CRYSTAL GROWTH & DESIGN
Phase-Dependent Emission of Naphthalene-Anthracene-Based Concave-Shaped Molecules
2006 VOL. 6, NO. 9 2086-2091
Hyuma Masu,† Ikuko Mizutani,‡ Yohei Ono,‡ Keiki Kishikawa,‡ Isao Azumaya,† Kentaro Yamaguchi,† and Shigeo Kohmoto*,‡ Faculty of Pharmaceutical Science at Kagawa Campus, Tokushima Bunri UniVersity, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan, and Department of Chemistry and Biotechnology, Faculty of Engineering, Chiba UniVersity, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan ReceiVed April 20, 2006; ReVised Manuscript ReceiVed June 22, 2006
ABSTRACT: Fluorescence spectra of aromatic chain imides possessing anthracene and naphthalene moieties were examined both in solution and in the solid state. Depending on the substituents at the imide nitrogen atom, their fluorescence spectra varied in the solid state. However, their spectra in solution were almost identical. In solution, emission corresponding to a naphthalene-anthracene exciplex was observed. In contrast, the imides possessing an intermolecular anthracene-anthracene interaction exhibited red-shifted fluorescence in the solid state. This red-shifted fluorescence could originate in an anthracene excimer or the exciplex formed from a sum of fluorophores. In contrast, compounds without this anthracene-anthracene interaction in the solid state had very similar solution and solid-state fluorescence spectra. Introduction The method of intermolecular stacking of aromatic moieties exerts great influence on the emission properties of aromatic compounds, especially for an effective excimer emission. Some devices have been made to produce excimer emission by using constrained media, such as zeolite supercages,1 hydrophobic nanocapsules,2 cyclodextrin cages,3 and layered solids,4 as well as in the solid state. Generally, such a stacking in an intermolecular way is difficult in diluted solution without the aid of rather strong intermolecular interactions such as hydrogen bonding.5 Therefore, a vivid contrast can be expected in the fluorescence spectra of aromatic compounds depending on the media in which the spectra were measured. We are interested in the concave-shaped compounds possessing two aromatic chromophores (A and B) connected with linkers. Depending on the method of arrangement of the molecules, three types of emission originating in (A-B)*, (A-A)*, and (B-B)* are possible. In diluted solution, these compounds may emit fluorescence corresponding to the exciplex (A-B)* of the two connected chromophores. If the same two chromophores are stacked together in the crystalline state, excimer emission corresponding to (A-A)* or (B-B)* is possible. As an example of such a system, we examined fluorescence behaviors of the concave-shaped aromatic chain imides6,7 possessing anthracene and naphthalene chromophores as an A-B system in solution and in the solid state. Anthracene and naphthalene moieties are key fluorophores in designing luminescent materials. The concave-shaped aromatic compounds have the advantage of easy stacking. They could be piled up easily by stacking to create columnar arrays of aromatic plates in their crystal packing. Similar to phenanthrene,8 it is generally known that anthracene does not emit excimer fluorescence either in the solid state or in solution at room temperature9 due to its efficient photodimerization.10 In some limited cases, anthracene derivatives have been known to emit excimer fluorescence in the solid state at room temperature due to their stacked structure of two anthracene moieties.11 Since the excimer fluorescence of an* Corresponding author. Phone: +81-43-290-3420. Fax: +81-290-3422. E-mail:
[email protected]. † Tokushima Bunri University. ‡ Chiba University.
