Phosphonic Acid Functionalized Asymmetric ... - ACS Publications

ARTICLE pubs.acs.org/Langmuir

Phosphonic Acid Functionalized Asymmetric Phthalocyanines: Synthesis, Modification of Indium Tin Oxide, and Charge Transfer Nathan W. Polaske, Hsiao-Chu Lin, Anna Tang, Mayunk Mayukh, Luis E. Oquendo, John T. Green, Erin L. Ratcliff, Neal R. Armstrong, S. Scott Saavedra, and Dominic V. McGrath* Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States

bS Supporting Information ABSTRACT: Metalated and free-base A3B-type asymmetric phthalocyanines (Pcs) bearing, in the asymmetric quadrant, a flexible alkyl linker of varying chain lengths terminating in a phosphonic acid (PA) group have been synthesized. Two parallel series of asymmetric Pc derivatives bearing aryloxy and arylthio substituents are reported, and their synthesis and characterization through NMR, combustion analysis, and MALDI-MS are described. We also demonstrate the modification of indium tin oxide (ITO) substrates using the PA functionalized asymmetric Pc derivatives and monitoring their electrochemistry. The PA functionalized asymmetric Pcs were anchored to the ITO surface through chemisorption and their electrochemical properties characterized using cyclic voltammetry to investigate the effects of PA structure on the thermodynamics and kinetics of charge transfer. Ionization energies of the modified ITO surfaces were measured using ultraviolet photoemission spectroscopy.

’ INTRODUCTION Phthalocyanines (Pcs) are a class of tetrapyrollic macrocycles with an aromatic 18 π-electron inner perimeter that possess many outstanding physical and chemical properties, including semiconductivity, high thermal and chemical stability, and high extinction coefficients with intense Q-band absorption in the visible region.1 As a result, Pcs are emerging as building blocks for advanced technologies, including organic field-effect transistors (OFETs)2 and organic photovoltaic (OPV) devices.3 Crucial to the performance of OPV devices is the charge-injection barrier between the hole-harvesting electrode (e.g., indium tin oxide (ITO) electrode) and the organic semiconductor.4 Furthermore, high series resistance (RS) arising from the electrical heterogeneity and surface roughness of the ITO surface often leads to low holeharvesting probabilities at the ITO
donor interface and poor OPV efficiencies. We envision that the presence of a robust ohmic contact at the ITO
donor interface will reduce RS and increase OPV efficiencies.5,6 Tethering a redox-active Pc monolayer to ITO is one strategy for creating ohmic contacts. Phosphonic acid (PA) derivatives are advantageous in that they form robust monolayers on ITO, with high surface loading, good hydrolytic stability, and, in the case of dipolar PAs, an ability to alter the effective work function of the oxide surface.7,8 In the present context, the PA tethering group provides for an efficient linkage between ITO and Pc, and may ultimately allow for the formation of hole-harvesting interlayer films that do not require the conducting polymer dispersion poly(3,4-ethylene-dioxythiophene)/ poly(styrenesulfonate) (PEDOT/PSS) as an intermediate layer.9 We herein report the synthesis of both metalated and free-base A3B-type asymmetric Pcs bearing, in the asymmetric quadrant, r 2011 American Chemical Society

a flexible alkyl linker of varying chain lengths terminating in a PA anchoring group. While the three symmetric quadrants help provide the necessary solubility in common organic solvents and the tunability of the Q-band absorption, the fourth, asymmetric quadrant facilitates tethering to the ITO via the PA. Though there are reports of tetra- and octasubstituted symmetric Pcs bearing PA groups,10 PA functionalized asymmetric Pcs have not been reported. PA functionalized symmetric Pcs have been adsorbed to oxide electrodes, but electrochemical characterization of these films has not been reported.11 Here two parallel series of asymmetric Pc derivatives bearing aryloxy and arylthio substituents have been prepared. The presence of sulfur atoms in the latter can (a) shift the Pc Q-band to the near-IR region, where the incident solar photon flux is relatively high, and (b) induce sulfur
sulfur noncovalent interactions, which can influence condensed-phase organization that is critical to OPV device performance.12,13 We also demonstrate modification of ITO substrates using the PA modified asymmetric Pc derivatives. These Pcs were chemisorbed to ITO and their electrochemical properties characterized using cyclic voltammetry to investigate the effects of PA tether length, peripheral atom substitution, and metal coordination on the thermodynamics and kinetics of charge transfer.

’ RESULTS AND DISCUSSION Synthesis of Phthalocyanines. Statistical Linstead cyclization was chosen as the preparation method for the asymmetric Received: August 11, 2011 Revised: October 20, 2011 Published: November 01, 2011 14900

dx.doi.org/10.1021/la203126c | Langmuir 2011, 27, 14900–14909

Langmuir Pcs. Before preparation of the desired Pcs, the required phthalonitriles (Pns) were synthesized. For the three symmetric quadrants of the asymmetric Pcs, we decided to use the aryloxyand arylthio-substituted Pns 5a and 5b. Previous reports have shown that incorporation of the aryloxy-substituted Pn 5a into both symmetric and asymmetric Pcs significantly improves solubility in common organic solvents (e.g., CH2Cl2, CHCl3, THF).14
16 Aryloxy-substituted Pn 5a was prepared according to the literature.16 To prepare 5b, 4-pentylbromobenzene (1) was allowed to react with 1-hexanethiol in the presence of Pd2(dba)3, 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (DDPPX), N,N-diisopropylethylamine (DIPEA), and dioxane under air-free conditions at 120 °C to give hexyl(4-pentylphenyl)Scheme 1

ARTICLE

sulfane (2) (Scheme 1).17 The hexyl group of 2 was then removed with Na0 in hexamethylphosphoramide (HMPA) at 120 °C18 to give 4-pentylthiophenol (3) in 65% yield from 1. Finally, reaction of 3 with 4,5-dichlorophthalonitrile (4) in the presence of K2CO3 in DMSO gave the arylthio-substituted Pn 5b in 71% yield. To incorporate the desired hydroxyl group in the asymmetric quadrant, 4-methoxybenzyl (PMB)-protected Pn 6 was selected to be condensed in combination with either aryloxy-Pn 5a or arylthio-Pn 5b during the statistical macrocyclization (Scheme 2). The PMB group can be removed under relatively mild conditions (TFA in CH2Cl2), and the resulting free hydroxyl group would allow for peripheral modification with various functionalized tethers required for surface attachment. To our delight, in addition to serving as a protecting group during the statistical macrocyclization, the PMB group indirectly assisted in the purification of the asymmetric Pcs. After the statistical macrocyclization using a 1:2 ratio of PMB-Pn 6 with either Pn 5a or Pn 5b, a chromatographically inseparable mixture of symmetric and asymmetric Pcs was obtained. We found that, after a crude chromatographic purification yielded a mixture of PMB-protected A3B (7a
d) and symmetric A4 (8a
d) Pcs, subjecting the mixture to PMB deprotection yielded a mixture of free hydroxyl A3B (9a
d) and symmetric A4 (8a
d) Pcs. This resultant mixture was then easily separable because of the increased polarity of hydroxyl-containing asymmetric Pcs 9a
d relative to PMB-protected Pcs 7a
d. Unmetalated and Zn(II) aryloxy-substituted asymmetric Pcs 9a and 9b, Zn(II) arylthio-substituted asymmetric Pc 9c, and symmetric Pcs 8a
d were prepared using this methodology. Unmetalated arylthiosubstituted asymmetric Pc 9d was found to be of unsuitable purity when prepared with these methods. Instead, Zn(II) was

Scheme 2

14901

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir

ARTICLE

Scheme 3

Figure 1. UV
vis spectra of unmetalated PA-Pcs 12a in TCE, 12b in CH2Cl2, and 12c in CHCl3. All solutions are [Pc] ≈ 10
6 M, and the spectra are normalized to the peak at 340 nm.

