Acceptor Segregated Ï-Stacking Arrays by Use of Shish-Kebab

Article Cite This: Macromolecules XXXX, XXX, XXX-XXX

pubs.acs.org/Macromolecules

Donor/Acceptor Segregated π‑Stacking Arrays by Use of ShishKebab-Type Polymeric Backbones: Highly Conductive Discotic Blends of Phthalocyaninatopolysiloxanes and Perylenediimides Tsuneaki Sakurai,*,† Satoru Yoneda,‡ Shugo Sakaguchi,† Kenichi Kato,§ Masaki Takata,§ and Shu Seki*,† †

Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan § Materials Visualization Photon Science Group, RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan ‡

S Supporting Information *

ABSTRACT: Construction of large-area electron donor−acceptor (D−A) interfaces and hole/electron pathways is important for photoconducting and photovoltaic functions. Although blends of Dand A-type discotic π-systems have a possibility to realize onedimensional charge carrier pathways as well as heterointerfaces, D− A segregated structures are difficult to develop by self-assembly because they are entropically unfavored structures. Here we report the use of shish-kebab-type hole-transporting discotic columns fixed by a self-threading polysiloxane chain and approach to such segregated nanostructures. Electron-donor/acceptor blends of soluble phthalocyaninatopolysiloxanes (Poly-SiPcs) and perylenedicarboximides (PDIs) were prepared, and their photoconductive property was investigated. Although Poly-SiPc1 shows a photoinduced charge separation with PDI1 analogous to the corresponding monomeric phthalocyanines (SiPc1 and H2Pc1), the Poly-SiPc1/PDI1 system displays a remarkably larger photoconductivity than SiPc1/PDI1 and H2Pc1/PDI1, which mostly results from the presence of hole-transporting pathways with the mobility μh,1D ∼ 0.1 cm2 V−1 s−1 in Poly-SiPc1 along the polysiloxane covalent bonds even upon mixing with PDI1. When π-stackable PDI2 is used instead of PDI1, X-ray diffraction analysis disclosed obvious signs of π-stacking periodicities for both Pc and PDI planes in the mixture, indicating the presence of donor−acceptor segregated domains of columnar structures. As a result, photoexcitation of Poly-SiPc1/PDI2 generates highly mobile holes and electrons, leading to the observation of a much larger conductivity.

■

packing structure.17 Intracolumnar separation is an entropically favored structure and often appeared in binary systems of different mesogens.20,21 In contrast to these patterns, realization of intercolumnar separation is still the challenging issue, since donor and acceptor, in general, favor the heterotropic interaction, and thus long-range single-component columns can hardly be formed (Figure 1b). In addition, such self-sortingtype nanostructures observed in bulk are entropically unfavorable except the self-sorting of a set of enantiomers.22,23 At the same time, intercolumnar segregation, affording large donor−acceptor interfaces as well as directional hole/electrontransporting pathways, is quite attractive for an efficient photovoltaic response.24−29 Here we report a novel approach toward this type of structural order, where phthalocyaninatopolysiloxanes (Poly-SiPcs) as an electron donor keep longrange hole-transporting one-dimensional pathways even in the

INTRODUCTION After the discovery of fast electrical conduction along their columnar axis,1−3 discotic columnar liquid crystals (LCs) have been widely studied as potential candidates for soft organic semiconductors.4−8 In such soft materials, blending of two compounds is one of the most simple methodologies to tune the materials property, which is analogous to the case with polymeric materials.9−12 Blending of two discotic LCs is more complicated rathar than calamitic ones13 because strong mesogenic interactions operate between two components.14 Nevertheless, we can briefly categorize their structural orders into the patterns described in Figure 1a.15 When considering electron-donor/acceptor binary discotic systems, reported examples include macroscopic segregation, alternate stacking, and intracolumnar separation. For example, macroscopic segregation takes place by mixing the discotic molecules carrying hydrophobic and hydrophilic chains.16 Alternate stacking is seen in the case with strong heterotropic interactions such as charge-transfer interaction.17−19 The sterically favored reason also leads to the alternating stacking mode with a tight © XXXX American Chemical Society

Received: September 18, 2017 Revised: November 5, 2017

A

DOI: 10.1021/acs.macromol.7b02020 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

phthalocyanine rings (Figure 1c). Furthermore, by mixing the phthalocyaninatopolysiloxanes with PDI compounds having πstacking capability instead of those with bulky substituents, much larger photoconductivity was observed due to the additional contribution of electron transports. The noteworthy is that remarkable improvement of photoconductivity was achieved by just blending two different discotic LC systems. Reported dyad-based complex molecular approaches30−35 as well as hydrogen-bond-assisted gelations36−38 are not given in the present work. Phthalocyaninatopolysiloxane (Poly-SiPc), often called “shish-kebab” polymer, is a unique polymer that was born over 50 years ago.39 It consists of one-dimensionally stacked phthalocyanine rings through polysiloxane backbones.40−52 The bond angle of Si−O−Si in this polymer was considered to adopt ca. 180°, which is suggested by reported single crystal structures of oligomers.49−52 Regardless of this unusual bond angles of main-chain polysiloxanes, Poly-SiPcs are thermally stable in ambient conditions. The stability was explained by the protection of siloxane bonds by π-electrons of Pc rings that avoids the attack of water, oxygen, and so on.41 The interplane periodicity of Pc rings was revealed to be 3.3−3.5 Å, which was a close distance among common discotic columnar LC materials. To afford processability and LC character, alkoxy substituents were introduced45−48 to these shish-kebab polymers. Also, their electrical conductivity has been evaluated by both direct-current and noncontact methods.44,45,53−56 Although the stacking geometry of Pc rings in shish-kebab polymer is different from that of conventional LC phthalocyanines, the intracolumnar charge carrier mobility was disclosed to be similar.53 Therefore, it is reasonable to use Poly-SiPcs as a kind of a long-range cluster of small molecular phthalocyanines.

Figure 1. (a) Schematic illustrations of possible structural orders in a binary mixture of discotic liquid crystalline compounds. Schematic illustrations of the possible structure and photoconducting events for (b) typical discotic donor/acceptor blends and (c) shish-kebab donor/ discotic acceptor blends.

presence of electron-accepting perylenedicarboximides (PDIs) having 2,5-di-tert-butylphenyl groups, and thus they undergo an efficient photoinduced charge separation followed by a subsequent hole electron transport along one-dimensional

Figure 2. Molecular structures of phthalocyaninatosilicon(IV) SiPc1, its polymer Poly-SiPc1, free-base phthalocyanine H2Pc1, and perylenedicarboximides PDI1 and PDI2. B


