Directed Organization of Dye Aggregates in Hydrogen-Bonded Host

Directed Organization of Dye Aggregates in Hydrogen-Bonded Host Frameworks Airon C. Soegiarto and Michael D. Ward* Department of Chemistry and the Molecular Design Institute, New York UniVersity, 100 Washington Square East, New York, New York 10003-6688

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 8 3803–3815

ReceiVed May 28, 2009

ABSTRACT: Organic laser dyes coumarin 1, coumarin 2, coumarin 102, coumarin 314, and coumarin 334 have been included in crystalline guanidinium organodisulfonate (GDS) host frameworks, forming stable inclusion compounds with lamellar architectures. The GDS hosts consist of 2D quasihexagonal hydrogen-bonded sheets with topologically complementary guanidinium (G) ions and the sulfonate (S) moieties of a variety of organodisulfonates that serve as “pillars” that connect opposing GS sheets, thus generating inclusion cavities between the sheets. These host frameworks display a variety of architectural isomers, including the so-called bilayer, simple brick, zigzag brick as well as two heretofore unreported framework isomers: double zigzag brick and a “chevron” brick. These isomers vary with respect to the connectivity between opposing GS sheets and the corresponding shape of the inclusion cavities. The preference for the framework isomers reflects a systematic templating role for the guest molecules, largely based on their steric requirements. The coumarin guests exhibit a distinct arrangement in each host-guest combination, resulting in a range of fluorescence emission wavelengths that differ from that observed for the monomeric form in dilute solutions. For example, the bilayer framework, which has narrow 1D pores, enforces the alignment of coumarin guests as head-to-tail arrays resembling J-aggregates. The simple brick structure, however, has wider 1D channels that permit the formation of linear arrays of face-to-face coumarin dimers resembling H-aggregates. The coumarin guests in the zigzag brick architecture are confined within isolated inclusion cavities as face-to-face dimers. In general, the maxima of the emission bands of the coumarin dyes in the bilayer structure are blue-shifted, while those in the simple brick and zigzag brick structures are red-shifted. The fluorescence reflects the unique guest-guest packing in each framework isomer as well as interactions between the coumarin guest and the organodisulfonate pillar. The ability to include laser dyes in high concentrations in a robust host framework with regulation of intermolecular association between the dye molecules may lead to new solid-state lasing materials that overcome some of the barriers encountered for dyes embedded as dilute solutes in amorphous solid-state matrices such as polymers, zeolites, and sol-gel glasses. Introduction The properties of molecular crystals are governed by the attributes of their molecular constituents and their solid-state arrangements, making control of crystal packing paramount when designing new materials with targeted functions. Computational methods for complete crystal structure predictionsincluding space group, lattice parameters, and atomic positionsscontinue to improve, but the lattice energy of different calculated forms of the same compound can differ by as little as a few kJ mol-1, making an unambiguous assignment of the lowest energy structure difficult.1-3 This has prompted the development of empirical guidelines for steering molecular assembly into prescribed crystal architectures based on well-defined structure-directing interactions, such as hydrogen bonding or metal coordination, which can override the cumulative effect of the multitude of weaker forces, such as van der Waals interactions. In this manner, solid-state architectures often can be anticipated from the symmetry of the molecular building blocks and the propagation of bonding between the structure-directing groups. Although empirical guidelines rarely lead to complete and precise structure prediction, architectures based on supramolecular networks that are robust toward the introduction of ancillary groups can permit systematic and rational manipulation of solid-state structure.4-13 An alternative strategy invokes the use of structurally robust host frameworks capable of including functional guest molecules in well-defined inclusion cavities, thus decoupling the design of structure, provided by the host framework, from function, introduced by the guest molecules. Such an approach promises * To whom correspondence should be addressed. E-mail: [email protected].

to simplify the design and synthesis of materials based on molecular crystals. Indeed, crystalline inclusion compounds14 have long been recognized as an approach to materials for optoelectronics15-17 and magnetics,18 storage of sensitive compounds,19 and chemical reactions under confinement.20 Consequently, many strategies for the synthesis of organic host frameworks have been explored.21 Most host frameworks, however, are limited with respect to accommodating guest molecules with wide-ranging sizes and shapes.22 Furthermore, structural modification of a particular host to adjust cavity size and shape usually results in unexpected changes in crystal architecture, often with loss of inclusion properties.23 As such, systematic control of these features can be challenging. These obstacles can be overcome with a host system in which the molecular components are assembled through strong, yet flexible, interactions that produce structurally persistent building blocks, thereby allowing interchange of components while still retaining the general structural features and supramolecular connectivity of the host lattice. Our laboratory has demonstrated that host frameworks consisting of guanidinium cations (G, [C(NH2)3]+) and various organomonosulfonates (MS ) R-SO3-, R ) aryl) or organodisulfonates (DS ) -O3S-R-SO3-, R ) aryl, alkyl) display an extraordinary capacity for the inclusion of guest of various shapes and sizes.13,16,24-26 The 3-fold symmetry and hydrogen-bonding complementarity of the G ions and the sulfonate moieties (S) prompt the formation of a two-dimensional (2D) quasihexagonal charge-assisted hydrogen-bonding network (Scheme 1),27-29 which has proven remarkably robust toward the introduction of various organic pendant groups attached to the sulfonate moieties. Occasionally, the GS sheet adopts a “shifted

10.1021/cg900578u CCC: $40.75  2009 American Chemical Society Published on Web 07/13/2009

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Soegiarto and Ward Scheme 1

ribbon” motif with either disruption of one of the six hydrogen bonds or retention of six hydrogen bonds, but with two of the hydrogen bonds weaker than in the quasihexagonal motif. The resilience of the GS network simplifies crystal design and synthesis by constraining the crystal packing in two dimensions so that the remaining third dimension can be engineered reliably through the introduction of interchangeable organosulfonate groups,30 which enforce inclusion cavities in the gallery regions between adjacent GS sheets.31 The peculiar reliability of the GS network has permitted control of crystal symmetry and lattice metrics, as well as the regulation of properties (e.g., second harmonic generation) through interchangeable guest molecules.16 Notably, the organodisulfonate pillars can extend from either side of the GS sheet producing different connectivities in the third dimension, forming either “bilayer” or “brick” architectures. In the bilayer form, the pillars project from the same side of each sheet, forming discrete bilamellae along the third dimension. The brick architectures, however, are continuous in 3D because pillars project from both sides of each GS sheet connecting adjacent sheets. The numerous possible intersheet connectivities in the third dimension, which are governed by the pattern of up/down projections of the pillars from the GS sheets (i.e., their “projection topologies”), are revealed by previously observed continuous framework isomers, including simple brick, zigzag brick, double brick, and V-brick (Scheme 2).32 Some of the brick frameworks exhibit a natural compliance due to puckering of the GS sheet about a hydrogen bond “hinge” joining adjacent hydrogenbonded ribbons, which permits the framework to “shrink-wrap” about guest molecules. Collectively, the interchangeability of the pillars, framework softness, and architectural isomerism allows the formation of inclusion cavities with a variety of sizes, heights, shapes, and chemical environments, permitting inclusion of a wide range of guests while enabling systematic design of inclusion compounds. Notably, the guests play an important role as templates that direct the assembly of the host frameworks toward architectures that are unique for a given host-guest combination, largely based on the steric requirements of the guest and the achievable size of the inclusion cavity.24,33 Our laboratory has demonstrated that that GS hosts can include dye molecules with peculiar motifs regulated by choice of the organodisulfonate pillar. Acentric chromophores formed polar arrays in an inherently centrosymmetric GS host through cooperative host-guest interactions.34 Inclusion compounds based on inherently polar GS frameworks that guided the assembly of polar arrays of guest molecules in one-dimensional channels exhibited second harmonic generation activity that scaled with the molecular hyperpolarizability of the guest molecules.16 Pyrene and perylene dye molecules have been included as either monomers or dimers through judicious

