Conformational Polymorphism of Octadehydrodibenzo [12] annulene

Conformational Polymorphism of Octadehydrodibenzo[12]annulene with Dimethyl Phthalate Moieties Ichiro Hisaki,* Yuu Sakamoto, Hajime Shigemitsu, Norimitsu Tohnai, and Mikiji Miyata* Department of Material and Life Science, Graduate School of Engineering, Osaka UniVersity, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 1 414–420

ReceiVed June 18, 2008; ReVised Manuscript ReceiVed September 28, 2008

ABSTRACT: In this study, we found that an octadehydrodibenzo[12]annulene derivative with two dimethyl phthalate moieties yielded three polymorphic crystals I, II, and III, in which the annulene core arranges in herringbone, parallel-π-stacked, and zigzagπ-stacked fashion, respectively. This is the first example for dehydroannulenes to show polymorphic crystal structures. These polymorphs are brought from varied conformations of the dimethyl phthalate moieties because the direction of the carbonyl oxygen atoms in the phthalate affects the manner of CH/O interaction abundantly observed in the present systems. It is also revealed that the decomposition temperature of the polymorphic crystals varied over a wide range of values (112-163 °C), even though the crystals are composed of an identical molecule. This indicates that the molecular arrangement might have significant influence on the thermal stability and/or intermolecular reactivity of the annulene. Introduction The conjugated macrocycles consisting of benzene rings and acetylene units, so-called dehydrobenzoannulenes (DBAs), have been substantially investigated as an attractive platform for functional materials.1 So far, functionalization of DBAs has been achieved by conjugating nitro/amino groups,2 crown ether,3 phthalocyanine,4 Ru(II)-coordinated dipyridophenazine,5 oxyphenylbenzene,6 and tetrathiafulvalene.7 In addition to molecular functionalization, construction of novel supramolecular assemblies based on DBA cores have also been reported, which include liquid crystals,8 vesicles,9 fibers,7 two-dimensional assemblies on a surface,10 and crystals.11 In the assemblies, molecular arrangements have an influence on its physical properties. This is especially crucial in the crystal state because the molecules are more closely packed than any other assembly states. Thus, the manipulation principle of the DBA arrangement in crystal is desperately needed. A naked DBA crystallizes into its intrinsic crystal structure via π/π and/or CH/π interactions, similar to the case of polycyclic aromatic hydrocarbons described by Desiraju and Gavezzotti.12 For example, DBA 1 crystallizes into a herringbone fashion via predominant CH/π interaction.11c,13 For modulation of molecular arrangement of the DBA core, we recently reported that DBA 2 functionalized by carboxyl groups formed an unusual face-to-face π-stacked one-dimensional assembly via hydrogen-bonds with dimethyl sulfoxide (DMSO) molecules, and that its single crystal had significantly large anisotropic charge mobility due to the one-dimensional superstructure.11c Among the DBA family, octadehydrodibenzo[12]annulene (3) is particularly attractive because of its potential for topochemical polymerization in the solid state. So far, great efforts have been made to achieve that.11a,b,14 During our study aiming to control molecular orientation and develop novel crystalline material based on 3, we came to the conclusion that phthalate derivative 4 exhibits three conformational polymorphic crystals, in which the annulene core arranges into three different patterns, i.e., herringbone, parallel-π-stacked, and zigzag-π-stacked structures. * Corresponding author. Fax: +81-6-6879-7406. Tel: +81-6-6879-7406. E-mail: [email protected] (I.H.); [email protected] (M.M.).