Article

Macromolecules

provided those under the 10 nm range (Figure 3c). Since PolySiPc1 adopts bottlebrush-shaped structure, its absolute value of averaged Dh does not offer exact information about the degree of polymerization. Nevertheless, it was clear that polymerization was successfully carried out in this case by qualitative comparison. Photoluminescence spectra in solutions revealed that PDI1 was highly emissive and Poly-SiPc1 was almost nonemissive (Figure 3b), which is well consistent with the previous reports.46,58 In the thin film, Poly-SiPc1 has a similar absorption spectral feature to its solution, where the observed peak top of Q-band appeared at 545 nm (Figure S4a). Namely, the remarkable blue-shift of Q-band originates from intrapolymer π−π interactions of Pc rings fixed through a polysiloxane covalent bond. In contrast, H2Pc1 showed a split Q-band at 663 and 701 nm in solution that is typical of free-base phthalocyanines (Figure 3a), while that band was blue-shifted down to 615 nm upon self-assembling into an H-aggregated columnar structure in the film state (Figure S4b).59,60 The stability of the columnar assembly was studied by differential scanning calorimetry (DSC) measurements and variable-temperature X-ray diffraction analysis. DSC measurements revealed that Poly-SiPc1 did not show obvious phase transitions over room temperature (Figure S5). They form hexagonal columnar structures with distinct interplane π−π distances of 3.3−3.4 Å up to 200 °C (Figure S6a). In contrast, SiPc1 has J-like π−π interactions due to the steric hindrance of axial hydroxy groups,45,46 resulting in the periodic spacing of 3.6−3.8 Å for the (001) plane (Figure S6c). These monomers started to polymerize upon elevating the temperature over 150 °C. H2Pc1 forms supramolecular columnar stacks with H-aggregation geometry in the condensed state. It has at least three different solid phases above −50 °C and undergoes a solid−LC transition to form a hexagonal columnar phase (Figures S5b and S6b). Even at 240 °C, the columnar stacks among H2Pc1 molecules were not dissociated. Meanwhile, PDI1 does not show obvious phase transitions (Figure S5c) and displayed a sharp diffraction peaks (Figure S6d), indicative of a highly crystalline material. PDI2 exhibited three solid phases between −50 and 250 °C (Figure S5d). Although its XRD patterns were not so simple (Figure S6e), PDI2 molecules most likely stack up on top of each, as its absorption spectrum followed a pattern with the larger transition from the ground to the second vibronic excited state (0 → 1, ⟨χ′v=1|χv=0⟩) than that to the lowest vibronic state (0 → 0, ⟨χ′v=1|χv=0⟩) (Figure S4e), which is characteristic of stacked PDI molecules.61−64 The HOMO and LUMO energy levels in films were estimated by photoelectron yield spectroscopy (∼HOMO level; Figure S8a) coupled with the observed optical absorption edges (HOMO−LUMO gap; Figure S4). Although the absorption edge of Poly-SiPc derivatives corresponds to a forbidden transition and absorption spectrum of monomeric SiPc was rather broad, HOMO and LUMO levels were approximately estimated as shown in Figure S8b, which well agrees with the previously reported related Pc and PDI materials.65−69 Based on these values, our Poly-SiPc and PDI derivatives most likely behave as electron donor−acceptor relationship and give rise to photoinduced charge separations. Later we would like to discuss this issue experimentally by employing photoluminescence spectroscopy. To demonstrate our strategy for realizing donor−acceptor segregated nanostructures using shish-kebab polymers, the CHCl3 solutions of the mixture Poly-SiPc1/PDI1 and H2Pc1/ PDI1 (from 100/2 to 100/100 in w/w ratio) were prepared

So far, there is no reported example using Poly-SiPcs as electron donor and mixed with electron accepting molecules.

■

RESULTS AND DISCUSSION In our previous work, introduction of linear alkoxy chains at all the eight peripheral positions was found to be effective for efficient polymerization of phthalocyaninato-dihydroxysilicon monomers (SiPc) in bulk.57 Thus, in the present work, methoxy and dodecyloxy groups were selected as side chains of the phthalocyaninato-dihydroxysilicon monomers. According to the reported procedure, SiPc1 (Figure 2) was synthesized via SiCl4-templated cyclization reactions of 1,3-diiminoisoindoline derivatives in quinoline (see Supporting Information). SiPc1 was obtained as a mixture of four regioisomers.57 As a reference compound, the metal-free analogue of SiPc1, H2Pc1, was synthesized by cyclization reactions of the corresponding phthalonitrile in dimethylaminoethanol. On the other hand, PDI was chosen as an electron-accepting core. PDI1, a derivative carrying 2,5-di-tert-butyl groups and having low aggregation tendency, was purchased and used as received. PDI2, designed to stack up via strong π−π interactions, was synthesized and unambiguously characterized by 1H NMR spectroscopy and MALDI-TOF-MS spectrometry (Figures S1− S3 in the Supporting Information). Shish-kebab-type polymer Poly-SiPc1 was prepared by polycondensation of SiPc1 heated at 200 °C under vacuum. As reported previously,57 polymerization was confirmed by absorption spectroscopy in solution, where the Q-band of Pcs was drastically blue-shifted (∼0.43 eV) upon polymerization (Figure 3a), indicating the construction of long-range H-

Figure 3. (a) Absorption spectra of SiPc1, Poly-SiPc1, H2Pc1, and PDI1 in CHCl3. (b) Photoluminescence spectra of SiPc1, Poly-SiPc1, H2Pc1, PDI1, and PDI2 in CHCl3 (10−6 M) photoexcited at 355 nm. (c) Hydrodynamic diameters of H2Pc1 (dark green), SiPc1 (pale green), and Poly-SiPc1 (purple) in CHCl3 analyzed by dynamic light scattering.

aggregated columns. The sharp Q-band of SiPc1 with a peak top at 680 nm was shifted and broadened in Poly-SiPc1 to show a top peak of 550 nm. Another evidence of sufficient polymerization completed was obtained by dynamic light scattering measurements. In diluted CHCl3 solution (∼10−7 M), Poly-SiPc1 indicated hydrodynamic diameters (Dh) ranging from 40 to 90 nm, whereas both SiPc1 and H2Pc1 C


Article

Macromolecules

Figure 4. Absorption spectra of (a) Poly-SiPc1/PDI1 and (b) H2Pc1/PDI1 in films with various blend ratios from 100/0 to 100/100 (w/w). Powder XRD patterns of (c) Poly-SiPc1/PDI1 and (d) H2Pc1/PDI1 with various blend ratios. Black, blue, light blue, beige, orange, red, and brown curves in graphs (a)−(d) correspond to the profiles of 100/0, 100/2, 100/5, 100/10, 100/20, 100/50, and 100/100 (w/w), respectively. AFM topographic (top) and phase (bottom) images of thin films of (e) Poly-SiPc1/PDI1 and (f) H2Pc1/PDI1 in various blend ratios. The size of the images is 5 × 5 μm.

and spin-coated into thin films. The absorption spectra of the Poly-SiPc1/PDI1 films appeared to be the superposition of original two spectra, though the wavelength ranges of the absorption bands for both compounds are somewhat overlapped (Figure 4a). On the other hand, H2Pc1/PDI1 displayed obvious red-shift of the Q-band for H2Pc1 by increasing the relative ratio of PDI1 (Figure 4b). These observations clearly

indicated that the stacking of Pc rings was kept in the PolySiPc1/PDI1 mixture, while noncovalent supramolecular stacks of H2Pc were dissociated via intercalation of PDI1 molecules. Next, XRD patterns were recorded to monitor the domains of columnarly stacked phthalocyanine and crystalline PDI1 molecules. As shown in Figures 4c and 4d, 2 wt % addition of PDI1 did not strongly affect the columnar assembly of both D