Scheme 2

selection of the pillar in the GS framework, and sulfonated dyes have been incorporated directly into the GS sheet.35 This unique ability to regulate aggregation state prompted us to examine whether functional dyes with more complex shapes and greater steric demands could be included in GS host frameworks, specifically coumarin dyes, which have been used for the fabrication of lasing materials. Coumarin derivatives are among the most frequently used lasing dyes due to their high quantum yield of fluorescence, absorption and emission in the near UV-visible 300-600 nm range, and good lasing properties.36-38 Laser performance, however, is adversely affected by aggregation, which leads to excited state quenching. Although aggregation and quenching can be circumvented by the use of dilute solutions (∼10-5 M),39,40 this approach can be impractical due to the need for bulky reservoirs and poor overall efficiency. Solid-state dye lasers have been fabricated by dispersing organic laser dyes in solid-state hosts such as clays,41 zeolites,42 polymers,43 sol-gel glasses,44 and nonporous crystals45 such as potassium dihydrogen phosphate and potassium sulfate. These materials promise miniaturization, reduced operating costs, and in some cases, improved photostability of the dyes.46-48 The operable dye concentration in these hosts, however, typically must be less than 10-2 M in order to minimize aggregation and any associated quenching.49 The ability to control the architecture of the GDS host frameworks through the proper combina-

Directed Organization of Dye Aggregates Scheme 3

tion of guest and organodisulfonate pillar presents an opportunity to regulate the aggregation state of included dye guests while attaining reasonably high solid-state concentrations (∼ 0.5 M). We describe herein a series of inclusion compounds, based on a variety of GDS host frameworks and coumarin guests, which illustrate the synergistic roles of pillar and guest size in determining framework architecture and the role of architecture on guest aggregation, which in turn affects the dye-based fluorescence from the inclusion compounds. Furthermore, the complex shapes of the coumarin guests produce two heretofore undiscovered frameworkssdouble zigzag brick and chevron bricksthat add to an already diverse set, further demonstrating the structural versatility of the GDS hosts. Results and Discussion Molecular Libraries and Inclusion Compound Synthesis. More than 200 examples of GDS inclusion compounds based on various combinations of arenedisulfonate or alkanedisulfonate pillars and molecular guests have amply demonstrated the structural versatility of this class of materials.16,24,26,29-31,33-35 The single crystal structures of these compounds have revealed that the inclusion cavity heights are governed largely by the length of the pillars, while the dimensionality and volumes of the individual inclusion cavities are governed by the framework architecture and steric character of the pillar. The framework architecture is sensitive to the particular combination of pillar and guest, with the latter serving as a template for the architecture that best accommodates its steric demands. Coumarin dyes differ substantially from the many guests that have been incorporated in GDS inclusion compounds thus far, particularly with respect to their relatively complex shape and large size, offering an opportunity to explore further the versatility of the GDS hosts while introducing functional properties in a wellbehaved host system. Furthermore, the tertiary amines can behave as hydrogen bond acceptor sites, thus testing the robustness of the GS sheet toward competitive hydrogenbonding groups.27-29,31 The inclusion capacity of the GDS frameworks for coumarin dyes was explored using a library of pillars, with lengths ranging from 8.5 Å to 14.6 Å (as measured by the separation between distal sulfur atoms), and five coumarin derivatives (Scheme 3). Of a total of 45 possible host-guest combinations based on this library, seventeen inclusion compounds were formed, seven with coumarin 1, one with coumarin 2, five with coumarin 102, two with coumarin 314, and two with coumarin 334. This trend suggests a decreasing proclivity for inclusion with increasing guest size. MoreoVer, inspection of Table 1 reveals that the framework architectures, for a given guest, systematically change from zigzag brick to simple brick to bilayer with increasing pillar height. The ODS and BBDS pillars are unique

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in that they form guest-free crystalline compounds. The crystal structure of G2ODS has been reported previously,35 and G2BBDS is reported here (Table 3). The coumarin inclusion compounds were prepared by slow evaporation of methanol solutions saturated with the selected GDS host and the coumarin dye. The inclusion compounds formed a variety of crystal habits; most were blocklike, but some formed plates and needles. Architectural Isomerism and Guest Packing. The GDS host with the longest pillarsazobenzene-4,4′-disulfonate (ABDS)sincludes coumarin 1 (C1) in the discrete bilayer architecture, with the stoichiometry G2ABDS · (1/2)(C1) (1a) (Figure 1). The host framework exhibits a “shifted ribbon” (Scheme 1) rather than the quasihexagonal GS sheet motif in which neighboring GS ribbons are shifted with respect to the ideal quasihexagonal arrangement by as much as a1/2, such that they are connected by one strong (G)N-H · · · O(S) H bond (dO · · · H ≈ 2.0 Å) and one weaker one (dO · · · H ≈ 2.5 Å). The shifted ribbon motif has been observed in roughly one-half of the bilayer inclusion compounds observed to date. This suggests that the effective loss of one hydrogen bond is compensated by favorable host-guest packing achieved due to the different configuration of the pillars in this motif.50 The shifted ribbon motif produces a near-rectangular pillar distribution on the GS sheet, in contrast to the trigonal arrangement of the quasihexagonal motif. Nonetheless, the configuration of the pillars on the GS sheet can be represented by “projection topology” maps using a hexagonal grid, with filled and unfilled circles signifying “up” and “down” projections, respectively (Figure 2). Although portrayed on a hexagonal grid, these maps adequately describe the projection topologies for the shifted-ribbon motifs. The pillars project from the same side of each sheet, spanning the gallery region between opposing GS sheets and forming one-dimensional channels coinciding with the crystallographic a-axis (perpendicular to the ribbon direction) and flanked by dense-packed walls of ABDS pillars. These channels are occupied by the C1 guest molecules, with each C1 guest spanning two ribbons along the a-axis. The average nominal width of a GS ribbon is 6.5 Å in the quasihexagonal motif, based on hundreds of GDS and GMS structures characterized in our laboratory. An analysis of numerous structures with the shifted ribbon motif, however, reveals an effective ribbon width of 6.2 Å due to the change in the geometry of the inter-ribbon hydrogen bonds. Consequently, a C1 guest, with a long axis measuring lg ) 11.7 Å (accounting for van der Waals radii), comfortably traverses two adjacent ribbons, which combined impose a length of 12.4 Å along the channel perpendicular to the ribbons (Scheme 1). The channel width (7.23 Å) is determined by the distance between nearest sulfonate groups in the major ribbon. Although disorder of the C1 guests precluded their refinement, the narrow width of the channels (∼3.5 Å after accounting for the van der Waals radii of the ABDS pillars), the host:guest stoichiometry (determined by 1H NMR), the inclusion cavity volume in the bilayer framework (Vinc ) 324 Å3; Table 1), and the guest volume per inclusion cavity (nVg ) 119 Å3) support a single-file head-to-tail array of C1 guests along the channel. The bilayer architecture also was observed for G2ABDS · (1/2)(C314) (2), G2ABDS · (3/4)(C102) (3),51 G2ABDS · (1/2)(C334) (4), and G2AQDS · (C2) (5). The guests in compound 5 are ordered, which allows confirmation of the head-to-tail ordering within single-file guest arrays coinciding with the channel (Figure 3). Whereas the long axes of the guests in compounds 1a-4 coincide with the channel directions and are parallel to the GS sheet, the long axes of the guests in compound 5 are nearly perpendicular to the GS sheets, while