Figure 2. UV
vis spectra of Zn(II)-PA-Pcs 12d
e in CH2Cl2/pyridine (95:5) at [Pc] ≈ 10
6 M and normalized to the peak at 360 nm.

removed from Pc 9c using pyridinium hydrochloride in pyridine at 120 °C to give pure unmetalated arylthio-substituted Pc 9d in 60% yield after flash chromatography.19 With the hydroxyl-containing asymmetric Pcs 9a
d in hand, we next incorporated the tethered PA functionalities. To test the feasibility of PA introduction, Pc 9a was first allowed to react with commercially available diethyl (3-bromopropyl)phosphonate (10a), giving diethyl phosphonate Pc 11a in 73% yield (Scheme 3). Conversion to PA-Pc 12a was accomplished smoothly in 85% yield with TMSBr in CH2Cl2. With the PA addition determined to be synthetically straightforward, unmetalated PA-Pcs 12b and 12c, along with Zn(II)-PA-Pcs 12d and 12e, were prepared with diethyl (10-bromodecyl)phosphonate (10b)20 to increase the alkyl linker length from 3 to 10. The solution-phase aggregation state of Pcs 12a
e was assayed by UV
vis spectroscopy. Pc 12a displayed significant solutionphase aggregation, as evidenced by the hypochromic and hypsochromic shift of the Q-band in the UV
vis spectrum relative to that of 12b (Figure 1). This solution-phase aggregation could lead to

difficulty during surface deposition, with aggregates being adsorbed rather than monomeric molecules, which could alter the structure of the resulting film. Lengthening the alkyl linker between the Pc and the PA to increase steric bulk of the substituents and/or incorporation of Zn(II) into the Pc to allow potential coordination of apical ligands may reduce solutionphase aggregation.21 Indeed, unmetalated PA-Pcs 12b and 12c exhibited significantly less solution-phase aggregation than 12a, although some Q-band suppression was still detected in the UV
vis spectra (Figure 1), indicative of some residual aggregation. However, Zn(II)-PA-Pcs 12d and 12e displayed very sharp and prominent Q-bands when 5% pyridine in CH2Cl2 was used as the solvent (Figure 2), indicating that dissolved monomers were the predominant form. Bathochromic shifts were observed in the UV
vis spectra when comparing the aryloxy-substituted PA-Pcs to their arylthio-substituted analogues. Specifically, arylthiosubstituted H2-Pc 12c displayed Q-band red shifts of 31 (QA) and 17 (QB) nm versus aryloxy-substituted H2-Pc 12b, while arylthio-substituted Zn-Pc 12e showed a Q-band red shift of 33 nm versus aryloxy-substituted Zn-Pc 12d. Electrochemical Studies of Phthalocyanines Adsorbed on ITO. Initially we assessed if PA functionalized Pcs adsorb to 14902

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir ITO via the PA moiety by comparing the behavior of the Zn(II) aryloxy-substituted symmetric Pc 8b and the PA functionalized Zn(II) aryloxy-substituted asymmetric Pc 12d. These molecules were incubated with ITO electrodes at a concentration of 100 μM for 3 h (in CH2Cl2 for 8b or 7:3 (v/v) acetonitrile/pyridine for 12d) followed by rinsing the electrode in the respective solvent. Representative CVs, measured over a scan range in which the first oxidation of 12d and 8b occurs, are shown in Figure 3. Redox activity was observed for 12d but not for 8b, which shows that rinsing the electrode with solvent was sufficient to remove any adsorbed 8b but not 12d. Since 8b lacks the PA linker that is present on 12d, we conclude that the adsorption of 12d to ITO occurs via the PA linker. The electrochemical properties of adsorbed films of Zn-Pc and unmetalated Pcs were compared. Films of Zn(II)-Pcs 12d and 12e were adsorbed for 3 h from 100 μM solutions, in which dissolved monomeric species are the predominant form. CVs are shown in Figure 4A. The pair of distinct peaks in the first oxidation process of both 12d and 12e shows that the electrochemically active adsorbed material is composed of two distinct subpopulations: one fraction with voltammetric peaks centered around midpoint potentials (E°0 ) of 0.30 and 0.34 V versus Fc/ Fc+ for 12d and 12e, respectively, and a second fraction having voltammetric peaks centered around E°0 values of 0.14 and 0.20 V versus Fc/Fc+ for 12d and 12e, respectively. Splitting of the redox waves of dissolved Pcs due to aggregation has been reported in numerous studies.22,23 By correlating spectral and electrochemical properties, the less positive redox couple has been assigned to molecular aggregates of Pcs whereas the more

ARTICLE

positive redox couple has been assigned to the monomeric Pcs. Thus, the redox couples at 0.30
0.34 and 0.14
0.20 V in Figure 4A are assigned to monomeric and aggregated species, respectively. Further support for these assignments, including a comparison to the solution electrochemistry of these molecules, is given in the Supporting Information. As discussed above, the predominant form of 12d and 12e dissolved in the solutions from which the respective films were adsorbed was monomeric (see Figure 2). The presence of aggregates in the films therefore indicates that they are formed after monomer adsorption, which in turn implies that an adsorbed monomer can laterally diffuse on the ITO surface to form intermolecular interactions with coadsorbed monomers. The difference in E°0 values of 12d and 12e is attributed to the different natures of the aryloxy and arylthio substituents. Introduction of electron-donating groups at the peripheral positions increases the electron density of the Pc core, making it more easily oxidized and less easily reduced.13,24 Both aryloxy and arylthio groups are electron-donating substituents. It was shown previously that peripheral arylthio substituents are less electrondonating than aryloxy groups,25 which explains the more positive E°0 value observed for the oxidation of 12e relative to 12d. After removal of the background charging current and integration over the entire voltammetric envelope (i.e., both monomeric and aggregated species, and assuming n = 1 for both), electrochemically active surface coverages26 were estimated to be 2.0  10
10 and 1.9  10
10 mol cm
2 for 12d and 12e, respectively (Table 1). The total surface coverage27 expected for Table 1. Midpoint Potential (E°0 ), Apparent Electron Transfer Rate Constant (ks,app), and Electroactive Surface Coverage (Γ) of PA-Pcs Deposited onto ITO Electrodes Γ  10
12 d a

b

M

c

n

E°0 (V vs Fc/Fc ) +


1

ks,app (s )

(mol cm
2)

compd

X

12a

O

H2

3

0.56

1.4

12b 12d

O O

H2 Zn

10 10

0.60 0.30 (0.14)e

1.3 1.6 (2.4)e

11 200

12e

S

Zn

10

0.34 (0.20)e

1.7 (2.4)e

190

6.3

a

Figure 3. Cyclic voltammograms showing the first oxidation of adsorbed films of 12d (solid line) and 8b (dashed line) on ITO in 0.3 M TBAP/CH3CN. The scan rate was 100 mV s
1.

Alkoxy or arylthio substituents. b Metalation. c Linker length. d The electroactive surface coverages were calculated from the mean of the integrated charge in the anodic and cathodic processes. A value of n = 1 was assumed for the anodic and cathodic reactions of both monomeric and aggregated species. e Values in parentheses are the results for the aggregated species.

Figure 4. Background-subtracted cyclic voltammograms showing the first oxidation of thin films of (A) monomeric (2) and aggregated (1) forms of Zn(II)-Pcs 12d (solid line) and 12e (dashed line) and (B) unmetalated Pcs 12a (solid line) and 12b (dashed line) on ITO in 0.3 M TBAP/CH3CN. The scan rate was 100 mV s
1. 14903

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir

ARTICLE

Figure 5. (A) UPS spectra of (i) air plasma treated ITO, (ii) 12d on ITO, and (iii) 12e on ITO. (B) Energy band diagram interpreted from the spectra in (A).

a close-packed monolayer of edge-on-oriented 12d (or 12e) monomers is calculated to be ca. 2.0  10
10 mol cm
2, whereas the surface coverage expected for a monolayer of 12d (or 12e) adsorbed in a flat orientation is calculated be only about 5  10
11 mol cm
2. The agreement between the calculated and measured surface coverages indicates that the 12d and 12e films are composed of approximately one close-packed monolayer of electroactive molecules having a predominantly upright orientation. In contrast, adsorption of an A4-type symmetric Pc should generate a more in-plane (i.e., flat) orientation, and data published by other groups support this idea. For example, the electroactive surface coverage of thiol- and amino-functionalized, A4-type symmetric Pcs on Au corresponds to about one monolayer of molecules adsorbed in a flat molecular orientation (which is about 1  10
10 mol cm
2 for these Pcs because they are smaller than 12d and 12e).28 On the basis of this comparison, adsorption of an A3B-type Pc produces a higher surface coverage and a more upright molecular orientation than adsorption of an A4-type Pc. Under the same adsorption conditions (100 μM for 3 h), the electrochemical activity of the unmetalated Pcs 12a and 12b on ITO was minimal and electroactive surface coverages could not be determined from the voltammograms. The adsorption conditions were then modified. Films were prepared from solutions of higher concentration (1 mM) using a longer immersion time (5 h), which produced measurable electrochemical activity (Figure 4B). Films of 12a and 12b exhibit a single peak for the first oxidation process. The voltammetric peaks are centered around E°0 values of 0.56 and 0.60 V for 12a and 12b, respectively, which suggests that only one form of unmetalated Pc was present in these films. It is unknown if this is a monomeric or aggregated form. However, because the films were adsorbed from solutions of high concentration in which aggregates are the predominant form (see spectra in Figure 1), it is likely that the adsorbed films of 12a and 12b are composed primarily of aggregated forms. Despite the fact that the films were adsorbed from solutions of relatively high concentration, the electroactive surface coverages of 12a and 12b were much lower than those of 12d and 12e (Table 1). A possible cause of this difference is a lower sticking coefficient and/or a lower lateral diffusion coefficient of the aggregated forms on the surface of ITO (the latter would lead to less efficient molecular packing).