Conventionally, the parent compound 3 is known to crystallize into the γ form uniquely,11a,15 and crystal structures of its derivatives were reported.11b,14,16 However, the present system is the first example for polymorphism of DBAs. Especially, the zigzag-π-stacked structure is hitherto unknown. Crystal polymorphism is one of the most significant topics in the fields of crystal engineering, supramolecular chemistry, and pharmaceutics. Particularly, conformational polymorphism is fundamental and is often observed in crystallization of a compound that contains a flexible moiety.17 For foundational investigation of the relationship among molecular conformations, intermolecular interactions, crystal structures, and physical properties, the appearance of polymorphic crystal structures is convenient. Moreover, control of the polymorphic crystal structures just by crystallization conditions such as temperature and solvents is able to contribute to easy modulation of molecular arrangements. In this paper, we describe and interpret the crystal structures of three polymorphs of DBA 4 on the basis of CH/O interaction and conformational diversity of the ester groups. It is also revealed that the decomposition temperature of the crystals depends upon their molecular arrangement. Experimental Section General Methods. 1H and 13C spectra were measured by a JEOL spectrometer (270 MHz for 1H and 67.5 MHz for 13C). Mass spectrum data were obtained from a JEOL JMS-700 instrument. Differential scanning calorimetry (DSC) analysis was performed on a Rigaku instruments DSC 8230 under an N2 purge from 30 to 200 °C at a heating rate of 5 °C min-1. Fourier transform infrared (FT-IR) spectra of the synthesized compounds in a KBr pellet were recorded using a Horiba FT-720 spectrometer. Dimethyl 4,5-Diiodophthalate (7). To a solution of diiodophthalic acid (6) (400 mg, 0.960 mmol), which was synthesized from phthalimide (5) in 79% according to the literature,18 dissolved in methanol (5 mL), was added dropwise SOCl2 (0.41 mL, 5.8 mmol). After being stirred under reflux for 26 h, the reaction mixture was quenched with saturated aqueous NaHCO3, extracted with CH2Cl2, dried over anhydrous MgSO4, and concentrated in vacuo to afford 7 (366 mg, 86%) as a pale yellow solid. 7: 1H NMR (270 MHz, CDCl3): δ 8.16 (s, 2H ArH), 3.89 (s, 6H, OCH3). Bis(trimethylsilylethynyl)benzene Derivative 8. To a mixture of 7 (5.00 g, 11.2 mmol), Pd(PPh3)2Cl2 (400 mg, 5.70 mmol), and CuI (350 mg, 1.80 mml) in tetrahydrofuran (THF; 150 mL) was added

10.1021/cg800643e CCC: $40.75  2009 American Chemical Society Published on Web 11/21/2008

Polymorphism of Octadehydrodibenzo[12]annulene Chart 1. Structures of Dehydrobenzo[12]annulenes

diisopropylamine (3.5 mL) and trimethylsilylacetylene (3.7 mL, 27 mmol), and the reaction was stirred overnight. The product was extracted by CH2Cl2, washed with brine, dried over anhydrous MgSO4, and concentrated in vacuo to afford 8 (3.90 g, 90%) as an orange oil. 8: 1H NMR (270 MHz, CDCl3): δ 7.79 (s, 2H ArH), 3.89 (s, 6H, OCH3), (s, 18H, Si(CH3)3). DBA 4. To a solution of 8 (1.00 g, 2.59 mmol) dissolved in THF (20 mL) was added a 1 M solution of tetrabutylammonium fluoride (TBAF) in THF (0.4 mL). The reaction was stirred at ambient temperature for 1 h. The reaction mixture was concentrated, extracted by CH2Cl2, and washed with water. After drying the organic layer with anhydrous MgSO4, the solvent was removed in vacuo to afford a dark oil. The resulting material was filtered through a short column chromatogram (silica gel, CH2Cl2), giving a yellow oil, and then used for the following step. To a O2 bubbled solution of CuCl (240 mg, 2.41 mmol) and the resultant diethynylphthalate derivative dissolved in CH2Cl2 (150 mL) was added N,N,N′,N′-tetramethylethylenediamine (7.20 mL, 47.8 mmol), and the reaction was stirred for 30 min at ambient temperature. The reaction mixture was quenched by 0.5 M HCl and extracted by CH2Cl2. After drying the organic layer over anhydrous MgSO4 followed by evaporating the solvent, the residue was filtered through a short column chromatogram (silica gel, CH2Cl2/AcOEt). The resultant mixture was washed by CHCl3 to isolate trimer 9 (95.2 mg, 15%) as a yellow precipitate, and the residue was purified by preparative highperformance liquid chromatography (HPLC) (CHCl3) to afford 4 (90.0 mg, 14%) as a yellow solid. 9: mp (dec.) 247 °C; 1H NMR (270 MHz, CDCl3): δ 8.04 (s, 6H ArH), 3.95 (s, 18H, CH3); 13C NMR (67.5 MHz, CDCl3): δ 166.3, 133.3, 132.0, 127.6, 80.42, 80.39, 53.1; IR (KBr) 2360, 1727 cm-1. 4: 1H NMR (270 MHz, CDCl3): δ 7.30 (s, 4H ArH), 3.89 (s, 12H, CH3); 13C NMR (67.5 MHz, CDCl3): δ 166.9, 134.1, 133.6, 129.6, 92.2, 87.2, 53.3; IR (KBr) 2337, 1728 cm-1; HR-MS (FAB-): m/z calcd for [M-] C28H16O8: 480.0845; found: 480.0842. Single-Crystal Diffraction. X-ray diffraction data were collected on a Rigaku R-AXIS RAPID diffractometer with a two-dimensional (2D) area detector with graphite monochromatized Cu KR radiation (λ ) 1.54187 Å). Direct methods (SIR-2004) were used for the structure solution.19 All calculations were performed with the observed reflections [I > 2σ(I)] by the program CrystalStructure crystallographic software packages20 except for refinement, which was performed using SHELXL97.21 All non-hydrogen atoms were refined with anisotropic displacement parameters, and hydrogen atoms were placed in idealized positions and refined as rigid atoms with the relative isotropic displacement parameters. Theoretical Study. The optimization of the conformers was performed by the density functional theory (DFT) method at the B3LYP/6-311** level equipped in Gaussian 03.22

