Perylene Diimide Triple Helix Formation in the Solid State - Crystal

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Cite This: Cryst. Growth Des. XXXX, XXX, XXX−XXX

Perylene Diimide Triple Helix Formation in the Solid State Published as part of a Crystal Growth and Design virtual special issue Honoring Prof. William Jones and His Contributions to Organic Solid-State Chemistry Sarah L. Haddow,† David J. Ring,† Hena Bagha,† Nicholas Pearce,† Harriet Nowell,‡ Alexander J. Blake,† William Lewis,† Jonathan McMaster,† and Neil R. Champness*,† †

School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, U.K. Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, U.K.

‡

S Supporting Information *

ABSTRACT: The structural characterization of single crystals of di-4-pyridyl-substituted 3,4,9,10-perylenetetracarboxylic diimide reveals a surprising triple helical arrangement. The intermolecular interactions that lead to such an arrangement are investigated by Hirshfeld surface analysis and indicate that the supramolecular structure arises due to a combination of C−H···O interactions and π−π stacking interactions between adjacent perylene diimide (PDI) species. The interplay of these interactions leads to the formation of a tubular structure enclosed by the triple helix of PDI molecules. In contrast, the analogous phenyl-substituted molecule forms a simple onedimensional stack of PDI molecules which is also unusual in that the perylene core adopts an essentially planar arrangement despite bay substitution.

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INTRODUCTION Rylene diimides and the specific family of perylene diimides (PDIs)1 have received extensive attention over many years due to their potential applications. The organization of PDIs in solution,2 on surfaces,3 and in the solid state4 can have a significant influence on the properties of the resulting material. In part, this is due to the interactions between adjacent molecules and the extent, as well as the nature, of aggregation effects. The influence of different stacking arrangements, for example, H- vs Jaggregation, can significantly influence the color of solid-state materials, and this has been extensively studied due to the application of PDIs as industrial dyes.5 The ability to control packing is significantly affected by functionalization of PDIs (Scheme 1). PDIs can readily be modified at the imide position, and the influence of imide substituents on the overall solid-state packing can be considerable, leading to different colors of closely related analogues.1,4,5 PDIs can also be functionalized on the perylene core in either the bay region1 or the ortho positions6,7 (Scheme 1) or through thionation8,9 of the imide carbonyl groups. Functionalization of the perylene core can have a significant influence on the electronic structure of the PDIs1,10 but can also influence the ability of the molecules to pack in the solid state, depending on the steric bulk and orientation of the substituents. Various degrees of substitution can be achieved from simple monosubstitution11 through to unusual octa-substituted species.12 The most common forms of substituted PDIs are tetraand disubstituted systems, both of which have been extensively © XXXX American Chemical Society

Scheme 1. Regions of PDI Species Where Functionalization Can Be Achieved and the Structure of 1

studied. In this article we have focused on disubstituted systems, which exist in two distinct isomeric arrangements, namely, 1,6 and 1,7. While both isomers exhibit twisting of the perylene core, the different substitutions can influence the solid-state stacking. In the limited number of examples where crystal structures of both 1,6 and 1,7 isomers have been reported,9,10,13,14 significant differences in the long-range order of the compounds is demonstrated. Bay-substituted PDIs also exhibit atropisomerism Received: September 7, 2017 Revised: December 1, 2017

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DOI: 10.1021/acs.cgd.7b01268 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

