ARTICLE pubs.acs.org/crystal
Deoxycholamide Crystalline Frameworks as a Platform of Highly-Efficient Fluorescence Materials Ichiro Hisaki,*,† Taketoshi Murai,† Hirohide Yabuguchi,† Hajime Shigemitsu,† Norimitsu Tohnai,†,‡ and Mikiji Miyata*,† † ‡
Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan PRESTO, Japan Science and Technology Agency (JST), Japan
bS Supporting Information ABSTRACT: To achieve spatially oriented molecular arrays with a wide range of dye molecules, an organic lattice framework is a promising platform, because its flexible superstructure connected by labile hydrogen bonds can tune the host framework to provide the dyes geometrically oriented in the appropriate inclusion spaces. In this Article, we demonstrate that inclusion crystalline lattice composed of deoxycholamide (DCM) can be applied as a platform to arrange various “skinny” dye molecules such as anthracene and 1,6-diphenylhexatriene into a tandemly aligned array without π/π stacking interactions in the inclusion channel. As compared to its parent compound deoxycholic acid (DCA), DCM forms additional NH 3 3 3 O interactions between DCM molecules, stabilizing the host framework. The density of the guest dyes included in the DCM channels can be controlled upon changing crystallization solvent: nonpolar solvents give inclusion crystals (ICs) containing a small amount of dye molecules (I-state), while polar ones give ICs whose channels are filled by tandemly arrayed dyes (F-state). ICs of dyes, even in the densely packed F-sate, exhibit fluorescence quantum yields higher than the naked dye crystals and comparable to the diluted solutions.
’ INTRODUCTION As exemplified for bacteriochlorophyll in the light-harvesting antenna complex,1 the molecular arrangements of organic dyes are crucial for photophysical properties of functional materials. To develop such materials with desired, well-organized dye superstructures, great efforts have been made on the design of highly directional noncovalent intermolecular interactions as well as on the modification of molecular structures.2,3 For achievement of spatially oriented molecular arrays, lattice frameworks are also promising platforms providing the dyes with geometrically restricted inclusion spaces. They include inorganic zeolite,4 metalorganic frameworks,5 and organic inclusion crystals (OICs).6 Advantages of lattice frameworks are as follows: (1) dyes can be aligned anisotropically in the spaces without burdensome chemical modifications, (2) molecules or molecular aggregates in the space are well separated from those in the adjacent channel by walls of the frameworks, preventing unfavorable intermolecular perturbation leading to fluorescence quenching by reabsorption, and (3) the wall also prevents the dyes from photoisomerizations associated with large structural changes, intermolecular photoreactions, and oxidative fading.7 Particularly, OICs consisting of flexible molecules and labile hydrogen bonds make their host-frameworks possible to accommodate guest molecules with various sizes and shapes in the channels by changing and tuning their superstructures. For example, we revealed that a series of cholic acid derivatives form a wide variety of lattice frameworks depending on the guest molecules.8,9 r 2011 American Chemical Society
To date, excellent optoelectronic systems based on OICs and the related thin films have been reported for perhydrotriphenylene by Oelkrug, Hanack, et al.,10 and deoxycholic acid (DCA) by Botta et al. or Zheng and Coppens, independently.11,12 In such systems, photophysical properties depending on the molecular arrangements, such as polarized emission and highly efficient excitation energy transfer between guest molecules, were achieved. In this study, deoxycholamide (DCM) was first applied to construct a new OIC capable of accommodating a wide range of dye molecules in the inclusion space.13 Amidation of the carboxyl group in DCA leads to an increase of hydrogen-bonding donors from one to two, that is, CO2H versus CONH2. Therefore, it is expected that the DCM framework is more robust than that of DCA due to additional hydrogen-bond formation among DCM molecules or that DCM behaves differently from DCA for the guest inclusion due to a hydrogen-bond formation between DCM and a guest molecule. Indeed, we previously reported that cholic acid (CA) and its amidated derivative cholamide (CM) are capable of accommodating opposite kinds of guest species in their channels, although they yield similar OIC frameworks and hydrogen-bonding networks.14,15 CM includes 50 or more alcohols, while CA mainly includes nonpolar compounds, for example, substituted benzene derivatives. Such a difference of the Received: July 20, 2011 Revised: August 16, 2011 Published: August 22, 2011 4652
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Chart 1. Steroidal Hosts and Guest Molecules
Figure 1. Schematic representation of ICs with (a) isolated and (b) fully aligned guest molecules in the channels, named I-state IC and F-state IC, respectively (abbreviation: I-IC and F-IC, respectively).