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Table 1. Structural Features for GS Inclusion Compounds with the General Formula GDS · n(guest) guest

host

compound #

framework architecture

lS-S(Å)a

n

nVg(Å3)

Vpillar(Å3)b

Vinc(Å3)b

Vcell(Å3)b

coumarin 1 Vg ) 238 Å3 lg ) 11.7 Åg hg ) 8.1 Åg

G2NDS G2ADS G2BPDS G2ODS G2BBDS G2SBDS G2ABDS G2ABDS G2BPDS G2ADS G2ODS G2ABDS G2BSPE G2BBDS G2ABDS

16 10 12 8 6 7f 1b 1af 13 11 9 3c,f 17d 14 2f

double zigzag brick zigzag brick simple brick simple brick simple brick simple brick simple brick bilayer zigzag brick zigzag brick simple brick bilayer chevron brick zigzag brick bilayer

8.5 10.8 10.6 11.9 12.7 12.8 12.5 12.5 10.6 10.8 11.9 12.5 N/A 12.7 12.5

4/3 2 2 2 2 2 2 1/2 2 2 2 3/4 1 2 1/2

317 476 476 476 476 476 476 119 504 504 504 189 291e 600 150

136 185 166 148 200 196 188 188 166 185 148 188 198 200 188

869 782 768 795 824 834 812 324 790 793 801 372 516 945 316

1335 1136 1105 1121 1190 1194 1168 703 1128 1145 1130 750 914 1313 697

G2BBDS G2ABDS

15f 4f

zigzag brick bilayer

12.7 12.7

2 1/2

546 136

200 188

932 321

1298 700

G2AQDS

5

bilayer

10.9

1

223

198

388

768

coumarin 102 Vg ) 252 Å3 lg ) 11.2 Åg hg ) 8.6 Åg coumarin 314 Vg ) 300 Å3 lg ) 14.4 Åg hg ) 8.3 Åg coumarin 334 Vg ) 273 Å3 lg ) 12.7 Åg hg ) 8.3 Åg coumarin 2 Vg ) 223 Å3 lg ) 11.9 Åg hg ) 7.8 Åg

a lS-S describes the intramolecular separation between distal sulfur atoms in each pillar. b The volumes of the guest molecules and pillars, Vg and Vpillar, respectively, were determined with a Connolly (van der Waals) surface using a probe radius of zero and ultrafine grid spacing, in the Accelrys Materials Studio v.4.2 modeling suite. These values Vpillar exclude the volume of the sulfonate groups, which combined would contribute 95 Å3 (average). The volumes tend to be systematically lower, by up to ca. 6%, than those determined by traditional means (see Kitaigorodski, A. I. Molecular Crystals and Molecules; Academic Press: New York, 1973; pp 18-21). The volume of each inclusion cavity, Vinc, was determined with a Connolly surface using probe radius ) 0.5 Å and an ultrafine grid spacing, after removal of guests and normalizing to one host formula unit. Vcell values are unit cell volumes normalized to one host formula unit. c The single crystal structures of these compounds could not be refined to R1 < 15%, but the assignment of the architecture is definitive and the host:guest ratio is determined by 1H NMR. d The chevron brick architecture differs from other entries in the table as the molecule bends such that the two sulfonate groups are incorporated into the same GS sheet. Consequently, the value of lS-S, normally calculated for the fully extended molecule, is not meaningful here. e nVguest includes one equivalent of methanol solvate 39 Å3. f Large crystals of these compounds occasionally grew as twins. g Values account for van der Waals radii.

Figure 1. The bilayer frameworks in (A) G2ABDS · (1/2)(C1) (1a) as viewed along the a-axis. The GS ribbons run parallel to the b-axis, such that the inclusion channels run parallel to the a-axis and perpendicular to the ribbons. (B) G2ABDS · (1/2)(C314) (2) as viewed along the a-axis. The GS ribbons run parallel to the b-axis, such that the inclusion channels run parallel to the a-axis and perpendicular to the ribbons. The ABDS pillars in 1a and 2 are tilted with respect to normal by φ ) 6.9° and 10.4° respectively. The disordered coumarin guests in both bilayer frameworks have been removed for clarity.

slightly tilted to accommodate the 11.9 Å length of the guest. Furthermore, slight buckling of the GS sheet, turnstile rotations of the pillars about the C-S bonds, and tilting of the pillars with respect to the mean plane of the GS sheets (defined by a tilt angle φ between the pillar axis and a normal to the GS sheets) assist in the packing of the pillars and guests (Figure 1 and 3). Increasing values of φ (i.e., greater tilt) would be expected to result in decreasing bilayer heights and decreasing

Figure 2. Top-view representations of the projection topologies of the organodisulfonate pillars on each individual GS sheet in various GDS hosts. Filled and open circles depict pillars projecting above and below the sheet, respectively. The “up” pillars connect to the adjacent GS sheet above the plane of the page, and the “down” pillars connect to the adjacent GS sheet below the plane of the page. The guanidinium ions reside on the undecorated nodes of the quasihexagonal tiling.

inclusion cavity volumes. The values of φ typically reflect the steric demands of the included guests (i.e., for a given pillar, smaller guests typically afford larger φ values). Surprisingly, the φ values for 1a, 2, and 4, all based on the ABDS pillar, increased with increasing guest height, contrary to expectations (C1, φ ) 6.9°, hg ) 8.1 Å, Vg ) 238 Å3; C334, φ ) 7.8°, hg

Directed Organization of Dye Aggregates

Figure 3. The bilayer framework in G2AQDS · (C2) (5): (top) As viewed nearly along the [11j0] channel direction. The host is rendered as ball-and-stick and the guest as spacefilling. (bottom) Top view of the pillar-guest packing as viewed along the c-axis. The guanidinium ions and the sulfonate oxygen atoms in the GS sheet have been removed. The sulfonate sulfur atoms are labeled “S”. The pillar carbon atoms are depicted as violet.