asymmetric unit, both of which are P atropisomers; M atropisomers are generated by symmetry to afford a system that has no overall chirality. The twist of the perylene, defined as the twist between the two naphthyl moieties of the perylene core, was found to be 21.47° or 23.02° for the two molecules in the asymmetric unit, a twist that is consistent with previous reports.9,10,13,14 The structure of 2 is somewhat surprising in that the perylene core does not exhibit a twist: the dihedral angle formed between the two naphthyl moieties is 0.0° (Figure 1b), i.e., a coplanar arrangement. The steric contribution of the phenyl substituents is observed in a substantial displacement of the carbon atom to which the phenyl groups are attached from the naphthyl plane (0.13 Å). In contrast, the maximum displacement of the equivalent atoms in 1 is 0.05 Å. Density functional theory (DFT) calculations on 1 and 2 show that the optimized structures in the gas phase are ca. 237 and 249 kcal mol−1, respectively, lower in energy than those derived from single point calculations of the X-ray crystallographic coordinates in the gas phase.26 Inspection of the gas phase conformation of 1 reveals a twist angle between the naphthyl moieties of the perylene core, of 23.19°, a value of similar magnitude to those observed experimentally. For 2 the naphthyl moieties are found to be coplanar in the calculated structure, just as in the crystallographic determination. A similar distortion of the phenyl-substituted carbon atom from the naphthyl plane is observed in the calculated structure of 2, but this is slightly elongated to 0.14 Å (vs 0.13 Å in the crystal structure). The small differences between the calculated and experimentally observed structures do not indicate a significant influence on the molecular structure as a result of crystal packing. The two compounds differ markedly in their packing arrangements (Figure 2). 2 adopts an arrangement that maximizes π−π stacking interactions between adjacent perylene cores with one-dimensional stacks formed parallel to the crystallographic a-axis (Figure 2a). The perpendicular distance between perylene planes in adjacent molecules is 3.39 Å with a centroid···centroid separation of 3.58 Å between overlapping rings. These short distances27 indicate a robust π−π interaction suggesting, perhaps, that these interactions encourage the unusual planarity of this disubstituted PDI (note discussion of DFT calculations above). In contrast, 1 adopts a highly unusual structure with trigonal crystallographic symmetry (Figure 2b); the compound crystallizes in the space group R3̅. The surprising symmetry of the longrange structure of 1 led us to investigate what intermolecular forces may be influencing the observed arrangement. Hirshfeld surface analysis28 of 1 reveals a number of intermolecular

as a result of twisting of the perylene core; however, isolation of individual P or M isomers is typically challenging due to the different arrangements being in dynamic equilibrium at room temperature.15−17 In this study we report a highly unusual solid-state structure adopted by a bis-pyridyl substituted PDI, N,N′-bis(n-butyl)-1,7di(4-pyridyl)-3,4,9,10-perylenetetracarboxylic acid diimide, 1. The compound was prepared as a mixture of isomers by a similar method to those reported previously,18 using a Suzuki coupling between N,N′-dibutyl-dibromoperylene-3,4,9,10-tetracarboxylic diimide and 2-(4-pyridyl)-4,4,5,5-tetramethyl-1,3-dioxaborolane. The 1,7 isomer was isolated by repeated recrystallization, layering hexane onto warmed solutions of 1 in CH2Cl2. Di-4pyridyl-substituted PDIs have been studied previously with a variety of imide functionalities;20−24 however, such systems have not been characterized by single crystal X-ray diffraction. Suitable crystals were grown using a layering method, hexane being layered over a solution of 1 in CHCl3, the two layers being allowed to slowly mix overnight. For comparison, the analogous phenyl-substituted compound, N,N′-bis(n-butyl)-1,7-di(phenyl)-3,4,9,10-perylenetetracarboxylic acid diimide, 2, was prepared,25 and crystals were grown in the same manner as 1. The single crystal structures of 1 and 2 present markedly different arrangements (Figures 1, 2). Both compounds have the

Figure 1. Views of the single crystal structures of (a) 1 and (b) 2. Note the twisted arrangement of the perylene core of 1 and the more planar arrangement of the perylene core in 2. Carbon−gray; hydrogen−white; nitrogen−blue; oxygen−red.

same substitution in the bay region, differing only in the nature of the substituent: 4-pyridyl in 1 vs phenyl in 2. In the case of 1, two crystallographically distinct PDI molecules are observed in the

Figure 2. Views of the packing observed in (a) 2 and (b) 1. Note the formation of extended stacks in the case of 2 but the formation of tubular structures with trigonal symmetry for 1. Carbon−gray; hydrogen−white; nitrogen−blue; oxygen−red. B



