Crystal Structures and Solid-State Optical Properties of

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DOI: 10.1021/cg101480x

Crystal Structures and Solid-State Optical Properties of Supramolecular Organic Fluorophore Composed of 1D Columnar Network Structure Consisting of Fluorescent 2-Naphthalenecarboxylic Acid

2011, Vol. 11 827–831

Noriaki Nishiguchi,† Tomohiro Sato,† Takafumi Kinuta,† Reiko Kuroda,‡ Yoshio Matsubara,*,† and Yoshitane Imai*,† †

Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan, and ‡Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan Received November 9, 2010; Revised Manuscript Received December 28, 2010

ABSTRACT: Supramolecular organic fluorophores composed of a one-dimensional (1D) column network structure were successfully developed using three types of 1-phenylethylamine derivatives as amine molecules and 2-naphthalenecarboxylic acid as a fluorescent acid molecule. These supramolecular organic fluorophores are formed by changing the style of the 1D columnar network structure and its packing arrangement, and their solid-state fluorescence properties are tuned according to their changes.

Introduction Solid-state optical properties of organic compounds are very important physical properties that must be considered while developing new functional materials. Organic compounds exhibiting solid-state fluorescence have attracted considerable attention because of their potential applications in various devices such as organic electroluminescence (EL) devices and optoelectronic devices.1 To date, many organic fluorophores exhibiting solid-state organic fluorescence have been developed; however, these fluorophores are composed only of a single molecule.2 Recently, two-component supramolecular organic fluorophores have attracted considerable attention because the solid-state optical properties of these fluorophores can be easily controlled by changing their component molecules.3 We have developed solid-state supramolecular organic fluorophores by combining two types of organic molecules (fluorescent carboxylic acid (or sulfonic acid) and chiral amine molecules).4 These supramolecular organic fluorophores are structurally composed of a characteristic one-dimensional (1D) columnar hydrogen- and ionic-bonded network structure formed by the association of carboxylate oxygen atoms of a carboxylic acid anion (or sulfonate oxygen atoms of a sulfonic acid anion) with the ammonium hydrogen atoms of a protonated amine. These supramolecular organic fluorophores offer functionalities because of the synergy effect derived from their characteristics such as the 1D columnar network structure and its packing arrangement in the solid state. However, a systematic study of the complexation behaviors, crystal structures, and solid-state optical properties of supramolecular organic fluorophores, having a 1D columnar network structure that is composed of carboxylic acid/ amine molecules, has not been reported. In this paper, we report the complexation behaviors, crystal structures, and solid-state optical properties of supramolecular

Chart 1

organic fluorophores having a 1D columnar network structure that is composed of a fluorescent 2-naphthalenecarboxylic acid molecule (1). Three types of basic aromatic amine molecules were used in this study, depending on how they affected the columnar network structure of the fluorophores and the packing of the network structure. The aromatic amine molecules were racemic (rac)-1-phenylethylamine (2), rac1-(p-tolyl)ethylamine (3), and rac-1-(4-methoxyphenyl)-ethylamine (4) (Chart 1). It is believed that the crystal structures and the optical properties of the resultant supramolecular organic fluorophores will play an important role in the development of solid-state supramolecular organic fluorophores. Experimental Section

*To whom correspondence should be addressed. For Y.I.: phone, þ1-66730-5880 ext 5241; fax, þ81-6-6727-2024; E-mail, [email protected]. jp. For Y.M.: E-mail, [email protected].

General Methods. All reagents were used directly as obtained commercially. Component molecule 1 and crystallization solvent MeOH were purchased from Wako Pure Chemical Industry. Component molecule rac-2 was purchased from Tokyo Kasei Kogyo Co., Ltd. Component molecules rac-3 and -4 were produced by mixing (R)-3 and (S)-3 and (R)-4 and (S)-4, respectively. Component molecules (R)-3, (S)-3, (R)-4, and (S)-4 were purchased from Tokyo Kasei Kogyo Co., Ltd. Formation of Complexes I-III by Crystallization from MeOH Solution. 1 (34 mg, 1.96  10-4 mmol) and rac-2 (or rac-3, rac-4) [2.00  10-4 mmol] were dissolved in MeOH solution (2 mL). After a week, a large number of crystals (crystals of complex I (28 mg) for 1/rac-2 system, crystals of complex II (26 mg) for 1/rac-3 system, and crystals of complex III (30 mg) for 1/rac-4 system) were obtained. The weight of crystal is equal to the total weight of the crystals of complexes I, II, and III obtained in one batch. X-ray Crystallographic Study of Complex I. X-ray diffraction data for single crystals were collected using BRUKER APEX. The