inclusion behavior is attributed to the difference of the weak hostguest interactions, such as NH 3 3 3 O, NH 3 3 3 π, and CH 3 3 3 π interactions, provided by amide and carboxylic groups.16 Herein, we first describe fluorescence properties of DCM crystals including various dye molecules, as shown in Chart 1. We compare the frameworks composed of DCA and DCM on the basis of their crystal structures. Subsequently, guest inclusion behavior, structure confirmation, and fluorescence properties of DCM inclusion crystals (ICs) of dyes are demonstrated. Interestingly, upon changing solvents applied for crystallization, the following two guest-states were achieved in the DCM crystals: I-state, in which the dye molecules are sparsely included, and thus isolated from neighbor dyes (Figure 1a), and F-state, in which the dye molecules fill the channel and are aligned with head-to-tail contacts (Figure 1b). In the latter part, ICs in the Iand F-states are abbreviated as I- and F-ICs, respectively. Dyes included in DCM crystals, even in densely aligned F-states, show fluorescence quantum yields higher than those of the naked-dye crystals (NCs) and comparable to those of the diluted solutions (DSs).
’ RESULTS AND DISCUSSION Comparison of DCM and DCA Inclusion Crystals. To preliminarily investigate the inclusion behavior of DCM, we crystallized DCM with various small guest molecules that we often applied for preparation of steroidal ICs, and consequently single crystals were crystallographically analyzed. In Figure 2, crystal structures of two representative ICs of DCM with acetonitrile and naphthalene (DCM/AcN and DCM/Naph, respectively) are shown, together with the corresponding ICs of DCA, that is, DCA/AcN and DCA/Naph,17 as references. Their crystallographic parameters are also shown in Table 1. Frameworks composed of DCM resemble those of DCA. The steroid, that is, DCM or DCA, formed a bilayered-structure, which consists of alternative stacking of hydrophilic and lipophilic layers.
The steroid molecules are connected through three networked intermolecular hydrogen bonds [for DCM, (i) O(C3) H 3 3 3 O0 (C24), (ii) N(C24)H 3 3 3 O(C12), and (iii) O(C12) H 3 3 3 O(C3); for DCA, (i) O(C3)H 3 3 3 O0 (C24), (ii) O(C24)H 3 3 3 O(C12), and (iii) O(C12)H 3 3 3 O(C3)] to construct a sheet motif laid on the ab plane. The sheet motif stacks with adjacent ones in the antiparallel manner with their lipophilic β-faces contacting each other through van der Waals interaction. A one-dimensional inclusion space runs through the lipophilic layers to accommodate the guest molecules. Table 2 shows lengths of the above hydrogen bonds. Although the patterns of the hydrogen-bonding networks are similar, DCM inclusion crystals have a longer N(C24)H 3 3 3 O(C12) bond length by ca. 0.28 Å than the corresponding O(C24) H 3 3 3 O(C12) bond length of DCA because of the amide group. This affects the periodic length of the inclusion channels: 7.272 Å for DCM/AcN, 7.114 Å for DCA/AcN, 7.338 Å for DCM/ Naph, and 7.294 Å for DCA/Naph. Furthermore, it is noteworthy that DCM crystals have additional N(C24)H 3 3 3 O(C3) interactions to connect the adjacent hydrogen-bonding networks. This connection is achieved only by DCM possessing two hydrogen-bond donors and probably makes the framework more robust than that of DCA. Structural Comparison of DCM/AcN and DCM/Naph. Careful observation of the crystal structures of DCM/AcN and DCM/Naph led the fact that relative positions of the neighboring layers are slightly different in these two crystals. In the DCM/ AcN crystal (Figure 2c), two methyl groups on the β-face of DCM, that is, C(18)H3 and C(19)H3, just face those of DCM laid in the adjacent layer, while in DCM/Naph (Figure 2d), the layer slips and the methyl groups are located in the staggered manner. The slip provides elongation of the distances between the adjacent layers by 0.34 Å (12.89 Å for DCM/AcN, while 13.23 Å for DCM/Naph), which is also obvious from their powder X-ray diffraction (PXRD) patterns that the (020) peak of DCM/Naph, attributed to the periodic distance between the layers, appears in a smaller angle region than the (002) peak of DCM/AcN (Figure 2e,f). The slip also yields the channels with different dimension so as to fit the size and shape of the guest molecules: cross-section of the channels, 2.8 6.1 Å2 for DCM/Naph crystal and 2.6 5.0 Å2 for DCM/AcN crystal. In the channel, acetonitrile molecules align with a 1:1 host/guest molar ratio (Figure 3a). In the crystal of DCM/Naph, naphthalene molecules are included with a 2:1 host/guest molar ratio. The molecular plane inclines by 16.8° against the columnar axis. Adjacent naphthalene molecules in the channel are not on the same plane but offset by 2.01 Å (Figure 3b). Interestingly, the neighboring naphthalene molecules are in contact just at their edges and have no significant π/π interactions due to the restricted space of the channel. Additionally, the guest molecules are apart from those in the adjacent channels by 4653
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Figure 2. Crystal packing diagrams (left) and hydrogen-bonding networks (right) in the crystals of (a) DCA/AcN, (b) DCA/Naph, (c) DCM/AcN, and (d) DCM/Naph. Simulated PXRD patterns of (e) DCM/AcN and (f) DCM/Naph focused on the (002) and (020) peaks, respectively. Atoms are drawn as thermal ellipsoids with 50% probability. Hydrogen atoms are partly omitted for clarity. Atomic colors: C (green), O (red), N (blue).
Table 1. Crystallographic Parameters of Steroidal Inclusion Crystals
Table 2. Hydrogen-Bond Lengths in DCM and DCA Inclusion Crystals
DCM/AcN DCM/Napha DCA/AcN DCA/Naph formula C26H44N2O3 C58H90N2O6 C26H43NO4 C58H88O8 host/guest ratio 1:1 2:1 1:1 2:1
a
fw
432.65
911.36
433.63
crystal system space group
orthorhombic monoclinic P21 P212121
a [Å]
7.27171(13) 7.3377(3)
7.11422(13) 7.2948(3)
b [Å]
13.2710(3)
26.4525(9)
13.5618(3)
26.2511(9)
c [Å]
25.7839(5)
13.2866(5)
25.7091(5)
13.5197(6)
α [deg]
90
90
90
90
β [deg]
90
91.334(2)
90
91.0190(19)
γ [deg]
90
90
90
90
V [Å2] Z
2488.22(8) 4
2578.23(17) 2480.45(8) 2 4
ia/Å
iib/Å
DCM/AcN
2.658
2.942
2.769
3.529
DCM/Naphe
2.666
2.894
2.753
3.504
2.622
2.930
2.787
3.657
2.710 2.693
2.658 2.640
2.673 2.687
2.710
2.645
2.670
913.33
orthorhombic monoclinic P212121 P21
2588.56(17) 2
dcalcd [g cm3]
1.155
1.174
1.161
1.172
T [K]
213
213
213
213
reflns observed
43 763
25 766
29 138
29 364
reflns unique
4512
8989
4539
9242
R1 (I > 2.00σ(I)) 0.0396
0.1176
0.0719
0.0722
Rw (all data)
0.1077
0.3462
0.2482
0.2020
CCDC no.b
827571
827572
827569
827570
Reference 17. b Reference 18.
ca. 13.3 Å. These indicate that the dyes included in the channel do not experience any fatal perturbation providing fluorescence
DCA/AcN DCA/Naphe
iiic/Å
ivd/Å
O(C3)H 3 3 3 O0 (C24). b N(C24)H 3 3 3 O(C12) or O(C24)H 3 3 3 O(C12). c O(C12)H 3 3 3 O(C3). d N(C24)H 3 3 3 O(C3). e Two kinds of values are observed because the crystals have two crystallographically independent DCM molecules. a
quench.19 Furthermore, judging from the channel dimensions of DCM/Naph, other dyes with “skinny” skeleton might be possible to accommodate in the channel. Next, various commercially available dyes were subjected to co-crystallization with DCM to obtain their ICs. Inclusion Behavior of Dyes 1 and 8. Despite our great effort, no single crystals were obtained from dyes 111 probably due to their molecule lengths discrepant with the channel’s periodic length. So, structures of the host frameworks and inclusion of the dye molecules are confirmed by PXRD analysis of the resultant crystalline powders and 1H NMR spectral measurements of solutions in which the crystal dissolved. First, to clarify whether the dyes are accommodated in the resultant crystals or not, co-crystallization of DCM with two specimen 4654
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Figure 3. One-dimensional array of (a) acetonitrile and (b) naphthalene molecules in the channels of DCM/AcN, and DCM/Naph crystals, respectively.