The effect of the central metal on the E°0 values of PA functionalized Pcs is apparent by comparing the data listed in Table 1. It is well-known that insertion of a metal ion in the Pc ring affects the electric field on the ligands,29 which shifts E°0 . Most of the published data on unmetalated and Zn(II)-Pcs show that the former are oxidized at more positive potentials, typically 200
300 mV, than the latter, consistent with our observations.22,30 Electron Transfer Kinetics. Table 1 lists apparent heterogeneous electron transfer rate constants (ks,app) for all four adsorbed films. These values were determined from the CV data using the method formulated by Laviron.31 Similar ks,app values of 1
2 s
1 were obtained for all four films. Although electroactive films of tethered Pcs have been prepared and characterized by other groups,28 as noted above, to our knowledge rate constants have not been reported for the first oxidation process. A comparison of the ks,app values of 12a (n = 3) and 12b (n = 10) is instructive. A higher ks,app value may be expected for 12a due to a smaller tunneling distance between the electroactive ring macrocycle and the electrode surface (distances are estimated to be 7.6 and 16 Å for 12a and 12b, respectively, assuming an all-trans conformation for the tether and a 0° tilt between the tether and the surface normal).32 However, similar ks,app values were determined, suggesting that tunneling through the carbon chain is not the ratedetermining step. The dependence of ks,app on tether structure and length in A3B-type Pcs adsorbed to ITO and other transparent conducting oxide electrodes will be the subject of future studies. UPS Studies of Phthalocyanines Adsorbed on ITO. The electrochemical data in Figure 4A and Table 1 suggest similar redox potentials of 0.3 and 0.35 V (vs Fc/Fc+) for the metalated Pcs 12d and 12e, respectively. Assuming an ionization energy (IE) of 4.9 eV for the Fc/Fc+ redox couple,33 this would indicate bulk ionization energies of 5.2 eV (12d) and 5.25 eV (12e) for the substituted Zn-Pcs, which is consistent with previous reports that estimate the IE of Zn-Pcs to be 5.2
5.3 eV.34 However, electrochemistry does not account for the formation of a surface or interfacial dipole, which is manifested in vacuum level shifts between the oxide and the Pc. It has been previously demonstrated that attachment of an organic modifier to ITO, through a phosphonic acid, can either increase or decrease the work function at the SAM
oxide interface due to the presence of a 14904

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir surface dipole, as dictated by the headgroup of the phosphonic acid modifier.6,8 Therefore, true estimates of ionization energies, which can impact OPV performance, must be measured directly using ultraviolet photoemission spectroscopy (UPS). We focused on only the Zn-Pc derivatives 12d and 12e, as these provided the highest coverages and charge transfer rates in Table 1. Figure 5A shows the UPS spectra for the bare ITO post air plasma treatment (i) and the ITO postmodification with 12d (ii) and 12e (iii) tethered to the ITO. Coverages for these films were consistent with those presented in Table 1. Figure 5B gives the resultant energy band diagrams, as interpreted from the UPS spectra. Optical gaps from Figure 2 (12d, 1.77 eV; 12e, 1.69 eV), calculated from the tangent of the absorbance onset, were used to estimate LUMO values from the initial IE. The work function of the air plasma ITO was measured to be 5.0 eV, consistent with previous reports.35 The work function was found to decrease to 4.13 eV upon modification of the ITO with 12d and to 4.35 eV upon modification with 12e. There is a feature at a unique energetic position just below the Fermi level for both 12d and 12e (∼0.2 to 0.3 eV below EF) that has not previously been seen for nonmodified Zn-Pcs (Figure 5A, curves ii and iii).34 The measured IE from this feature, defined as the onset of the peak, was 4.33 eV for 12d and 4.69 eV for 12e, indicating a much greater difference between the two Pcs in ionization energy than what was predicted by electrochemistry. However, the onset for the second predominant peak, much more similar to the HOMO peak of Zn-Pc, HOMO0 , yielded an IE0 of 5.98 eV for 12d and 5.94 eV for 12e. The disparity between the solid-state UPS measurements and solution-phase electrochemical measurements can be partially explained by the local shift in the vacuum level (ΔEvac =
0.7 to
0.9 eV) upon modification, which can be attributed to a change in the local dipole at the oxide
modifier interfaces. Coverages for 12d and 12e were found to be similar, so we do not expect the differences in IE to be due to partial coverages. Because of the local vacuum level shift upon modification of the ITO with the Pcs, the IE of the modifiers lies within 0.2
0.3 eV of the Fermi level. There is no barrier to hole collection between the Pcs (12d or 12e) and the ITO, but there is a small barrier (0.2
0.3 eV) for hole injection into the Pc. Therefore, charge transfer from the Pc layer into the ITO is not expected to be contact limited, and assuming energetic alignment with the subsequent donor layers, a bulk-limited or ohmic contact at the Pc-modified TCO
donor interface is expected. Future work will focus on the evaluation of the collection efficiency of these Zn-Pc modifers.

’ CONCLUSION We have reported the synthesis and characterization of a novel series of aryloxy- and arylthio-substituted asymmetric Pcs 12a
e containing PA anchoring groups in their respective asymmetric quadrants. Asymmetric Pcs can be immobilized on the surface of ITO by adsorption via the PA group and form stable films. Electrochemical characterization shows near monolayer surface coverage is achieved when the dissolved molecules are monomeric rather than aggregated, although both monomeric and aggregated forms are present in the film. Kinetic studies show no dependence of the apparent heterogeneous electron transfer rate constants on tether length, which suggests that tunneling through the tethered carbon chain is not the rate-determining step. Ionization energies of the modified ITO surfaces were measured by UPS and verify no barrier to hole collection at the modified ITO surface.

ARTICLE

’ EXPERIMENTAL SECTION Synthesis Materials and Methods. NMR data were collected on Bruker 500 and 600 MHz spectrometers running Xwinnmr (Bruker). Chemical shifts were referenced to the deuterated solvent resonance for 1 H (7.26 ppm for CDCl3 and 6.00 for trichloroethylene-d2 (TCE-d2)) and 13C (77.0 ppm for CDCl3) NMR. Chemical shifts for 31P NMR were referenced to H3PO4 (0 ppm). UV
vis measurements were performed using a Shimadzu UV-2401PC UV
vis spectrophotometer. Molar absorptivity (ε) values were calculated from Beer’s law plots using three data points. All melting points reported were uncorrected. All chemicals were purchased from commercial suppliers and used as received unless otherwise noted. Pn 5a was prepared according to the literature.16 Substrate Preparation. ITO on glass with a layer thickness of ∼100 nm and a sheet resistance of ∼15 Ω/cm2 was purchased from Colorado Concept Coating, LLC. The ITO electrodes were cleaned by lightly scrubbing with detergent (diluted Triton X-100) for 1 min, followed by successive sonication in detergent, deionized (DI) water, and ethanol for 15 min each. DI water was obtained from a Barnstead Nanopure system with a measured resistivity of 18.3 MΩ 3 cm. Cleaned ITO electrodes were stored in ethanol. The electrode surface was then activated in an air plasma cleaner (PDC-3XG, Harrick Scientific, Ossining, NY) for 15 min at medium radio frequency (rf) level immediately before use. Electrochemical Characterization of Pcs on ITO. Pcs were deposited on ITO by immersing cleaned and surface-activated electrodes at room temperature into a 1 mM solution in TCE for 5 h (12a and 12b), a 100 μM solution in CH3CN/pyridine (7:3) (12d) for 3 h, or a 100 μM solution in CH2Cl2 (12e) for 3 h. The electrodes were then rinsed with a copious amount of solvent and dried with a stream of nitrogen before electrochemical characterizations. Cyclic voltammetry measurements were performed with a standard three-electrode configuration (electroactive area 0.071 cm2) using a CH420A potentiostat (CH Instruments, Inc., Austin, TX). Ultraviolet Photoemission Spectroscopy. UPS studies were performed with a Kratos Axis Ultra X-ray photoelectron spectrometer with a He(I) excitation source (21.2 eV). A
9.00 V bias was applied to the sample to further enhance the collection of lowest kinetic energy electrons. The Fermi level reference was established on a freshly evaporated Au surface. 4-Pentylbenzenethiol (3). A heavy-walled Schlenk flask was charged with 4-pentylbromobenzene (1) (10.0 g, 44.0 mmol), 1-hexanethiol (7.80 g, 66.0 mmol), DDPPX (1.27 g, 2.20 mmol), Pd2(dba)3 (1.00 g, 1.10 mmol), DIPEA (11.4 g, 88.1 mmol), and dioxane (50 mL). Three cycles of freeze
pump
thaw were performed, followed by sealing the flask with a Teflon stopcock. The resulting reaction mixture was heated in an oil bath set to 120 °C with stirring for 20 h, at which point the vessel was removed from the oil bath and allowed to cool to rt. Hexanes (50 mL) were then added, and the mixture was filtered through a small plug of Celite. The filtrate was collected, the solvent removed under reduced pressure, and the orange residue isolated by distillation (110
115 °C at 0.15 Torr) to give crude 2 as a yellow oil (11.0 g): 1H NMR (500 MHz, CDCl3) δ 7.24 (d, J = 9 Hz, 2H), 7.09 (d, J = 9 Hz, 2H), 2.88 (t, J = 8 Hz, 2H), 2.56 (t, J = 8 Hz, 2H), 1.65
1.57 (m, 4H), 1.42
1.38 (m, 2H), 1.36
1.25 (m, 8H), 0.90
0.84 (m, 6H); 13C NMR (125 MHz, CDCl3) δ 140.8, 133.4, 129.5, 128.9, 35.4, 34.2, 31.44, 31.36, 31.1, 29.2, 28.5, 22.52, 22.51, 14.0. Crude hexyl(4-pentylphenyl)sulfane (2) (10.0 g, 37.9 mmol) was dissolved in HMPA (30 mL) in a three-neck flask. The flask was purged with Ar, followed by portionwise addition of freshly cut pieces of Na metal (8.75 g, 379 mmol). The reaction mixture was heated in an oil bath set to 120 °C with stirring for 20 h, at which point the contents were removed from the oil bath and allowed to cool to rt. The liquid portion of the reaction mixture was then poured into ether (150 mL), while being careful not to include any Na metal. The ether mixture was then neutralized with Dowex H+ resin and filtered and the 14905