) 8.3 Å, Vg ) 273 Å3; C314, φ ) 10.4°, hg ) 8.3 Å, Vg ) 300 Å3), suggesting peculiar effects of guest shape on framework structure. Examination of the more than 200 GDS inclusion compounds synthesized in our laboratory reveals, for a particular guest, a preference for the more open brick frameworks as the pillar length is decreased. This can be attributed to the larger attainable inclusion cavities in the brick frameworks. Occasionally, however, guests that would be expected to fit comfortably within the bilayer framework can template a brick form. This can occur when the inclusion of multiple guest molecules is favored by the formation of stable guest aggregate motifs in the solid state, thus requiring the larger overall inclusion volume of the brick forms. Furthermore, the brick framework is inherently more “compliant” than the bilayer owing to the ability of the GS sheet to pucker, which permits the framework to “shrink-wrap” more easily about guests that otherwise appear suitable for inclusion by the bilayer framework. These attributes of the brick frameworks appear to be evident from a comparison of compounds G2ABDS · (1/2)(C1) (1a), G2ABDS · 2(C1) (1b), G2BBDS · 2(C1) (6; BBDS ) bibenzyl-4,4′-disulfonate), and G2SBDS · 2(C1) (7; SBDS ) trans-stilbene-4,4′-disulfonate). Whereas 1a crystallizes in bilayer framework, 6 and 7, with only slightly longer pillars, adopt simple brick architectures with highly puckered GS sheets (θIR(6) ) 100.7°; θIR(7) ) 107.1°). The substantial puckering in 6 (Figure 4) and 7 reflects the small size of these guests and suggests that their corresponding bilayer frameworks are at the threshold of stability, most likely due to inefficient packing within the rigid bilayer framework for 6 and 7, which would have larger gallery heights compared with 1a. Interestingly, C1 guests in G2ABDS host also can adopt the simple brick framework (1b) in addition to the bilayer, albeit with a different host:guest stoichiometry. In 1b, the GS sheets


Figure 4. Simple brick G2BBDS · 2(C1) (6): (top) As viewed along the channel (a-axis). The host is rendered as ball-and-stick and the guest as spacefilling. (bottom) Top view of the pillar-guest packing as viewed along the b-axis. The guanidinium ions and the sulfonate oxygen atoms in the GS sheet have been removed. The sulfonate sulfur atoms are labeled “S”. The pillar carbon atoms are depicted as violet.

are less puckered than 6 and 7, with θIR ) 134.4°, reflecting the need to accommodate the C1 guests within the inclusion cavity of the shorter ABDS pillar. Unlike 1a, the C1 guests in the brick frameworks of 1b, 6, and 7 form linear arrays of dimers confined within one-dimensional channels of a highly puckered framework that permits dense packing. In this case, the guests are nestled within the canopies of the highly puckered sheets, which allows their long axes to orient perpendicular to the mean plane of the GS sheets. Notably, the host:guest stoichiometry is 1:0.5 for compound 1a, but 1:2 for compounds 1b, 6, and 7, reflecting the larger inclusion cavity volume overall of the brick frameworks. The observation of stoichiometric inclusion in compounds 1b, 6, and 7 reflects the ability of the simple brick frameworks to form commensurate inclusion compounds because of their inherent conformational softness, which may not be possible for C1 in the less compliant bilayer form. Compounds 6 and 7 appear to be exceptions to a general rule in which the selectivity for the bilayer and simple brick isomers are governed simply by the relative sizes of the pillar and guest;35 that is, a long pillar-small guest combination will adopt the bilayer architecture whereas a short pillar-large guest will adopt the simple brick framework. This trend is exemplified in the inclusion compounds of guanidinium octane-1,8-disulfonate, G2ODS · 2(C1) (8) and G2ODS · 2(C102) (9), which form simple brick architectures (Figure 5) rather than the bilayer observed for these same guests in G2ABDS (lS · · · SODS ) 11.9 Å; lS · · · SABDS ) 12.5 Å). Although the volume of the ODS pillar is less than that of the ABDS pillar, which presumably would favor the bilayer framework, it would appear that the smaller pillar length reduces the separation between opposing GS sheets to the extent that the C1 and C102 guests cannot fit in the bilayer

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Figure 6. Schematic top views of the gallery regions in the simple brick hosts for three different rotations of the pillars, depicted as gray ellipses: (a) Molecular planes of the pillars are aligned along b1 and orthogonal to the ribbon direction, producing 1-D channels, flanked by the pillars, of width a1. (b) Molecular planes of the pillars are aligned along a1 and parallel to the ribbon direction, producing 1-D channels, flanked by the pillars, of width b1. (c) The pillar rotation is intermediate between (a) and (b), generating a 2-D continuous guest network in which guests can surround the pillars.

Figure 5. (A) Simple brick G2ODS · 2(C1) (8): (left) As viewed along the major channel direction (a-axis). The host is rendered as ball-andstick and the guest as spacefilling. (right) Top view of the pillar-guest packing as viewed along the b-axis. The guanidinium ions and the sulfonate oxygen atoms in the GS sheet have been removed. The sulfonate sulfur atoms are labeled “S”. The pillar carbon atoms are depicted as violet. (B) Simple brick G2ODS · 2(C102) (9): (left) As viewed along the channel direction (a-axis). (right) Top view of the pillar-guest packing as viewed along the b-axis.

gallery. The 1:2 host:guest stoichiometry observed for 8 and 9 is identical to that of compounds 6 and 7, but the GS sheets are less puckered, with θIR ) 106.51° and 124.87°, respectively. The smaller degree of puckering reflects the need for the host with the shorter ODS pillar to accommodate the guests by increasing the size of the individual inclusion cavities. The maximum inclusion cavity (Vincmax) available in a simple brick host with a given pillar could be determined based on the dependence of Vinc on θIR, lS · · · S, and the intrinsic molecular volume of the host (Vincmax is achieved at θIR ∼ 130°).24 The conformationally flexible ODS pillar also adopts an all anti pillar conformation, which maximizes the inclusion cavity volume. In contrast, guest-free G2ODS forms zigzag brick architecture in which the pillar adopts a gauche-(anti)5-gauche conformation that collapses the gallery region between the GS sheets.35 Whereas GS sheet puckering in these brick frameworks principally influences the inclusion cavity volume and the number of accompanying guests, pillar rotation governs the dimensionality of inclusion cavities (Figure 6). One-dimensional channels with widths equal to a1 (minus the van der Waals width), flanked by a solid wall of pillars, run along b1 if the molecular planes of the pillars are orthogonal to the ribbon direction (coinciding with a1 in Scheme 1). Conversely, the gallery region contains 1-D channels with widths equal to b1 (minus the van der Waals width of the pillars), flanked by a solid wall of pillars, if the molecular planes of the pillars are parallel to the ribbon direction, as in 9. Intermediate degrees of pillar rotation, as observed in 6, 7, and 8, afford 2-D continuous inclusion cavities within the galleries that can be described as two intersecting 1-D channels, a “minor” channel with width a1 and a wider “major” channel with width b1. These conformers differ substantially with respect to the shape and size of the individual cavities. Regardless, the simple brick framework

