Article pubs.acs.org/cm
Altering the Polymorphic Accessibility of Polycyclic Aromatic Hydrocarbons with Fluorination Anna M. Hiszpanski,†,‡ Arthur R. Woll,§ Bumjung Kim,∥,# Colin Nuckolls,∥ and Yueh-Lin Loo*,†,⊥ †
Department of Chemical and Biological Engineering and ⊥Andlinger Center for Energy and the Environment, Princeton University, Princeton, New Jersey 08544, United States ‡ Materials Science Division, Lawrence Livermore National Laboratory, Livermore, California 94551, United States § Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, United States ∥ Department of Chemistry, Columbia University, New York, New York 10027, United States S Supporting Information *
ABSTRACT: Substituting hydrogen with fluorine is an extensively employed strategy to improve the macroscopic properties of compounds for use in fields as diverse as pharmaceutics and optoelectronics. The role fluorine substitution plays on polymorphismthe ability of a compound to adopt more than one crystal structurehas not been previously studied. Yet, this understanding is important as different polymorphs of the same compound can result in drastically different bulk properties (e.g., solubility, absorptivity, and conductivity). Strategies to either promote or suppress the crystallization of particular polymorphs are thus desired. Here, we show that substituting hydrogen with fluorine affects the polymorphic behavior of contorted hexabenzocoronene (cHBC). A polycyclic aromatic hydrocarbon and molecular semiconductor, cHBC exhibits two polymorphs (i.e., P21/c crystal structure which we refer to as polymorph I and a triclinic crystal structure which we refer to as polymorph II) that are accessible through postdeposition processing of amorphous films. While the same two polymorphs remain accessible in fluorinated derivatives of cHBC, fluorination appears to favor the formation of polymorph I, with progressively smaller energy barrier for transformation from polymorph II to polymorph I with fluorination.
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poly(vinylidene fluoride), PVDF, which in turn changes the preferred molecular packing and yields a ferroelectric crystal structure.8−10 More generally, the role that fluorine plays in directing the molecular packing (i.e., crystal engineering) has long been of interest. A classic example is the case of benzene and hexafluorobenzeneboth liquids at room temperature that upon mixing cocrystallize to form a solid due to strong electrostatic forces that arise from the pair’s opposing quadrupoles.11−13 By comparison, most other intermolecular fluorine-based interactions (i.e., C−F···H, F···F, and C−F···π) are considered weak and traditionally have not been considered to influence molecular packing. However, recent work has demonstrated that these weak interactions can in fact impact intermolecular packing.14−16 Despite fluorine substitution being so prevalent, the precise influence it has on intermolecular interactions and thereby crystal engineering is still developing.14−16 Because a molecule’s crystal structure can drastically changes its bulk material properties, molecules that can naturally adopt
INTRODUCTION A recent trend in the design of both pharmaceutical compounds and organic semiconductors has been to substitute hydrogen atoms with fluorine atoms to advantageously tune molecular properties.1−3 For example, in pharmaceuticals, fluorination has been shown to improve the bioavailability and pharmacokinetic profile of numerous drug candidates once they enter the bloodstream. Accordingly, nearly 20−25% of pharmaceutical drugs being developed are fluorinated.2−5 Likewise, aromatic fluorination lowers via inductive effects the molecular orbital energy levels of organic semiconductors, stabilizing them against degradation in air and improving electron injection into and electron extraction from external electrodes.1,6,7 One of the reasons fluorination has proven to be a particularly popular strategy is that fluorine’s van der Waal radius is only slightly larger than hydrogen’s and C−F and C− H bonds are comparable in length despite fluorine being almost twice as electronegative as hydrogen. Thus, fluorine substitution offers a means of significantly tuning the electronic properties of a molecule without necessitating bulky substituents that can potentially change a molecule’s conformation. Nevertheless, under some circumstances, such conformational changes can be desirable. For example, fluorination can induce a conformational changes in the polymer backbone of © 2017 American Chemical Society
Received: February 14, 2017 Revised: April 24, 2017 Published: April 25, 2017 4311
DOI: 10.1021/acs.chemmater.7b00627 Chem. Mater. 2017, 29, 4311−4316
Article
Chemistry of Materials
Figure 1. Chemical structures of contorted hexabenzocoronene, cHBC, and the series of fluorinated derivatives studied.