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As anticipated for PDIs disubstituted in the bay region,9,10,13,14 and in contrast to 2, the twisted configuration of the perylene core leads to the formation of pairs of molecules (Figure 4a). The pyridyl substituents protrude from both faces of the pair, allowing maximal π−π interactions between pairs of PDIs. A range of centroid···centroid separations is observed with the shortest being 3.66 Å. As noted above, each pair of molecules comprises atropisomers of the same chirality, P with P and M with M. Inspection of the Hirshfeld surfaces indicates that the most significant intermolecular interactions involve the (C)hydrogens meta and ortho to the pyridyl nitrogen. It is anticipated that pyridyl C−H groups are better hydrogen bond donors than phenyl analogues due to their more acidic nature. One of the meta C−H groups is involved in a C−H···O hydrogen bond that links pairs of PDI molecules (C···O = 3.472(3) Å, H···O = 2.52 Å, ∠C−H−O = 175.0°). C−H···O hydrogen bonds involving pyridyl ortho hydrogen atoms link PDI molecules from different pairs, leading to the extended structure. One carbonyl group per PDI pair is involved in C−H···O interactions to two adjacent PDI molecules with one of the interactions being significantly longer than the other (C···O = 3.288(4) Å, H···O = 2.40 Å, ∠C− H−O = 155.0°; C···O = 3.54 Å, H···O = 2.63 Å, ∠C−H−O = 159.7°) (see Supporting Information). These intermolecular ortho C−H···O interactions lead to trimeric arrangements of PDI molecules (layer A, Figure 4b). If one then considers the partner PDIs from the PDI pairs (layer B), a bilayer of PDI trimers (AB) is observed (Figure 4c). A view perpendicular to the crystallographic c-axis shows that these bilayers of trimers are stacked to form a helical, tubular structure, with the bilayers adopting an ABBAABBA arrangement (Figure 4d).

interactions which contribute to the overall stacking arrangement (Figure 3).

Figure 3. Hirshfeld surface calculated for 1 illustrating the intermolecular C−H···O interaction between one of the C−H ortho to the pyridyl nitrogen and carbonyl group on an adjacent PDI. The surface is colored to represent the value dnorm which describes the distance between the Hirshfeld surface of the pro-molecule and the closest nuclei outside the surface. Red spots represent short intermolecular contacts arising from C−H···O interactions between neighboring molecules.

Figure 4. Views of the structure of 1. (a) PDI pairs of molecules of 1 indicating π−π interactions between the molecules; (b) trimer of PDIs formed by intermolecular C−H···O interactions between the C-Hs ortho to the pyridyl nitrogen and carbonyl groups on adjacent PDIs, viewed along the crystallographic c-axis; (c) layer A (magenta) with accompanying molecules from PDI pairs, layer B (blue) viewed along the c-axis; (d) helical, tubular structure of 1 viewed along the a-axis. Note the alternating ABBAABBA arrangement of the trimer layers. In (a) and (b) carbon−gray; hydrogen−white; nitrogen−blue; oxygen−red. In (b) dotted lines indicate C−H···O interactions. C



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Figure 5. Views of the helical structures observed within 1. (a) an individual helix formed through the arrangement of PDI pairs viewed perpendicular to the c-axis; (b) the three helices within a tube of 1, viewed parallel to the c-axis; (c) a space-filling view of the triple helix perpendicular to the c-axis. In (a) carbon−gray; hydrogen−white; nitrogen−blue; oxygen−red. In (b) and (c) each helix is represented in a different color.

Figure 6. UV−visible spectra for 1 (red) and 2 (blue) solution spectra (CH2Cl2 solution) shown with continuous line; thin film, deposited from CH2Cl2 solution, shown with dotted line.

films of 1 and 2 (Figure 6; see Supporting Information for details). The profile of the UV−visible spectrum for both compounds is consistent with spectra of other similarly substituted PDIs.10,13,14,29 Thus, two maxima are observed for both compounds in the range ca. 500−550 nm [λmax = 505, 540 nm (1); 529, 552 nm (2)] with the peak to higher wavelength exhibiting the greater intensity. In contrast, the spectra of thin films of the two compounds show a reversal in intensity of these peaks with the absorption to lower wavelength exhibiting greater absorbance; this intensity reversal is consistent with intermolecular stacking being observed in the thin films29,30 and is accompanied by a small bathochromic shift for compound 1 but not 2 [514, 549 nm (1); 529, 552 nm (2)]. No peak is observed at wavelengths greater than 600 nm, suggesting that J-aggregates are absent, and as no hypsochromic shift is observed it can be concluded that H-aggregation is, similarly, not observed. Thus, it can be concluded that the stacking arrangement in the films of these materials is not well-defined.