thracene derivatives is so limited, it is worth studying the factors that govern the molecular assembly of anthracene derivatives leading to an efficient stacking of anthracene moieties in their crystals. In addition to π-π interaction, a weak intermolecular interaction, such as the CH/π interaction,12 might play a pivotal role in molecular assembly of aromatic compounds. In our aromatic imides, naphthalene-anthracene exciplex emission based on an intramolecular interaction could be expected in solution. In contrast, anthracene-anthracene excimer emission could be expected in their solid-state spectra depending on the degree of intermolecular stacking of anthracene moieties. Single-crystal X-ray structures of six aromatic imides, 1, 2, 3, 4, 5, and 9, examined in this study were already reported by us in the study of intramolecular asymmetric [4 + 4] photocycloaddition for absolute asymmetric synthesis in the solid state.13 In the previous study, we examined the molecular structures of them to determine the geometrical parameters for the solidstate intramolecular photochemical [4 + 4] cycloaddition between the anthracene and naphthalene chromophores. In the present study, we have examined their phase-dependent fluorescence and also the relation between their packing structures and fluorescence properties together with those of newly prepared compounds, 6, 7, 8, and 10. Experimental Section Materials and Methods. All the reagents and solvents employed were commercially available and used as received without further purification. Spectroscopic grade solvents were used for UV-vis and fluorescence measurements. FT-IR spectra were recorded on a JASCO FT/IR-410 spectrometer. 1H and 13C NMR spectra were recorded on JEOL JNM-LA400 and JNM-LA500 spectrometers for samples in CDCl3 with Me4Si as an internal standard. Mass spectra were measured with JEOL JMS-AX500 and JMS-HX110 mass spectrometers. Elemental analyses were performed on a Perkin-Elmer 240 analyzer. UV-vis absorption spectra were measured on a JASCO V-550 spectrometer and reported in λmax and max. Fluorescence spectra were measured on a JASCO FP-750 spectrometer. Syntheses. The previously reported imides 1, 2, 3, 4, 5, and 9 and amide 11 were synthesized and purified according to the procedure described in ref 13. Other new compounds were prepared by the similar procedure. (a) N-(9-Anthrylcarbonyl)-N-[(2-bromophenyl)methyl]naphthylcarboxamide (6). To a solution of N-(2-bromophenyl)methyl-9-
10.1021/cg060232v CCC: $33.50 © 2006 American Chemical Society Published on Web 07/21/2006
Naphthalene-Anthracene-Based Concave-Shaped Molecules anthrylcarboxamide (500 mg, 0.92 mmol) in dry toluene (50 mL) was added triethylamine (0.13 mL, 0.94 mmol) and 1-naphthoyl chloride (0.3 mL, 2.0 mmol). After heating for 20 h, the resulting mixture was washed with diluted HCl solution and brine. The organic layer was dried over anhydrous MgSO4 and concentrated in vacuo. The product was recrystallized from hexane/ethyl acetate to give yellow blocks. Mp 174-176 °C. IR (KBr) 1655 cm-1; UV-vis (MeCN) λmax (max) 322 (6000), 378 (4920), 396 nm (4600); 1H NMR (CDCl3, 400 MHz) δ 7.92 (dd, J ) 7.8, 1.2, 1H), 7.88 (d, J ) 8.7, 2H), 7.68 (d, J ) 8.0, 1H), 7.38-7.53 (m, 6H), 7.31 (t, J ) 7.0, 2H), 7.18-7.27 (m, 2H), 7.14 (d, J ) 7.3, 1H), 7.06 (t, J ) 7.0, 1H), 6.93 (d, J ) 8.3, 1H), 6.72 (t, J ) 7.4, 1H), 6.65 (d, J ) 8.4, 1H), 6.41 (t, J ) 8.0, 1H), 5.80 (s, 2H); 13C NMR (CDCl3, 125 MHz) δ 173.03, 172.15, 136.20, 133.21, 132.03, 132.03, 131.97, 131.74, 129.97, 129.89, 129.38, 129.17, 128.53, 128.21, 128.07, 127.58, 127.12, 126.35, 125.65, 125.40, 125.06, 124.56, 124.03, 123.01, 122.91, 48.01; MS (FAB) m/z 543 (M+). Anal. Calcd for C33H22BrNO2: C, 72.45; H, 4.07; N, 2.36. Found: C, 72.80; H, 4.07; N 2.57. (b) N-(9-Anthrylcarbonyl)-N-[(3-bromophenyl)methyl]naphthylcarboxamide (7). In a similar manner as for 6, 7 was obtained as yellow powder. Mp 106-108 °C. IR (KBr) 1655 cm-1; UV-vis (MeCN) λmax (max) 319 (5510), 381 (4510), 400 nm (4080); 1H NMR (CDCl3, 400 MHz,) δ 8.09 (t, J ) 1.5, 1H), 7.82 (d, J ) 7.6, 1H), 7.69 (br, 2H), 7.56 (dq, J ) 8.3, 0.9, 1H), 7.54 (s, 1H), 7.46 (d, J ) 8.6, 2H), 7.41-7.35 (m, 2H), 7.29 (td, J ) 7.5, 0.9, 2H), 7.25 (d, J ) 8.2, 1H), 7.12 (td, J ) 7.5, 0.9, 1H), 6.92 (d, J ) 8.2, 1H), 6.81(dd, J ) 7.0, 0.9, 1H), 6.76 (td, J ) 7.6, 1.2, 1H), 6.64 (d, J ) 8.3, 1H), 6.39 (d, J ) 7.3, 1H), 6.37 (d, J ) 7.3, 1H), 5.59 (s, 2H); 13C NMR (CDCl3, 125 MHz,) δ 173.45, 172.34, 139.23, 133.26, 133.26, 132.33, 132.04, 131.29, 130.32, 129.97, 129.42, 128.95, 128.86, 128.71, 128.52, 128.26, 128.14, 127.22, 127.11, 126.35, 125.51, 123.05, 123.14, 122.89, 122.73, 47.64; MS (FAB) m/z 543 (M+), found 543. Anal. Calcd for C33H22BrNO2: C, 72.45; H, 4.07; N, 2.36. Found: C, 72.57; H, 3.95; N 2.44. (c) N-(9-Anthrylcarbonyl)-N-[(4-bromophenyl)methyl]naphthylcarboxamide (8). In a similar manner as for 6, 8 was obtained as yellow blocks recrystallized from hexane/ethyl acetate. Mp 152-153 °C. IR (KBr) 1655 cm-1; UV-vis (MeCN) λmax (max) 322 (5500), 379 (4800), 398 nm (4450); 1H NMR (CDCl3, 400 MHz,) δ 7.78 (d, J ) 8.4, 2H), 7.67 (br. 2H), 7.63 (d, J ) 8.3, 1H), 7.46 (d, J ) 8.3, 2H), 7.38 (t, J ) 7.5, 2H), 7.21-7.33 (m, 4H), 7.12 (t, J ) 8.0, 2H), 6.91 (d, J ) 8.2, 1H), 6.77 (d, J ) 7.0, 1H), 6.74 (td, J ) 8.5, J ) 0.9, 1H), 6.62 (d, J ) 8.2, 1H), 6.38 (t, J ) 7.3, 1H), 5.60 (s, 2H); 13C NMR (CDCl3, 125 MHz) δ 173.50, 136.15, 132.40, 132.08, 131.92, 130.00, 128.86, 128.70, 128.54, 128.27, 128.15, 127.21, 127.09, 126.33, 125.51, 125.06, 125.03, 123.16, 122.89, 47.50; HRMS (FAB) calcd for C33H22BrNO2 (M+) 543.0834, found 543.0810. (d) N-(9-Anthrylcarbonyl)-N-[(1-naphthyl)methyl]]naphthylcarboxamide (10). In a similar manner as for 6, 10 was obtained as yellow crystals recrystallized from hexane/ethyl acetate. Mp 210-213 °C. IR (KBr) 1655 cm-1; UV-vis (MeCN) λmax (max) 323.5 (6550), 379.5 (5300), 397.5 nm (4900); 1H NMR (CDCl3, 400 MHz,) δ 8.92 (d, J ) 8.3, 1H), 7.99 (d, J ) 6.3, 1H), 7.95 (d, J ) 8.3, 1H), 7.87 (dd, J ) 8.7, 0.8, 2H), 7.79 (td, J ) 7.6, 1.2, 1H), 7.61 (td, J ) 7.5, 0.9, 1H), 7.38-7.56 (m, 8H), 7.30 (t, J ) 7.5, 2H), 7.19 (d, J ) 8.2, 1H), 7.07 (td, J ) 7.4, 1.2, 1H), 6.84 (d, J ) 8.2, 1H), 6.68 (td, J ) 7.5, 1.4, 1H), 6.58 (d, J ) 8.4, 1H), 6.51 (dd, J ) 7.2, 1.2, 1H), 6.19 (d, J ) 7.2, 1H), 6.17 (d, J ) 7.2, 1H); HRMS (FAB) calcd for