Article

Macromolecules Poly-SiPc1 and H2Pc1, where the diffraction peaks of πstacking periodicity at 2θ = 18°−19° were observed in the XRD patterns. As the PDI1 ratio became larger, broader and smaller peaks were appeared in XRD, which reflects the decreased structural order upon addition of PDI1 molecules. Upon further addition, a notable difference emerged between PolySiPc1 and H2Pc1. The H2Pc1/PDI1 system still afforded broad and featureless diffraction patterns even in the 100/100 (w/w) mixture (Figure 4d). Contrary to that, Poly-SiPc1/ PDI1 blends containing over 20 wt % PDI1 exhibited a set of small but sharp diffraction peaks at 2θ = 4.2°, 4.9°, and 9.3° (Figure 4c). Although these peaks do not correspond to those observed in their constituent system of Poly-SiPc1 or PDI1 (Figure S6), the sharpness of the peaks implied that the crystalline domains of PDI1 were the possible reason to provide these peaks. Together with the absorption spectral information, we propose a possible description for these blend systems as shown in Figure 5. Namely, PDI1 cannot intercalate

Importantly, it was revealed that the domain size decreases upon addition of PDI1. In AFM images, no drastic changes in the domain size were confirmed (Figure 4e). Nevertheless, slight decreases were implied. On the other hand, the domain sizes obviously decreased for the H2Pc1/PDI1 system. In summary, PDI1 molecules are mesoscopically segregated with Poly-SiPc1 but miscible with H2Pc1 (Figure 5). Donor− acceptor shish-kebab structures71 were formed by the simple blends of Poly-SiPc1/PDI1. The size of these donor/acceptor domains is possibly tunable by the film preparation processes. With the contrast of nanostructures in the D−A blends in mind, photoinduced charge carrier transport property was investigated. In order to address the possibility of photoinduced charge separation to allow charge carriers, fluorescence spectra were recorded in the solid films. As shown in Figures 6a and 6c,

Figure 5. Schematic illustrations of proposed structural changes in phthalocyanine assembly upon mixing of PDI1 for (a−c) Poly-SiPc1 and (d−f) H2Pc1.

Figure 6. Photoluminescence spectra in films of Poly-SiPc1 (blue), H2Pc1 (green), PDI1 (orange), PDI2 (red), Poly-SiPc1/PDI1 (100/ 50 w/w, purple), Poly-SiPc1/PDI1 (100/100 w/w, pink), H2Pc1/ PDI1 (100/50 w/w, light green), and H2Pc1/PDI1 (100/100 w/w, dark green) photoexcited at (a, b) 480 nm and (c, d) 355 nm. (b) and (d) are the magnified spectra of four blend samples in (a) and (c).

between Pc rings of Poly-SiPc1 because of the siloxane bonds and thus dispersed at boundaries of hexagonal columnar domains of Poly-SiPc1s (Figure 5b). When further amounts are added, PDI1s form nuclei and their crystalline domains are grown (Figure 5c), resulting in the observation of sharp diffraction peaks in XRD. In contrast, PDI1 molecules are intercalated into H2Pc1 columns and H-like stackings are partially dissociated (Figure 5e,f), as revealed by absorption spectroscopy (Figure 4b). At the same time, sharp diffraction peaks were not seen in this mixture in XRD, indicating the absence of sufficiently grown crystalline domains. Although the domain size analysis of these kinds of blended materials is generally difficult, analyses of XRD peaks by the Scherrer equation and atomic force microscopy (AFM) observation of the film surfaces were carried out. Since the most intense diffraction peak for H2Pc1 is not a single peak but overlap of several diffractions, we focused on the analysis of the Poly-SiPc1/PDI1 system. By applying the Scherrer equation to the observed (100) peaks (2θ ∼ 2.5°, Figure 4c),70 domain sizes were roughly estimated as D = 23−40 nm (Table S1).

only PDI1 showed large fluorescence intensity in the solid films, where its emission with a peak top of ca. 630 nm is assigned to be an excimer emission.72−74 When focused onto the D−A blend films (100/50 and 100/100 w/w, Figures 6b and 6d), it clearly indicated that the emission of PDI1 in the blend films was quenched drastically, which supports photoinduced charge separation. Furthermore, the emission from PDI1 in the H2Pc/PDI1 blends appeared at the shorter wavelength range than 630 nm. A typical example is the dark green curve in Figure 6d (λex = 355 nm, λem,max ∼ 520 nm), suggesting that excimer formation is suppressed. This is due to the mixed stack structures for the H2Pc1/PDI1 blends, leading to the molecularly dispersed PDI1 in the present system. This signature of the dispersion was not seen in the Poly-SiPc/PDI1 blends. Overall, fluorescence spectroscopy in the solid films further support our proposed nano/meso structure as schematically shown in Figure 5. The flash-photolysis time-resolved microwave conductivity (FP-TRMC) technique is a device-less convenient method, where charge carriers are transiently generated in film samples E


Article

Macromolecules

Figure 7. FP-TRMC profiles of dropcast films of (a) Poly-SiPc1/PDI1, (b) H2Pc1/PDI1, and (c) SiPc1/PDI1 with various blend ratios. Black, blue, light blue, beige, orange, red, and brown curves in graphs (a)−(c) correspond to the profiles of 100/0, 100/2, 100/5, 100/10, 100/20, 100/50, and 100/100 (w/w), respectively. Summary of the evaluated charge carrier generation efficiency ϕ for (d) Poly-SiPc1/PDI1 and (f) H2Pc1/PDI1 and hole mobility μhole for (e) Poly-SiPc1/PDI1 and (g) H2Pc1/PDI1.

case of active layers in bulk heterojunction photovoltaic cells. In our blend films, the ϕ values were estimated by means of transient absorption spectroscopy (TAS) of the identical films used for FP-TRMC.85 The absorption peak intensity of radical anion of PDI derivatives at around 710 nm was monitored (Figures S10 and S11) and then combined with the reported absorption coefficient of PDI186,87 to calculate the ϕ values. ∑μ was calculated by the obtained ϕ from TAS and (ϕ∑μ)max from FP-TRMC,88 and this value virtually represents μh because electron mobility of PDI1 was suppressed by its bulky substituents (Figure S9). As a result, ϕ and μh values were estimated for the Poly-SiPc1/PDI1 system as summarized in Figures 7d and 7e. Despite the moderate S/N ratio of the TAS measurements in the films, we can conclude that ϕ depends on the blend ratios whereas the μh was almost constant (∼0.04−0.05 cm2 V−1 s−1) among four blends.89 Therefore, the above picture of Poly-SiPc1/PDI1 was supported. The decrease of ϕ values in the 100/100 mixture may be dominantly explained by two reasons. One is the decline of D−A interfacial area. The other is that the charge carrier generation efficiency through the PDI exciton is relatively poor.90 Meanwhile, in the reference H2Pc1/PDI1 system, PDI1 molecules were intercalated to the columns. Thus, mixing with PDI1 decreases μh of H2Pc1 (Figure 7g), while ϕ may increase due to the enlarged donor−acceptor interfaces (Figure 7f). Consequently, the trade-off between μh and ϕ only resulted in the slight increase or even decrease of (ϕ∑μ)max (Figure 7b). It should be noted that another reference SiPc1/PDI1 system, similar to the H2Pc1/PDI1 blends, only showed slight increase in (ϕ∑μ)max (Figure 7c). Motivated by the enhanced conductivity in Poly-SiPc1/ PDI1 blends, PDI2 was next employed instead of PDI1 to demonstrate the coexistence of mesoscopically segregated Pc and PDI arrays. We expected that Poly-SiPc1/PDI2 displayed much larger conductivity than Poly-SiPc1/PDI1 because of the contribution of electron mobility along stacked PDI molecules. The absorption spectra of blend films of Poly-SiPc1/PDI2 appeared to be the superposition of the pristine two spectra (Figure 8a). Then, XRD patterns of the blends were revealed