more than one crystal structure or polymorph without any changes in molecular conformation are of great interest. Indeed, the ability to controllably access specific polymorphs with desired properties is important in the development of many small-molecule-based products. Typically, different polymorphs are accessed by changes in crystallization conditions.17 However, here we determine how fluorination, already a common chemical modification in pharmaceutical compounds and organic semiconductors, can affect polymorph accessibility, implicating the role of fluorination in modifying the ease with which distinct polymorphs are accessed in aromatic molecules. Specifically, we study the crystallization behavior of a series of fluorinated derivatives of contorted hexabenzocoronene (cHBC), a polycyclic aromatic hydrocarbon and molecular semiconductor previously shown to exhibit polymorphism.18 Importantly, upon thermal evaporation to form a thin film, cHBC and its fluorinated derivatives all adopt the same chair molecular conformation19 and they form amorphous films that can be subsequently crystallized using postdeposition processing conditions.18,20,21 Thus, our system provides a common starting point across molecules in this series. We previously found that the parent compound of cHBC adopts one of two different crystal structures depending on postdeposition processing conditions.18 Thermally annealing an amorphous thin film of cHBC induces crystallization of a monoclinic crystal structure with P21/c space group symmetry that we refer to as polymorph I; solvent-vapor annealing with tetrahydrofuran vapor induces crystallization of polymorph II a second, likely triclinic, crystal structure whose lattice dimensions and intermolecular packing have not yet been elucidated. Here, we applied these same two processing routes to induce crystallization of a series of four fluorinated cHBC derivatives,19,20 with increasing number of fluorines on the peripheral aromatic rings and whose chemical structures are shown in Figure 1. Such fluorinated derivatives are of general utility in organic electronics as electron acceptors.21 We have found that these fluorinated cHBC derivatives exhibit polymorphism like the parent cHBC compound though their polymorphic transformations, tracked in situ via grazingincidence X-ray diffraction (GIXD), are distinctly different. These findings point to how fluorination may be used more generally as a strategy to fine-tune the likelihood of accessing specific crystal structures.
Figure 2. One-dimensional X-ray diffraction traces generated by azimuthally integrating the corresponding two-dimensional X-ray diffraction patterns of cHBC, 8F-, 12F-, 16F-, and 20F-cHBC thin films that were either (a) thermally annealed or (b) THF-vaporannealed, resulting in polymorph I and polymorph II, respectively.
or tetrahydrofuran-vapor (THF-vapor) annealing. Figure 2a contains the diffraction traces generated from two-dimensional grazing-incidence X-ray diffraction (2D-GIXD) images of films of cHBC, 8F-, 12F-, 16F-, and 20F-cHBC after thermal annealing on a hot plate at 240 °C for 30 min (see Figure S1 of the Supporting Information for 2D-GIXD images). The diffraction traces of the fluorinated cHBCs look qualitatively similar to one another and to that of cHBC, which indicates similarities in the crystal structures adopted across these derivatives. We were able to grow via physical-vapor transport crystals of 8F-cHBC and 16F-cHBC (from ref 19) for singlecrystal diffraction. Both these compounds adopt monoclinic crystal structures with P21/c space group symmetries that exhibit similar molecular packing motifs and lattice parameters to cHBC’s P21/c crystal structure (see Figure S2). (cHBC: a = 12.299 Å, b = 7.928 Å, c = 13.998 Å, α = γ = 90.0°, β = 90.12°. 8F-cHBC: a = 12.104 Å, b = 8.399 Å, c = 14.421 Å, α = γ = 90.0°, β = 90.29°. 16F-cHBC: a = 12.966 Å, b = 8.566 Å, c = 14.310 Å, α = γ = 90.0°, β = 99.12°.) Simulated powderdiffraction patterns generated from these crystal structures match the X-ray diffraction traces of films of 8F- and 16FcHBC, confirming that the films adopt the P21/c crystal structure on thermal annealing. While we do not have single crystals of 12F- and 20F-cHBC, the similarities between the diffraction traces of thermally annealed films of cHBC and the four fluorinated cHBC derivatives suggest that 12F- and 20FcHBC, like cHBC, 8F-cHBC, and 16F-cHBC, also adopt monoclinic crystal structures having the P21/c space group symmetry with comparable molecular packing. We refer to these P21/c crystal structures as polymorph I. Polymorph I is most readily identified in diffraction traces by the position of its primary reflection, corresponding to its (100) reflection, which occurs at approximately q = 0.5 Å−1 in the X-
