 nm; HPLC (20% DMF, 80% AcCN) RT (min) = 12.59 (>99.9%). 2.3.5. Synthesis of 4-(3-pentadecylphenoxy)-phthalonitrile (PDP, 5). In a procedure adapted from Duff et al.,16 3-pentadecylphenol (30.45 g, 90% pure technical grade, 90 mmol), potassium carbonate (12 g, 87 mmol), and 4-nitrophthalonitrile (15 g, 86.6 mmol) were mixed in dimethylsulfoxide (DMSO, 118.9 g, 108 mL) under a constant stream of inert Argon gas, and heated to 90 °C for 3 h. Upon cooling to room temperature, the contents of the reaction were poured into a large (500 or 1000 mL) separation funnel, and the product was extracted three times with an equal volume of ethyl ether (25 30 mL of H2O were added to cause phase separation). The ethyl ether partitions were combined, dried with anhydrous MgSO4, and filtered. Rotary evaporation was used to remove the ethyl ether. The oily residue was removed by flash chromatography on silica with DCM as the eluent. Removal of the DCM by rotary evaporation yielded a tan powder. Yield 25.5 g (69%). 1H NMR (400 MHz, CD2Cl2, Me4Si) 7.74 (d, 1H), 7.37 (t, 1H), 7.30 (d, 1H), 7.24 7.28 (m, 1H), 7.15 (d, 1H), 6.91 (d, 2H), 2.65 (t, 2H), 1.59 1.67 (m, 2H), 1.23 (s, 24H), 0.88 (t, 3H); UV vis (CHCl3) λmax = 260 and 304 nm; HPLC (20% DMF, 80% AcCN) RT (min) = 6.27 (>99.9%). 2.3.6. Synthesis of Chlorotrispentadecylphenoxyboronsubphthalocyanine (Cl-(PDPhO)3BsubPc, 6a). PDP (2, 17.880 g, 41.52 mmol), boron trichloride (100 mL, 1.0 M in heptane), and DCB (286 g, 220 mL) were mixed together in a 500 mL roundbottom flask under a constant stream of inert Argon gas. The heptane 10911

dx.doi.org/10.1021/ie200480x |Ind. Eng. Chem. Res. 2011, 50, 10910–10917

Industrial & Engineering Chemistry Research

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Table 1. Polymer Lacquer Formulations PS

PMMA

PMAN

polymer

0.955 g

1.079 g

0.519 g

solvent system

3.195 g (2:1 THF:toluene)

3.071 g (2:1 THF:toluene)

3.631 g (2:1 acetone:cyclohexanone)

BsubPc derivative

0.131 g

0.131 g

0.131 g

dibutylphthalate

0.100 g

0.100 g

0.100 g

Figure 1. Photostability experimental set up is shown. Inset is a BsubPc doped film coated onto a draw down sheet (A). This window faces northwest, and the coatings were all hung on the inside of the glass.

was distilled off using a side arm with a short path condenser, and the remaining mixture was heated to 180 °C for 1.5 h. After cooling to room temperature, the DCB was removed using rotary evaporation. The pure product was obtained by Kauffmann column chromatography on Alumina with DCM as the eluent. Removal of the DCM by rotary evaporation yielded a purple waxy solid. Yield 9.94 g (54%). 1H NMR (400 MHz, CDCl3, SiMe4) 8.73 8.84 (mr, 3H), 8.27 8.35 (mr, 3H), 7.55 7.64 (mr, 3H), 7.30 7.38 (mr, 3H), 7.08 (t, 3H), 6.93 7.03 (mr, 6H), 2.60 2.70 (mr, 6H), 1.58 1.70 (mr, 6H), 1.23 (m, 68H), 0.87 (t, 9H); UV vis (CHCl3) λmax = 571 nm; GPC RT (min) = 6.79 (>99.9%). 2.3.7. Synthesis of Phenoxytrispentadecylphenoxyboronsubphthalocyanine (PhO-(PDPhO)3BsubPc, 6b). Cl-(PDPhO)3BsubPc (6a, 4.0 g, 3 mmol) and phenol (1.41 g, 15 mmol) were mixed together in 35 mL of toluene in a round bottomed flask under a steady