Table 3. Composition Ratios of DCM/1 and DCM/8 Crystallized by Using Various Solvents solvent
d.e.a
DCM:1:(Sol)b
DCM:8:(Sol)b
chloroform
4.8
1:0.04:(0.41)
1:c:(0.26)
dichloromethane
a
9.1
ethyl acetate acetone
8.6 21
acetonitrile
37
c
1:c:(0.55)
c
1: :(0.48) 1:0.20:(d)
1:0.13:(0.08) 1:0.15:(d)
1:0.27:(d)
1:0.16:(d)
1: :(0.52)
b
d.e. denotes dielectric constant. Molar ratio of the solvents was described in parentheses. c Molar ratio was not determined due to limit of NMR measurements. d Molar ratio was not determined due to overlapping of signals.
dyes 1 and 8, respectively, was performed by using various solvents, and 1H NMR spectra of the resultant crystals dissolved in CHCl3 were measured. In Table 3, molecular ratios of DCM, dyes, and solvents are listed. Recrystallization with less polar solvents gave crystals mainly including solvent molecules instead of the dyes. Especially, the crystals obtained from dichloromethane solutions contain only a small amount of the dyes. In this case, the obtained crystals homogeneously emitted blue fluorescence, although guests in the ICs were not detected by 1H NMR spectroscopy due to limit of sensitivity. We named such status of the dyes as I-state. In contrast, recrystallization with polar solvents gave fluorescent guest-rich inclusion crystals due to the fact that the lipophilic channel of DCM prefers accommodating hydrophobic guests to the polar solvent molecules. Particularly, crystallization from acetonitrile solutions yielded ICs densely containing dye molecules: host/guest ratios for 1 and 8 are 4:1 and 6:1, respectively. The latter ratio is, especially, the maximum ratio for the molecule of 8 to be accommodated in the channel, considering its molecular size and the dimension of the inclusion channel of DCM inclusion crystals. Therefore, the dye molecules are expected to be densely packed with a tandem array arrangement in the channels as shown in Figure 1b. We named such status of the dyes as F-state. Next, to confirm the structures of the I- and F-ICs of DCM/1 and DCM/8, the obtained crystals were subjected to PXRD analysis, and the consequence patterns were compared to those of the well-defined ICs, DCM/AcN and DCM/Naph (Figure 4). The pattern of the I-IC of DCM/1 obtained from dichloromethane solution, Figure 4a(ii), shows peaks at 6.94°, 7.60°, and 9.58°, which corresponded to the (002), (011), and (012)
Figure 4. Selected PXRD patterns of (a) DCM/1 and (b) DCM/8 crystals obtained from the solutions of (i) chloroform, (ii) dichloromethane, (iii) ethyl acetate, (iv) acetone, and (v) acetonitrile. The patterns of DCM/AcN and DCM/Naph are present at the bottom as references.