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RESULTS AND DISCUSSION Like the parent compound of cHBC,20 8F-, 12F-, 16F-, and 20F-cHBC form amorphous thin films when they are thermally evaporated atop SiO2 substrates.21 To induce crystallization, we subjected films of the fluorinated cHBC derivatives to one of two postdeposition processing treatmentsthermal annealing 4312
DOI: 10.1021/acs.chemmater.7b00627 Chem. Mater. 2017, 29, 4311−4316
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Chemistry of Materials ray diffraction traces of cHBC and its fluorinated derivatives. The precise placement of this reflection varies between 0.48 and 0.53 Å−1 due to subtle changes in the characteristic spacing in the (100) direction as the extent of fluorination varies across the series of derivatives. The most notable difference between the polymorph I crystal structures of cHBC, 8F-cHBC, and 16F-cHBC lies along the b-axis, which corresponds to the intermolecular π-stacking direction, as shown in Figure S1. The unit cell length along the b-axis is 7.93 Å for cHBC, 8.40 Å for 8F-cHBC, and 8.57 Å for 16F-cHBC. Despite an 8% expansion in this direction, the crystal structures of the fluorinated cHBC derivatives are comparable, and the molecular packing motif of these compounds remains unchanged with fluorination. Figure 2b contains the diffraction traces generated from 2DGIXD images of films of fluorinated cHBCs after they had been annealed with THF-vapor for 4 h. The diffraction traces of the THF-vapor annealed films of the fluorinated cHBCs look qualitatively similar to one another and also to that of cHBC after it had been THF-vapor-annealed. The similarities in the diffraction patterns of cHBC and its fluorinated derivatives after THF vapor annealing suggest that they adopt similar crystal structures. This crystal structure is distinct from the polymorph I crystal structure adopted by thermally annealed films. For films of cHBC derivatives that were THF-vapor-annealed, the primary reflection occurs at approximately q = 0.7 Å−1, with its precise placement varying between 0.66 and 0.71 Å−1 depending on the extent of fluorination. This polymorph, likely belonging to the triclinic system, is referred to as polymorph II.18 The reflection at q = 0.5 Å−1 that is characteristic of polymorph I is absent. That films of cHBC and its fluorinated derivatives access polymorph I and polymorph II whenever they undergo thermal annealing and THF-vapor annealing, respectively, suggests that the processing pathway influences polymorphic selection more significantly than fluorination. To assess possible polymorphic transformations, we took films of fluorinated cHBC derivatives having polymorph I or polymorph II and subjected them to additional postdeposition processing. Thermally annealed films of fluorinated cHBC derivatives containing polymorph I showed no change upon subsequent exposure to THF vapor (see Figure S3) for as long as 6 h. This result was surprising as thermally annealed films of cHBC having polymorph I readily transform to polymorph II with THF vapor annealing.18 We also reversed the processing route, taking polymorph IIcontaining, THF-vapor-annealed films of fluorinated cHBC derivatives and thermally annealing them. We performed this thermal annealing in situ and tracked the structural evolution with 2D-GIXD experiments using a custom-built tube furnace.18,22 Figure 3 shows the diffraction traces extracted from 2D-GIXD images as the films were thermally annealed at the specified temperatures. The topmost trace in each panel in Figure 3 corresponds to the diffraction trace taken at room temperature and is shown for reference. The silicon platform that held the sample substrate was then rapidly heated, and the subsequent traces capture any transformation that took place at these elevated temperatures. The traces show a gradual disappearance of the reflection at q = 0.7 Å−1 that is associated with polymorph II and the concomitant appearance of the reflection at q = 0.5 Å−1 associated with polymorph I. In a comparison of the topmost and bottom-most diffraction traces, it is apparent that the fluorinated cHBC films with polymorph II have all transformed to polymorph I. This result is also
Figure 3. Diffraction traces of THF-vapor-annealed 8F-, 12F-, 16F-, and 20F-cHBC films tracking the irreversible transformation from polymorph II to polymorph I during isothermal annealing at temperatures specified in each graph.