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir filtrate extracted with H2O (3  200 mL). The organic layer was collected, dried over MgSO4, and filtered and the filtrate concentrated under reduced pressure. The residue was purified by distillation (70
72 °C at 0.2 Torr) to give 3 (4.67 g, 65% yield from 1): 1H NMR (500 MHz, CDCl3) δ 7.12 (d, J = 9 Hz, 2H), 6.97 (d, J = 9 Hz, 2H), 3.30 (s, 1H), 2.46 (t, J = 8 Hz, 2H), 1.53
1.46 (m, 2H), 1.25
1.18 (m, 4H), 0.81 (t, J = 7 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 140.7, 129.8, 129.2, 126.8, 35.3, 31.4, 31.1, 22.5, 14.0. 4,5-Bis((4-pentylphenyl)thio)phthalonitrile (5b). A roundbottom flask was charged with 4,5-dichlorophthalonitrile (4) (3.00 g, 15.2 mmol), 3 (6.85 g, 38.1 mmol), K2CO3 (10.5 g, 76.1 mmol), and DMSO (50 mL). The flask was purged with N2, followed by heating in an oil bath set to 80 °C for 20 h, at which point the reaction mixture was removed from the oil bath and allowed to cool to rt. After the reaction mixture was poured into H2O (250 mL), the newly formed solid was filtered and washed several times with H2O. The yellow solid was airdried for 2 h, followed by recrystallization from EtOH (∼350 mL) to give 5b (5.25 g, 71% yield) as a feathery off-white solid: 1H NMR (500 MHz, CDCl3) δ 7.46 (d, J = 9 Hz, 4H), 7.33 (d, J = 9 Hz, 4H), 6.94 (s, 2H), 2.69 (t, J = 8 Hz, 4H), 1.71
1.65 (m, 4H), 1.40
1.35 (m, 8H), 0.92 (t, J = 7 Hz, 6H); 13C NMR (125 MHz, CDCl3) δ146.3, 144.4, 135.4, 130.8, 129.3, 124.8, 115.5, 111.3, 35.7, 31.5, 30.8, 22.5, 14.0; MS (MALDI) m/z (M)+ calcd for C30H32N2NaS2+ 507.3, found 507.1. Anal. Calcd for C30H32N2S2: C, 74.34; H, 6.65; N, 5.78. Found: C, 74.60; H, 7.00; N, 5.88. 4-((4-Methoxybenzyl)oxy)phthalonitrile (6). A round-bottom flask was charged with 4-nitrophthalonitrile (3.00 g, 17.3 mmol), 4-methoxybenzyl alcohol (3.59 g, 26.0 mmol), K2CO3 (4.78 g, 34.6 mmol), and DMSO (100 mL). The reaction mixture was purged with Ar and heated to 50 °C with stirring for 16 h. Then the reaction mixture was cooled to rt, followed by addition of H2O (200 mL). The resulting solid was filtered and washed several times with H2O. The crude solid was recrystallized from EtOAc to give 6 (3.20 g, 70% yield) as a flaky white solid: mp 138
140 °C; 1H NMR (600 MHz, CDCl3) δ 7.69 (d, J = 9 Hz, 1H), 7.34
7.31 (m, 3H), 7.26
7.24 (m, 1H), 6.95
6.92 (m, 2H), 5.09 (s, 2H), 3.82 (s, 3H); 13C NMR (150 MHz, CDCl3) δ 161.7, 160.0, 135.1, 129.4, 126.4, 119.9, 119.7, 117.3, 115.6, 115.2, 114.2, 107.2, 70.9, 55.3; MS (EI) m/z (M)+ calcd for C16H12N2O2+ 264.1, found 264.1. Anal. Calcd for C16H12N2O2: C, 72.72; H, 4.58; N, 10.60. Found: C, 72.55; H, 4.96; N, 10.66. Symmetric Pcs 8a
d. These Pcs were obtained during the preparation of asymmetric Pcs 9a
d. During the final chromatographic separation in each case, an initial band of Pc ran with the solvent front. These bands were collected and identified as symmetric Pcs 8a
d. Data for 2,3,9,10,16,17,23,24-octakis(4-pentylphenoxy)phthalocyanine (8a): 1H NMR (400 MHz, CD2Cl2/pyridine-d5 (95:5)) δ 9.00 (s, 8H), 7.24 (d, J = 8 Hz, 16H), 7.15 (d, J = 8 Hz, 16H), 2.65 (t, J = 8 Hz, 16H), 1.68
1.66 (m, 16H), 1.40
1.36 (m, 32H), 0.93 (t, J = 7 Hz, 24H); UV
vis (CHCl3) Q-band λmax 669 and 704 nm (ε = 3.7  105); MS (MALDI) m/z (M)+ calcd for C120H130N8O8+ 1811.0, found 1811.4. Data for (2,3,9,10,16,17,23,24-octakis(4-pentylphenoxy)phthalocyanine)zinc(II) (8b): 1H NMR (400 MHz, CD2Cl2/pyridine-d5 (95:5)) δ 9.00 (s, 8H), 7.24 (d, J = 8 Hz, 16H), 7.15 (d, J = 8 Hz), 2.64 (t, J = 8 Hz, 16H), 1.67
1.65 (m, 16H), 1.39
1.33 (m, 32H), 0.93 (t, J = 7 Hz, 24H); UV
vis (CHCl3) Q-band λmax 682 nm (ε = 3.8  105); MS (MALDI) m/z (M)+ calcd for C120H128N8O8Zn+ 1872.9, found 1873.1. Data for (2,3,9,10,16,17,23,24-octakis((4-pentylphenyl)thio)phthalocyanine)zinc(II) (8c): 1H NMR (500 MHz, CDCl3/pyridine-d5 (95:5)) δ 9.03 (s, 8H), 7.50 (d, J = 9 Hz, 16H), 7.26
7.23 (m, 16H), 2.67 (t, J = 8 Hz, 16H), 1.69
1.67 (m, 16H), 1.36
1.34 (m, 32H), 0.87 (t, J = 7 Hz, 24H); UV
vis (CHCl3) Q-band λmax 716 nm (ε = 8.9  105); MS (MALDI) m/z (M)+ calcd for C120H128N8S8Zn+ 2000.7, found 2001.0. Anal. Calcd for C120H128N8S8Zn: C, 71.91; H, 6.44; N, 5.59. Found: C, 71.66; H, 6.82; N, 5.58.

ARTICLE

Data for 2,3,9,10,16,17,23,24-octakis((4-pentylphenyl)thio)phthalocyanine (8d): 1H NMR (500 MHz, CDCl3) δ 8.83 (s, 8H), 7.53 (d, J = 8 Hz, 16H), 7.35
7.27 (m, 16H), 2.69 (t, J = 8 Hz, 16H), 1.69 (br s, 16H), 1.38
1.36 (m, 32H), 0.89 (t, J = 7 Hz, 24H); UV
vis (CHCl3) Q-band λmax 712 and 738 nm (ε = 2.5  105); MS (MALDI) m/z (M)+ calcd for C120H130N8S8+ 1938.8, found 1939.0. Anal. Calcd for C120H130N8S8: C, 74.26; H, 6.75; N, 5.77. Found: C, 73.87; H, 6.93; N, 5.59.