through photoinduced charge separation and their local motions are monitored by dielectric loss spectroscopy using a resonant cavity.75−79 Since this alternating-current method eliminates the contact resistance and also minimizes the effect of grain boundaries, it serves as an effective tool to trace the role of nanostructures on local-scale charge transport property.80−84 The film samples were prepared by dropcasting the CHCl3 solution of the discotic blends (or single components) onto a quartz substrate and dried under ambient conditions first and then under vacuum. Upon photoexcitation with laser pulses at 355 nm, both the pristine Poly-SiPc1 and H2Pc1 films exhibited a prompt rise and slow decay profiles of reflected microwave changes. The analyzed data, shown in Figures 7a and 7b (black curves), denote the time in x-axis and ϕ∑μ in y-axis, where ϕ and ∑μ represent the charge carrier generation efficiency (generated charge carrier density/incident photon density) and the sum of the hole/electron mobilities, respectively. The observed maximum conductivity, (ϕ∑μ)max, marked 2.0 × 10−5 cm2 V−1 s−1 for both the Poly-SiPc1 and H2Pc1 films. However, a significant difference was observed upon blended with PDI1. Poly-SiPc1/PDI1 films yielded larger maximum conductivity values than that of Poly-SiPc1 alone. By increasing the PDI contents from 100/2 to 100/50 (w/w), the values of (ϕ∑μ)max explicitly got larger (Figure 7a). Then, coming to the blend with 100/100 ratio, the value of (ϕ∑μ)max was again dropped. In sharp contrast, H2Pc1 did not result in distinct increase of conductivity upon addition of PDI1 at the ratio 100/2−100/100 (w/w) (Figure 7b). One can understand this remarkable contrast based on their nanostructures. In the case of Poly-SiPc1/PDI1 blends, intrapolymer hole-transporting ability (∼hole mobility μh) is ensured, while bulky substituents of PDI1 suppress the intermolecular electron transports (μe ∼ 0) (Figure S9). The generated excitons are most likely charge-separated into holes and electrons at the Poly-SiPc1/PDI1 interfaces, where the charge carrier generation efficiency ϕ depends on parameters related to the miscible state such as interfacial areas. Therefore, ϕ values possibly change depending on the blend ratios and film fabrication processes, which is seen in the F


Article

Macromolecules

Figure 8. (a) Thin-film absorption spectra and (b) powder XRD patterns of Poly-SiPc1/PDI2 with various blend ratios. (c) AFM topographic (top) and phase (bottom) images of dropcast films of Poly-SiPc1/PDI2 in various blend ratios. The size of the images is 5 × 5 μm. (d) Schematic illustration of possible structure in Poly-SiPc1/PDI2 blend. (e) FP-TRMC profiles of Poly-SiPc1/PDI2 with various blend ratios. Purple, blue, beige, orange, red, brown, and black curves in graphs (a), (b), and (e) correspond to the profiles of 100/0, 100/10, 100/20, 100/50, 100/100, 100/ 200, and 0/100 (w/w), respectively. Summary of the evaluated (f) charge carrier generation efficiency ϕ and (g) hole mobility μh of phthalocyanines in each mixture.

consider that shish-kebab-type polymer structure again avoids the intercalation of PDI2 molecules into the spaces among stacked Pc rings, resulting in the formation of segregated Pc/ PDI domains. After it was confirmed that a pure PDI2 film only showed the (ϕ∑μ)max value of 1.5 × 10−5 cm2 V−1 s−1 in FP-TRMC (Figure S9), the behavior of donor−acceptor blends was investigated. As we expected, the Poly-SiPc1/PDI2 films indeed exhibited ca. 4 times larger (ϕ∑μ)max values than that observed for Poly-SiPc1/PDI1 as well as longer carrier

basically in the same way. When drawing attention to the XRD charts at 2θ = 15°−20°, one can recognize that diffraction peaks of crystalline intermolecular stacking of PDI2 (2θ ∼ 17.5°) and periodic stacking of Poly-SiPc1 (2θ ∼ 18.5°) were both clearly observed in all the blend samples (Figure 8b). It indicated the coexistence of Poly-SiPc1 and PDI2 stacked domains in the mixtures (Figure 8d). In AFM images (Figure 8c), macroscopic phase separation was suggested in the blends containing larger amount of PDI2 (e.g., 100/100 and 100/150 w/w), where onedimensional crystalline fibers were appeared to develop. We G


Article

Macromolecules lifetimes (Figure 8e). These two facts indicate that large photocurrent can potentially be extracted from Poly-SiPc1/ PDI2 mixtures. The maximum conductivity values increased upon addition of PDI2 up to the blend ratio of 100/150 (w/w) and then dropped at 100/200. As studied similarly by TAS measurements (Figure S12), the contribution of ϕ and ∑μ values was separated as summarized in Figures 8f and 8g. It is difficult for this case to control the largeness of the D−A heterointerface area and thus the estimated ϕ values do not follow the clear tendency. In addition, crystallinity of PDI2 domains in the film may change in each blend ratio, giving rise to the different μe values of PDI2. However, the most important point we would like to emphasize here is that the values of the sum of the mobilities estimated in Poly-SiPc1/ PDI2 are larger than the case of Poly-SiPc1/PDI1 in all the blends. Namely, coexistence of hole (Pc) and electron (PDI) pathways can be realized by use of a shish-kebab-shaped polymer scaffold.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (T.S.). *E-mail [email protected] (S.S.). ORCID

Shu Seki: 0000-0001-7851-4405 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was partially supported by Grant-in-Aid for Scientific Research Nos. 26810049, 17H04880, 26102011, 15K21721, and 26249145 from Japan Society for the Promotion of Science (JSPS). We thank Dr. Noriyuki Uchida and Prof. Takuzo Aida in The University of Tokyo for DLS measurements and Dr. Akinori Saeki in Osaka University for helpful discussions. The synchrotron radiation experiments were performed at BL44B292 in SPring-8 with the approval of RIKEN (Proposals 20120100 and 20130011). T.S. thanks the Japan Society for the Promotion of Science for a Young Scientist Fellowship.