surprising as this transformation from polymorph II to polymorph I was not observed for the parent cHBC compound.18 Figure 4 is a processing map summarizing these results, and it indicates how polymorphs I and II can be accessed in
Figure 4. Scheme illustrating the processing routes applied to thin films of fluorinated cHBCs and the polymorphs accessed. The processing map is the reverse of what has been published for cHBC in ref 18.
fluorinated cHBC thin films. Polymorph I can be accessed from thin films of fluorinated cHBC derivatives that are either amorphous or exhibit polymorph II whereas polymorph II can only be accessed from amorphous films of the fluorinated cHBC derivatives under the wide range of processing conditions we have explored. This observation is the reverse of what we had seen with thin films of cHBC,18 and suggests that polymorph I is favored with fluorination of cHBC. To study the kinetics of this transformation, we thermally annealed films of fluorinated cHBC derivatives at temperatures where the transformation from polymorph II to polymorph I took place within 20−45 min as this time scale allowed us to capture the complete polymorphic transformation using our in situ 2D-GIXD setup with sufficient temporal resolution to extract meaningful kinetics. For the transformation from polymorph II to polymorph I to take place within 20−45 min, 16F- and 20F-cHBC thin films had to be annealed at approximately 200−240 °C whereas 8F-and 12F-cHBC had to be annealed at substantially higher temperatures of approx4313
DOI: 10.1021/acs.chemmater.7b00627 Chem. Mater. 2017, 29, 4311−4316
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Chemistry of Materials imately 290−315 °C. This difference in temperature implies that the energy barrier to transform 8F- and 12F-cHBC to polymorph I is higher than the energy barrier to transform 16Fand 20F-cHBC. By monitoring the kinetics of transformation from polymorph II to polymorph I of these fluorinated derivatives, we have quantified their energy barriers. The intensities of the primary reflections at q = 0.5 and 0.7 Å−1 associated with polymorph I and polymorph II, respectively, scale with the presence of each of the polymorphs in the films. Thus, we can track the transformation from polymorph II to polymorph I by quantifying the fractional integrated intensities of these primary reflections. We calculated the fraction of material transformed to polymorph I by dividing the integrated intensity of the reflection at q = 0.5 Å−1 by the sum of the integrated intensities of the reflections at q = 0.5 and 0.7 Å−1. It was unnecessary to first normalize the integrated intensities of the two reflections by their corresponding quantities when the sample is fully converted because the latter two quantities are comparable. Furthermore, because we azimuthally integrate 2D X-ray diffraction images to generate the 1D diffraction traces, the total integrated intensities of polymorph I and polymorph II are independent of any preferential out-of-plane ordering of crystals in the thin film. Figure 5a shows the fraction of polymorph I in a 20F-cHBC film upon isothermal annealing at 231 °C. This polymorphic transformation of 20F-cHBC, as well as those of 8F-, 12F-, and 16F-cHBC, can be described by second-order Avrami kinetics.23−25 Given that the films are only 100 nm thick and therefore the spherulitic superstructures are much larger than the thickness of the films, the second-order Avrami kinetics imply heterogeneous nucleation by defects on the substrates’ surfaces followed by two-dimensional growth.26 From the Avrami kinetics, a temperature-dependent rate constant, k, for the polymorphic transformation can be extracted. Performing a series of such isothermal transformations allows us to fit the rate constants and temperatures of transformations to the Arrhenius equation, from which the activation energy can be extracted (Figure 5b).27,28 Based on this analysis, we estimate the energy barrier for transformation from polymorph II to polymorph I to be 27 ± 1 kcal/mol in 16F-cHBC thin films and 38 ± 5 kcal/mol in 20F-cHBC thin films. Obtaining meaningful and reproducible energy barriers for the polymorph II to polymorph I transformation in 8F- and 12F-cHBC thin films is more challenging than those for 16Fand 20F-cHBC thin films because the temperatures required to transform 8F- and 12F-cHBC films are so high that the films can undergo concurrent sublimation. Thus, the integrated intensities tracked are both functions of the polymorphic change and sublimation that is taking place during isothermal annealing. While we cannot quantify the energy barriers for the polymorphic transformation of 8F- and 12F-cHBC, we are certain that they are greater than those for 16F- and 20F-cHBC films given the higher temperatures that are required for transformation to take place (290−315 °C versus 200−240 °C) over comparable time scales. This trend, coupled with the fact that cHBC does not transform from polymorph II to polymorph I upon thermal annealing, suggests that the energy barrier to transform polymorph II to polymorph I generally increases with decreasing fluorination. To gain insight on why the energy barrier for transformation decreases with fluorination, we examined the known crystal structures of other polycyclic aromatic hydrocarbons and their
Figure 5. (a) Isothermal transformation of a THF-vapor-annealed 20F-cHBC from polymorph II to polymorph I at 231 °C. The red line reveals a fit of the data to the second-order Avrami equation. (b) An Arrhenius plot yielding energy barriers of 27 ± 1 and 38 ± 5 kcal/mol, respectively, for 16F-cHBC (black circles) and 20F-cHBC (red squares) thin films to transform from polymorph II to polymorph I. n = 2 for both derivatives, representing second-order Avrami kinetics.