reflections (2θ = 6.94°, 7.56°, and 9.70°, respectively) of the DCM/AcN crystal. The pattern of F-IC of DCM/1 obtained from the acetonitrile solution shows peaks at 6.62°, 7.26°, and 9.62°, which corresponded to the (020), (011), and (021) reflections (2θ = 6.62°, 7.34°, and 9.36°, respectively) of the DCM/Naph crystal. The IC obtained from the chloroform solution showed two significant peaks at 6.62° and 6.68°, indicating coexistence of two or more host frameworks. Similarly, the I-IC of DCM/8 showed the pattern agreed with those of DCM/AcN, while that in the F-state did with those of DCM/Naph, although the peak at 6.50° is slightly shifted into the small angle region as compared to the corresponding one of DCM/Naph. According to the results described above, it is possible to distinguish DCM framework types on the basis of the peaks appearing in the range of 2θ = 510°; the I-ICs of DCM/1 and DCM/8 show the PXRD patterns similar to that of DCM/AcN, while the F-ICs of DCM/1 and DCM/8 exhibit a pattern similar to that of DCM/Naph. Fluorescence Properties of ICs of DCM/1 and DCM/8. To investigate the emission properties of the I- and F-ICs of DCM/1 and DCM/8, fluorescence spectra of the ICs obtained from the five solutions described above were measured. As shown in Figure 5a, fluorescence spectra of the DCM/1 differed in relative intensity of the 00 transition band of anthracene at 388 nm upon changing a crystallization solvent. The band, clearly observed for the I-state, became decayed in the F-sate, probably due to fluorescence reabsorption or spatially restricted circumstances of the dye. Contrary to DCM/1, the fluorescence spectra of DCM/8 show unambiguous changes: relative intensity of the 02 transition band at 447 nm increased in the spectrum of the F-state, accompanied by decay of the 00 transition band at 401 nm. These significant spectral changes of DCM/8 as compared to DCM/1 are attributed to conformational change of the rotationally flexible molecular shape of 8.20 In connection with the guest arrangements, it is reasonable to conclude that dyes in the channel are aligned with their long axis parallel to the channel axis (i.e., head-to-tail arrangement) as described in refs 10a and 11. Dyes in such insulated surroundings are, therefore, prevented from π/π interaction in cofacial arrangement 4655
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Figure 5. Solid-state fluorescence spectra of (a) DCM/1 and (b) DCM/8 crystals obtained from the solutions of chloroform (solid in gray), dichloromethane (dash in gray), ethyl acetate (dotted in black), acetone (dash in black), and acetonitrile (bold solid in black). Inset: Magnified spectra of DCM/1. Figure 7. Selected PXRD patterns of DCM inclusion crystals of (a) 1, (b) 2, (c) 3, (d) 4, (e) 5, (f) 6, (g) 7, (h) 8, (i) 9, as well as DCM/AcN and DCM/Naph as references.
Figure 6. Normalized fluorescence (a and c) and excitation (b and d) spectra of 1 and 8, respectively, in the following states: DSs (dash in black), NCs (bold solid in gray), I-ICs (thin solid in gray), and F-ICs (bold solid in black). Excitation wavelength for all cases: 350 nm except 1 in DS (340 nm). Detected wavelength in excitation spectra for 1, 400 nm (DS), 428 nm (I- and F-ICs), and 446 nm (NC); for 8, 410 nm (DS), 445 nm (I- and F-ICs), and 460 nm (NC).
and dipoledipole coupling in side-by-side arrangement with adjacent dyes: an interchannel distance of 9.012 Å is enough to make such interactions ineffective. Indeed, fluorescence quantum yields (ΦF) of the I- and F-states are comparable for both cases of DCM/1 and DCM/8: ΦF values of the I- and F-states for DCM/ 1 are 0.23 and 0.23, respectively, and those for DCM/8 are 0.87 and 0.94, respectively. Furthermore, fluorescence properties of the I- and F-ICs were compared to those of dilute solutions (DSs) and naked dye crystals (NCs) as shown in Figure 6a,c. The I- and F-ICs of 1 show slightly red-shifted spectra by ca. 5 nm as compared to the DS's spectrum, while they are more structured and blue-shifted by 18 nm as compared to the NC, indicating that the dyes in the channels are well isolated and are prevented from perturbative ππ interactions. Similarly, in the case of 8, the I- and F-ICs show red-shifted spectra by ca. 12 nm as compared to the DS,