always produces a wider channel compared to the bilayer framework. The width of the 1-D channel in 9 and the width of the “major” channels in 6, 7, and 8 are governed by the lattice parameter, b1, which depends on θIR (b1 ) 13.0 sin(θIR/2) Å). In contrast, the width of the 1-D channels in the bilayer framework is governed by the lattice constant within the GS ribbon, a1 (7.5 ( 0.2 Å). The wider channels enable the C1 and C102 guests in 6, 7, 8, and 9 to form a “chain” of faceto-face dimers along the channel. The interplanar separations within each dimer range from 3.40 Å to 3.45 Å. The coumarin molecules in each dimer in 6, 7 and 8 are related by inversion, as warranted by their centrosymmetric space group. In 9, however, the average molecular planes of the C102 molecules in each dimer are not parallel to one another, exhibiting a small dihedral angle of 2.80°. The molecules within the dimer are not related by inversion, and compound 9 crystallizes in the polar space group P21. Furthermore, the carbonyl oxygen on the C102 guest forms (G)N-H · · · O(C102) hydrogen bonds with the guanidinium ion, disrupting the GS sheet and producing a shifted-ribbon motif. The coumarin guests in compounds 6-9 are oriented with their long axes nearly parallel to the pillar axes, which can be attributed to the comparable length of the guests and their respective pillars. Consequently, the coumarin guests exhibit edge-to-face contacts with the molecular plane of the pillars. Inclusion compounds G2ADS · 2(C1) (10) and G2ADS · 2(C102) (11) exhibit the zigzag brick architecture instead of the simple brick framework observed for these guests with ODS, BBDS, and SBDS pillars. This shift in architecture reflects the inability of the shorter ADS pillar to accommodate these guests in the corresponding simple brick framework. Instead, the guests template the formation of the zigzag brick framework, which has discrete inclusion cavities, enclosed by four flanking ADS pillars, capable of including the C1 and C102 guests as face-to-face dimers. The interplanar separations of the C1 and C102 dimers in 10 and 11 are 4.9 Å and 3.7 Å, respectively. The coumarin molecules within each dimer are related by inversion, and 10 and 11 crystallize in the centrosymmetric orthorhombic space group Pbca. The coumarin guests are oriented with their long axes nearly parallel with the long axes of the pillars, which can be attributed to the similar lengths of the guests and pillars. The dimers exhibit edge-to-face contacts with the molecular planes of the ADS pillars and with coumarin dimers in neighboring inclusion cavities (Figure 7). The steric origins of architectural isomerism also are evident in G2BPDS (BPDS ) biphenyl-4,4′-disulfonate) and G2BBDS


Figure 7. (A) Zigzag brick G2ADS · 2(C1) (10): (left) As viewed along the b-axis. The host is rendered as ball-and-stick and the guest as spacefilling. (right) Top view of the pillar-guest packing as viewed along the c-axis. The guanidinium ions and the sulfonate oxygen atoms in the GS sheet have been removed. The sulfonate sulfur atoms are labeled “S”. The pillar carbon atoms are depicted as violet. (B) Zigzag brick G2ADS · 2(C102) (11): (left) As viewed along the b-axis. (right) Top view of the pillar-guest packing as viewed along the c-axis.

Figure 8. (A) Simple brick G2BPDS · 2(C1) (12) as viewed along the channel direction (b-axis). (B) Zigzag brick G2BPDS · 2(C102) (13) as viewed along the c-axis. (C) Zigzag brick G2BBDS · 2(C314) (14) as viewed along the a-axis. (D) Zigzag brick G2BBDS · 2(C334) (15) as viewed along the c-axis. The host is rendered as ball-and-stick and the guest as spacefilling.

inclusion compounds (Figure 8). In G2BPDS · 2(C1) (12), the C1 guests (Vg ) 238 Å3) template the simple brick architecture, with Vinc ) 768 Å3. The bulkier C102 guests (Vg ) 252 Å3) in G2BPDS · 2(C102) (13), however, template the zigzag brick


Figure 9. Double zigzag brick G2NDS · (4/3)(C1) (16): (top) As viewed along the b-axis. The host is rendered as ball-and-stick and the guest as spacefilling. (bottom) Top view of the pillar-guest packing as viewed along the c-axis. Two uniquely sized and shaped inclusion cavities in this architecture are depicted by the red and blue outlines. The guanidinium ions and the sulfonate oxygen atoms in the GS sheet have been removed. The sulfonate sulfur atoms are labeled “S”. The pillar carbon atoms are depicted as violet.

structure, with a larger Vinc ) 790 Å3. Similarly, C314 (Vg ) 300 Å3) in G2BBDS · 2(C314) (14) and C334 (Vg ) 273 Å3) in G2BBDS · 2(C334) (15) template the zigzag brick architectures with inclusion cavity volumes at Vinc14 ) 945 Å3 and Vinc15 ) 932 Å3, whereas the smaller C1 guest templates the simple brick architecture in 6, with Vinc ) 824 Å3. The general trends observed above for guest templating of the zigzag G2BPDS and G2BBDS hosts reveal a size threshold beyond which guests cannot be accommodated within the simple brick form in a given pillar, thus promoting the formation of the zigzag brick framework. This simple brick-zigzag brick isomerism has been observed previously in other GDS inclusion compounds.35 The simple and zigzag brick isomers differ only with respect to the connectivity between the sheets such that the total volume occupied by the pillars (i.e., the volume of the hosts) between the GS sheets is identical for these isomers. Consequently, for a given pillar, both architectures possess the same overall inclusion cavity volume for a flat GS sheet, although the size and shape of the individual cavities are different. The egg-carton puckering of the zigzag brick frameworks also increases the volume of each inclusion cavity beyond the value that can be realized with a flat sheet, although this architecture is more rigid compared with the simple brick form because of the absence of a 1-D hydrogen bonding “hinge”. In principle, the infinite 2-D character of the GS sheet allows an indefinite number of projection topologies and, therefore, an unlimited number of possible continuous brick-like framework isomers, each with a unique inclusion cavity shape. Indeed, G2NDS · (4/3)(C1) (16), with the shortest pillar in the library used here, exhibits a “double zigzag architecture”, with a topology that has been predicted35 but not heretofore observed (Figure 2 and 9). This architecture exhibits a projection topology in which the pillars on adjacent ribbons orient... up, up, down, up, up, down ... and... down, down, up, down, down, up ... across the GS sheet (overall the number of pillars projecting from opposing sides of the sheet is identical). Like the zigzag brick