fluorinated derivatives. Though the crystal structure of every molecule is unique, polycyclic aromatic hydrocarbons have been shown to typically crystallize in one of two general classes of packing motifs depending on the balance of intermolecular C···C and C···H interactions, or alternatively referred to as π···π and C−H···π interactions. Some general rules of thumb for characterizing their crystallization behavior have thus been developed.29−32 Molecules with more C−H···π than π···π interactions tend to crystallize with a herringbone packing motif characterized by edge-to-face packing.29,33 Conversely, molecules with more π···π than C−H···π interactions tend to adopt a brickwork-type packing motif characterized by face-to-face packing.29,33 The rules that govern packing of contorted aromatics are more diverse due to the many types of intramolecular interactions possible.29 These rules of thumb based on the ratio of C···C to C···H interactions have generally only been applied to polycyclic aromatic hydrocarbons29−32,26 but not their fluorinated derivatives. Substituting hydrogen with fluorine will naturally reduce C···H interactions, thereby increasing the ratio of C···C to C···H interactions for a fluorinated derivative compared to 4314
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behavior of a compound. Using cHBCa polycyclic aromatic hydrocarbon and organic semiconductor with known polymorphismand its fluorinated derivatives as a family of model compounds, we have elucidated how fluorination affects polymorphic behavior. We found that even with extensive fluorination, fluorinated cHBC derivatives can access polymorphs (polymorph I and polymorph II) similar to those adopted by the unsubstituted parent compound. This finding suggests that fluorination may be an effective means of tuning the molecular properties of a compound without significantly altering its crystal structure. However, while polymorph I and polymorph II are both accessible to the fluorinated cHBC derivatives, the ease with which they are accessed is altered with fluorination. Our study suggests fluorination as an effective means of favoring the access of one polymorph over another.
its parent compound. Indeed, to this point, Sun et al. found that perfluoroalkylation of several small aromatic molecules enhances their π···π interactions and reduces C−H···π interactions.34 We hypothesize that this increase in the ratio of C···C to C···H (or π···π to C−H···π) interactions caused by fluorination results in molecules that typically adopt herringbone packing motifs to favor brickwork packing motifs instead. Indeed, we have found several other examples in the literature that support this hypothesis. For example, Cho et al. found that the crystal structure of condensed tetracyclic aromatic compounds switched from a herringbone packing to a brickwork packing with partial fluorination of the molecule.35 Similarly, Mori et al.36 and Tan et al.37 found that hexa-perihexabenzocoronene, a closely related molecule to cHBC but that is planar in its conformation, also switched from a herringbone packing to a brickwork packing with fluorination and chlorination, respectively. Studying a number of fluorinated derivatives of perylene bisimide, Schmidt et al. similarly observed a change from herringbone to brickwork packing for the most fluorinated and contorted derivatives.38 Turning our attention back to our family of cHBC derivatives, the polymorph I crystal structures of cHBC and its fluorinated derivatives can be classified as brickwork packing. Though we cannot say conclusively without its crystal structure, we believe that polymorph II has a herringbone packing motif given the similarities between its X-ray diffraction trace and that of yet another known polymorph of unsubstituted cHBC that belongs to the Pbcn space group and has a herrginbone motif.18 If this is indeed the case, the preference