C37H25NO2 (M+) 515.1885, found 515.1840. (e) [4 + 4] Cycloadduct (13). An attempt was made to prepare 12 from the reaction of anthracene-9-carbonyl chloride and (S)-1-(1naphthyl)ethylamine in a similar manner as for 6. However, during the synthesis, spontaneous [4 + 4] cycloaddition proceeded to result in the formation of cycloadduct 13. Mp > 300 °C (dec); 1H NMR (CDCl3, 400 MHz,) δ 8.48 (d, J ) 8.7, 1H), 8.21 (d, J ) 7.2, 1H), 7.96 (d, J ) 8.2, 1H), 7.93 (d, J ) 8.2, 1H), 7.64 (m, 2H), 7.56 (t, J ) 7.5, 1H), 6.91-6.75 (m, 13H), 6.60 (tt, J ) 7.6, 1.4, 2H), 6.22 (d, J ) 7.5, 2H), 4.56 (s, 2H), 2.34 (d, J ) 7.0, 3H); 13C NMR (CDCl3, 125 MHz) δ 176.20, 142.61, 142.48, 139.81, 139.67, 133.81, 133.23, 130.96, 129.22, 129.14, 129.04, 128.95, 127.59, 127.42, 127.21, 127.10, 126.68, 126.56, 125.94, 125.85, 125.71, 125.24, 125.20, 125.17, 125.09, 123.27, 123.51, 67.00, 53.20, 53.15, 53.10, 47.74, 47.69, 18.03; HRMS (ESI) calcd for C42H29NNaO2 (M + Na+) 602.2096, found 602.2124. X-ray Crystallography. X-ray intensity data were measured on a Bruker Smart 1000 CCD diffractometer (for 6 and 13), Bruker ApexII CCD diffractomerter (for 8), or Rigaku AFC7S four-circle diffracto-
Crystal Growth & Design, Vol. 6, No. 9, 2006 2087 Scheme 1.
Concave-Shaped Molecules Examined
meter (for 10). All structures were solved by direct methods with SHELXS-97, and the non-hydrogen atoms were refined anisotropically against F2, with full-matrix least-squares methods in SHELXL-97.14 All hydrogen atoms were positioned geometrically and refined as riding. Crystal data for 6, 8, 10, and 13 are available as Supporting Information.
Results and Discussion Aromatic imides possessing naphthalene (Nap) and anthracene (An) moieties, 6, 7, 8, and 10 (Scheme 1), were newly prepared and single-crystal X-ray diffraction analysis of 6, 8, and 10 was carried out. Compound 7 did not afford single crystals. Fluorescence spectra of 1-10 were measured in solution (CH3CN) and in the solid state (powdered crystals). All the compounds examined by single-crystal X-ray diffraction analysis have the concave-shaped structures (Figure 1). The naphthalene and anthracene moieties are overlapped. The torsion angles between the two aromatic π-planes defined by four carbons participating in [4 + 4] photocycloaddition are 42.3°, 44.9°, and 37.5° for 6, 8, and 10, respectively. They are within the same range, 35°-49°, observed for 1, 2, 3, 4, 5, and 9. The dihedral angels between the two aromatic π-planes are 26.8°, 26.9°, and 30.9° for 6, 8, and 10, respectively, which are close
Figure 1. ORTEP diagrams of 6 (a, top view, and b, side view), 8 (c), and 10 (d).
2088 Crystal Growth & Design, Vol. 6, No. 9, 2006
Masu et al.
Table 1. Fluorescence Data and the An-An Distances compd
λem (nm)a in CH3CN
λem (nm)a in the solid state
An-An (Å)b
1 2 3 4 5 6 7 8 9 10 11
481 483 480 482 481 483 486 483 481 481 409
462 531 535 473 459 522 522 533 514 461 426
c 3.77 3.70 c c 3.80 d 3.70 3.87 c d
a λ ) 280 nm. b The intermolecular anthracene-anthracene (centroidex centroid) distance obtained from single-crystal X-ray diffraction analysis. c Two anthracene moieties are not overlapped. d Single crystals were not obtained.