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Soegiarto and Ward Table 2. Absorption and Emission νmax for the Inclusion Compounds

compound (no.) G2ABDS · (1/2)(C1) (1a) G2ABDS · (3/4)(C102) (3) G2BBDS · 2(C1) (6) G2SBDS · 2(C1) (7) G2ODS · 2(C1) (8) G2ODS · 2(C102) (9) G2ADS · 2(C1) (10) G2ADS · 2(C102) (11) G2BPDS · 2(C1) (12) G2BPDS · 2(C102) (13) G2NDS · (4/3)(C1) (16) C1 (10-5 M in methanol) C102 (10-5 M in methanol)

Figure 10. Chevron brick G2BSPE · (C102) · (methanol) (17): (left) As viewed along the a-axis. The host is rendered as ball-and-stick and the guest as spacefilling. (right) The chevron brick framework with guests removed.

architecture, the double zigzag framework is rigid as puckering of the GS sheet is impossible. The double zigzag version, however, possesses two unique inclusion cavities between the adjacent GS sheets (Figure 9). One of the inclusion cavities is enclosed by six surrounding NDS pillars (“hexagonal” cavity) while the other is enclosed by four NDS pillars (“quadrilateral” cavity). The C1 guests are confined as centrosymmetric faceto-face dimers in both types of cavities, but the interplanar separation is 3.45 Å in the hexagonal cavity and 4.6 Å in the quadrilateral cavity. The long axes of the C1 guests are nearly orthogonal to the pillar axis of the NDS, which reflects the substantial difference in length of C1 (11.7 Å) and the NDS pillar (8.5 Å). Consequently, the C1 guest lies horizontally in the cavity rather than vertically. The C1 dimers exhibit a number of edge-to-face contacts with the surrounding NDS pillars as well as with the neighboring dimers in adjacent cavities. Architectural Isomers with Bent Pillars. The flexible pillar 1,2-bis(4-sulfophenoxy)ethane (BSPE) introduces conformational freedom that permits formation of a “chevron” brick framework observed for G2BSPE · (C102) · (methanol) (17), in which the sulfonate groups of each pillar are contained within the same GS sheet instead of within opposing sheets. Consequently, the projection topology for each sheet is identical to that of the double brick structure (Figure 10), but the sheets assemble in the third dimension through noncovalent interactions between the chevrons on opposing sheets rather than through covalent bridges. Although this configuration has the potential to create very wide channels along a1 (parallel to the GS ribbons), the molecular planes of the BSPE pillars block the channels along a1, instead forming “pockets” along b1 (orthogonal to the GS ribbons) due to the extensive puckering of the GS sheets. This puckering actually occurs about (G)N-H · · · O(S) hydrogen-bonding hinges between pairs of GS ribbons, producing two unique θIR values (97.07° and 132.17°). The C102 guests are confined by the pockets, precluding the formation of dimers to the extent that the guests are included as isolated monomers. Excitation and Emission Spectra of Embedded Coumarin Dyes. The inclusion compounds described here display a range of GDS framework architectures, each with a uniquely sized and shaped cavity that governs the organization of the coumarin dye guests, which is reflected by the color of the macroscopic crystals (Figure 11) and their corresponding absorption and emission spectra. The coumarin guests in the bilayer frameworks are arranged as head-to-tail arrays along

framework architecture bilayer bilayer simple brick simple brick simple brick simple brick zigzag brick zigzag brick simple brick zigzag brick double zigzag brick

λmax (nm)a absorption

emission

374 394 376 379 380 389 379 384 383 384 385 375 390

441 446 453 494 451 480 473 533 466 491 463 450 468

a See Figure S4 in the Supporting Information, for absorption and emission spectra.

Figure 11. Various crystal habits with Miller indices indicating the most prominent faces or axes, when assignable. Crystals shown grew to approximately 1 mm long.

1D inclusion channels, as face-to-face dimers in the wider 1D channels of the simple brick frameworks, as isolated faceto-face dimers in the zigzag brick frameworks, and as monomers in the chevron architecture. In all these cases, the coumarin guest aggregation is unlike that observed in single crystals of the pure guest (see Figure S3 in the Supporting Information), revealing the ability of the GDS frameworks to regulate the aggregation of dye molecules and enforce nonnative motifs. These various coumarin aggregation motifs, as well as an apparent role for host-guest interactions, are revealed in the reflectance absorption and fluorescence emission of the embedded C1 and C102 guests (Figure 12, Table 2). The absorption spectra of dye aggregates are usually very distinct from those of their corresponding monomeric forms. Blue (hypsochromic) shifts in the excitation (absorption) band are commonly observed for H-aggregates,52,53 in which the dye molecules are associated through π-π stacking of aromatic rings. Red (bathochromic) shifts in the absorption band are usually attributed to the formation of J-aggregates (J for Jelly, one of the first investigators of the phenomenon),54,55 in which arene moieties of the dye molecules are associated through edgeto-face or edge-to-edge (i.e., “head-to-tail”) contact. These spectral shifts have been explained in terms of molecular exciton coupling theory (i.e., coupling of transition moments of the constituent dye molecules),56 which is valid if the interaction between orbitals of constituent molecules is negligible.57 C102


Figure 12. The photoluminescence spectrum of (top) C1 and (bottom) C102 in various GDS host frameworks. The spectra of each coumarin dye in its crystalline form and dissolved in methanol (10-5 M) are provided for comparison. All intensity values are normalized.

guests embedded in simple brick (compound 9) and zigzag brick (11 and 13) frameworks pack as face-to-face H-aggregated dimers and exhibit the expected blue shifts in the absorption peak when compared with the monomeric form in dilute methanolic solution. C102 guests in the bilayer structure (3) pack as edge-to-edge J-aggregates, in a single file, and exhibit the expected red shift in the absorption peak. The absorption spectra of C1 aggregates in both the bilayer and brick structures, however, display the opposite behavior. For example, the absorption peaks of C1 J-aggregates in bilayer structure (1a) are blue-shifted as compared with its monomeric form, while those of C1 H-aggregates in brick structures (such as 7 and 10) are red-shifted. This apparently anomalous blue shift in compound 1a may reflect the face-to-face arrangement of the monomeric C1 guests with the aromatic organodisulfonate pillars in the bilayer framework. Although disorder of the C1 guests in bilayer compound 1a precludes direct assignment of this arrangement, the orientation of the pillars with respect to the inclusion channels and the width of the channels support a face-to-face host-guest motif, which may be expected to produce a blue shift like that observed in an H-aggregate. Conversely, the red shift in the excitation spectra for C1 guests in the brick frameworks, organized as face-to-face H-aggregates, may be due to edge-to-face J-aggregate-like contacts between coumarin dimers and the neighboring pillars (interplanar angles ranging from 20° to 90°). In the case of the zigzag brick or double zigzag brick architectures, edge-to-face contacts between dye dimers in adjacent cavities may contribute further to the observed red shift. Based on the aggregation structures of the coumarin guests and the molecular exciton theory, the emission spectra of the