while they are more structured and blue-shifted by 25 nm as compared to the NC's spectrum. Fluorescence quantum yields (ΦF) for the I- and F-ICs of 1 (0.23) are comparable to those in the DS (0.36),21 although the values of the ICs of 1 remain lower than those of the corresponding NC (0.43).22 On the other hand, values of ΦF for the ICs of 8 in I- and F-states, which are comparable to those in the DS (0.93), were much higher than those of the corresponding NC (0.50). The fluorescence decay curve of the F-IC of 1 (Figure S1) was fitted biexponentially with lifetimes of τ1 = 0.08 ns and τ2 = 3.58 ns, while mono- and triexponential decay of DS with τ = 4.07 ns and NC with τ1 = 1.46 ns, τ2 = 5.50 ns, and τ3 = 20.47 ns, respectively. The F-IC of 8 shows biexponential fluorescence decay (τ1 = 0.97 ns and τ2 = 2.69 ns), while the DS and NC do mono- (τ = 1.04 ns) and tri- (τ1 = 0.34 ns, τ2 = 1.46 ns, and τ3 = 4.87 ns) exponential decay, respectively. Figure 6b,d shows excitation spectra of 1 and 8, respectively, in each state. The DSs of 1 and 8 exhibit well-structured spectra (drawn in a dash line) with bands at 324, 340, 357, and 376 nm for 1 and 341, 357, and 375 nm for 8. The NCs, on the other hand, show the red-shifted, broadened, but still well-structured spectrum with a band at 338, 361, 381, and 408 nm for 1 and 370, 393, and 418 nm for 8 as shown with a gray line. It is noteworthy that the I- and F-ICs, whose fluorescence profiles are similar, show different excitation spectral profiles. Spectra of F-ICs of 1 and 8 (bold back line) show slightly red-shifted and much less structured profiles as compared to those of the I-ICs (thin black line). These results indicate that the dyes in F-ICs have weak intermolecular interactions with the neighboring dyes, such as edge-to-edge interactions. Additionally, the spectral intensity of the F-ICs is highly maintained in a wide range of excitation wavelengths (ca. 250390 nm for 1 and 250420 nm for 8). These results are also presumably due to the molecular arrangements that the dyes densely align one-dimensionally in the channel. Inclusion of Other Dyes and Their Fluorescence Properties in the F-ICs. To investigate optical properties of the F-ICs containing other dyes 27 and 911, co-crystallization of DCM with the dyes is performed according to the method applied for the preparation of the F-ICs of 1 and 8, and the resultant crystals were subjected to PXRD analysis to confirm their structures. PXRD patterns of the crystals of DCM with 19 are shown in Figure 7. 4656
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Figure 8. Normalized fluorescence spectra of (a) 5, (c) 6, (e) 7, and (g) 9 and the corresponding excitation spectra (bh) in each state: DSs (dash in black), F-ICs (bold solid in black), and NCs (bold solid in gray). Excitation wavelength for 5, 310 nm (DS), 345 nm (F-IC), and 350 nm (NC); for 6, 340 nm (DS), 350 nm (F-IC), and 350 nm (NC); for 7, 300 nm (DS) and 400 nm (F-IC), and for 9, 429 nm (DS), 350 nm (FIC), and 400 nm (NC). Detected wavelength in excitation spectra for 5, 395 nm (DS), 407 nm (F-IC), and 433 nm (NC); for 6, 428 nm (DS), 452 nm (F-IC), and 490 nm (NC); for 7, 470 nm (DS) and 620 nm (FIC), and for 9, 493 nm (DS), 540 nm (F-IC), and 600 nm (NC). Spiked bands marked with asterisk are artifacts. Fluorescence and excitation spectra of NC for 7 are not present due to its absence of fluorescence.
Dyes 10 and 11 gave no ICs because they are too bulky to be accommodated in the steroidal channel. Dyes 2 and 4 yielded ICs in which both the I- and the F-states concurrently exist, judging from the two peaks at 2θ = 6.58° and 6.92° in Figure 7b,d, respectively. This indicates that dyes with relatively small molecular sizes do not prefer to be packed densely even by crystallization from acetonitrile solutions. The patterns of 3, 7, and 9 agree with that of DCM/Naph, indicating formation of F-ICs. Oligoenes 5 and 6 also gave F-ICs, although their peaks at 6.66° and 6.74°, respectively, are slightly shifted into a wide angle region due to their narrow di- and triene moieties. Therefore, DCM can be a superior platform to densely accommodate various dyes in the channels. Subsequently, fluorescence properties were investigated on F-ICs that exhibit their fluorescence bands in visible regions, that is, dyes 5, 6, 7, and 9. Figure 8 shows their fluorescence and excitation spectra, combined with those of the corresponding