An alternative view of the structure of 1 is to consider the arrangement of individual PDI pairs and how these are positioned with respect to each other. If one considers a given PDI pair and then the adjacent PDI pairs in closest proximity, then a helix is formed parallel to the c-axis (Figure 5a). These helices are subcomponents of the tubular structures observed in the extended structure of 1 (see Figure 2b). PDI pairs alternate in terms of their atropisomerism, P-pairs alternating with M-pairs, along the main axis of the helix. Each tubular feature comprises three such helices, each running parallel to the c-axis such that a triple helix is observed (Figure 5b,c). The structure is perhaps even more surprising considering that there are no substantial intermolecular interactions between adjacent PDI pairs, and therefore specific interactions that generate the helical structure are not readily identified. Powder X-ray diffraction (PXRD) patterns of the two compounds were recorded (see Supporting Information for both experimental and calculated patterns), and comparison to patterns calculated from the single crystal data show that the structures are maintained in bulk samples. In the case of compound 2 the PXRD shows a good match for the pattern calculated from the single crystal structure. In the case of 1 it is evident that the structure is largely maintained, but some amorphous material is also observed, possibly due to loss of crystallinity under the conditions of the experiment. The effect of packing on the UV−visible spectra of each compound was also assessed by investigating the spectra of thin

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CONCLUSIONS The two structures herein present unusual packing arrangements for disubstituted PDI molecules. Compound 2 is perhaps more typical of the structures observed for such systems, but the unanticipated planarity of the perylene core allows greater π−π stacking interactions despite the bay substitution. This planarity facilitates the formation of extended PDI stacks more reminiscent of structures exhibited by PDIs which are not D



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substituted in the bay region.1,4,5 In sharp contrast, compound 1 exhibits a highly unusual structure that is also unanticipated. 1 forms pairs of PDI molecules commonly observed for disubstituted PDI molecules,9,10,13,14 but the arrangement of these pairs into a triple helical arrangement is entirely unexpected. Inspection of the structure of 1 does not give a clear rationale for the helical structure, but consideration of Hirshfeld surface plots allow the identification of weak C−H···O interactions leading to the formation of trimeric arrangements of PDIs which in turn stack to form the tubular structure. Indeed, the structures amply demonstrate the difficulty in predicting the structures of this important class of molecules and the wider difficulties encountered in crystal engineering.

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Details of crystallographic structural refinement and additional figures (PDF) Accession Codes

CCDC 1570979−1570980 (for 1 and 2, respectively) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/ data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Corresponding Author

*E-mail: [email protected].