stream of inert Argon gas, and refluxed for 17 h. After cooling, the toluene was removed by rotary evaporation, and the pure product was obtained by Kaufmann column chromatography on alumina with DCM as the eluent. Removal of the DCM by rotary evaporation yielded a purple waxy solid. Yield: 4.03 g (96%). 1H NMR 400 MHz (CDCl3) 8.69 8.78 (mr, 3H), 8.24 8.31 (mr, 3H), 7.50 7.62 (mr, 3H), 7.29 7.37 (mr, 3H), 7.06 (t, 3H), 6.76 (t, 2H), 6.61 (t, 1H), 5.38 (d, 2H), 2.57 2.68 (mr, 6H), 1.64 (s, 7H), 1.23 (m, 74H), 0.87 (t, 9H); UV vis (CHCl3) λmax = 570 nm; GPC RT (min) = 6.80 (>99.9%). 2.3.8. Synthesis of 3-Pentadecylphenoxytrispentadecylphenoxyboronsubphthalocyanine (PDPhO-(PDPhO)3BsubPc, 6c). Cl-(PDPhO)3BsubPc (6a, 4.63 g, 3.5 mmol) was mixed with PDPh (2.14 g, 7 mmol) in DCB (13 g, 10 mL) in a cylindrical vessel fitted with a reflux condenser and argon inlet. The mixture 10912



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Scheme 1. Synthesis of BsubPc Dyes, Pentadecylphenoxy-BsubPc (2) and Pentadecylphenoxy-F12BsubPc (4), from Cl-BsubPc (1) and Br-F12BsubPc (3), Respectivelya

a

Conditions: (i) toluene, reflux.

was stirred and heated at reflux under a constant pressure of argon for 2 h. The DCB was removed under rotary evaporation after cooling. The pure product was obtained by Kaufmann column chromatography on alumina with DCM as the eluent. Removal of the DCM by rotary evaporation yielded a purple waxy solid. Yield 3.03 g (55%). 1H NMR (400 MHz, CDCl3, SiMe4) 8.68 8.77 (mr, 3H), 8.23 8.31 (mr, 3H), 7.51 7.59 (mr, 3H), 7.29 7.37 (mr, 4H), 7.06 (t, 4H), 6.91 7.01 (mr, 5H), 6.65 (t, 2H), 6.43 (d, 1H), 5.22 (s, 1H), 5.16 (d, 1H), 2.52 2.66 (mr, 8H), 2.19 (t, 1H), 1.56 1.69 (mr, 8H), 1.04 1.42 (mr, 99H), 0.85 0.89 (mr, 12H); UV vis (CHCl3) λmax = 568 nm; GPC RT (min) = 6.66 (>99.9%). 2.4. Formulation of the Lacquers. PS films were cast from a lacquercontaining PS (0.955 g), THF (2.130 g), toluene (1.065 g), dibutylphthalate (0.100 g), and a BsubPc derivative (0.131 g) (Table1). PMMA films were cast from a lacquer containing PMMA (1.079 g), THF (2.047 g), toluene (1.024 g), dibutylphthalate (0.100 g), and BsubPc derivative (0.131 g). The ingredients were added to a 2 dram vial, sealed, and placed on the LabQuake Shaker Rotisserie, which rotated the blends overnight in a dark space (inside a bench) so as to minimize any photodegradation prior to the study. 2.5. Casting the Polymer Films. Using a pipet, a portion of polymer lacquer solution was placed on a Printing Ink Drawdown Sheet. Immediately after this, a No. 2 K Hand Coater Bar was placed parallel to and above the deposited material, and a swift motion toward the body with a slight downward pressure was used to cast the film. The result was a thin (estimated as 12 μm by R K Print Coat Instruments Ltd. for the No 2. Hand Coater Bar), transparent magenta streak coating part of the paper, seen in the insert (A) of Figure 1. The paper was then placed in an oven at 65 °C for 10 min to ensure the solvent was evaporated. 2.6. Photo-Stability Measurements. The films containing the BsubPc derivatives were kept out of sunlight until they were all ready to be hung in the window, which faces northwest, at 200 College Street in Toronto, Ontario, Canada (latitude: 43.6587, Longitude: 79.3960). The set up is illustrated in Figure 1. Tape held the samples up against the inside of the window, ensuring that the coating faced outside. Over the course of 10 weeks, the samples were simultaneously removed from the window to be measured by the Integrating Sphere, and put back into the window immediately after measurement. Measurements were taken twice each day for the first few days of exposure and subsequently decreased in frequency thereafter. Weather conditions were recorded daily, as well as daylight hours.