embedded coumarin dyes are expected to show the same behavior as the excitation spectra; that is, blue shift for H-aggregates and red shift for J-aggregates. Instead, we observe here that the luminescence (emission) of the C1 and C102 guests included in the bilayer architecture (where the coumarin guests pack as J-aggregates) is blue-shifted relative to its monomeric form in dilute methanolic solution (Figure 12) and red-shifted in the simple brick, zigzag brick or double zigzag brick frameworks where the coumarin guests pack as H-aggregates. This is contrary to expectations, suggesting emission behavior that is influenced by the host and the particular arrangements of the coumarin guests with respect to the organodisulfonate pillars. Collectively, the trends in the absorption and emission spectra implicate interactions between the coumarin guests and organodisulfonate pillars. The shifts in fluorescence observed for the continuous brick frameworks vary substantially among the different hosts (Figure 12), exhibiting increasing red shifts with increasing π conjugation length of the organodisulfonate pillar. For example, the emission shift of C1 dimers in G2ODS host (consisting of an alkanedisulfonate pillar) is negligible compared with C1 monomer in methanol solution, but it is substantial (44 nm red shift) in G2SBDS · 2(C1). The origin of the shifts may be affected, however, by several other factors, including the overlap and intermolecular separation of the dye molecules within the dimers and between dimers in adjacent inclusion cavities in the zigzag brick frameworks. Moreover, the absorption and emission spectra of coumarin dyes are known to be sensitive to the polarity of their environment, as evidenced by solvatochromic effects observed for dilute monomer solutions. Coumarins typically exhibit red shifts with increasing solvent polarity, for example, λmax (emission) for C1 in solution increases in the order cyclohexane (393 nm) < benzene (410 nm) < acetonitrile (437 nm) < methanol (450 nm) < water (468 nm). This phenomenon occurs because of the large dipole moment change involved during S0 f S1 transition in coumarins and the subsequent lowering of the energy of the more strongly polarized excited state.58 Indeed, ab initio computations have revealed that the structure of the excited state of the coumarin dyes is the intramolecular charge transfer (ICT) electronic configuration of the ground state.59 The coumarin guests in the GS inclusion compounds, however, are confined by polar hydrogen-bonded sheets above and below the gallery region, but within the galleries by nonpolar pillars and other guests with moderate dipoles. The red shift with increasing π conjugation length of the pillars may be associated with a corresponding increase in polarizability,60 which would be expected to stabilize any increased charge separation during formation of excited states through dipole-induced dipole interaction. Indeed, the Stokes shift (i.e., the difference between the absorption and emission maxima) for the C1 guests increases from 71 nm in G2ODS host to 115 nm in G2SBDS host. Unraveling the role of the host and the guest packing in the optical properties of the confined coumarin molecules will require more detailed characterization of the spectral characteristics (e.g., lifetime, optical anisotropy) combined with computational studies aimed at determining the electronic structure of the dyes in their various aggregated states. Summary The remarkable structural diversity shown by these lamellar GS inclusion compounds once again reveals the remarkable ability of GS host frameworks to adapt to the size and shape requirements of the guest molecules, even for the large and

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Table 3. Crystallographic Information for GDS · n(coumarin) Inclusion Compounds formula formula wt crystal system space group color a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) temp (K) Z R1 [I > 2σ(I)] wR2 [I > 2σ(I)] GOF

formula formula wt crystal system space group color a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) temp (K) Z R1 [I > 2σ (I)] wR2 [I > 2σ(I)] GOF

formula formula wt crystal system space group color a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) temp (K) Z R1 [I > 2σ(I)] wR2 [I > 2σ(I)] GOF

formula formula wt crystal system space group color a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) temp (K) Z R1 [I > 2σ(I)] wR2 [I > 2σ(I)] G.O.F.

G2ABDS · (1/2)(C1) (1a)

G2ABDS · 2(C1) (1b)

G2ABDS · (1/2)(C314) (2)

G2ABDS · (1/2)(C334) (4)

G2AQDS · (C2) (5)

C21H28.5N8.5O7S2 576.17 triclinic P1j orange 6.1980(9) 7.2218(10) 16.044(2) 98.721(2) 96.478(2) 93.288(3) 703.26(17) 200(2) 1 0.0546 0.1522 0.925

C42H54N10O10S2 923.07 monoclinic P21 red-orange 7.4073(5) 26.7956(17) 12.3008(7) 90 106.8300(10) 90 2336.9(3) 200(2) 2 0.0435 0.1104 1.017

C23H29.5N8.5O8S2 617.20 triclinic P1j red-orange 6.2094(6) 7.2165(7) 15.7926(15) 96.330(2) 96.881(2) 93.186(2) 696.59(12) 200(2) 1 0.0373 0.1094 1.089

C22.5H28.5N8.5O7.5S2 602.19 triclinic P1j red 6.2233(2) 7.1835(2) 15.9689(5) 98.037(2) 96.969(2) 93.053(2) 699.86(4) 100(2) 1 0.0483 0.1349 1.104

C29H33N7O10S2 703.74 triclinic P1j red 7.6405(5) 14.0326(9) 16.1930(10) 65.485(3) 76.713(3) 86.331(3) 1536.39(17) 100(2) 2 0.0344 0.1024 1.031

G2BBDS · 2(C1) (6)

G2SBDS · 2(C1) (7)

G2ODS · 2(C1) (8)

G2ODS · 2(C102) (9)

G2ADS · 2(C1) (10)

C44H58N8O10S2 923.10 monoclinic P21/n light yellow 7.5933(8) 32.042(4) 9.7843(11) 90 91.672(2) 90 2379.6(4) 200(2) 2 0.0389 0.0995 1.009

C44H56N8O10S2 921.09 monoclinic P21/n yellow 7.6611(4) 31.3689(16) 9.9610(5) 90 94.1320(10) 90 2387.6(2) 200(2) 2 0.0430 0.1253 1.053

C38H62N8O10S2 855.10 monoclinic P21/n light yellow 7.6955(12) 28.666(5) 10.1866(16) 90 93.618(2) 90 2242.7(6) 173(2) 2 0.0337 0.0908 1.034

C42H62N8O10S2 903.12 monoclinic P21 yellow 7.3931(2) 26.6667(8) 11.7311(3) 90 102.3820(10) 90 2258.99(11) 100(2) 2 0.0442 0.1123 1.105

C44H54N8O10S2 919.10 orthorhombic Pbca yellow-green 14.5643(11) 11.7978(9) 26.4477(19) 90 90 90 4544.4(6) 173(2) 4 0.0359 0.0985 1.027

G2ADS · 2(C102) (11)

G2BPDS · 2(C1) (12)

G2BPDS · 2(C102) (13)

G2BBDS · 2(C314) (14)

G2BBDS · 2(C334) (15)

C48H54N8O10S2 967.12 orthorhombic Pbca green 13.8848(4) 12.2852(4) 26.8605(9) 90 90 90 4581.8(3) 100(2) 4 0.0541 0.1478 1.064