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DSs and NCs. Fluorescence quantum yields (ΦF) and lifetimes (τ) of the DSs, F-ICs, and NCs are also shown in Table 4. In excitation spectra of each dye, the long wavelength edge of the F-IC’s spectrum is located between that of the DS and NC. As described for the F-ICs of 1 and 8, the excitation spectra of these dyes also show structureless profiles. The F-IC of 5 exhibits structured fluorescence spectrum with clear bands at 386 and 407 nm, which are red-shifted by ca. 15 nm as compared to those of the DS, while they are blue-shifted by ca. 25 nm as compared to those of the NC (Figure 8a). The fluorescence quantum yield of the F-IC (0.87) is larger than the DS’s (0.42) and comparable with the NC’s (0.84). Its homologue triene derivative 6, on the other hand, shows no significant spectral differences between the F-IC and DS as shown in Figure 8b, and their ΦF values are also similar: 0.68 for the F-IC and 0.650.80 for the DS. Interestingly, although the NCs of 5 and 6 have similar molecular packing manners as well as molecular structures,26,27 the NC of 6 shows a significantly lower ΦF value as compared to that of 5. This fluorescence quench were brought from nonradiative processes such as transcis isomerization.28 Stilbene derivative 7 shows almost no fluorescence in the NC state due to strong interactions between the donor and acceptor moieties, while a structureless fluorescence band at 597 nm was observed in the F-IC state (Figure 8c). The band was significantly red-shifted by ca. 70 nm as compared to that of the DS, and, moreover, the ΦF value of the F-IC is much less small than the DS’s, indicating that interactions provided from the head-to-tail contact of 7 result fluorescence quench, although the dyes are isolated from those in the neighbor channels. The F-IC of 9 gave a narrow fluorescence band at 518 nm, red-shifted by 57 nm as compared to the DS and blue-shifted by 52 nm with the NC. The ΦF value of the F-IC is 0.90, comparable with the DS’s (0.94) and much larger than the NC’s (0.12). These results indicate that dyes in the channels, even aligned densely, provide highly efficient fluorescence as compared to their solid states and comparable to their diluted solutions. To investigate fluorescence behavior in more detail, fluorescence lifetimes were measured for the F-ICs, as well as DSs and NCs (Figures S1S6). Interestingly, the F-ICs shown exhibit bior triexponetial fluorescence decay except for 1 (Table 4), indicating the fluorescence process involves more than two excited states. Such excited states are probably brought from (1) intermolecular interactions such as edge-to-edge interaction between neighboring dyes, in the channel, and/or (2) varied molecular conformations statistically forced in the channel. However, although the fluorescence process is not simply observed for the DSs, the inclusion platform constructed from DCM achieved efficient fluorescence of various dyes.
’ CONCLUSION In summary, we first demonstrated that deoxycholamide (DCM) can be applied as a platform for inclusion crystals of various dye molecules. As compared to its parent compound, DCM forms additional NH 3 3 3 O interactions between DCM molecules, stabilizing the host frameworks. Inclusion density of the guest dyes can be controlled upon changing crystallization solvents: nonpolar solvents such as dichloromethane give ICs that contained less dye molecules, while polar solvents such as acetonitrile give ICs in which the dyes are arrayed tandemly with high density. ICs of dyes show fluorescence quantum yields higher than naked-dye crystals and comparable to diluted solution 4657
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Table 4. Fluorescence Quantum Yields and Lifetimes of Dyes in DSs, F-ICs, and GCs λemmax/nm DSa 1
400
F-IC 405
quantum yielda NC
DS
423
b
0.36
F-IC 0.23
lifetime g,h,i/ns DSa
NC
4.07 ( 0.02
c
0.43
F-IC
NC
0.08 ( 0.05 (0.26)
1.46 ( 0.18 (0.28)
3.58 ( 0.03 (0.74)