■

CONCLUSION In conclusion, inspired by the shish-kebab-shaped one-dimensional phthalocyanine polymers, we tried to prepare discotic blends of a phthalocyaninatopolysiloxane (Poly-SiPc) and perylenedicarboximide (PDI) as an electron donor and acceptor. Because of the presence of polysiloxane covalent bonds axially developed to link the phthalocyanine rings, πstacked columnar structures are preserved in the mixtures of a Poly-SiPc derivative and PDI compound with bulky substituents. On the other hand, intermolecular π−π stacks of analogous monomeric H2Pcs are dissociated by the intercalation of PDIs. In Poly-SiPc/PDI blends, one-dimensional hole-transporting SiPc columns and large donor−acceptor interfaces are constructed, enabling the large photoconductivity detected by the flash-photolysis time-resolved microwave conductivity technique. When PDI compounds with π-stacking capability were used, the prepared Poly-SiPc/PDI blends showed much larger conductivity via constructing both onedimensional SiPc arrays for hole transport and stacking PDIs for electron transport that were clearly confirmed by absorption spectroscopy and X-ray diffraction analysis. Considering the morphology control of bulk heterojunction films in the organic photovoltaic research field,24−29 the precise control of photoinduced charge carrier generation efficiency is needed toward the application stage by changing the domain sizes and interfacial area of electron donor (Poly-SiPc) and acceptor (PDI) components. Nevertheless, our present work sheds light on the first demonstration of the use of shish-kebab-type Pc polymer in donor−acceptor blends and the obvious effect of siloxane backbones on the enhanced photoconductivity in the blends. Considering the character of Si-centered macrocycles grown from a surface of metaloxide electrodes,91 development of vertically aligned Poly-SiPcs from ITO electrodes combined with the acceptor materials will further highlight the potential of phthalocyaninatopolysiloxanes for photoconductive and photovoltaic organic soft materials.

■

Details of synthesis and characterization (NMR and MALDI-TOF-MS), electronic absorption spectra, photoelectron yield spectra, differential scanning calorimetry thermograms, X-ray diffraction patterns, flash-photolysis time-resolved microwave conductivity data, and transient absorption spectra (PDF)

■

REFERENCES

(1) Schouten, P. G.; Warman, J. M.; de Haas, M. P.; Fox, M. A.; Pan, H.-L. Charge migration in supramolecular stacks of peripherally substituted porphyrins. Nature 1991, 353, 736−737. (2) Adam, D.; Closs, F.; Frey, T.; Funhoff, D.; Haarer, D.; Ringsdorf, H.; Schuhmacher, P.; Siemensmeyer, K. Transient Photoconductivity in a Discotic Liquid Crystal. Phys. Rev. Lett. 1993, 70, 457−460. (3) Adam, D.; Schuhmacher, P.; Simmerer, J.; Häussling, L.; Siemensmeyer, K.; Etzbachi, K. H.; Ringsdorf, H.; Haarer, D. Fast photoconduction in the highly ordered columnar phase of a discotic liquid crystal. Nature 1994, 371, 141−143. (4) Sergeyev, S.; Pisula, W.; Geerts, Y. H. Discotic liquid crystals: a new generation of organic semiconductors. Chem. Soc. Rev. 2007, 36, 1902−1929. (5) Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Hägele, C.; Scalia, G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics. Angew. Chem., Int. Ed. 2007, 46, 4832−4887. (6) Pisula, W.; Feng, X.; Müllen, K. Tuning the Columnar Organization of Discotic Polycyclic Aromatic Hydrocarbons. Adv. Mater. 2010, 22, 3634−3649. (7) Kaafarani, B. R. Discotic Liquid Crystals for Opto-Electronic Applications. Chem. Mater. 2011, 23, 378−396. (8) Wöhrle, T.; Wurzbach, I.; Kirres, J.; Kostidou, A.; Kapernaum, N.; Litterscheidt, J.; Haenle, J. C.; Staffeld, P.; Baro, A.; Giesselmann, F.; Laschat, S. Discotic Liquid Crystals. Chem. Rev. 2016, 116, 1139− 1241. (9) Flory, P. J. Thermodynamics of High Polymer Solutions. J. Chem. Phys. 1942, 10, 51−61. (10) Scott, R. L. The Thermodynamics of High Polymer Solutions. V. Phase Equilibria in the Ternary System: Polymer 1Polymer 2 Solvent. J. Chem. Phys. 1949, 17, 279. (11) Slonimskiĭ, G. L. Mutual Solubility of Polymers and Properties of Their Mixtures. J. Polym. Sci. 1958, 30, 625−637. (12) Bohn, L. Incompatibility and Phase Formation in Solid Polymer Mixtures and Graft and Block Copolymers. Rubber Chem. Technol. 1968, 41, 495−513.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b02020. H


Article

Macromolecules

Crystalline Oligothiophene-C60 Dyads. J. Am. Chem. Soc. 2008, 130, 8886−8887. (31) Li, W.-S.; Saeki, A.; Yamamoto, Y.; Fukushima, T.; Seki, S.; Ishii, N.; Kato, K.; Takata, M.; Aida, T. Use of Side-Chain Incompatibility for Tailoring Long-Range p/n Heterojunctions: Photoconductive Nanofibers Formed by Self-Assembly of an Amphiphilic Donor− Acceptor Dyad Consisting of Oligothiophene and Perylenediimide. Chem. - Asian J. 2010, 5, 1566−1572. (32) Hayashi, H.; Nihashi, W.; Umeyama, T.; Matano, Y.; Seki, S.; Shimizu, Y.; Imahori, H. Segregated Donor−Acceptor Columns in Liquid Crystals That Exhibit Highly Efficient Ambipolar Charge Transport. J. Am. Chem. Soc. 2011, 133, 10736−10739. (33) Dössel, L. F.; Kamm, V.; Howard, I. A.; Laquai, F.; Pisula, W.; Feng, X.; Li, C.; Takase, M.; Kudernac, T.; De Feyter, S.; Müllen, K. Synthesis and Controlled Self-Assembly of Covalently Linked Hexaperi-hexabenzocoronene/Perylene Diimide Dyads as Models To Study Fundamental Energy and Electron Transfer Processes. J. Am. Chem. Soc. 2012, 134, 5876−5886. (34) Kamei, T.; Kato, T.; Itoh, E.; Ohta, K. Discotic liquid crystals of transition metal complexes 47: synthesis of phthalocyanine-fullerene dyads showing spontaneous homeotropic alignment. J. Porphyrins Phthalocyanines 2012, 16, 1261−1275. (35) Wang, C.-L.; Zhang, W.-B.; Sun, H.-J.; van Horn, R. M.; Kulkarni, R. R.; Tsai, C.-C.; Hsu, C.-S.; Lotz, B.; Gong, X.; Cheng, S. Z. D. A Supramolecular “Double-Cable” Structure with a 12944 Helix in a Columnar Porphyrin-C60 Dyad and its Application in Polymer Solar Cells. Adv. Energy Mater. 2012, 2, 1375−1382. (36) Sugiyasu, K.; Kawano, S.; Fujita, N.; Shinkai, S. Self-Sorting Organogels with p-n Heterojunction Points. Chem. Mater. 2008, 20, 2863−2865. (37) Molla, M. R.; Das, A.; Ghosh, S. Chiral induction by helical neigbour: spectroscopic visualization of macroscopic-interaction among self-sorted donor and acceptor π-stacks. Chem. Commun. 2011, 47, 8934−8936. (38) Prasanthkumar, S.; Ghosh, S.; Nair, V. C.; Saeki, A.; Seki, S.; Ajayaghosh, A. Organic Donor−Acceptor Assemblies form Coaxial p− n Heterojunctions with High Photoconductivity. Angew. Chem., Int. Ed. 2015, 54, 946−950. (39) Joyner, R. D.; Kenney, M. E. A Phthalocyaninosiloxane. Inorg. Chem. 1962, 1, 717−718. (40) Schoch, K. F.; Kundalkar, B. R.; Marks, T. J. Conductive Polymers Consisting of Partially Oxidized, Face-to-Face Linked Metallomacrocycles. J. Am. Chem. Soc. 1979, 101, 7071−7073. (41) Dirk, C. W.; Inabe, T.; Schoch, K. F.; Marks, T. J. Cofacial Assembly of Partially Oxidized Metallomacrocycles as an Approach to Controlling Lattice Architecture in Low-Dimensional Molecular Solids. Chemical and Architectural Properties of the “Face-to-Face” Polymers [M(phthalocyaninato)O]n, Where M = Si, Ge, and Sn. J. Am. Chem. Soc. 1983, 105, 1539−1550. (42) Diel, B. N.; Inabe, T.; Lyding, J. W.; Schoch, K. F.; Kannewurf, C. R.; Marks, T. J. Cofacial Assembly of Partially Oxidized Metallomacrocycles as an Approach to Controlling Lattice Architecture in Low-Dimensional Molecular Solids. Chemical, Structural, Oxidation State, Transport, Magnetic, and Optical Properties of Halogen-Doped [M(phthalocyaninato)O]n Macromolecules, Where M = Si, Ge, and Sn. J. Am. Chem. Soc. 1983, 105, 1551−1567. (43) Orthmann, E.; Wegner, G. Preparation of Ultrathin Layers of Molecularly Controlled Architecture from Polymeric Phthalocyanines by the Langmuir-Blodgett-Technique. Angew. Chem., Int. Ed. Engl. 1986, 25, 1105−1107. (44) Sirlin, C.; Bosio, L.; Simon, J. Spinal Columnar Liquid Crystals based on Octasubstituted Phthalocyanine Siloxane Derivatives. J. Chem. Soc., Chem. Commun. 1988, 236−237. (45) Sauer, T.; Wegner, G. Control of the discotic to isotropic transition in alkoxy-substituted silicondihydroxo-phthalocyanines by axial substituents. Mol. Cryst. Liq. Cryst. 1988, 162, 97−118. (46) van der Pol, J. F.; Zwikker, J. W.; Warman, J. M.; de Haas, M. P. Synthesis and Transport Properties of Rigid Poly(Ooctasubstituted