Results and Discussion Synthesis and Crystallization. The synthetic route of 4 is shown in Scheme 1. Phthalic acid derivative 6, which was derived from phthalimide (5) through iodization followed by hydrolysis, was methyl-esterated to give dimethyl phthalate derivative 7. Cross-coupling reaction of 7 with trimethylsilylacetylene yielded diethynylbenzene derivative 8. Desilylation of 8 and subsequent oxidation cyclization gave 4 together with trimeric macrocycle 9. During crystallization of 4, we found that slow evaporation of chloroform/acetone solution in a refrigerator at 2 °C coinstantaneously provided three kinds of crystals, which differ

Crystal Growth & Design, Vol. 9, No. 1, 2009 415 Scheme 1. Synthesis of DBA 4a

a TMSA: trimethylsilylacetylene, TBAF:tetrabutylammonium fluoride, TMEDA: N,N,N′,N′-tetramethylethylenediamine.

Figure 1. Photography of crystals with platelet-like (I), columnar (II), and spear-like (III) morphology.

from one another in morphology, i.e., platelet-like, columnar, and spear-like crystals I, II, and III, respectively, as shown in Figure 1, although the platelet-like crystal was rarely yielded under these conditions. Although completely selective formation has not yet been achieved, crystal III tends to grow predominantly by a slow evaporation of acetone or chloroform/methanol solution, while relatively rapid evaporation of chloroform/ methanol yields crystal II preferentially. Crystal I was obtained together with crystals II and/or III, when the benzene solution was evaporated at room temperature (Supporting Information, Figures S1-S3). Crystal Structures. Crystal structures and data of the three polymorphic crystals are shown in Figure 2 and Table 1, respectively.23 Crystals I, II, and III belong to the space group P21/c, P-1, and P21/c, respectively. It is worth noting that 4I and 4III have an inversion center, while 4II does not, where 4I-4III denote conformers of 4 observed in crystals I-III, respectively (Figure 2a,d,g). In crystal I, the molecules pack in a herringbone fashion with their long axes parallel to one another (Figure 2b,c). The annulene (A) perpendicularly contacts the adjacent one (B) with

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Figure 2. Polymorphic crystal structures of 4 for crystals I (a-c), II (d-f), and III (g-i). Thermal ellipsoid plots with 50% probability. In the packing diagram, the annulene moieties are drawn by the space-fill model. Table 1. Crystallographic Data and Summary of Data Collection and Structure Refinement Parameters

formula formula weight crystal size [mm] crystal system space group a [Å] b [Å] c [Å] R [°] β [°] γ [°] V [Å3] Z Dc [g/cm3] num. of uni. ref. num. of obs. ref. Rint R1 (F2 < 2σ (F2)) Rw (all data) GOF 2θmax [°] ref./para. temperature [K] CCDC

I

II

III

C28H16O8 480.43 0.18 × 0.09 × 0.05 monoclinic P21/c (#14) 13.0212(6) 9.1207(4) 9.5017(4) 90 97.460(3) 90 1118.89(8) 2 1.426 2037 11204 0.112 0.0821 0.2653 1.070 136.4 12.42 153 701679

C28H16O8 480.43 0.40 × 0.10 × 0.10 triclinic P1j (#2) 7.9839(2) 8.8536(3) 16.1096(5) 85.170(2) 87.758(2) 74.583(2) 1093.69(6) 2 1.459 3911 13385 0.055 0.0460 0.1373 1.135 136.4 12.00 153 701680