Figure 3. Columnar packing structure of 2 (distances in Å).
Scheme 2.
Figure 2. Fluorescence spectra of 11 in CH3CN (a) and in the solid state (b) and 3 in CH3CN (c) and in the solid state (d).
to those of others (25°-30°, except 1 at 14.5°). The distances between the centroids of the naphthalene and anthracene moieties are 3.68, 3.67, and 3.71 Å for 6, 8, and 10, respectively, which are similar to those of 1, 2, 3, 4, 5, and 9 (3.4-3.7 Å). Table 1 shows their fluorescence data and the intermolecular distance (An-An). All the compounds showed almost the same broad fluorescence spectra in CH3CN. Their fluorescence maximum wavelengths (λem) are in the very narrow range 480486 nm in CH3CN. In contrast, their fluorescence in the solid state varied considerably (459-545 nm) depending on the substituent at the imide nitrogen atom. They can be classified into two categories according to their fluorescence behaviors. The first category is the group of compounds (2, 3, 6, 7, 8, and 9) whose fluorescence in the solid state shows longer wavelength maxima than those in solution. In the second category of compounds (1, 4, 5, and 10), their emission maxima in the solid state are slightly shorter than those in solution. For example, the λem of compound 3 showed a red shift from 480 nm in CH3CN to 535 nm in the solid state (Figure 2). However, the λem of 5 was blue-shifted from 481 nm in solution to 459 nm in the solid state. These differences could originate in their crystal packing. The amide 11 without a naphthalene moiety showed the typical fluorescence corresponding to the monomer emission of anthracene with vibronic structure in solution and in the solid state. It showed a slight bathochromic shift in the solid state. We re-examined the single-crystal structures of 1-5 and 9 and examined those of new compounds 6, 8, and 10. It is quite obvious that two anthracene moieties overlap in the compounds showing red-shifted fluorescence. The torsion angle and dihedral angle between the two anthracene π-planes are 0° for all of
Spontaneous [4 + 4] Cycloaddition
them, indicating their perfect stacking. The packing structure of 2 shows the well-overlapped array of naphthalene and anthracene moieties forming a columnar structure as shown in Figure 3. They are packed in the order Nap-Nap-An-An-NapNap-An-An. The distances between the rings (the centroidcentroid) are 3.73, 3.67, and 3.77 Å for Nap-Nap (intermolecular), Nap-An (intramolecular), and An-An (intermolecular), respectively. The results indicate that these aromatic rings are well-packed by π-π stacking. The CH/π interaction between the benzene ring of the benzyl group and the adjacent naphthalene hydrogen atom (the distance of 2.84 Å) is also playing an important role for the creation of this aromatic columnar structure. Due to this An-An stacking, compound 2 showed fluorescence (λem 531 nm) possibly corresponding to its anthracene excimer in solid state. The λem of anthracene excimer was reported to show λem 480 nm for 9-anthracene carboxylic acid15 in the solid state and 500 nm for anthracene itself in NaY zeolitic nanocavities.1 In our recent work of aromatic chain imides possessing naphthalene chromophores, red shifts in fluorescence were observed as the number of chromophores increased.7 Thus, it might be also possible to consider that this fluorescence originated in the exciplex formed from a sum of the fluorophores. As a control experiment, an attempt was made to prepare the concave-shaped imide with two anthracene moieties, 12. In this compound, the two
Figure 4. ORTEP diagram of 13.
Naphthalene-Anthracene-Based Concave-Shaped Molecules
Crystal Growth & Design, Vol. 6, No. 9, 2006 2089
Scheme 3. Generation of Metastable Anthracene Excimer by Photodissociation of a Cyclomer in a Matrix16
anthracene moieties could overlap intramolecularly, which is ideal for the generation of an anthracene excimer. However, a spontaneous [4 + 4] cycloaddition reaction took place during the synthesis of 12, which resulted in the formation of cycloadduct 13 (Scheme 2). The compound seems to be extremely sensitive to light. The structure of 13 was unequivocally determined by single-crystal X-ray diffraction analysis (Figure 4). An attempt to generate 12 by thermal cycloreversion of 13 failed due to the decomposition of 13. At the moment, we have no direct evidence to determine that the fluorescence originates either in the anthracene excimer or in the exciplex formed from a sum of the fluorophores. It is reported that anthracene excimer fluorescence for the bis-anthracene compound 14 linked with the ether chain (-CH2-O-CH2-) was not observed at room temperature. However, when the corresponding photocyclomer 15 was photodissociated at 77 K in methylcyclohexane matrix, gener-
Figure 6. Columnar packing structure of 9 (distances in Å).