(13) Araya, K.; Iwasaki, K. Solubility parameters of liquid crystals. Mol. Cryst. Liq. Cryst. 2003, 392, 49−57. (14) Kranig, W.; Boeffel, C.; Spiess, H. W.; Karthaus, O.; Ringsdorf, H.; Wüstefeld, R. 2H NMR studies of phase behaviour and molecular motions of doped discotic liquid-crystalline systems. Liq. Cryst. 1990, 8, 375−388. (15) Pisula, W.; Kastler, M.; Wasserfallen, D.; Robertson, J.; Nolde, F.; Kohl, C.; Müllen, K. Pronounced Supramolecular Order in Discotic Donor−Acceptor Mixtures. Angew. Chem., Int. Ed. 2006, 45, 819. (16) Thiebaut, O.; Bock, H.; Grelet, E. Face-on Oriented Bilayer of Two Discotic Columnar Liquid Crystals for Organic Donor-Acceptor Heterojunction. J. Am. Chem. Soc. 2010, 132, 6886−6887. (17) Bengs, H.; Renkel, R.; Ringsdorf, H.; et al. Discotic charge transfer complexes: influence of acceptor main-chain polymers on structure and mesophase behaviour of 2,3,6,7,10,11-hexapentyloxytriphenylene. Makromol. Chem., Rapid Commun. 1991, 12, 439−446. (18) Arikainen, E. O.; Boden, N.; Bushby, R. J.; Lozman, O. R.; Vinter, J. G.; Wood, A. Complimentary Polytopic Interactions. Angew. Chem., Int. Ed. 2000, 39, 2333−2336. (19) Klivansky, L. M.; Hanifi, D.; Koshkakaryan, G.; Holycross, D. R.; Gorski, E. K.; Wu, Q.; Chai, M.; Liu, Y. A complementary diskshaped π-electron donor−acceptor pair with high binding affinity. Chem. Sci. 2012, 3, 2009−2014. (20) Zucchi, G.; Donnio, B.; Geerts, Y. H. Remarkable Miscibility between Disk- and Lathlike Mesogens. Chem. Mater. 2005, 17, 4273− 4277. (21) Zucchi, G.; Viville, P.; Donnio, B.; Vlad, A.; Melinte, S.; Mondeshki, M.; Graf, R.; Spiess, H. W.; Geerts, Y. H.; Lazzaroni, R. Miscibility between Differently Shaped Mesogens: Structural and Morphological Study of a Phthalocyanine-Perylene Binary System. J. Phys. Chem. B 2009, 113, 5448−5457. (22) Takanishi, Y.; Takezoe, H.; Suzuki, Y.; Kobayashi, I.; Yajima, T.; Terada, M.; Mikami, K. Spontaneous Enantiomeric Resolution in a Fluid Smectic Phase of a Racemate. Angew. Chem., Int. Ed. 1999, 38, 2353−2356. (23) Roche, C.; Sun, H.-J.; Prendergast, M. E.; Leowanawat, P.; Partridge, B. E.; Heiney, P. A.; Araoka, F.; Graf, R.; Spiess, H. W.; Zeng, X.; Ungar, G.; Percec, V. Homochiral Columns Constructed by Chiral Self-Sorting During Supramolecular Helical Organization of Hat-Shaped Molecules. J. Am. Chem. Soc. 2014, 136, 7169−7185. (24) Yang, F.; Shtein, M.; Forrest, S. R. Controlled growth of a molecular bulk heterojunction photovoltaic cell. Nat. Mater. 2004, 4, 37−41. (25) Bredas, J.-L.; Norton, J. E.; Cornil, J.; Coropceanu, V. Molecular Understanding of Organic Solar Cells: The Challenges. Acc. Chem. Res. 2009, 42, 1691−1699. (26) Jin, S.; Supur, M.; Addicoat, M.; Furukawa, K.; Chen, L.; Nakamura, T.; Fukuzumi, S.; Irle, S.; Jiang, D. Creation of Superheterojunction Polymers via Direct Polycondensation: Segregated and Bicontinuous Donor−Acceptor π-Columnar Arrays in Covalent Organic Frameworks for Long-Lived Charge Separation. J. Am. Chem. Soc. 2015, 137, 7817−7827. (27) Nakano, K.; Tajima, K. Organic Planar Heterojunctions: From Models for Interfaces in Bulk Heterojunctions to High-Performance Solar Cells. Adv. Mater. 2017, 29, 1603269. (28) Collado-Fregoso, E.; Hood, S. N.; Shoaee, S.; Schroeder, B. C.; McCulloch, I.; Kassal, I.; Neher, D.; Durrant, J. R. Intercalated vs Nonintercalated Morphologies in Donor−Acceptor Bulk Heterojunction Solar Cells: PBTTT:Fullerene Charge Generation and Recombination Revisited. J. Phys. Chem. Lett. 2017, 8, 4061−4068. (29) Griffin, M. P.; Gearba, R.; Stevenson, K. J.; van den Bout, D. A.; Dolocan, A. Revealing the Chemistry and Morphology of Buried Donor/Acceptor Interfaces in Organic Photovoltaics. J. Phys. Chem. Lett. 2017, 8, 2764−2773. (30) Li, W.-S.; Yamamoto, Y.; Fukushima, T.; Saeki, A.; Seki, S.; Tagawa, S.; Masunaga, H.; Sasaki, S.; Takata, M.; Aida, T. Amphiphilic Molecular Design as a Rational Strategy for Tailoring Bicontinuous Electron Donor and Acceptor Arrays: Photoconductive Liquid I