3. RESULTS AND DISCUSSION 3-Pentadecylphenol is the hydrogenated form of cardanol (3pentadecadienylphenol) which is itself a component of cashew nutshell oil/liquid. It is commercially available from the Cardolite Corporation at 90% 3-pectadecylphenol whereby the remaining 10% consists of unsaturated C15 variants. Owing to its unique chemical structure, having both aromatic and aliphatic components, 3-pentadecylphenol is well-known to have the reactivity of a phenol as well as the greasy properties expected from a hydrocarbon of moderate length. This makes it ideal as a solubilizing molecular fragment for BsubPcs. For that reason 3-pentadecylphenol was first used to derivatize the axial position of the pigment-like Cl-BsubPc. Using the method of Torres et al.,14 3-pentadecylphenol was reacted with the labile B Cl bond to produce an oil soluble (i.e., solvent soluble) BsubPc dye, 3-pentadecylphenoxy-BsubPc (PDPhO-BsubPc, 2, Scheme 1). This approach required Cl-BsubPc (1) as a starting material. Since a reliable commercial source of Cl-BsubPc (in terms of purity) could not be identified, we synthesized Cl-BsubPc in our own laboratory in gram scale quantities (at ∼99% purity) from BCl3 and phthalonitrile using the method of Zyskowski13 with slight modifications. In contrast, we have found the method of Zyskowski13 to be unsuitable for the synthesis of peripherally fluorinated-ClBsubPc derivatives starting from tetrafluorophthalonitrile and BCl3. To synthesize a suitable precursor for the fluorinated BsubPc dye (PDPhO-F12BsubPc, 4, Scheme 1), we used the method of Sharman and van Lier,15 with slight modifications, which uses BBr3 to produce bromododecafluoroboronsubphthalocyanine (Br-F12BsubPc, 3, Scheme 1).8a Subsequent reaction of Br-F12BsubPc with 3-pentadecylphenol produced the desired fluorinated BsubPc dye (PDPhO-F12BsubPc, 4) in good yield in a reasonable time. While the Zyskowski method was not successful with tetrafluorophthalonitrile, we have found the method to be amenable to the use of many other phthalonitriles as starting materials, which upon reaction with BCl3 produces the desired Cl-BsubPc derivatives. Included in the list of compatible phthalonitriles is 4-(3-pentadecylphenoxy)-phthalonitrile16 (PDP, 5, Scheme 2) which facilitates access to another key precursor in our study: chlorotrispentadecylphenoxyboronsubphthalocyanine (Cl(PDPh)3BsubPc, 6a, Scheme 2). Cl-(PDPh)3BsubPc was subsequently reacted with phenol and 3-pentadecylphenol to produce additional BsubPc dyes PhO-(PDPh)3BsubPc and PDPhO-(PDPh)3BsubPc (6b and 6c, respectively, Scheme 2). 10913



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Scheme 2. Synthesis of BsubPc Dyes, Containing Pentadecylphenoxy Fragements around the Periphery (6a c)a

a

Conditions: (i) DMSO, K2CO3, 90 °C, 3 h. (ii) BCl3 (1.0 M in heptanes), 1,2-dichlorobenzene, reflux. (iii) R OH, toluene, reflux.

All BsubPc dyes were purified by chromatography, either by Kauffmann chromatography or by standard column chromatography. Both methods are enabled by the solubility of the derivatives in organic solvents, and the chromatographic process is aided by the strong color which can be seen traveling down the respective chromatography column. Identity, purity, and spectroscopic characteristics were confirmed for each BsubPc dye using standard methods, the details of which are provided in the Experimental Section. For compounds 6a, 6b, and 6c, the NMR spectra contain multiples resonances because of the presence of constitutional isomers resulting from the relative position of the pentadecylphenoxy fragments around the BsubPc ligand. As such, these resonances are labeled “mr” in the Experimental Section, standing for “multiple resonances”. We would highlight the use of low molecular weight GPC analysis to monitor the reactions and confirm the purity of compounds 6a, 6b, and 6c which all contain the large pentadecylphenoxy fragments around the peripheral groups and thus have relatively large molecular weight compared to their precursors. All BsubPc derivatives reported herein have an oil solubility greater than 10 2 M, making them practical dyes unlike the relatively insoluble Cl-BsubPc and associated derivatives with solubilities in the 10 3 M to 10 4 M range.11 Thus, each is amenable to dissolution in a solvent common to it and a polymer. We therefore doped each BsubPc dye into two different polymer binders, polystyrene (PS) and polymethylmethacrylate (PMMA), and coated each from a lacquer onto printing ink drawdown paper (Figure 1A). We then simultaneously mounted each coating to the inside face of the windows of our laboratory (which is on the third story and faces northwest, Figure 1) and monitored the degradation of the BsubPc dyes from exposure to real sunlight as a function of time using absorption spectroscopy. As a point of comparison, each compound was also coated onto a printing ink drawdown paper without a lacquer. We were therefore