2,3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-hydroxyphthalocyanine (9a). Pn 6 (1.75 g, 6.55 mmol), Pn 5a15 (6.00 g, 13.1 mmol), DBU (2.99 g, 13.1 mmol), LiBr (57 mg, 0.66 mmol), and 1-pentanol (250 mL) were combined in a round-bottom flask. The reaction mixture was purged with Ar and heated to 155 °C with stirring for 16 h. The mixture was cooled to rt and precipitated from MeOH. The resulting green solid was filtered and washed several times with MeOH. A mixture of phthalocyanines was isolated by flash chromatography (silica gel, CH2Cl2/hexanes (3:2)). The resulting green solid was dissolved in CH2Cl2 (20 mL), followed by addition of TFA (5 mL) with stirring. After 2 h, the solvents were removed under reduced pressure, and the residue was purified by flash chromatography (silica gel, CH2Cl2/ hexanes (3:2) to CH2Cl2) to give 9a (840 mg, 13% yield) as a green solid: 1H NMR (500 MHz, CD2Cl2) δ 8.55
7.60 (br m, 9H), 7.55
6.75 (br m, 24H), 2.87
2.23 (br m, 12H), 1.84
1.58 (br m, 12H), 1.51
1.19 (br m, 24H), 1.10
0.81 (br m, 18H); UV
vis (CHCl3) Q-band λmax 670 and 703 nm (ε = 1.8  105); MS (MALDI) m/z (M)+ calcd for C98H102N8O7+ 1502.8, found 1503.1.

(2,3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-hydroxyphthalocyanine)zinc(II) (9b). Pn 6 (580 mg, 2.18 mmol), Pn 5a15 (2.00 g, 4.36 mmol), DBU (500 mg, 3.27 mmol), Zn(OAc)2 (600 mg, 3.27 mmol), and 1-pentanol (50 mL) were combined in a round-bottom flask. The reaction mixture was purged with Ar and heated to 155 °C with stirring for 10 h. The mixture was cooled to rt and precipitated from MeOH. The resulting green solid was filtered and washed several times with MeOH. A mixture of phthalocyanines was isolated by flash chromatography (silica gel, CH2Cl2/MeOH (97:3)). The resulting green solid was dissolved in CH2Cl2 (45 mL), followed by addition of TFA (5 mL) with stirring. After 2 h, the solvents were removed under reduced pressure, and the residue was purified by flash chromatography (silica gel, CH2Cl2/ acetone (96:4)) to give 9b (520 mg, 15% yield) as a green solid: 1H NMR (500 MHz, CD2Cl2/pyridine-d5 (95:5)) δ 11.65 (br s, 1H), 9.05 (d, J = 5 Hz, 1H), 8.93
8.85 (m, 6H), 8.66 (s, 1H), 7.62 (d, J = 5 Hz), 7.30
7.10 (m, 24H), 2.70
2.64 (m, 12H), 1.71
1.64 (m, 12H), 1.42
1.38 (m, 24H), 0.97
0.92 (m, 18H); UV
vis (CHCl3) Q-band λmax 682 nm (ε = 2.9  105); MS (MALDI) m/z (M)+ calcd for C98H100N8O7Zn+ 1564.7, found 1564.7. Anal. Calcd for C98H100N8O7Zn: C, 75.10; H, 6.43; N, 7.15. Found: C, 74.77; H, 6.70; N, 6.90.

(2,3,9,10,16,17-Hexakis((4-pentylphenyl)thio)-23-hydroxyphthalocyanine)zinc(II) (9c). Pn 6 (690 mg, 2.58 mmol), Pn 1b (2.50 g, 5.17 mmol), DBU (590 mg, 3.87 mmol), Zn(OAc)2 (710 mg, 3.87 mmol), and 1-pentanol (50 mL) were combined in a round-bottom flask. The reaction mixture was purged with Ar and heated to 155 °C with stirring for 10 h. The mixture was cooled to rt and precipitated from MeOH. The resulting green solid was filtered and washed several times with MeOH. A mixture of phthalocyanines was isolated by flash chromatography (silica gel, CH2Cl2/MeOH (97:3)). The resulting green solid was dissolved in CH2Cl2 (22.5 mL), followed by addition of TFA (2.5 mL) with stirring. After 2 h, the solvents were removed under reduced pressure, and the residue was purified by flash chromatography (silica gel, CH2Cl2 to CH2Cl2/acetone (96:4)) to give 9c (370 mg, 13% yield) as a green solid: 1H NMR (500 MHz, CD2Cl2: pyridine (95:5)) δ 9.05 (d, J = 1.5 Hz, 2H), 9.02
8.97 (m, 3H), 8.86 (d, J = 9 Hz, 1H), 8.59 (d, J = 1.5 Hz, 1H), 8.56 (s, 1H), 7.68
7.25 (m, 25H), 2.75
2.65 (m, 12H), 1.81
1.70 (m, 12H), 1.50
1.29 (m, 24H), 0.95
0.83 (m, 18H); UV
vis (CHCl3) Q-band λmax 714 nm (ε = 3.2  105); 14906

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir MS (MALDI) m/z (M)+ calcd for C98H100N8OS6Zn+ 1660.6, found 1660.6. Anal. Calcd for C98H100N8OS6Zn: C, 70.75; H, 6.06; N, 6.74. Found: C, 70.45; H, 6.20; N, 6.60.

2,3,9,10,16,17-Hexakis((4-pentylphenyl)thio)-23-hydroxyphthalocyanine (9d). Method A. Pn 6 (829 mg, 3.10 mmol), Pn 1b (3.00 g, 6.20 mmol), DBU (709 mg, 4.65 mmol), LiBr (135 mg, 1.55 mmol), and 1-pentanol (50 mL) were combined in a round-bottom flask. The reaction mixture was purged with Ar and heated to 155 °C with stirring for 10 h. The mixture was cooled to rt and precipitated from MeOH. The resulting green solid was filtered and washed several times with MeOH. A mixture of phthalocyanines was isolated by flash chromatography (silica gel, CH2Cl2/MeOH (97:3)). The resulting green solid was dissolved in CH2Cl2 (45 mL), followed by addition of TFA (5 mL) with stirring. After 2 h, the solvents were removed under reduced pressure, and the residue was purified by flash chromatography (silica gel; CH2Cl2/hexanes (1:1) to CH2Cl2/hexanes (4:1), followed by hexanes/EtOAc (9:1) to hexanes/EtOAc (3:1)) to give 9d (150 mg, 3% yield) as a green solid. This method was found to not give product of suitable purity, as determined by 1H NMR and gel permeation chromatography (GPC) analysis. Method B. A heavy-walled Schlenk flask was charged with 9c (200 mg, 0.12 mmol), pyridine hydrochloride (4.0 g), and pyridine (8.0 mL). The flask was sealed, followed by heating to 120 °C in an oil bath for 22 h. The mixture was then removed from the oil bath and was allowed to cool to rt. Then H2O (30 mL) was added and the suspension centrifuged. The supernatant was poured off, and the green solid was purified by flash chromatography (silica gel, CH2Cl2/hexanes (4:1)) to give 9d (115 mg, 60% yield) as a green solid: 1H NMR (500 MHz, CDCl3) δ 8.87 (s, 1H), 8.77 (s, 1H), 8.60
8.52 (m, 2H), 8.35
8.24 (m, 2H), 7.98
7.84 (m, 2H), 7.69
7.20 (m, 25H), 2.75
2.63 (m, 12H), 1.81
1.64 (m, 12H), 1.47
1.35 (m, 24H), 1.05
0.84 (m, 18H); UV
vis (CHCl3) Q-band λmax 710 and 720 nm (ε = 2.1  105); MS (MALDI) m/z (M)+ calcd for C98H102N8OS6+ 1598.7, found 1598.8. Anal. Calcd for C98H102N8OS6: C, 73.55; H, 6.42; N, 7.00. Found: C, 73.28; H, 6.80; N, 7.01. Diethyl (10-Bromodecyl)phosphonate (10b)20. A mixture of 1,10-dibromodecane (4.30 g, 14.4 mmol) and triethyl phosphite (477 mg, 2.87 mmol) was sealed in a microwave vessel and reacted at 150 W for 2.5 min. After being cooled to rt, the mixture was purified by flash chromatography (silica gel, CH2Cl2/acetone (85:15)) to give 10b (650 mg, 63% yield) as a colorless oil: 1H NMR (600 MHz, CDCl3) δ 4.10
4.03 (m, 4H), 3.38 (t, J = 7 Hz, 2H), 1.85
1.80 (m, 2H), 1.72
1.66 (m, 2H), 1.60
1.53 (m, 2H), 1.41
1.26 (m, 18H); 13C NMR (150 MHz, CDCl3) δ 61.32, 61.28, 33.9, 32.8, 30.6, 30.5, 29.3, 29.2, 29.0, 28.7, 28.1, 26.1, 25.2, 22.4, 22.3, 16.5, 16.4.