Figure 7. Packing structures of 1 (a), 4 (b), 5 (c), and 10 (d) (distances in Å).
Figure 5. Columnar packing structure of 3 (a), 6 (b), and 8 (c). Distances between the centroids of two adjacent aromatic rings and CH/π interactions are presented (distances in Å).
ated 14 showed excimer fluorescence (Scheme 3).16 The result was explained by the generation of the desirable fixed conformation of 14 required for anthracene excimer; two anthracene moieties were strongly overlapped. The maximum emission of photogenerated 14 (λem 550 nm) is close to those of our compounds in the solid state whose crystal structure showed intermolecular overlapping of anthracene moieties. It is noteworthy to mention that the anthracene-naphthalene system linked with the propane linker or other linkers with chain length of three carbon units do not emit exciplex fluorescence at room temperature. Single-crystal X-ray diffraction analysis of them showed that the linkers have linear conformations, and they are
2090 Crystal Growth & Design, Vol. 6, No. 9, 2006
Masu et al.
Figure 8. Interccolumnar interactionssshort contacts observed in 2 (a), 3 (b), 6 (c), and 8 (d). The CH/π, CH‚‚‚O, Br/π, and Br‚‚‚Br interactions are presented (distances in Å).
not concave-shaped molecules.17 Similar to 14, it was only observed by photodissociation of the photocyclomer.18 Similar columnar structures, the stacking of anthracene and naphthalene moieties, were observed for 3, 6, and 8 (Figure 5). The inter-An-An distances are 3.73, 3.82, and 3.72 Å for 3, 6, and 8, respectively. Similarly, the CH/π interactions between the benzene ring of the benzyl group and the adjacent naphthalene hydrogen atoms were observed in 6. Though N-propyl derivative 9 possessed a different packing structure, it showed red-shifted fluorescence. The two adjacent anthracene moieties were stacked intermolecularly. However, the intermolecular stacking of naphthalene moieties was not observed due to the CH/π interactions between the hydrogen atom of the propyl group and the naphthalene moiety with the distance of 2.78 Å (Figure 6). This CH/π interaction interrupted the creation of aromatic columnar structure. In their packing, only two molecules are π-stacked. It is interesting that the degree of red shift in λem is related to the distance between the two stacked anthracene moieties. The shorter the distance (stronger stacking) becomes, the longer the λem shifts. The imide 3 with the shortest distance (3.70 Å) showed the longest λem (535 nm). The shortest λem (514 nm) was observed for 4 with the longest An-An distance (3.87 Å) in this category of compounds. In contrast to these compounds, the compounds in the second category (1, 4, 5, and 10) do not have An-An stacking in their packing structure. All these compounds have different packing structure. Orthogonal arrangement of molecules was observed in the packing structure of 1. CH/π and CH‚‚‚O15 interactions
were responsible for its packing (Figure 7a). CH/π interactions were observed between one of the naphthalene and anthracene hydrogen atoms and the anthracene and phenyl rings with the distances 2.87 and 2.80 Å, respectively. The CH‚‚‚O interaction (2.48 Å) was found between the imide carbonyl and one of the hydrogen atoms of the anthracene ring. The substituted methyl groups of benzene rings of 2 and 3 are important to furnish aromatic columnar structure. Alternate piling of aromatic rings, Nap-An-Nap-An, was observed for 4 with the intermolecular distance of 3.96 Å for Nap-An (Figure 7b). Two molecules were stacked via Nap-Nap with the distance of 3.78 Å in 5 (Figure 7c). The CH‚‚‚O