5.50 ( 0.21 (0.61) 20.47 ( 1.22 (0.11)
5
376
408
432
0.35d0.42b
0.87
0.524 ( 0.003
0.84
0.22 ( 0.09 (0.28)
1.89 ( 0.06 (0.84)
0.99 ( 0.04 (0.56)
4.71 ( 0.22 (0.16)
6.21 ( 0.21 (0.16) 6
7 8
427
470 410
432
460
0.33e
598 422
0.63d0.80b
444
0.93b
0.68
8.26 ( 0.03
0.02
0.84 ( 0.03 (0.54)
0.08 0.94
0.50
0.79 ( 0.18 (0.16)
0.36 ( 0.02 (0.60)
3.41 ( 0.13 (0.76) 9.58 ( 0.83 (0.08)
2.16 ( 0.31 (0.30) 7.89 ( 0.67 (0.10)
0.17 ( 0.03 (0.85)
3.08 ( 0.05 (0.46)
0.93 ( 0.06 (0.15)
1.04 ( 0.01
0.97 ( 0.02 (0.93)
0.34 ( 0.05 (0.18)
2.69 ( 0.19 (0.07)
1.46 ( 0.05 (0.75)
0.49 ( 0.13 (0.17)
0.64 ( 0.07 (0.17)
2.15 ( 0.07 (0.67) 8.46 ( 0.31 (0.16)
2.83 ( 0.38 (0.50) 7.26 ( 0.19 (0.33)
4.87 ( 0.36 (0.07) 9
462
515
576
0.94f
0.90
2.31 ( 0.01
0.12
a
The values in cyclohexane for 1, 7, and 8, in hexane for 5 and 6, and in chloroform for 9. b Reference 21. c Reference 22. d Reference 23. e Reference 24. Reference 25. g Measured in cyclohexane solution at 1.0 10 6 M. h The amplitude in the parentheses. i χ2: DSs of 1 (1.213), 5 (0.736), 6 (1.116), 7 (1.098), 8 (1.098), 9 (0.995); F-ICs of 1 (1.313), 5 (1.075), 6 (1.344), 7 (1.456), 8 (1.249), 9 (1.172); NCs of 1 (1.117), 5 (1.171), 6 (1.171), 8 (1.173), 9 (1.277). f
states, even in the densely aligned F-states. The present study can contribute to the development of efficient fluorescent solid materials.
’ EXPERIMENTAL SECTION Preparation of ICs. A mixture of DCM (1 equiv), a dye (23 equiv), and an organic solvent (chloroform, dichloromethane, ethyl acetate, acetone, or acetonitrile) was heated to dissolve the dye in the solvent. Subsequently, a minimal amount of methanol was added with heating to dissolve DCM. The mixture was then left at room temperature until crystalline material precipitated. The mixture was filtered, and the resulting precipitate was washed with dichloromethane, yielding the crystal including dye. The ratio of dye contained in the crystal depended on which organic solvent was applied. A F-IC was obtained from the acetonitrile solution, while a I-IC was from the dichloromethane solution, as described before. X-ray Diffraction Analysis. X-ray diffraction data of DCA/AcN, DCA/Naph, DCM/AcN, and DCM/Naph were collected on a Rigaku R-AXIS RAPID diffractometer with a 2-D area detector using graphitemonochromatized Cu Kα radiation (λ = 1.54187 Å). Direct methods (SIR-2004)29 were used for the structure solution. All calculations were performed with the observed reflections [I > 2σ(I)] by the program CrystalStructure crystallographic software packages30 except for refinement, which was performed using SHELXL-97.31 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. PXRD data were collected on a Rigaku RINT-2000 using graphite-monochromatized Cu Kα radiation (λ = 1.54187 Å) at room temperature. Solid-State Fluorescence Spectroscopy and Quantum Yield Determination. Fluorescence and excitation spectra measurements and fluorescence quantum yield determination were performed by using a FP-6500 spectrofluorometer (JASCO) with an ISF-513
fluorescence integrate sphere unit (JASCO). Samples for fluorescence quantum yield determination were sealed into a handmade quartz cell under N2 gas and subjected to the measurements. Fluorescence decay time and lifetime were obtained using HORIBA FluoroCube and the software (Data Station v.2.4 and DAS 6) equipped in the apparatus.
’ ASSOCIATED CONTENT
bS
Supporting Information. Crystallographic information files (CIFs) of the DCM and DCA inclusion crystals, and fluorescence decay curves of ICs, DSs, and NCs of 1, 5, 6, 7, 8, and 9. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Tel./fax: +81-6-6879-7406. E-mail:
[email protected]. jp (I.H.);
[email protected] (M.M.).
’ ACKNOWLEDGMENT This work was partially supported by KAKENHI (22651042, 21245035, 22685014, and 22108517). We thank Dr. K. Miura and Dr. S. Baba (JASRI) for their helpful discussion. N.T. thanks JST for financial support. ’ REFERENCES (1) McDermott, G.; Prince, S. M.; Freer, A. A.; HawthornthwaiteLawless, A. M.; Papiz, M. Z.; Cogdell, R. J.; Isaacs, N. W. Nature 2002, 374, 517–521. (2) Encyclopedia of Supramolecular Chemistry; Atwood, J. L., Steed, J. W., Eds.; Marcel Dekker: New York, 2004; Vols. 12. 4658
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