3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-(diethyl (3-oxypropyl)phosphonate)phthalocyanine (11a). Pc 9a (1.0 g, 0.66 mmol) was dissolved in DMF (20 mL), followed by addition of diethyl (3-bromopropyl)phosphonate (10a) (260 mg, 0.98 mmol), K2CO3 (140 mg, 0.98 mmol), and KI (20 mg, 0.098 mmol). The reaction mixture was purged with Ar and heated to 100 °C for 2 h. After the mixture was cooled to rt, the solvent was removed under reduced pressure and the residue purified by flash chromatography (silica gel, CH2Cl2/acetone (85:15)) to give 11a (820 mg, 73% yield) as a green solid: 1H NMR (500 MHz, CD2Cl2) δ 8.69
8.62 (m, 1H), 8.33 (br s, 2H), 8.30
8.15 (m, 3H), 8.00 (br s, 2H), 7.63
7.57 (m, 1H), 7.40
7.15 (m, 24H), 4.28 (br s, 2H), 4.25
4.11 (m, 4H), 2.74
2.50 (m, 12H), 2.40
2.26 (m, 2H), 2.18
2.08 (m, 2H), 1.79
1.62 (m, 12H), 1.50
1.32 (m, 30H), 1.04
0.91 (m, 18H); 31P NMR (121 MHz, pyridine-d5) δ 32.14; UV
vis (CHCl3) Q-band λmax 669 and 703 nm (ε = 3.2  105); MS (MALDI) m/z (M)+ calcd for C105H117N8O10P+ 1680.9, found 1680.7. Anal. Calcd for C105H117N8O10P: C, 74.97; H, 7.01; N, 6.66. Found: C, 74.88; H, 7.40; N, 6.64.

2,3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-(diethyl (10oxydecyl)phosphonate)phthalocyanine (11b). Pc 9a (180 mg,

ARTICLE

0.120 mmol) was dissolved in DMF (5 mL), followed by addition of 10b20 (50 mg, 0.180 mmol), K2CO3 (25 mg, 0.180 mmol), and KI (3 mg, 0.018 mmol). The reaction mixture was purged with Ar and heated to 120 °C for 2 h. After the mixture was cooled to rt, the solvent was removed under reduced pressure and the residue purified by flash chromatography (silica gel, CH2Cl2/acetone (4:1)) to give 11b (160 mg, 75% yield) as a green solid: 1H NMR (600 MHz, CD2Cl2) δ 8.38 (br s, 1H), 8.13
8.00 (m, 4H), 7.97 (br s, 1H), 7.79 (br s, 2H), 7.45
7.00 (m, 25H), 4.17 (br s, 2H), 4.11
4.06 (m, 4H), 2.74
2.61 (m, 12H), 2.06
2.03 (m, 2H), 1.82
1.62 (m, 18H), 1.61
1.55 (m, 2H), 1.54
1.35 (m, 32H), 1.34 (t, J = 9 Hz, 6H), 1.09
0.90 (m, 18H); 31P NMR (202 MHz, pyridine-d5) δ 32.65; UV
vis (CHCl3) Q-band λmax 669 and 703 nm (ε = 2.4  105); MS (MALDI) m/z (M)+ calcd for C112H131N8O10P+ 1779.0, found 1778.9. Anal. Calcd for C112H131N8O10P: C, 75.56; H, 6.29; N, 6.29. Found: C, 75.59; H, 7.80; N, 6.22.

2,3,9,10,16,17-Hexakis((4-pentylphenyl)thio)-23-(diethyl (10-oxydecyl)phosphonate)phthalocyanine (11c). Pc 9d (90 mg, 0.056 mmol) was dissolved in DMF (5 mL), followed by addition of 10b20 (30 mg, 0.084 mmol), K2CO3 (12 mg, 0.084 mmol), and KI (3 mg, 0.017 mmol). The reaction mixture was purged with Ar and heated to 120 °C for 2 h. After the mixture was cooled to rt, the solvent was removed under reduced pressure and the residue purified by flash chromatography (silica gel, CH2Cl2/MeOH (95:5)) to give 11c (90 mg, 85% yield) as a green solid: 1H NMR (500 MHz, CD2Cl2) δ 8.82 (s, 1H), 8.64 (s, 1H), 8.50
8.32 (m, 2H), 8.26 (br s, 1H), 8.11 (br s, 1H), 8.03 (br s, 1H), 7.84 (br s, 1H), 7.73
7.19 (m, 25H), 4.36 (br s, 2H), 4.10
4.00 (m, 4H), 2.74
2.60 (m, 12H), 2.22
2.18 (m, 2H), 1.83
1.61 (m, 20H), 1.52
1.25 (m, 38H), 1.01
0.85 (m, 18H); 31P NMR (202 MHz, CD2Cl2) δ 32.55; UV
vis (CHCl3) Q-band λmax 706 and 721 nm (ε = 2.0  105); MS (MALDI) m/z (M)+ calcd for C112H131N8O4PS6+ 1874.8, found 1875.0. Anal. Calcd for C112H131N8O4PS6: C, 71.68; H, 7.04; N, 5.97. Found: C, 71.38; H, 7.36; N, 6.00.

(2,3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-(diethyl (10oxydecyl)phosphonate)phthalocyanine)zinc(II) (11d). Pc 9b (250 mg, 0.160 mmol) was dissolved in DMF (5 mL), followed by addition of 10b20 (87 mg, 0.240 mmol), K2CO3 (33 mg, 0.240 mmol), and KI (13 mg, 0.080 mmol). The reaction mixture was purged with Ar and heated to 120 °C for 2 h. After the mixture was cooled to rt, the solvent was removed under reduced pressure and the residue purified by flash chromatography (silica gel, CH2Cl2/EtOAc (97:3)) to give 11d (203 mg, 71% yield) as a green solid: 1H NMR (500 MHz, CD2Cl2/ pyridine-d5 (95:5)) δ 9.15 (d, J = 10 Hz, 1H), 9.05 (s, 1H), 8.95
8.93 (m, 5H), 8.77 (d, J = 1.5 Hz, 1H), 7.65 (dd, J = 10 Hz and J = 1.5 Hz, 1H), 7.30
7.14 (m, 24H), 4.46 (t, J = 6 Hz, 2H), 4.05
4.00 (m, 4H), 2.72
2.65 (m, 12H), 2.03
1.98 (m, 2H), 1.73
1.65 (m, 16H), 1.62
1.58 (m, 2H), 1.53
1.47 (m, 2H), 1.43
1.37 (m, 32H), 1.29 (t, J = 6 Hz, 6H), 0.98
0.92 (m, 18H); UV
vis (CHCl3) Q-band λmax 682 nm (ε = 4.0  105); MS (MALDI) m/z (M)+ calcd for C112H129N8O10PZn+ 1840.9, found 1840.9. Anal. Calcd for C112H129N8O10PZn: C, 72.96; H, 7.05; N, 6.08. Found: C, 72.69; H, 7.44; N, 6.16.

(2,3,9,10,16,17-Hexakis((4-pentylphenyl)thio)-23-(diethyl (10-oxydecyl)phosphonate)phthalocyanine)zinc(II) (11e). Pc 9c (200 mg, 0.121 mmol) was dissolved in DMF (10 mL), followed by addition of 10b20 (65 mg, 0.181 mmol), K2CO3 (25 mg, 0.181 mmol), and KI (10 mg, 0.0605 mmol). The reaction mixture was purged with Ar and heated to 120 °C for 2 h. After the mixture was cooled to rt, the solvent was removed under reduced pressure and the residue purified by flash chromatography (silica gel, hexanes/EtOAc (4:1) to hexanes/ EtOAc (3:2) to hexanes/EtOAc (2:3)) to give 11e (180 mg, 77% yield) as a green solid: 1H NMR (500 MHz, CD2Cl2/pyridine-d5 (95:5)) δ 9.03 (s, 1H), 8.99 (s, 1H), 8.97 (s, 1H), 8.93
8.90 (m, 2H), 8.82 (d, J = 10 Hz, 1H), 8.67 (s, 1H), 8.50 (s, 1H), 7.69
7.20 (m, 25H), 4.43 (t, J = 6 Hz, 2H), 4.06
4.00 (m, 4H), 2.80
2.54 (m, 12H), 2.23
2.10 (m, 2H), 1.88
1.79 (m, 2H), 1.76
1.65 (m, 14H), 1.64
1.52 (m, 4H), 14907

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir

ARTICLE

1.53
1.23 (m, 38H), 1.01
0.82 (m, 18H); 31P NMR (202 MHz, pyridine-d5) δ 32.56; UV
vis (CHCl3) Q-band λmax 711 nm (ε = 3.5  105); MS (MALDI) m/z (M)+ calcd for C112H129N8O4PS6Zn+ 1936.7, found 1936.8. Anal. Calcd for C112H129N8O4PS6Zn: C, 69.34; H, 6.70; N, 5.78. Found: C, 69.38; H, 7.04; N, 5.79.

P NMR (202 MHz, pyridine-d5) δ 28.65; UV
vis (TCE) Q-band λmax 683 nm (ε = 8.7  104); MS (MALDI) m/z (M)+ calcd for C108H121N8O10PZn+ 1784.8, found 1784.9.