interaction between the imide carbonyl and one of the hydrogen atoms of the 4-fluorophenyl group (2.64 Å) is responsible for the orthogonal array of its packing. A similar Nap-Nap stacking (3.68 Å) was observed in 10 (Figure 7d). The intermolecular CH/π interaction was observed between the anthracene moiety and the neighboring hydrogen atom (4position) of the naphthylmethyl group. This interaction prevents a continuous stacking of the aromatic moieties, which results in the orthogonal array of the molecules. Intramolecular stacking of Nap-An might be rather distorted in the solid state due to its rigid conformation compared to that in solution. This might cause the blue shifts in λem of these molecules in solid state. Among the compounds examined, the methyl- and bromosubstituted N-benzyl derivatives showed the red shift in their solid-state fluorescence. To find out the role of these substituents for the efficient formation of columnar structures in crystal packing, intercolumnar interactions of 2, 3, 6, and 8 were
Naphthalene-Anthracene-Based Concave-Shaped Molecules
examined. Figure 8 shows the short contacts observed between the columns. The CH/π, CH‚‚‚O,19 Br‚‚‚Br,20 and Br/π21 interactions were observed between the ortho- and parasubsituted N-benzyl groups and the neighboring molecules in their single crystal X-ray structures. It clearly shows that the ortho- and para-substituted N-benzyl groups help the intercolumnar interactions. Bromine atom contributes to create columnar structures of 6 and 8 by Br/π and Br‚‚‚Br interactions, respectively. The distance between the bromine atom and the centroid of the adjacent benzene ring of the naphthalene moiety is 4.04 Å in 6. This is rather shorter than the frequently observed distance (around 5 Å).22 The angle between the vector along the aryl centroid-Br line and the perpendicular vector originating in the aryl center (the plane normal) is also rather small (39.4°).22 A type I Br-Br interaction23 was observed in 8. The Br-Br distance (3.49 Å) and the angle Br-Br-C (141°) in 8 are the typical values for them. These weak intermolecular interactions originating in substituted N-benzyl groups are essential for efficient packing to create aromatic columnar array. Conclusion We have examined the relation between the fluorescence and the packing structure of the concave-shaped aromatic imines possessing anthracene and naphthalene moieties. Some of them showed well-stacked arrays of these aromatic moieties creating an aromatic columnar structure. In these compounds, distinctive differences in fluorescence properties were observed depending on the phases in which the spectra were measured, either in solution or in the solid phase. A red shift of λem was observed in the solid state in these compounds due to the anthracene excimer or the exciplex formed by a sum of the fluorophores. In contrast, Nap-An exciplex emission was observed in solution. Weak intermolecular interactions, such as CH/π and Br‚‚‚Br play a pivotal role for the creation of an aromatic columnar array. The CH/π interaction disturbs the creation of such a columnar array in the compounds showing the blueshifted λem in solid state. Supporting Information Available: The crystallographic information files (CIF) and tables of crystal data and structure refinements of compounds 6, 8, 10, and 13 (for other compounds, see ref 13). This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) Kwon, O.-H.; Yu, H.; Jang, D.-J. J. Phys. Chem. B 2004, 108, 39703974. (2) Kaanumalle, L. S.; Gibb, C. L. D.; Gibb, B. C.; Ramamurthy, V. J. Am. Chem. Soc. 2005, 127, 3674-3675.