for polymorph I over polymorph II with fluorination of cHBC is consistent with the broader phenomenon in the literature where the brickwork packing motif is favored over the herringbone packing motif with fluorination of other polycyclic aromatic hydrocarbons.35,36,38,39 We speculate that because most of the unsubstituted parent polycyclic aromatic hydrocarbons in the literature35,36,38,39 access only the herringbone packing motif, a distinct switchover from herringbone to brickwork packing motifs above some critical level of fluorination is observed. However, because the parent cHBC compound appears to lie at an intermediary balance of C···C and C···H interactions where it can access both herringbone and brickwork packing motifs (likely due to its nonplanarity), we believe that both packing motifs remain accessible to the fluorinated derivatives of cHBC, as well. And this is manifested as a decrease in the energy barrier to transform to the brickwork-packing polymorph I with increased fluorination. Interestingly, that the energy barrier for accessing polymorphs is tunable appears to be generalizable across molecules with disparate chemistries. We observe, for example, that the energy barrier to access the herringbone packing motif of naphthalene tetracarboxylic diimide derivatives increases with an increasing extent of fluorination on the alkyl chain.40,41 These results are consistent with our findings with cHBC despite the fact that the chemical structure of the compound is entirely different and fluorination takes place on the alkyl side chains as opposed to directly on the core. In aggregate, these results suggest that using fluorination to change the accessibility of different polymorphs may be more broadly applicable.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.7b00627. Experimental details; 2D-GIXD patterns of 8F-, 12F-, 16F-, and 20F-cHBC with postdeposition processing; visual comparison of cHBC, 8F-cHBC, and 12F0cHBC polymorph I crystal structures; diffraction traces of thermally annealed films of cHBC and fluorinated derivatives having polymorph I and showing no polymorphic transformation with subsequent THFvapor annealing (PDF) 8F-cHBC CIF data (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Colin Nuckolls: 0000-0002-0384-5493 Yueh-Lin Loo: 0000-0002-4284-0847 Present Address #
Department of Chemistry, New Jersey City University, Jersey City, New Jersey. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank Dr. Matthew Bruzek and Prof. John Anthony (University of Kentucky, Lexington, KY) for providing the fluorinated pentacene quinone precursor used in the synthesis of fluorinated cHBC derivatives (NSF DMR103527). The authors also thank Aaron and Wesley Sattler of the Parkin Group (Columbia University) for solving the 8FcHBC crystal structure. This work was supported by the NSF MRSEC program through the Princeton Center for Complex Materials (DMR-0819860 and DMR-1420451) and the SOLAR Initiative at the NSF (DMR-10135217). GIXD experiments were conducted at CHESS, which is supported by NSF and NIH/NIGMS under award DMR-1332208. A.M.H. acknowledges support through the National Defense Science and Engineering Graduate (NDSEG) Fellowship (Air Force Office of Scientific Research 32 CFR 168a). B.K. and C.N. acknowledge support from the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy
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CONCLUSIONS While fluorination is a commonly utilized chemical modification to tune molecular properties for diverse applications, less understood are the effects fluorination has on the polymorphic 4315