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Table 1. Crystal Form and Solid-State Fluorescence Spectral Data of Complexes I-III complex

crystal color

crystal shape

λem/nma

ΦF

I II III

colorless colorless colorless

plate plate needle

351 368 349

0.10 0.02 0.06

a Excited wavelengths are 332, 331, and 326 nm for complexes I-III, respectively.

crystal structures were solved by the direct method5 and refined by full-matrix least-squares using SHELXL97.5 The diagrams were prepared using PLATON.6 Absorption corrections were performed using SADABS.7 Nonhydrogen atoms were refined with anisotropic displacement parameters, and hydrogen atoms were included in the models in their calculated positions in the riding model approximation. Crystallographic data for I: C8H11N 3 C11H8O2, M = 293.35, space group P1, a = 6.0867(19) A˚, b = 10.568(3) A˚, c = 12.745(4) A˚, R = 105.127(5)°, β = 101.795(5)°, γ = 98.292(6)°, V = 757.5(4) A˚3, Dc = 1.286 gcm-3, z = 2, μ(Mo KR) = 0.083 mm-1, 4595 reflections measured, 3268 unique, final R(F2) = 0.0861 using 2601 reflections with I > 2.0σ(I), R(all data) = 0.0708, T = 115(2) K. CCDC 791336. Crystallographic data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (þ44)1223-336-033; [email protected]. ac.uk). X-ray Crystallographic Study of Complex II. Crystallographic data for II: C9H13N 3 C11H8O2, M = 307.38, space group P21/n, a = 5.6930(5) A˚, b = 9.1762(8) A˚, c = 30.950(3) A˚, β = 94.519(2)°, V = 1611.8(2) A˚3, Dc = 1.267 gcm-3, z = 4, μ(Mo KR) = 0.081 mm-1, 9702 reflections measured, 3686 unique, final R(F2) = 0.0584 using 3166 reflections with I > 2.0σ(I), R(all data) = 0.0685, T = 115 (2) K. CCDC 791337. X-ray Crystallographic Study of Complex III. Crystallographic data for III: C9H13NO 3 C11H8O2, M = 323.38, space group P21/c, a = 7.2024(5) A˚, b = 6.0955(4) A˚, c = 37.705(3) A˚, β = 90.5240(10)°, V = 1655.28(19) A˚3, Dc = 1.298 gcm-3, z = 4, μ(Mo KR) = 0.087 mm-1, 13966 reflections measured, 3813 unique, final R(F2) = 0.0457 using 3293 reflections with I > 2.0σ(I), R(all data) = 0.0530, T = 115(2) K. CCDC 791338. Measurement of Solid-State Fluorescence Spectra. A solid-state fluorescence spectra (λem) and absolute photoluminescence quantum yield (ΦF) were measured by Absolute PL quantum yield measurement system (C9920-02, Hamamatsu Photonics KK) under air atmosphere at room temperature. The excited wavelengths are 332, 331, and 326 nm for complexes I-III, respectively.

Results and Discussion The formation of 1/2-4 supramolecular organic fluorophores was attempted via crystallization from methanol (MeOH) solution. A mixture of 1 and 2-4 was dissolved in the MeOH solution and left to stand at room temperature. After a week, a large number of crystals of supramolecular complexes I-III composed of 1 and 2-4 were obtained. The most serious problem in solid-state organic fluorophores is fluorescence quenching in the crystalline state. To study the solid-state optical properties of the obtained supramolecular complexes I-III, the solid-state fluorescence spectra of these complexes were measured. The crystal form and solid-state fluorescence spectral data of complexes I-III are presented in Table 1. Complexes I-III exhibit fluorescence in the solid state. The solid-state fluorescence maximum (λem) for complex I is observed at 351 nm, and the absolute value of the photoluminescence quantum yield (ΦF) for complex I is 0.10 in the solid state. The values of solid-state λem and ΦF in complexes I-III are different from each other depending on the type of component amine molecules combined.

Figure 1. Crystal structure of I. (a) Pseudo-21-helical columnar network structure composed of 1, (R)-2, and (S)-2 observed along the c axis. (b) Packing structure observed along the a axis. The solid arrow A indicates the intercolumnar naphthalene-benzene edgeto-face interactions. The solid arrows B and C indicate the intercolumnar benzene-naphthalene edge-to-face interactions. The solid circle represents a helical columnar network structure. (c) Packing structure observed along the c axis.