C28H16O8 480.43 0.70 × 0.10 × 0.10 monoclinic P21/c (#14) 12.0874(4) 12.7221(4) 7.1581(3) 90 97.640(2) 90 1090.99(7) 2 1.462 1991 12077 0.061 0.0433 0.1225 1.080 136.5 12.14 113 701681

the interplanar angle of 85.1°, while it has little π/π contact with the next cofacial molecule (C); the distance between A and C is 3.83 Å. Herringbone packing is well-known to be dominated by intermolecular CH/π interaction and is the simplest and the most fundamental for the linear fused polycyclic aromatic hydrocarbons such as naphthalene, anthracene, tetracene, and pentacene. Indeed, CH/π contact was observed between C(11)H · · · C(14C) with a distance of H · · · C ) 2.95 Å, as shown in Figure 3. The carbonyl oxygen atoms in the phthalate moieties participate in CH/O interactions, including O(3) · · · H-C(10A), O(3) · · · H-C(7B), O(1) · · · H-C(10C), and O(3) · · · H-C(7D) [distances between the O and H atoms: 2.64, 2.69, 2.45, and 2.56 Å, respectively; symmetry code: (A) x, 1/2-y, -1/2+z; (B) 2-x, -1/2+y, 1.5-z; (C) x, 1.5-y, -1/ 2+z; (D) 2-x, 1/2+y, 1.5-z] to connect the adjacent molecules in a herringbone manner. In crystal II, the molecule packs in a parallel-π-stacked fashion, as shown in Figure 2e,f. The distance between the adjacent annulene planes is 3.41 Å. The annulene arranged into

a parallel-π-stacked fashion is generally expected to undergo topochemical polymerization at the diyne moieties when the relative orientation, i.e., distance and angle, of the diyne moieties is suitable for the reaction. In this case, however, the annulene stacked alternatively, and thus the butadiyne arrangement is not appropriate for the reaction. As in the case of crystal I, the ester moieties participate in intermolecular CH/O interactions. As shown in Figure 4, one carbonyl oxygen atom O(7) participates in the self-complementary interaction of the methyl ester groups, O(7) · · · H-C(24A) and O(7A) · · · H-C(24), with a distance of O · · · H ) 2.52 Å [symmetry code: (A) 2-x, 2-y, -z]. Another two carbonyl oxygen atoms O(1) and O(5) form CH/O interactions with the aromatic hydrogen atoms [O(1) · · · H-C(11C) and O(5) · · · H-C(25B) symmetry code: (B) 1+x, y, z; (C) -1+x, y, z] with distances of O · · · H ) 2.52 and 2.48 Å, respectively, which align the molecules along the crystallographic a axis to yield a two-dimensional layer structure. The fourth carbonyl oxygen atom O(3) contacts the methoxy hydrogen atom of the annulene lying on the next layer [(O(3) · · · H-C(24D) with a distance of O · · · H ) 2.70 Å; symmetry code: (D) x, -1+y, 1+z]. In crystal III, the molecules pack into a zigzag-π-stacked fashion. The molecule stacks with the adjacent molecule with the a distance of ca. 3.4 Å, and staggers by ca. 116° to yield the 21 helical tape (Figure 2h,i). In this system, π/π stacking occurs between the benzene rings. As shown in Figure 5, one carbonyl oxygen atom in the each phthalate moiety participates in in-plane self-complementary CH/O interactions, C(4B)-H · · · O(1), C(4)-H · · · O(1B), C(4E)-H · · · O(1A), and C(4A)-H · · · O(1E) with a distance of H · · · O ) 2.31 Å to form a layered one-dimensional network along the crystallographic b axis. The other carbonyl oxygen atom in the phthalate forms CH/O interaction with the adjacent molecule in the next layer: O(3) · · · H-C(10C), O(3) · · · H-C(7C), O(3A) · · · H-C(7D), and O(3A) · · · H-C(10D) with distances of O · · · HC(10) ) 2.56 Å and O · · · HC(7) ) 2.41 Å [symmetry code: (A) 2-x, 1-y, 2-z; (B) 2-x, 2-y, 2-z; (C) 1-x, 2-y, 1-z, (D) 1+x, -1+y, 1+z, (E) x, -1+y, z]. DSC Analysis. To reveal the thermal stability of the crystals, DSC analysis was performed on them. As shown in Figure 6, crystals I, II, and III show exothermic peaks at 112, 140, and 163 °C, respectively. These peaks did not appear in the second

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Figure 3. Selected molecular packing diagrams of crystal I. (a) top view, (b) side view. Symmetry code: (A) x, 1/2-y, -1/2+z; (B) 2-x, -1/2+y, 1.5-z; (C) x, 1.5-y, -1/2+z; (D) 2-x, 1/2+y, 1.5-z.