2,3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-((3-oxypropyl)phosphonic acid)phthalocyanine (12a). Pc 11a (500 mg,

0.026 mmol) was dissolved in CH2Cl2 (2 mL) in a round-bottom flask. The reaction vessel was purged with Ar, followed by dropwise addition of (TMS)Br (20 mg, 0.13 mmol). The reaction mixture was stirred at rt for 20 h. Once complete, the reaction was quenched with MeOH, followed by removal of solvent under reduced pressure. The green residue was suspended in MeOH and centrifuged. The supernatant was discarded, resuspended in MeOH, and centrifuged again. This cycle was repeated with acetone (2) and finally MeOH (2), followed by drying under high vacuum to give 12e (45 mg, 94% yield) as a green solid: 1H NMR (600 MHz, CD2Cl2/pyridine-d5 (95:5)) δ 8.81
8.36 (m, 8H), 8.02 (br s, 1H), 7.74
7.20 (m, 24H), 4.34 (br s, 2H), 2.76
2.61 (m, 12H), 2.13 (br s, 2H), 1.70
1.21 (m, 52H), 1.14
0.45 (m, 18H); 31P NMR (202 MHz, CD2Cl2/pyridine-d5 (95:5)) δ 31.05; UV
vis (CHCl3) Q-band λmax 716 nm (ε = 1.3  105); MS (MALDI) m/z (M)+ calcd for C108H121N8O4PS6Zn+ 1880.7, found 1880.9.

0.297 mmol) was dissolved in CH2Cl2 (20 mL) in a round-bottom flask. The reaction vessel was purged with Ar, followed by dropwise addition of (TMS)Br (228 mg, 1.49 mmol). The reaction mixture was stirred at rt for 16 h. Once complete, the reaction was quenched with H2O, followed by removal of CH2Cl2 under reduced pressure. The resulting green solid was filtered and washed several times with MeOH. The solid was then precipitated from MeOH again, filtered, and washed several times with MeOH. Then the green solid was precipitated from acetone, filtered, washed several times with acetone and MeOH, and dried under high vacuum to give 12a (410 mg, 85% yield) as a green solid: 1H NMR (600 MHz, TCE-d2, 393 K) δ 8.70
7.70 (br m, 8H), 7.50
7.00 (m, 25H), 4.62 (br s, 2H), 2.85
2.40 (m, 16H), 1.85
1.68 (m, 12H), 1.51
1.41 (m, 24H), 1.08
0.90 (m, 18H); 31P NMR (121 MHz, pyridine-d5) δ 29.20; UV
vis (TCE) Q-band λmax 636 nm (ε = 7.7  104); MS (MALDI) m/z (M)+ calcd for C101H109N8O10P+ 1624.7, found 1624.7.

2,3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-((10-oxydecyl)phosphonic acid))phthalocyanine (12b). Pc 11b (100 mg, 0.056 mmol) was dissolved in CH2Cl2 (5 mL) in a round-bottom flask. The reaction vessel was purged with Ar, followed by dropwise addition of (TMS)Br (45 mg, 0.29 mmol). The reaction mixture was stirred at rt for 20 h. Once complete, the reaction was quenched with MeOH, followed by removal of solvent under reduced pressure. The green residue was suspended in MeOH and centrifuged. The supernatant was discarded, resuspended in MeOH, and centrifuged again. This cycle was repeated with acetone (2) and finally MeOH (2), followed by drying under high vacuum to give 12b (80 mg, 83% yield) as a green solid: 31 P NMR (202 MHz, pyridine-d5) δ 30.05; UV
vis (TCE) Q-band λmax 674 and 702 nm (ε = 7.4  104); MS (MALDI) m/z (M)+ calcd for C108H123N8O10P+ 1722.9, found 1722.9.

2,3,9,10,16,17-Hexakis((4-pentylphenyl)thio)-23-((10-oxydecyl)phosphonic acid))phthalocyanine (12c). Pc 11c (90 mg, 0.048 mmol) was dissolved in CH2Cl2 (3 mL) in a round-bottom flask. The reaction vessel was purged with Ar, followed by dropwise addition of (TMS)Br (37 mg, 0.24 mmol). The reaction mixture was stirred at rt for 20 h. Once complete, the reaction was quenched with MeOH, followed by removal of solvent under reduced pressure. The green residue was suspended in MeOH and centrifuged. The supernatant was discarded, resuspended in MeOH, and centrifuged again. This cycle was repeated with acetone (2) and finally MeOH (2), followed by drying under high vacuum to give 12c (70 mg, 77% yield) as a green solid: 31P NMR (202 MHz, CDCl3) δ 36.22; UV
vis (CHCl3) Q-band λmax 705 and 719 nm (ε = 7.5  104); MS (MALDI) m/z (M)+ calcd for C108H123N8O4PS6+ 1818.8, found 1819.0.

(2,3,9,10,16,17-Hexakis(4-pentylphenoxy)-23-((10-oxydecyl)phosphonic acid))phthalocyanine)zinc(II) (12d). Pc 11d (50 mg, 0.027 mmol) was dissolved in CH2Cl2 (2 mL) in a roundbottom flask. The reaction vessel was purged with Ar, followed by dropwise addition of (TMS)Br (21 mg, 0.14 mmol). The reaction mixture was stirred at rt for 16 h. Once complete, the reaction was quenched with MeOH, followed by removal of solvent under reduced pressure. The green residue was suspended in MeOH and centrifuged. The supernatant was discarded, resuspended in MeOH, and centrifuged again. This cycle was repeated with acetone (2) and finally MeOH (2), followed by drying under high vacuum to give 12d (40 mg, 82% yield) as a green solid: 1H NMR (600 MHz, CD2Cl2/pyridine-d5 (95:5)) δ 8.67
8.19 (m, 8H), 7.60
6.94 (m, 25H), 4.37 (br s, 2H), 2.71
2.61 (m, 12H), 2.09 (br s, 2H), 1.79
1.20 (m, 52H), 1.05
0.93 (m, 18H);

31

2,3,9,10,16,17-Hexakis((4-pentylphenyl)thio)-23-((10-oxydecyl)phosphonic acid))phthalocyanine (12e). Pc 11e (50 mg,

’ ASSOCIATED CONTENT

bS

Supporting Information. Electrochemical studies of dissolved phthalocyanines. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Phone: (520) 626-4690. Fax: (520) 621-8407.

’ ACKNOWLEDGMENT This research was supported as part of the Center for Interface Science: Solar-Electric Materials (CIS:SEM), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DE-SC0001084. ’ REFERENCES (1) Claessens, C. G.; Hahn, U.; Torres, T. Chem. Rec. 2008, 8, 75–97. (2) Bouvet, M. Anal. Bioanal. Chem. 2006, 384, 366–73. (3) Placencia, D.; Wang, W. N.; Shallcross, R. C.; Nebesny, K. W.; Brumbach, M.; Armstrong, N. R. Adv. Funct. Mater. 2009, 19, 1913–21. (4) Park, Y.; Choong, V.; Gao, Y.; Hsieh, B. R.; Tang, C. W. Appl. Phys. Lett. 1996, 68, 2699–2701. (5) (a) Campbell, I. H.; Rubin, S.; Zawodzinski, T. A.; Kress, J. D.; Martin, R. L.; Smith, D. L.; Barashkov, N. N.; Ferraris, J. P. Phys. Rev. B 1996, 54, R14321–23. (b) Ratcliff, E. L.; Zacher, B.; Armstrong, N. R. J. Phys. Chem. Lett. 2011, 2, 1337–1350. (6) Sharma, A.; Kippelen, B.; Hotchkiss, P. J.; Marder, S. R. Appl. Phys. Lett. 2008, 93, 163308/1–163308/3. (7) (a) Vioux, A.; Le Bideau, J.; Mutin, P. H.; Leclercq, D. Top. Curr. Chem. 2004, 232, 145
74. (b) Bardecker, J. A.; Ma, H.; Kim, T.; Huang, F.; Liu, M. S.; Cheng, Y.-J.; Ting, G.; Jen, A. K. Y. Adv. Funct. Mater. 2008, 18, 3964–71. (8) (a) Koh, S. E.; McDonald, K. D.; Holt, D. H.; Dulcey, C. S.; Chaney, J. A.; Pehrsson, P. E. Langmuir 2006, 22, 6249–6255. (b) Li, H.; Paramonov, P.; Bredas, J. L. J. Mater. Chem. 2010, 20, 2630–37. (c) Hotchkiss, P. J.; Li, H.; Paramonov, P. B.; Paniagua, S. A.; Jones, S. C.; Armstrong, N. R.; Bredas, J. L.; Marder, S. R. Adv. Mater. 2009, 21, 4496–501. (d) Sharma, A.; Haldi, A.; Hotchkiss, P. J.; Marder, 14908