X-ray crystallographic analyses of complexes I-III were attempted to study their crystal structures. The crystal structure of complex I is shown in Figure 1.8 The stoichiometry of crystal I is 1:(R)-2:(S)-2 = 1:0.5:0.5, and its space group is P1. This complex possesses a 1D columnar hydrogen- and ionic-bonded network structure along the a axis (Figure 1a). This 1D columnar network structure exists as rac-pseudo-21-helical columns composed of 1, (R)-2, and (S)-2. In this column, the linkages consist mainly of carboxylate oxygen atoms from the carboxylic acid anion of 1 and ammonium hydrogen atoms from the protonated amines of 2. Each column interacts via one intercolumnar naphthalene-benzene edge-to-face interaction between the hydrogen atom of the naphthalene ring in 1 and the benzene ring of (S)-2 (or (R)-2) along the c axis (2.88 A˚, as indicated by the solid arrow A in Figure 1b), and two benzenenaphthalene edge-to-face interactions between the hydrogen atom of the benzene ring of (S)-2 (or (R)-2) and the naphthalene ring in 1 along the c axis (2.91 and 2.76 A˚, as indicated by the solid arrows B and C in Figure 1b).9 The assembly of these rac-pseudo-21-helical columns (indicated by the solid circle in

Article

Figure 2. Crystal structure of II. (a) Pseudo-21-helical columnar network structure composed of 1, (R)-3, and (S)-3 observed along the b axis. (b) Packing structure observed along the a axis. The solid arrows A and B indicate the intracolumnar naphthalene-benzene edge-to-face and CH-π interactions. The solid arrows C, D, and E indicate the intercolumnar naphthalene-benzene, benzene-naphthalene edge-to-face, and CH-π interactions, respectively. The solid circle represents a helical columnar network structure. (c) Packing structure observed along the b axis.

Figure 1b) is responsible for the formation of a supramolecular organic fluorophore (Figure 1b,c). The crystal structure of complex II is shown in Figure 2. The stoichiometry of complex II is 1:(R)-3:(S)-3 = 1:0.5:0.5, and its space group is P21/n. This complex also possesses a 1D columnar supramolecular hydrogen- and ionic-bonded network along the a axis (Figure 2a). It is interesting to note that the packing of this 1D column structure is different from that of complex I. This 1D column structure is a rac-pseudo-21helical columnar network structure composed of 1, (R)-3, and (S)-3 along the a axis (Figure 2a). This column was mainly formed by the carboxylate oxygen atoms of the carboxylic acid anions and the ammonium hydrogen atoms of the protonated amine. Moreover, the intracolumnar naphthalene-benzene edge-to-face interactions (2.89 A˚, as indicated by the solid arrow A in Figure 2b) between the hydrogen atom of the naphthalene ring in 1 and the benzene ring of (R)-3 and (S)-3, and the CH-π interaction between the methyl group in (R)-3 and (S)-3 and the naphthalene ring in 1 (2.77 A˚, as indicated by solid arrow B in Figure 2b) also maintain this racpseudo-21-helical columnar network structure.9 Complex II is formed by the assembly of this rac-pseudo-21-helical column

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Figure 3. Crystal structure of III. (a) Chiral 21-helical columnar network structure composed of 1 and (R)-4 observed along the a axis. (b) Packing structure observed along the b axis. The solid arrow A indicates the intracolumnar naphthalene-benzene edgeto-face interactions. The solid arrows B, C, and D indicate the intercolumnar naphthalene-benzene, benzene-naphthalene edgeto-face, and CH-π interactions, respectively. The solid circle represents a helical columnar network structure. (c) Packing structure observed along the a axis.

(indicated by the solid circle in Figure 2b) through three types of intercolumnar interactions (Figure 2b,c):9 (a) the naphthalene-benzene edge-to-face interaction (2.96 A˚, as indicated by the solid arrow C in Figure 2b) between the hydrogen atom of the naphthalene ring in 1 and the benzene ring of (R)-3 and (S)-3, (b) the benzene-naphthalene edge-toface interaction (2.82 A˚, as indicated by the solid arrow D in Figure 2b) between the hydrogen atom of the benzene ring of (R)-3 and (S)-3 and the naphthalene ring in 1, and (c) the CH-π interaction between the methyl group in (R)-3 and (S)-3 and the naphthalene ring in 1 (2.72 A˚, as indicated by solid arrow E in Figure 2b). The crystal structure of complex III is shown in Figure 3. The stoichiometry of crystal III is 1:(R)-4:(S)-4 = 1:0.5:0.5, and its space group is P21/c. This complex also possesses a 1D columnar supramolecular hydrogen- and ionic-bonded network structure along the b axis, which is the same as that in complexes I and II (Figure 3a). Moreover, the intracolumnar naphthalene-benzene edge-to-face interactions (2.93 A˚, as indicated by the solid arrow A in Figure 3b) between the hydrogen atom of the naphthalene ring in 1 and the benzene ring of (R)-4 (or (S)-4) are observed, which are similar to those observed in the case of complex II.9 This complex also consists of two types of chiral helical columns with opposite