EXPERIMENTAL SECTION

ORCID

N,N′-Dibutyl-1,7-di(4-pyridyl)perylene-3,4,9,10-tetracarboxylic Diimide, 1. A Schlenk flask was charged with N,N′-dibutyl-1,7dibromoperylene-3,4,9,10-tetracarboxylicdiimide (299 mg, 0.4 mmol), 2-(4-pyridyl)-4,4,5,5-tetramethyl-1,3-dioxaborolane (201 mg, 1.0 mmol), Pd(PPh3)4 (103 mg, 0.1 mmol), 2 M potassium carbonate (5 mL), and THF (50 mL) under dinitrogen. The mixture was heated at reflux with vigorous stirring for 22 h. After being cooled to room temperature, the mixture was diluted with diethyl ether and washed three times with saturated aqueous NaCl. After drying over anhydrous MgSO4, the solvent was removed under reduced pressure to yield a red solid. The crude product was purified via silica gel column chromatography (99% CHCl3/ 1% MeOH), and repeated recrystallization (CHCl3/MeOH) was performed to remove the 1,6-isomer (yield 182 mg, 63%). A ratio of 100:4 of 1,7:1,6-isomer was obtained shown by 1 H NMR. 1 H NMR (400 MHz, CDCl3): 1,7 isomer: δH = 8.79 (d, 4H, 3J = 8 Hz), 8.56 (s, 2H), 8.24 (d, 2H, 3J = 8 Hz), 7.78 (d, 2H, 3J = 8 Hz), 7.51 (d, 4H, 3J = 8 Hz), 4.20 (t, 4H, 3J = 8 Hz), 1.71 (m, 4H), 1.47 (q, 4H, 3J = 8 Hz), 0.99 ppm (t, 6H, 3J = 8 Hz). 1,6 isomer: δH = 8.79 (d, 4H, 3J = 8 Hz), 8.58 (s, 2H), 8.22 (d, 2H, 3J = 8 Hz), 7.80 (d, 2H, 3J = 8 Hz), 7.41 (d, 4H, 3J = 8 Hz), 4.20 (t, 4H, 3J = 8 Hz), 1.71 (m, 4H), 1.47 (q, 4H, 3J = 8 Hz), 0.99 ppm (t, 6H, 3J = 8 Hz). 13 C NMR (400 MHz, CDCl3): δC = 162, 151.4, 149.6, 137.9, 134.3, 133.5, 132.1, 130.6, 129.7, 128.7, 127.7, 123.5, 122.7, 122.4, 40.3, 30.0, 20.1, 13.6 ppm. MS (MALDI-TOF) M/ z−: 656.3 (M−, dipyridyl-PTCDI, major product), 657.4 (M−, monopyridyl-PTCDI). IR (CHCl3 solution, cm−1) 3690, 3631, 2992, 2945, 2839, 2360, 2341, 1772, 1698, 1658, 1600, 1466, 1436, 1410, 1335, 1243, 1136, 1084, 1016, 863, 827, 651. UV/vis (CHCl3, conc. 1 ×10−4 M) λmax = 302, 410, 505, 519 nm. Elemental analysis calcd. for C42H32O4N2 Expected % C 76.81; H 4.91; N 8.53. Found % C 73.7; H 4.93; N 8.06 (discrepancies in the values are accounted for with solvent included in the structure; see discussion of X-ray structure). Crystal Data for 1. 2(C42H32N4O4)·0.7(CHCl3)·0.15(C6H14). Trigonal, space group R3̅, a = b = 52.965(1), c = 13.9492(2), Å, V = 33888.8(14) Å3, Z = 18, Dcalc = 1.291 g cm−3, μ = 0.185 mm−1, F(000) = 13748. A total of 140 200 reflections were collected, of which 26 531 were unique, with Rint = 0. 056. Final R1 (wR2) = 0.0601 (0.1958) with GOF = 1.08. 2, N,N′-Dibutyl-1,7-diphenylperylene-3,4,9,10-tetracarboxylic diimide, was prepared in an analogous manner to 1 and ref 25. Crystal Data for 2. C44H34N2O4. Triclinic, space group P1̅, a = 4.9438(4), b = 11.5020(11), c = 14.2974(13) Å, α = 85.985(5), β = 82.424(6), γ = 79.183(6)°, V = 790.73(12) Å3, Z = 1, Dcalc = 1.375 g cm−3, μ = 0.088 mm−1, F(000) = 344. A total of 12 730 reflections were collected, of which 3606 were unique, with Rint = 0.090. Final R1 (wR2) = 0.1015 (0. 2570) with GOF = 1.07.

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AUTHOR INFORMATION

William Lewis: 0000-0001-7103-6981 Jonathan McMaster: 0000-0003-0917-7454 Neil R. Champness: 0000-0003-2970-1487 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Engineering and Physical Sciences Research Council (EP/K01773X/1) for support, Diamond Light Source for access to beamline I19 at Diamond Light Source and the EPSRC UK National Crystallography Service at the University of Southampton for the collection of crystallographic data. N.R.C. gratefully acknowledges receipt of a Royal Society Wolfson Merit Award.

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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.cgd.7b01268. E



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Perylene Diimide Triple Helix Formation in the Solid State - Crystal

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