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(21) Hiszpanski, A. M.; Saathoff, J. D.; Shaw, L.; Wang, H.; Kraya, L.; Lüttich, F.; Brady, M. A.; Chabinyc, M. L.; Kahn, A.; Clancy, P.; Loo, Y.-L. Halogenation of a Nonplanar Molecular Semiconductor to Tune Energy Levels and Bandgaps for Electron Transport. Chem. Mater. 2015, 27, 1892−1900. (22) van Laake, L.; Hart, A. J.; Slocum, A. H. Suspended heated silicon platform for rapid thermal control of surface reactions with application to carbon nanotube synthesis. Rev. Sci. Instrum. 2007, 78, 083901. (23) Avrami, M. Kinetics of phase change I - General theory. J. Chem. Phys. 1939, 7, 1103−1112. (24) Avrami, M. Kinetics of Phase Change. II Transformation-Time Relations for Random Distribution of Nuclei. J. Chem. Phys. 1940, 8, 212−224. (25) Avrami, M. Granulation, Phase Change, and Microstructure Kinetics of Phase Change. III. J. Chem. Phys. 1941, 9, 177−184. (26) Papon, P.; Leblond, J.; Meijer, P. H. E. The Physics of Phase Transitions: Concepts and Applications, 2nd ed.; Springer: Paris, 2002. (27) Liu, S.; Yu, Y.; Cui, Y.; Zhang, H.; Mo, Z. Isothermal and nonisothermal crystallization kinetics of nylon-11. J. Appl. Polym. Sci. 1998, 70, 2371−2380. (28) Cebe, P.; Hong, S.-D. Crystallization behaviour of poly(etherether-ketone). Polymer 1986, 27, 1183−1192. (29) Desiraju, G. R.; Gavezzotti, A. Crystal structures of polynuclear aromatic hydrocarbons - Classification, rationalization, and prediction from molecular structure. Acta Crystallogr., Sect. B: Struct. Sci. 1989, 45, 473−482. (30) Spackman, M. A.; McKinnon, J. J. Fingerprinting intermolecular interactions in molecular crystals. CrystEngComm 2002, 4, 378−392. (31) Schatschneider, B.; Phelps, J.; Jezowski, S. A new parameter for classification of polycyclic aromatic hydrocarbon crystalline motifs: a Hirshfeld surface investigation. CrystEngComm 2011, 13, 7216−7223. (32) Loots, L.; Barbour, L. J. A simple and robust method for the identification of pi-pi packing motifs of aromatic compounds. CrystEngComm 2012, 14, 300−304. (33) Tiekink, E. R. T. Molecular crystals by design? Chem. Commun. 2014, 50, 11079−11082. (34) Sun, H.; Tottempudi, U. K.; Mottishaw, J. D.; Basa, P. N.; Putta, A.; Sykes, A. G. Strengthening π−π Interactions While Suppressing Csp2−H···π (T-Shaped) Interactions via Perfluoroalkylation: A Crystallographic and Computational Study That Supports the Beneficial Formation of 1-D π−π Stacked Aromatic Materials. Cryst. Growth Des. 2012, 12, 5655−5662. (35) Cho, D. M.; Parkin, S. R.; Watson, M. D. Partial Fluorination Overcomes Herringbone Crystal Packing in Small Polycyclic Aromatics. Org. Lett. 2005, 7, 1067−1068. (36) Mori, T.; Kikuzawa, Y.; Takeuchi, H. N-type field-effect transistor based on a fluorinated-graphene. Org. Electron. 2008, 9, 328−332. (37) Tan, Y.-Z.; Yang, B.; Parvez, K.; Narita, A.; Osella, S.; Beljonne, D.; Feng, X.; Müllen, K. Atomically precise edge chlorination of nanographenes and its application in graphene nanoribbons. Nat. Commun. 2013, 4, 2646. (38) Schmidt, R.; Oh, J. H.; Sun, Y.-S.; Deppisch, M.; Krause, A.-M.; Radacki, K.; Braunschweig, H.; Könemann, M.; Erk, P.; Bao, Z.; Würthner, F. High-Performance Air-Stable n-Channel Organic Thin Film Transistors Based on Halogenated Perylene Bisimide Semiconductors. J. Am. Chem. Soc. 2009, 131, 6215−6228. (39) Salini, P. S.; Rajagopal, S. K.; Hariharan, M. HaloacetylationDriven Transformation of Sandwich Herringbone to Lamellar/ Columnar Packing in Pyrene. Cryst. Growth Des. 2016, 16, 5822−5830. (40) Purdum, G. E.; Yao, N.; Woll, A.; Gessner, T.; Weitz, R. T.; Loo, Y.-L. Understanding Polymorph Transformations in Core-Chlorinated Naphthalene Diimides and their Impact on Thin-Film Transistor Performance. Adv. Funct. Mater. 2016, 26, 2357−2364. (41) Purdum, G.; Loo, Y.-L. Personal communication. Department of Chemical and Biological Engingeering, Princeton University, Princeton, NJ, March 2016.
Sciences, U.S. Department of Energy (DOE), under Award No. DE-FG02-01ER15264. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC5207NA27344. LLNL-JRNL-713258.
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DOI: 10.1021/acs.chemmater.7b00627 Chem. Mater. 2017, 29, 4311−4316