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chiralities: one is composed of 1 and (S)-4, and the other is composed of 1 and (R)-4. In this complex, this helical column is quite different from that observed in complexes I and II. In complexes I and II, the two naphthalene rings of 1 along one helical column exist in opposite directions (Figures 1a and 2a). On the other hand, in complex III, the two naphthalene rings of 1 exist in the same direction (Figure 3a). This implies that the helical column in complexes I and II is a pseudo-21-helical column, and the helical column in complex III is a 21-helical column. Complex III is formed by the assembly of this chiral 21-helical column (indicated by the solid circle in Figure 3b) with opposite chiralities through the following three types of intercolumnar interactions (Figure 3b,c):9 (a) the naphthalene-benzene edge-to-face interaction (2.86 A˚, as indicated by the solid arrow B in Figure 3b) between the hydrogen atom of the naphthalene ring in 1 and the benzene ring of (R)-4 (or (S)-4), (b) the benzene-naphthalene edge-to-face interaction (2.98 A˚, as indicated by the solid arrow C in Figure 3b) between the hydrogen atom of the benzene ring of (R)-4 (or (S)-4) and the naphthalene ring in 1, and (c) the CH-π interaction between the methyl group in (R)4 (or (S)-4) and the naphthalene ring in 1 (2.55 A˚, as indicated by solid arrow D in Figure 3b). These X-ray crystallographic analyses suggest that these supramolecular organic fluorophores are formed by the following two steps: (a) a 1D columnar supramolecular hydrogen- and ionic-bonded network structure suitable for a component amine molecule is formed by selecting the chirality of component amine molecule and tuning the direction of the naphthalene ring of 1 and (b) a supramolecular organic fluorophore suitable for a columnar network structure is formed by varying the packing arrangement of the columnar network structure. Although the solid-state fluorescence maxima (λem) of complexes I and III are similar, the solid-state λem and the photoluminescence quantum yields (ΦF) of these complexes differ on the basis of component amine molecules. While comparing the parameters of complexes I and III with complex II, it is found that the distance between the naphthalene rings along the helical column decreases from 6.09 A˚ for complex I and 6.10 A˚ for complex III to 5.70 A˚ for complex II (AA, Figures 1a, 2a, and 3a). Moreover, the crystal density (1.267 gcm-3) of complex II was found to be lower than that of complexes I and III (1.286 and 1.298 g cm-3, respectively). The solid-state λem of complexes I and III are similar; they are different from that of complex II. In addition, the solid-state ΦF of complex II is lower than that of complexes I and III. It is thought that although the reason for the difference in these solid-state optical properties from the structural viewpoint is attributed to the difference in the crystal structures of the above-mentioned complexes, especially, the thin packing style (crystal density) of complex II cannot suppress the concomitant nonradiative processes and decrease the solid-state ΦF of II. Conclusions Supramolecular organic fluorophores were successfully formed using fluorescent 2-naphthalenecarboxylic acid and three types of rac-1-phenylethylamine derivatives. On the basis of X-ray crystallographic analyses, these supramolecular organic fluorophores can be obtained via the following two steps: (a) a 1D columnar network structure suitable for component molecules is formed and (b) a supramolecular complex suitable for packing is formed by varying the packing

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arrangement of the 1D column. Their solid-state optical properties can be controlled by changing the type of the amine component molecule. In other words, their solid-state optical properties can be controlled by changing the style of 1D columnar network structure and its packing arrangement. It is believed that the crystal structures and the optical properties of the above-mentioned supramolecular complexes will be useful in the development of novel solid-state supramolecular organic fluorophores. Acknowledgment. This work was supported by a Grant-inAid for Scientific Research (no. 22750133) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan, and a research grant from Konika Minoluta Science and Technology Foundation. Supporting Information Available: Crystallographic reports (CIF) of complexes I-III. This material is available free of charge via the Internet at http://pubs.acs.org.

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(8) Lemmerer and co-workers have reported the crystal structure of complex I. However, because the temperature of measurement was 173 K, we remeasured this complex at 115 K for unification of the temperature of measurement in three complexes I-III. Lemmerer, A.; Bourne, S. A.; Ferandes, M. A. CrystEngComm 2008, 10, 1605– 1612. (9) Determined by PLATON geometry calculation.