Article

Macromolecules Phthalocyaninatosiloxanes). Recl. Trav. Chim. Pay. B 1990, 109, 208− 215. (47) Sielcken, O. E.; van de Kuil, L. A.; Drenth, W.; Schoonman, J.; Nolte, R. J. M. Phthalocyaninato Polysiloxanes Substituted with Crown Ether Moieties. J. Am. Chem. Soc. 1990, 112, 3086−3093. (48) Engelkamp, H.; van Nostrum, C. F.; Nolte, R. J. M.; Engelkamp, H.; van Nostrum, C. F.; Picken, S. J. Shish kebab-like chirality. Chem. Commun. 1998, 34, 979−980. (49) Ciliberto, E.; Doris, K. A.; Pietro, W. J.; Reisner, G. M.; Ellis, D. E.; Fragala, I.; Herbstein, F. H.; Ratner, M. A.; Marks, T. J. π−π Interactions and Bandwidths in “Molecular Metals”. A Chemical, Structural, Photoelectron Spectroscopic, and Hartree-Fock-Slater Study of Monomeric and Cofacially Joined Dimeric Silicon Phthalocyanines. J. Am. Chem. Soc. 1984, 106, 7748−7761. (50) Sasa, N.; Okada, K.; Nakamura, K.; Okada, S. Synthesis, structural and conformational analysis and chemical properties of phthalocyaninatometal complexes. J. Mol. Struct. 1998, 446, 163−178. (51) Cammidge, A.; Nekelson, F.; Helliwell, M.; Heeney, M.; Cook, M. A Capping Methodology for the Synthesis of Lower μ-Oxophthalocyaninato Silicon Oligomers. J. Am. Chem. Soc. 2005, 127, 16382−16383. (52) Yang, Y.; Samas, B.; Kennedy, V. O.; Macikenas, D.; Chaloux, B. L.; Miller, J. A.; Speer, R. L.; Protasiewicz, J.; Pinkerton, A. A.; Kenney, M. E. Long, Directional Interactions in Cofacial Silicon Phthalocyanine Oligomers. J. Phys. Chem. A 2011, 115, 12474−12485. (53) Schouten, P. G.; Warman, J. M.; de Haas, M. P.; van der Pol, J. F.; Zwikker, J. W. Radiation-Induced Conductivity in Polymerized and Nonpolymerized Columnar Aggregates of Phthalocyanine. J. Am. Chem. Soc. 1992, 114, 9028−9034. (54) Šilerová, R.; Kalvoda, L.; Neher, D.; Ferencz, A.; Wu, J.; Wegner, G. Electrical Conductivity of Highly Organized LangmuirBlodgett Films of Phthalocyaninato-Polysiloxane. Chem. Mater. 1998, 10, 2284−2292. (55) Rengel, H.; Gattinger, P.; Šilerová, R.; Neher, D. Conductivity Measurements of Electrochemically Oxidized Langmuir-Blodgett Films of Phthalocyaninato-Polysiloxane. J. Phys. Chem. B 1999, 103, 6858−6862. (56) Gattinger, P.; Rengel, H.; Neher, D.; Gurka, M.; Buck, M.; van de Craats, A. M.; Warman, J. M. Mechanism of Charge Transport in Anisotropic Layers of a Phthalocyanine Polymer. J. Phys. Chem. B 1999, 103, 3179−3186. (57) Yoneda, S.; Sakurai, T.; Nakayama, T.; Kato, K.; Takata, M.; Seki, S. Systematic studies on side-chain structures of phthalocyaninato-polysiloxanes: Polymerization and self-assembling behaviors. J. Porphyrins Phthalocyanines 2015, 19, 160−170. (58) Rademacher, A.; Markle, S.; Langhals, H. Losliche PerylenFluoreszenzfarbstoffe rnit hoher Photostabilität. Chem. Ber. 1982, 115, 2927−2934. (59) Markovitsi, D.; Lécuyer, I.; Simon, J. One-Dimensional Triplet Energy Migration in Columnar Liquid Crystals of Octasubstituted Phthalocyanines. J. Phys. Chem. 1991, 95, 3620−3626. (60) Ban, K.; Nishizawa, K.; Ohta, K.; Shirai, H. Discotic liquid crystals of transition metal complexes 27: supramolecular structure of liquid crystalline octakis- alkylthiophthalocyanines and their copper complexes. J. Mater. Chem. 2000, 10, 1083−1090. (61) Cormier, R. A.; Gregg, B. A. Self-Organization in Thin Films of Liquid Crystalline Perylene Diimides. J. Phys. Chem. B 1997, 101, 11004−11006. (62) Struijk, C. W.; Sieval, A. B.; Dakhorst, J. E. J.; van Dijk, M.; Kimkes, P.; Koehorst, R. B. M.; Donker, H.; Schaafsma, T. J.; Picken, S. J.; van de Craats, A. M.; Warman, John M.; Zuilhof, Han; Sudhölter, E. J. R. Liquid Crystalline Perylene Diimides: Architecture and Charge Carrier Mobilities. J. Am. Chem. Soc. 2000, 122, 11057−11066. (63) Wang, W.; Li, L.-S.; Helms, G.; Zhou, H.-H.; Li, A. D. Q. To Fold or to Assemble? J. Am. Chem. Soc. 2003, 125, 1120−1121. (64) Shaller, A. D.; Wang, W.; Li, A.; Moyna, G.; Han, J. J.; Helms, G. L.; Li, A. D. Q. Sequence-Controlled Oligomers Fold into Nanosolenoids and Impart Unusual Optical Properties. Chem. - Eur. J. 2011, 17, 8350−8362.