able to form two structure property relationships, each being photo-oxidative stability as a function of BsubPc dye molecular structure. Specifically: (a) By comparison between BsubPc derivatives 2, 4, and 6c (all containing a pentadecylphenoxy group in the axial position) we can study the effect of peripheral substitution. Peripherally fluorinated BsubPcs17 have been widely synthesized and studied to date;7,8,10 however, little is known in regards to BsubPcs with peripheral ether groups. The direct comparison of each will determine the effect of electron withdrawing (F) or electron donating (pentadecylphenoxy) substituents on the photooxidative stability. (b) For (PDPh)3BsubPc derivatives 6a, 6b, and 6c we can study the effect of phenoxylation in place of halogenation at the axial position on the photo-oxidative stability. Figures 2 summarizes the results of the photostability experiments. Beginning with PDPhO-BsubPc (2), the bare dye (labeled “no polymer binder” in Figure 2) coated onto printing ink drawdown paper degraded to a point of being colorless after approximately 1000 h (normalized absorption = 0), whereas the ability to dope the BsubPc dye into a polymer film resulted in an extension of its normalized absorption = 0 point to just under 2000 h. The fluorinated dye (PDPhO-F12BsubPc, 4) showed increased photostability. Bare coatings of 4 did not completely bleach until approximately 1600 h (Figure 2b). When doped into either PS or PMMA the polymer doped samples of PDPhOF12BsubPc remained magenta colored beyond the limits of our study (>2000 h). A comparison of the photo-oxidative stability of BsubPc dyes 6a, 6b, and 6c highlights a slightly inconsistent result (Figures 1c e). We observed that 6a and 6b had comparable photostabilities as both bare and doped into both PS and PMMA, thus hinting that the presence of a halogen or phenoxy fragment in the axial 10914



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Figure 2. Normalized absorption as a function of time for BsubPc dyes: (a) 2; (b) 4; (c) 6a; (d) 6b; (e) 6c; Legend: (, no polymer binder; 9, PMMA polymer binder; b, PS polymer binder.

position has little effect on the photostability of this selection of BsubPc derivatives. However, the stability of 6c (with a 3-pentadecylphenoxy fragment in the axial position) was particularly low indicating that the degradation of these compounds may be more complicated. We have noted that compound 6c also exhibited a poor shelf life: after three months of storage in the solid state and in a sealed vial protected with aluminum foil in a drawer, 6c had visibly decreased color intensity but was still magenta. This instability is an indicator that the peripheral pentadecylphenoxy groups may accelerate the degradation of BsubPcs regardless of exposure to sunlight. This observation is further exemplified by an overall survey of Figures 1a e. A

comparison of three BsubPc dyes, 2, 4, and 6c, can be made, each having different peripheral substituents (H, F and 3-pentadecylphenoxy, respectively) and a 3-pentadecylphenoxy fragment in the axial position. Regardless of the polymer in which these derivatives were doped, BsubPc dye 4, with fluoro peripheral substituents, has the best photo-oxidative stability, followed by hydrogen and finally 3-pentadecylphenoxy. This trend suggests that the presence of electron-donating oxygen (ether/phenoxy) groups around the peripheral groups is detrimental to the photooxidative stability whereas the presence of the electron-withdrawing fluorine atom is beneficial. The difference between hydrogen and fluorine is consistent with the results outlined in 10915


Industrial & Engineering Chemistry Research the Kimberly Clark patent.9 We can therefore conclude that the placement of the 3-pentadecylphenoxy fragment in the axial position is sufficient to produce dye with >10 2 M solubility without compromising the stability of the compound. As a final comment, the results presented above were obtained in and around the spring of 2010. We have actually conducted the photostability experiment of compounds 6a, 6b, and 6c twice, the first time in and around fall of 2009. When the experiment was repeated in the spring of 2010, compound 6c was partially degraded because of the aforementioned poor shelf life. We elected to perform the study regardless using normalized absorbance as a measure of further degradation. In the spring experiments (outlined above) we observed that the degradation of compound 6c in a PS matrix occurred at a higher rate, reaching the minimum absorbance at 650 h, compared to 1040 h in the fall study. These two studies both fell within about 6 weeks of the equinox, so the amount of sunlight hours per day were approximately equivalent. The consistency of our rather crude experimental method is illustrated in Supporting Information, Figure S1 where the lifetimes of compounds 6a, 6b, and 6c are compared in the two studies. The effect of the partial degradation of compound 6c can be seen in the PS films; however, the rest of the data suggests the behaviors are remarkably similar.