Figure 4. Selected molecular packing diagrams of crystal II. Molecules located in the different layers are colored in green. Symmetry code: (A) 2-x, 2-y, -z (B) 1+x, y, z; (C) -1+x, y, z; (D) x, -1+y, 1+z.

Figure 5. Selected molecular packing diagram of crystal III. Molecules located in the different layers are described in different colors (green, gray, and red). Symmetry code: (A) 2-x, 1-y, 2-z; (B) 2-x, 2-y, 2-z; (C) 1-x, 2-y, 1-z, (D) 1+x, -1+y, 1+z, (E) x, -1+y, z.

cycle. After the analysis, insoluble black materials, which maintain the morphology of the corresponding powder crystals, were obtained, although characterization has not succeeded. It is noteworthy that the decomposition temperature varied over

a wide range of values, even though the crystals are composed of an identical molecule. The difference of the decomposition temperature among them is probably provided by their different molecular arrangements. The arrangement might have significant

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Figure 6. DSC analysis of the crystals I (a), II (b), and III (c).

Figure 8. Conformations of dimethyl phthalate optimized by the B3LYP/6-311G** level (a) and those observed in crystals I, II, and III (b). Hydrogen atoms are omitted for clarity. Table 2. Calculated Torsion Angle of the Methyl Ester Moietiesa

Figure 7. Six conformations of dimethyl phthalate classified on the basis of the directions of the carbonyl oxygen atoms.

influence on the thermal stability of the molecule and/or intermolecular reactivity, especially at the distorted diyne moieties. Conformation of Phthalate Moieties. It is obvious that phthalate has a conformation in which the carbonyl moieties simultaneously do not lie on the coplane of the benzene ring as a result of steric hindrance, leading to the flexible and diverse conformation. Directionality of a carbonyl oxygen atom with electrostatic negative charge can drastically change the electronic property of the molecular surface and, thus, intermolecular interactions including CH/O interaction. Indeed, electrostatic potential surface for 4II, for example, shows totally different charge distribution in both molecular faces; one face is polar and the other is apolar, while 4I has identical molecular faces (Figure S4, Supporting Information). When considering the direction of the carbonyl oxygen atoms, we can classify the conformations into six types: i-vi, schematic representations, which are shown in Figure 7.24 In the six conformations, i-iii are anticipated to be less stable due to the steric hindrance between the oxygen atoms, while iv-vi are more stable than the formers. To evaluate the structure and stability of these conformations, the DFT calculation at the B3LYP/6-311G** level were performed on conformers of dimethyl phthalate iv-vi. In Figure 8a, the optimized structures of iv-vi are shown. Each shows no imaginary frequency, indicating that the conformer has minimum energy. The energy differences among these three conformations are less than 1 kcal/mol: v and vi are more stable than iv only by 0.7 and 0.8 kcal/mol, respectively, with consideration of the zeropoint energies. A conformation with the ester moieties perpendicular to each other (Ts), which is the transition state, was also subjected to calculation, indicating

I II III iv v vi

R1

R2

R3

R4

point group

-39.77 -40.41 -69.03 134.38 38.40 52.77

-47.66 +135.16 -10.78 134.38 38.40 -152.66

+39.77 -51.90 +69.03

+47.66 +146.20 +10.78

Ci C1 Ci C2 C2 C1

a R(n) denotes a torsion angle of C(an)-C(bn)-C(cn)-O(dn) (n ) 1, 2, 3, and 4).