(65) Sauer, T.; Caseri, W.; Wegner, G. Novel phthalocyanine polymers for applications in optical devices. Mol. Cryst. Liq. Cryst. 1990, 183, 387−402. (66) Park, S.; Kampen, T. U.; Zahn, D. R. T.; Braun, W. Energy level alignment driven by electron affinity difference at 3,4,9,10-perylenetetracarboxylic dianhydride/n-GaAs(100) interfaces. Appl. Phys. Lett. 2001, 79, 4124−4126. (67) Delgado, M. C. R.; Kim, E.-G.; da Silva Filho, D. A.; Bredas, J.-L. Tuning the Charge-Transport Parameters of Perylene Diimide Single Crystals via End and/or Core Functionalization: A Density Functional Theory Investigation. J. Am. Chem. Soc. 2010, 132, 3375−3387. (68) Hiroshiba, N.; Hayakawa, R.; Chikyow, T.; Yamashita, Y.; Yoshikawa, H.; Kobayashi, K.; Morimoto, K.; Matsuishi, K.; Wakayama, K. Energy-level alignments and photo-induced carrier processes at the heteromolecular interface of quaterrylene and N,N′dioctyl-3,4,9,10-perylenedicarboximide. Phys. Chem. Chem. Phys. 2011, 13, 6280−6285. (69) Wu, S.-H.; Li, W.-L.; Chu, B.; Su, Z.-S.; Zhang, F.; Lee, C. S. High performance small molecule photodetector with broad spectral response range from 200 to 900 nm. Appl. Phys. Lett. 2011, 99, 023305. (70) Kouwer, P. H. J.; Jager, W. F.; Mijs, W. J.; Picken, S. J. Charge Transfer Complexes of Discotic Liquid Crystals: A Flexible Route to a Wide Variety of Mesophases. Macromolecules 2002, 35, 4322−4329. (71) Bu, L.; Pentzer, E.; Bokel, F. A.; Emrick, T.; Hayward, R. C. Growth of Polythiophene/Perylene Tetracarboxydiimide Donor/ Acceptor Shish-Kebab Nanostructures by Coupled Crystal Modification. ACS Nano 2012, 6, 10924−10929. (72) Margulies, E. A.; Shoer, L. E.; Eaton, S. W.; Wasielewski, M. R. Excimer Formation in Cofacial and Slip-Stacked Perylene-3,4:9,10Bis(dicarboximide) Dimers on a Redox-Inactive Triptycene Scaffold. Phys. Chem. Chem. Phys. 2014, 16, 23735−23742. (73) Dutta, A. K.; Kamada, K.; Ohta, K. Langmuir−Blodgett Films of Nonamphiphilic N,N′-Bis(2,5-Di-tert-butylphenyl)-3,4,9,10-Perylenedicarboximide: A Spectroscopic Study. Langmuir 1996, 12, 4158− 4164. (74) Chen, Y.; Spiering, A. J. H.; Karthikeyan, S.; Peters, G. W. M.; Meijer, E. W.; Sijbesma, R. P. Mechanically Induced Chemiluminescence from Polymers Incorporating a 1,2-Dioxetane Unit in the Main Chain. Nat. Chem. 2012, 4, 559−562. (75) de Haas, M. P.; Warman, J. M. Photon-induced molecular charge separation studied by nanosecond time-resolved microwave conductivity. Chem. Phys. 1982, 73, 35−53. (76) Warman, J.; van de Craats, A. Charge mobility in discotic materials studied by PR-TRMC. Mol. Cryst. Liq. Cryst. 2003, 396, 41− 72. (77) Saeki, A.; Seki, S.; Sunagawa, T.; Ushida, K.; Tagawa, S. Chargecarrier dynamics in polythiophene films studied by in-situ measurement of flash-photolysis time-resolved microwave conductivity (FPTRMC) and transient optical spectroscopy (TOS). Philos. Mag. 2006, 86, 1261−1276. (78) Saeki, A.; Koizumi, Y.; Aida, T.; Seki, S. Comprehensive Approach to Intrinsic Charge Carrier Mobility in Conjugated Organic Molecules, Macromolecules, and Supramolecular Architectures. Acc. Chem. Res. 2012, 45, 1193−1202. (79) Seki, S.; Saeki, A.; Sakurai, T.; Sakamaki, D. Charge carrier mobility in organic molecular materials probed by electromagnetic waves. Phys. Chem. Chem. Phys. 2014, 16, 11093−11113. (80) Nair, V. S.; Mukhopadhyay, R. D.; Saeki, A.; Seki, S.; Ajayaghosh, A. A p-gel scaffold for assembling fullerene to photoconducting supramolecular rods. Sci. Adv. 2016, 2, e1600142. (81) Tsutsui, Y.; Schweicher, G.; Chattopadhyay, B.; Sakurai, T.; Arlin, J.-B.; Ruzié, C.; Aliev, A.; Ciesielski, A.; Colella, S.; Kennedy, A. R.; Lemaur, V.; Olivier, Y.; Hadji, R.; Sanguinet, L.; Castet, F.; Beljonne, D.; Cornil, J.; Samorì, P.; Seki, S.; Geerts, Y. H. Unraveling Unprecedented Charge Carrier Mobility through Structure Property Relationship of Four Isomers of Didodecyl[1]benzothieno[3,2-b] [1]benzothiophene. Adv. Mater. 2016, 28, 7106−7114. J


Article

Macromolecules (82) Ikeda, T.; Tamura, H.; Sakurai, T.; Seki, S. Control of optical and electrical properties of nanosheets by the chemical structure of the turning point in a foldable polymer. Nanoscale 2016, 8, 14673−14681. (83) Leung, F. K.-C.; Ishiwari, F.; Kajitani, T.; Shoji, Y.; Hikima, T.; Takata, M.; Saeki, A.; Seki, S.; Yamada, Y. M. A.; Fukushima, T. Supramolecular Scaffold for Tailoring the Two-Dimensional Assembly of Functional Molecular Units into Organic Thin Films. J. Am. Chem. Soc. 2016, 138, 11727−11733. (84) Mondal, T.; Sakurai, T.; Yoneda, S.; Seki, S.; Ghosh, S. Semiconducting Nanotubes by Intrachain Folding Following Macroscopic Assembly of a Naphthalene−Diimide (NDI) Appended Polyurethane. Macromolecules 2015, 48, 879−888. (85) Saeki, A.; Seki, S.; Koizumi, Y.; Tagawa, S. Dynamics of photogenerated charge carrier and morphology dependence in polythiophene films studied by in situ time-resolved microwave conductivity and transient absorption spectroscopy. J. Photochem. Photobiol., A 2007, 186, 158−165. (86) Ford, W. E.; Hiratsuka, H.; Kamat, P. V. Photochemistry of 3,4,9,10-Perylenetetracarboxyiic Dianhydride Dyes. 4. Spectroscopic and Redox Properties of Oxidized and Reduced Forms of the Bis(2,5di-tert-butyiphenyl) imide Derivative. J. Phys. Chem. 1989, 93, 6692− 6696. (87) Gosztola, D.; Niemczyk, M. P.; Svec, W.; Lukas, A. S.; Wasielewski, M. R. Excited Doublet States of Electrochemically Generated Aromatic Imide and Diimide Radical Anions. J. Phys. Chem. A 2000, 104, 6545−6551. (88) The μ values are constant and independent of the time, while ϕ values are a function of time because of the recombination and/or trap of the charge carriers after their generation induced by the photoexcitation. The ϕ values discussed in the text and figures are indeed maximum values of ϕ (=ϕmax). (89) The slight increase of μh in proportion as the PDI1 ratio, if any, might come from the electron mobility of aggregated PDI1s even though its bulky substituents suppress electron transport. (90) Saeki, A.; Ohsaki, S.-I.; Seki, S.; Tagawa, S. Electrodeless Determination of Charge Carrier Mobility in Poly(3-hexylthiophene) Films Incorporating Perylenediimide as Photoconductivity Sensitizer and Spectroscopic Probe. J. Phys. Chem. C 2008, 112, 16643−16650. (91) Lee, D.; Morales, G.; Lee, Y.; Yu, L. Cofacial porphyrin multilayers via layer-by-layer assembly. Chem. Commun. 2006, 100− 102. (92) Kato, K.; Tanaka, H. Visualizing charge densities and electrostatic potentials in materials by synchrotron X-ray powder diffraction. Adv. Phys. X 2016, 1, 55−80.

K


Acceptor Segregated Ï-Stacking Arrays by Use of Shish-Kebab

Recommend Documents

Acceptor Segregated Ï-Stacking Arrays by Use of Shish-Kebab