4. CONCLUSION We have synthesized a series of BsubPc dyes which use the 3-pentadecylphenoxy molecular fragment to impart oil solubility (>10 2 M) to a class of compounds which generally have limited solubility. We have subsequently doped each dye into films of polystyrene (PS) and polymethylmethyacrylate (PMMA) and studied the relative photo-oxidative stability of each BsubPc dye. On the basis of our data and observations, we have formed the following structure property relationships: (a) By comparison of the photostabilities of compounds 2, 4, and 6c we have found the peripheral groups have the greatest effect on the photostability of this series of BsubPc derivatives; notably, the 3-pentadecylphenoxy substituent is undesirable and fluoro substituent is desirable. (b) Through examination of (PDPh)3BsubPc derivatives 6a, 6b, and 6c we may conclude that phenoxylation in place of halogenation makes little difference to the corresponding photostability of the BsubPc derivative. More generally, we can conclude that the presence of the 3-pentadecylphenoxy fragment in the axial position of BsubPc is sufficient to achieve an oil soluble dye with >10 2 M solubility, without compromising the photo-oxidative stability of the compound. In contrast, its presence around the periphery is extremely detrimental to photo-oxidative stability, regardless of the fragment on the axial position. ’ ASSOCIATED CONTENT

bS

Supporting Information. A comparison of the photostabilities of compounds 6a, 6b, and 6c at two different times of the year, fall and spring. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