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909

Langmuir S. R.; Kippelen, B. J. Appl. Phys. 2009, 105, 074511/1–074511/6. (e) Sharma, A.; Hotchkiss, P. J.; Marder, S. R.; Kippelen, B. J. Appl. Phys. 2009, 105, 084507. (f) Paniagua, S. A.; Hotchkiss, P. J.; Jones, S. C.; Marder, S. R.; Mudalige, A.; Marrikar, F. S.; Pemberton, J. E.; Armstrong, N. R. J. Phys. Chem. C 2008, 112, 7809–7817. (9) (a) Groenendaal, L.; Jonas, F.; Freitag, D.; Pielartzik, H.; Reynolds, J. R. Adv. Mater. 2000, 12, 481–94. (b) Hanson, E. L.; Guo, J.; Koch, N.; Schwartz, J.; Bernasek, S. L. J. Am. Chem. Soc. 2005, 127, 10058–62. (10) (a) Boyle, R. W.; Vanlier, J. E. Synlett 1993, 351–52. (b) Boyle, R. W.; Vanlier, J. E. Synthesis 1995, 1079–80. (c) Sharman, W. M.; Kudrevich, S. V.; vanLier, J. E. Tetrahedron Lett. 1996, 37, 5831–34. (d) Lukyanets, E. A. J. Porphyrins Phthalocyanines 1999, 3, 424–32. (e) Markl, G.; Gschwendner, K.; Rotzer, I.; Kreitmeier, P. Helv. Chim. Acta 2004, 87, 825–44. (f) Ivanov, A. V.; Kabanova, K. V.; Breusova, M. O.; Zhukov, I. V.; Tomilova, L. G.; Zefirov, N. S. Russ. Chem. Bull. 2008, 57, 1665–70. (11) Johnev, B.; Fostiropoulos, K. Sol. Energy Mater. Sol. Cells 2008, 92, 393–396. (12) (a) Smestad, G. P.; Krebs, F. C.; Lampert, C. M.; Granqvist, C. G.; Chopra, K. L.; Mathew, X.; Takakura, H. Sol. Energy Mater. Sol. Cells 2008, 92, 371–73. (b) Kobayashi, N.; Ogata, H.; Nonaka, N.; Luk’yanets, E. A. Chem.—Eur. J. 2003, 9, 5123–34. (13) Minch, B. A.; Xia, W.; Donley, C. L.; Hernandez, R. M.; Carter, C.; Carducci, M. D.; Dawson, A.; O’Brien, D. F.; Armstrong, N. R. Chem. Mater. 2005, 17, 1618–27. (14) Chen, X.; Salmon, T. R.; McGrath, D. V. Org. Lett. 2009, 11, 2061–2064. (15) W€ohrle, D.; Eskes, M.; Shigehara, K.; Yamada, A. Synthesis 1993, 194–96. (16) Haas, M.; Liu, S.-X.; Neels, A.; Decurtins, S. Eur. J. Org. Chem. 2006, 5467–5478. (17) Itoh, T.; Mase, T. Org. Lett. 2004, 6, 4587–4590. (18) Kottani, R.; Mebi, C. A.; Swenson, M. A.; Senef, S.; Nichol, G. S.; Lichtenberger, D. L.; Evans, D. H.; Glass, R. S. Manuscript in preparation. (19) Alzeer, J.; Roth, P. J. C.; Luedtke, N. W. Chem. Commun. 2009, 1970–1971. (20) Villemin, D.; Simeon, F.; Decreus, H.; Jaffres, P.-A. Phosphorus Sulfur 1998, 133, 209–13. (21) (a) Brewis, M.; Hassan, B. M.; Li, H.; Makhseed, S.; McKeown, N. B.; Thompson, N. J. Porphyrins Phthalocyanines 2000, 4, 460–464. (b) Kernag, C. A.; McGrath, D. V. Isr. J. Chem. 2009, 49, 9–21. (22) (a) Alemdar, A.; Ozkaya, A. R.; Bulut, M. Polyhedron 2009, 28, 3788–96. (b) Koc, I.; Camur, M.; Bulut, M.; Ozkaya, A. R. Can. J. Chem. 2010, 88, 375–82. (23) (a) Giraudeau, A.; Louati, A.; Gross, M.; Andre, J. J.; Simon, J.; Su, C. H.; Kadish, K. M. J. Am. Chem. Soc. 1983, 105, 2917–19. (b) Koca, A.; Bayar, S.; Dincer, H. A.; Gonca, E. Electrochim. Acta 2009, 54, 2684–92. (c) Manivannan, V.; Nevin, W. A.; Leznoff, C. C.; Lever, A. B. P. J. Coord. Chem. 1988, 19, 139–58. (d) Fourie, E.; Swarts, J. C.; Chambrier, I.; Cook, M. J. Dalton Trans. 2009, 1145–54. (e) Kobayashi, N.; Nakajima, S.-I.; Ogata, H.; Fukuda, T. Chem.—Eur. J. 2004, 10, 6294–312. (f) Matlaba, P.; Nyokong, T. Polyhedron 2002, 21, 2463–72. (g) Boulas, P. L.; Gomez-Kaifer, M.; Echegoyen, L. Angew. Chem., Int. Ed. 1998, 37, 216–47. (24) (a) Koca, A.; Ozkaya, A. R.; Selcukoglu, M.; Hamuryudan, E. Electrochim. Acta 2007, 52, 2683–90. (b) Mack, J.; Kobayashi, N. Chem. Rev. 2010, 111, 281–321. (c) Schlettwein, D.; Yoshida, T. J. Electroanal. Chem. 1998, 441, 139–46. (d) Yilmaz, I.; Kocak, M. B. Polyhedron 2004, 23, 1279–85. (e) Zagal, J. H.; Gulppi, M. A.; Cardenas-Jiron, G. Polyhedron 2000, 19, 2255–60. (f) Xu, H.; Shen, T.; Zhou, Q.; Shen, S.; Liu, J.; Li, L.; Zhou, S.; Zhang, X.; Yu, Q.; Bi, Z.; Xiao, X. J. Photochem. Photobiol., A 1992, 65, 267–76. (25) Li, R. J.; Zhang, X. X.; Zhu, P. H.; Ng, D. K. P.; Kobayashi, N.; Jiang, J. Z. Inorg. Chem. 2006, 45, 2327–34. (26) Finklea, H. O. In Modified Electrodes; Fujihara, M., Rubinstein, I., Rusling, J. F., Eds.; Encyclopedia of Electrochemistry, Vol. 10;

ARTICLE

Bard, A. J., Stratmann, M., Eds.; Wiley: Weinheim, Germany, 2007; pp 629
630. (27) The projected surface area of an edge-on Pc molecule is estimated to be 85 Å2. (28) (a) Agboola, B.; Westbroek, P.; Ozoemena, K. I.; Nyokong, T. Electrochem. Commun. 2007, 9, 310–316. (b) Akinbulu, I. A.; Khene, S.; Nyokong, T. Electrochim. Acta 2010, 55, 7085–7093. (c) Mashazi, P.; Antunes, E.; Nyokong, T. J. Porphyrins Phthalocyanines 2010, 14, 932–947. (d) Somashekarappa, M. P.; Keshavayya, J.; Sampath, S. Pure Appl. Chem. 2002, 74, 1609–1620. (29) (a) Lever, A. B. P.; Minor, P. C. Inorg. Chem. 1981, 20, 4015–17. (b) Lever, A. B. P.; Milaeva, E. R.; Speier, G. In Phthalocyanines: Properties and Applications; Leznoff, C. C., Lever, A. B. P., Eds.; VCH: New York, 1993; Vol. 3, pp 1
69; (c) Lever, A. B. P.; Licoccia, S.; Magnell, K.; Minor, P., C.; Ramaswamy, B. S. In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K. M., Ed.; American Chemical Society: Washington, DC, 1982; Vol. 201, pp 237
252. (30) (a) Biyiklioglu, Z.; Guener, E. T.; Topcu, S.; Kantekin, H. Polyhedron 2008, 27, 1707–1713. (b) Swarts, J. C.; Langner, E. H. G.; Krokeide-Hove, N.; Cook, M. J. J. Mater. Chem. 2001, 11, 434–443. (31) Laviron, E. J. Electroanal. Chem. 1979, 101, 19–28. (32) (a) Finklea, H. O.; Hanshew, D. D. J. Am. Chem. Soc. 1992, 114, 3173–81. (b) Li, T. T. T.; Weaver, M. J. J. Am. Chem. Soc. 1984, 106, 6107–8. (c) Smalley, J. F.; Feldberg, S. W.; Chidsey, C. E. D.; Linford, M. R.; Newton, M. D.; Liu, Y. P. J. Phys. Chem. 1995, 99, 13141–49. (33) (a) Kelly, C. P.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2007, 111, 408–422. (b) Pavlishchuk, V. V.; Addison, A. W. Inorg. Chim. Acta 2000, 298, 97–102. (34) (a) Chen, L.; Yang, L. G.; Yang, Z. S.; Shi, M. M.; Wang, M.; Chen, H. Z.; Zhang, W. H.; Xu, F. Q. J. Phys. Chem. C 2009, 113, 17160–17169. (b) Gao, W. Y.; Kahn, A. Org. Electron. 2002, 3, 53–63. (35) (a) Armstrong, N. R.; Veneman, P. A.; Ratcliff, E.; Placencia, D.; Brumbach, M. Acc. Chem. Res. 2009, 42, 1748–1757. (b) Choi, J. H.; Lee, E. S.; Choi, S. H.; Baik, H. K.; Song, K. M.; Lim, Y. S.; Lee, S. M. J. Vac. Sci. Technol., A 2005, 23, 1479–1482.

14909

dx.doi.org/10.1021/la203126c |Langmuir 2011, 27, 14900–14909