Crystal Growth & Design, Vol. 6, No. 9, 2006 2091 (3) Ikeda, H.; Iidaka, Y.; Ueno, A. Org. Lett. 2003, 5, 1625-1627. (4) Amicangelo, J. C.; Leenstra, W. R. J. Am. Chem. Soc. 2003, 125, 14698-14699. (5) Lewis, F. D.; Yang, J.-S.; Stern, C. L. J. Am. Chem. Soc. 1996, 118, 2772-2773. (6) Kohmoto, S.; Tatsuno, C.; Masu, H.; Kishikawa, K.; Yamamoto, M. J. Chem. Soc., Perkin Trans. 1 2000, 4464-4468. Masu, H.; Ohmori, K.; Kishikawa, K.; Yamamoto, M.; Yamaguchi, K.; Kohmoto, S. Anal. Sci. 2005, 21, x33-x34. Masu, H.; Ohmori, K.; Kishikawa, K.; Yamamoto, M.; Yamaguchi, K.; Kohmoto, S. Bull. Chem. Soc. Jpn. 2005, 78, 1127-1131. (7) Masu, H.; Sakai, M.; Kishikawa, K.; Yamamoto, M.; Yamaguchi, K.; Kohmoto, S. J. Org. Chem. 2005, 70, 1423-1431. (8) Nakamura, Y.; Tsuihiji, T.; Mita, T.; Minowa, T.; Tobita, S.; Shizuka, H. Nishimura, J. J. Am. Chem. Soc. 1996, 118, 1006-1012. (9) Chandross, E. A. J. Chem. Phys. 1965, 43, 4175-4176. Chandross, E. A.; Ferguson, J. J. Chem. Phys. 1966, 45, 3564-3567. (10) McCullough, J. J. Chem. ReV. 1987, 87, 811-860. Becker, H.-D. Chem. ReV. 1993, 93, 145-172. (11) Becker, H.-D.; Sandros, K.; Skelton, B. W.; White, A. H. J. Phys. Chem. 1981, 85, 2930. Endo, K.; Ezuhara, T.; Koyanogi, M.; Masuda, H.; Aoyama, Y. J. Am. Chem. Soc. 1997, 119, 499-505. (12) Nishio, M.; Umezawa, Y.; Hirota, M.; Takeuchi, Y. Tetrahedron 1995, 51, 8665-8701. Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π Interaction, EVidence, Nature, and Consequences; WileyVCH: New York, 1998. Xie, Z.; Liu, L.; Yang, B.; Yang, G.; Ye, L.; Li, M.; Ma, Y. Cryst. Growth Des. 2005, 5, 1959-1964. (13) Kohmoto, S.; Ono, Y.; Masu, H.; Kishikawa, K.; Yamamoto, M. Org. Lett. 2001, 3, 4153-4155. (14) Sheldrick, G. M. Programs for crystal structure solution (SHELXS97) and refinement (SHELXL-97); University of Go¨ttingen: Go¨ttingen Germany, 1997. (15) Ito, Y.; Fujita, H. J. Org. Chem. 1996, 61, 5677-5680. (16) Desvergne, J.-P.; Bitit, N.; Castellan, A.; Bouas-Lauvent, H. J. Chem. Soc., Perkin Trans. 2 1983, 109-114. (17) Mori, Y.; Maeda, K. J. Chem. Soc., Perkin 2 1996, 113-119. (18) Furguson, J. Mau, A. W. H.; Whimp, P. O. J. Am. Chem. Soc. 1979, 101, 2370-2377. (19) Baures, P. W.; Rush, J. R.; Schroeder, S. D.; Beatty, A. M. Cryst. Growth Des. 2002, 2, 107-110. (20) Lieberman, H. F.; Davey, R. J.; Newsham, D. M. T. Chem. Mater. 2000, 12, 490-494. Bosch, E.; Barnes, C. L. Cryst. Growth Des. 2002, 2, 299. Reddy, C. M.; Kirchner, M. T.; Gundakaram, R. C.; Padmanabhan, K. A.; Desiraju, G. R. Chem.sEur. J. 2006, 12, 22222234. (21) Rahman, A. N. M. M.; Bishop, R.; Craig, D. C.; Scudder, M. L. Org. Biomol. Chem. 2004, 2, 175-182. Adams, H.; Cockroft, S. L.; Guardigli, C.; Hunter, C. A.; Lawson, K. R.; Perkins, J.; Spey, S. E.; Urch, C. J.; Ford, R. ChemBioChem 2004, 5, 657-665. (22) Swierczynski, D.; Luboradzki, R.; Dologonos, G.; Lipkowski, J.; Schneider, H.-S. Eur. J. Org. Chem. 2005, 1172-1177. (23) Lu. Y.; Zou, J.; Wang, H.; Yu, Q.; Zhang, H.; Jiang, Y. J. Phys. Chem. A 2005, 109, 11956-11961.
CG060232V