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’ ACKNOWLEDGMENT The authors would like to acknowledge funding provided by the Ontario Centres of Excellence (OCE) Centre for Energy and the Natural Sciences and Engineering Research Council of Canada (NSERC). Neither funding source nor their representatives had any role in the preparation of this manuscript. ’ REFERENCES (1) Claessens, C. G.; Torres, T. Subphthalocyanine Enantiomers: First Resolution of a C3 Aromatic Compounds by HPLC. Tetrahedron Lett. 2000, 41, 6361. (2) Meller, A.; Ossko, A. Phthalocyaninartige Bor-Komplexe. Monatsh. Chem. 1972, 103, 150. (3) Kobayashi, N.; Kondo, R.; Nakajima, S.; Osa, T. New Route to Unsymmetrical Phthalocyanine Analogues by the Use of Structurally Distorted Subphthalocyanines. J. Am. Chem. Soc. 1990, 112, 9640. (4) (a) Diaz-Garcia, M. A.; Agullo-Lopez, M.; Sastre, A.; Torres, T.; Torruellas, W. E.; Stegeman, G. I. Third Harmonic Generation Spectroscopy of Boron Subphthalocyanine. J. Phys. Chem. 1995, 99, 14988. (b) Ledoux, I.; Zyss, J. From One- to Two-Dimensional Complexes for Quadratic Nonlinear Optics: the Influence of Ligand and Complexing Metal Atoms. Pure Appl. Opt. 1996, 5, 603. (c) Sastre, A.; Torres, T.; Diaz-Garcia, M. A.; Agullo-Lopez, F.; Dhenaut, C.; Brasselet, S.; et al. Subphthalocyanines: Novel Targets for Remarkable Second-Order Optical Nonlinearities. J. Am. Chem. Soc. 1996, 118, 2746. (d) Sastre, A.; del Rey, B.; Torres, T. Synthesis of Novel Unsymmetrically Substituted Push-Pull Phthalocyanines. J. Org. Chem. 1996, 61, 8591. (e) Geyer, M.; Plenzig, F.; Rauschnabel, J.; Hanack, M.; del Rey, B.; Sastre, A.; et al. Subphthalocyanines: Preparation, Reactivity and Physical Properties. Synthesis 1996, 1139. (f) del Rey, B.; Keller, U.; Torres, T.; Rojo, G.; Agullo-Lopez, F.; Nonell, S.; et al. Synthesis and Nonlinear Optical, Photophysical, and Electrochemical Properties of Subphthalocyanines. J. Am. Chem. Soc. 1998, 120, 12808. (g) Martin, G.; Rojo, G.; Agullo-Lopez, F.; Ferro, V. R.; Garcia de la Vega, J. M.; Martinez-Diaz, M. V.; et al. Subphthalocyanines and Subnaphthalocanines: Nonlinear Quasi-Planar Octapolar Systems with Permanent Polarity. J. Phys. Chem. B 2002, 106, 13139. (h) Claessens, C. G.; Gonzalez-Rodriguez, D.; Torres, T. Subphthalocyanines: Singular Nonplanar Aromatic Compounds Synthesis, Reactivity and Physical Properties. Chem. Rev. 2002, 102, 835. (5) Xu, H.; Jiang, X.-J.; Chan, E. Y. M.; Fong, W.-P.; Ng, D. K. P. Synthesis, Photophysical Properties and in vitro Photodynamic Activity of Axially Substituted Subphthalocyanines. Org. Biomol. Chem. 2007, 5, 3987. (6) Adachi, K.; Watarai, H. Binding Behavior of SubphthalocyanineTagged Testerone with Human Serum Albumin at the n-Hexane/Water Interface. Anal. Chem. 2006, 78, 6840. (7) (a) Gommans, H.; Aernouts, T.; Verreet, B.; Heremans, P.; Medina, A.; Claessens, C. G.; et al. Perfluorinated Subphthalocyanine as a New Acceptor Material in a Small-Molecule Bilayer Organic Solar Cell. Adv. Funct. Mater. 2009, 19, 3435. (b) Biwu, M.; Woo, C. H.; Miyamoto, Y.; Frechet, J. M. Solution Processing of a Small Molecule, Subphthalocyanine, for Efficient Organic Photovoltaic Cells. J. Chem Mater. 2009, 21, 1413. (8) (a) Morse, G. E.; Helander, M. G.; Maka, J. F.; Lu, Z. H.; Bender, T. P. Fluorinated Phenoxy Boron Subphthalocyanines in Organic LightEmitting Diodes. ACS Appl. Mater. Interfaces 2010, 2 (7), 1934. (b) Diaz, D. D.; Bolink, H. J.; Cappelli, L.; Claessens, C. G.; Coronado, E.; Torres, T. Subphthalocyanines as Narrow Band Red-Light Emitting Materials. Tetrahedron Lett. 2007, 48, 4657. (9) Nohr, R. S.; MacDonald, J. G.; Novel Subphthalocyanine Colorants, Ink Compositions, and Methods of Making the Same. KimberleyClark Worldwide Incorporated, International Patent WO 00/71621 A1, 2000. (10) Kipp, R. A.; Simon, J. A.; Beggs, M.; Ensley, H. E.; Schmehl, R. H. Photophysical and Photochemical Investigation of a Dodecafluorosubphthalocyanine Derivative. J. Phys Chem. A 1998, 102, 5659. 10916



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(11) Morse, G. E.; Paton, A. S.; Lough, A.; Bender, T. P. Chloro Boron Subphthalocyanine and its Derivatives: Dyes, Pigments, or Something in Between? Dalton Trans. 2010, 39, 3915. (12) Pauly, S. Polymer Handbook. Permeability and Diffusion Data, 4th ed; Brandrup, J., Immergut, E. A., Brulke, E. A., Akiro, A., Bloch, D. R., Eds.; John-Wiley & Sons: New York, 2005. (13) Zyskowski, C. D.; Kennedy, V. O. Compounds in the Series from Boron Subphthalocyanine to Boron Subnaphthalocyanine. J. Porphyrins Phthalocyanines. 2000, 4, 707. (14) Claessens, C. G.; Gonzalez-Rodriguez, D.; del Rey, B.; Torres, T.; Mark, G.; Schuchmann, H. P.; et al. Highly Efficient Synthesis of Chloro- and Phenoxy Substituted Subphthalocyanines. Eur. J. Org. Chem. 2003, 2547. (15) Sharman, W. M.; van Lier, J. E. Synthesis and Photodynamic Activity of Novel Asymetrically Substituted Fluorinated Phthalocyanines. Bioconjugate Chem. 2005, 16, 1166. (16) Duff, J. M.; Mayo, J. M.; Gaynor, R. E.; Banning, J. H.; Meinhardt, M. B.; Hu, N.-X. et al. Methods for Preparing Phthalocyanine Compositions. Xerox Corporation U.S. Patent 6476219 B1, 2002. (17) Beggs, M. Ph.D. Dissertation, Tulane University, New Orleans, LA, 1997.

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Boron Subphthalocyanine Dyes: 3 ... - American Chemical Society

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