that the rotation barrier of the phthalate is 12.5 kcal/mol. Thus, any conformer is accessible. Conformational diversity of the methyl ester moiety can be described by using the torsion angle R(n) ) C(an)-C(bn)C(cn)-O(dn),25 where n (n ) 1-4) denotes the position of the ester moiety in the molecule (see Figure 2a). The conformation for the phthalate moieties of 4I-4III and their R(n) values as well as those of iv-vi are shown in Figure 8b and Table 2, respectively. The two phthalate moieties in 4I-4III have the same conformation with one another, even in the case of 4II, which has no centrosymmetry in the molecule. According to our classification, the phthalate moieties of 4I, 4II, and 4III have v, vi, and v conformation, respectively, although 4III has conformation close to Ts. The methyl phthalate of 4I has a conformation similar to that of the calculated conformer v: deviation from the optimized conformation is 1.4-9.3° for R(n). The carbonyl oxygen atoms directing upward and downward of the plane with 45° proximity of the torsion angle allow the molecules to pack into the herringbone fashion. In crystal II, all carbonyl oxygen atoms are directed to the same side of the annulene plane, and the torsion of the carbonyl groups from the plane of the benzene ring is relatively averaged compared with that in conformer vi. Interestingly, two carbonyl oxygen atoms of 4II with relatively larger R(n) values of -40.4 and -51.9° participate in CH/O interaction with the aromatic hydrogen atoms (see, for example, O(5) · · · C(25B) in Figure 4) to yield coplanar layer arrangement of the annulenes. This is made possible by nonlinear CH/O interaction (angle of C-H-O ) 147.8-156.5°), thus indicating tolerant directionality of CH/O interaction. Conformer 4III has

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that the decomposition temperature of the polymorphic crystals depends on the molecular arrangement. This indicates that the molecular packing manner might have significant influence on the thermal stability and/or intermolecular reactivity of the annulene in the crystalline state. Acknowledgment. This work was supported by a Grant-inAid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. Supporting Information Available: Photos of the crystals, X-ray crystallographic information files (CIFs) for crystals I, II, and III, the detail of the CSD search, and the conformational calculation results. This information is available free of charge via the Internet at http:// pubs.acs.org. Figure 9. Distribution of the conformation type of 64 methyl and/or ethyl phthalates within 56 crystal structures registered in the CSD. (A) 3,6-disubstituted, (B) 3-substituted, (C) 3,6-unsubstituted phthalate.

R values of (69.0 and (10.8°, which differ from those of conformer v by up to 30.6°. The carboxyl oxygen atoms with values of (10.8° participate in self-complementary CH/O interaction with the aromatic hydrogen atoms (see, for example, O(1) · · · H-C(4B) and O(1B) · · · H-C(4) in Figure 5). Thus, the carbonyl moiety is forced to lie on almost the same plane with the benzene ring, despite the energetically unfavorable conformation. On the other hand, the other carbonyl oxygen atoms form CH/O interaction with methoxy groups out of the plane, leading to a large R(n) value of (69.0°. Interestingly, the ivtype conformation was not observed in this study, probably because the arrangement of the carbonyl oxygen is not favorable for making a network via CH/O interaction. CSD Database Search. To investigate the conformation of phthalates in the reported crystal structures, a Cambridge Structural Database (CSD) search was performed. The survey on CSD (v. 5.27) gave 56 structures of methyl and/or ethyl phthalate derivatives. Considering an asymmetric unit composed of two molecules or molecules having two independent phthalate moieties, a total of 64 samples were classified on the basis of the conformation type (see Supporting Information). Interestingly, their conformation types are mainly v and vi (totally 65% with 42 examples), while vi is much less (13% with eight examples) than the former two (Figure 9). We also found conformation, so-called coplanar conformation, similar to Ts (6% with four examples). When the bulkiness of the substituents at the adjacent positions of the phthalate ester moiety, i.e., 3and 6-positions of the benzene ring, are considered, the structures are classified into four categories: namely, (A) 3,6disubstituted, (B) 3-substituted, and (C) 3,6-unsubstituted phthalate derivatives, and (D) others that include 1,2,3-tri-, 1,2,3,4tetra-, 1,2,3,4,5-penta-, and 1,2,3,4,5,6-hexacarboxylate derivatives. This classification reveals that minor conformer iv tends to exhibit in category A, sterically crowded phthalate derivatives. Conclusion In this paper, we first described three conformational polymorphic crystal structures of octadehydrodibenzo[12]annulene derivative 4 having two methyl phthalate moieties. In the structures, the annulene core arranges in herringbone, parallelπ-stacked, and zigzag-π-stacked fashion. The polymorphic structures are brought from varied conformations of the methyl phthalate moieties because the direction of the carbonyl oxygen atoms in the phthalate affects the manner of CH/O interaction abundantly observed in the present systems. We also revealed

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