C42H54N8O10S2 895.05 orthorhombic Pna21 yellow 22.348(3) 7.2898(9) 27.136(3) 90 90 90 4420.8(9) 200(2) 4 0.0427 0.1141 1.018

C46H54N8O10S2 943.10 orthorhombic Aba2 yellow 13.1383(14) 27.585(3) 12.4518(13) 90 90 90 4512.7(8) 173(2) 4 0.0308 0.0773 0.945

C52H62N8O14S2 1087.22 monoclinic P21/c yellow-green 12.6639(6) 31.3013(15) 13.2474(7) 90 90.765(3) 90 5250.8(4) 100(2) 4 0.0490 0.1264 1.075

C50H58N8O12S2 1027.16 orthorhombic Pca21 orange-brown 13.5107(5) 30.2800(11) 12.6926(4) 90 90 90 5192.6(3) 200(2) 4 0.0813 0.2415 1.063

G2NDS · (4/3)(C1) (16)

G2BSPE · (C102) · (MeOH) (17)

G2BBDS

C334

C30.67H40.67N7.33O8.67S2 714.85 monoclinic P21/c green 21.2661(5) 12.6664(3) 19.8581(5) 90 93.2330(10) 90 5340.6(2) 100(2) 4 0.0372 0.0946 1.016

C33H45N7O11S2 779.88 monoclinic Cc green 7.5443(4) 28.7511(13) 16.8787(8) 90 93.225(3) 90 3655.3(3) 100(2) 4 0.0401 0.1088 1.08

C16H24N6O6S2 460.53 triclinic P1j colorless 6.6862(7) 7.7976(8) 10.6689(12) 100.038(4) 98.454(4) 106.649(4) 513.20(9) 100(2) 1 0.0321 0.0979 1.132

C17H17N1O3 283.32 monoclinic C2/c red 29.6484(15) 16.7796(8) 23.3020(12) 90 110.434(2) 90 10863.0(9) 100(2) 32 0.1125 0.356 1.387

awkwardly shaped coumarin dyes. Furthermore, the inclusion cavity environment and framework topology can be adjusted by the choice of pillar systematically changing from zigzag brick

to simple brick to bilayer with increasing pillar height. In many of these cases, steric complementarity between the guests (either as monomers or dimers) is the main structure-directing force,


in which the guests effectively serve as templates to generate their respective frameworks, thus optimizing host-guest and guest-guest packing. The systematic and adjustable GS architectural isomerism as well as the uniquely sized and shaped inclusion cavities provided by each framework isomer promise better control of guest packing, which is crucial step to the design and synthesis of functional inclusion compounds for applications such as magnetic, optoelectronics, and lasers. The control of dye aggregation in the solid-state GS frameworks demonstrates that the local structure (and aggregation) of the guest molecules can be regulated, leading to optical properties in the confined host matrix that differ from those attainable in solution. Furthermore, the high concentration of dye in the GS frameworks (approaching 0.5 M), combined with the ability to tune the emission wavelength through choice of dye and adjustment of framework architecture, suggests a new route to a new class of efficient laser dye crystals. Experimental Section Materials and General Procedures. Guanidine carbonate salt, tetrafluoroboric acid, 2,6-naphthalenedisulfonic acid disodium salt, Amberlyst 36 (wet) ion-exchange resin, and coumarin 1 (7-diethylamino-4-methylcoumarin) were purchased from Sigma-Aldrich (Milwaukee, WI). Coumarin 2 (4,6-dimethyl-7-ethylaminocoumarin), coumarin 102 (2,3,6,7-tetrahydro-9-methyl-1H,5H-quinolizino(9,1-gh)coumarin),coumarin314(1,2,4,5,3H,6H,10H-tetrahydro-9-carbethoxy[1]benzopyrano(9,9a,1-gh)-quinolizin-10-one), and coumarin 334 were purchased from Acros (Geel, Belgium). 4,4′-Biphenyldisulfonic acid and anthraquinone-2,6-disulfonic acid disodium salt were purchased from TCI America (Tokyo, Japan). These chemicals were used without further purification. The potassium salt of 2,6-anthracenedisulfonate,61 the sodium salt of 4,4′-azobenzenedisulfonate,62 the sodium salt of 4,4′disulfostilbene,63 and the sodium salt of 1,8-octanedisulfonate64 were prepared according to published procedures. All solvents and other starting materials were purchased as ACS grade from Aldrich or Alfa Aesar (Ward Hill, MA) and were used as received. Metal salts of the sulfonic acids were converted to the acid form by passing them through an Amberlyst 36 (wet) ion-exchange column. G2NDS, G2BPDS, G2AQDS, G2ADS, G2ABDS, G2SBDS, and G2ODS precipitate, as acetone clathrates, by direct reaction of guanidinium tetrafluoroborate, prepared by neutralization of guanidinium carbonate with tetrafluoroboric acid, with the corresponding disulfonic acid in acetone. These compounds readily lose enclathrated acetone under ambient conditions to yield pure guanidinium organodisulfonate apohosts. The compounds reported here were crystallized from methanolic solutions containing the dissolved apohost and the corresponding guest where applicable. The stoichiometries of the resulting inclusion compounds tend to be independent of the host:guest stoichiometric ratios during crystallization. The stoichiometries of all inclusion compounds were confirmed by 1H NMR spectroscopy in addition to single-crystal structure determinations. 1 H NMR spectra were recorded on a Varian INOVA 300 MHz spectrometer or a Bruker AV-400 spectrometer operating at 400 MHz. [Guanidinium]2[4,4′-bibenzyldisulfonate], G2BBDS. Chlorosulfonic acid (4.43 mL; 7.88 g, 67.6 mmol) was added slowly via syringe to a chilled (-15 °C) round-bottom flask containing 20 mL of anhydrous chloroform and 5.00 g (4.66 mL; 29.4 mmol) of bibenzyl, all under a nitrogen atmosphere. After fifteen minutes, the chloroform and excess chlorosulfonic acid were decanted from the oily residue. The oil was further rinsed with chloroform (20 mL), dissolved in acetone, and then treated with an acetone solution of G[BF4]. The G2BBDS · (acetone)n precipitate was filtered and dried under vacuum to give 9.22 g (20.5 mmol) of pure, white G2BBDS (70% yield). 1H NMR (dimethyl sulfoxide-d6, 400 MHz, J/Hz): δ 7.50 (d, 4H, 2J ) 8, 2-H), 7.18 (d, 4H, 2J ) 8, 3-H), 6.92 (s, 12H, G), 2.86 (s, 4H, 1-CH2). [Guanidinium]2[1,2-bis(sulfophenoxy)ethane], G2BSPE. Chlorosulfonic acid (2.2 mL; 3.7 g, 32 mmol) was added slowly via syringe to a chilled (-15 °C) round-bottom flask containing 20 mL of anhydrous chloroform and 3.43 g (16 mmol) of 1,2-diphenoxyethane, all under a nitrogen atmosphere. After one hour, the reacting vessel was charged with 50 mL of chloroform and the precipitate collected by vacuum filtration. The precipitate was further rinsed with chloroform

Crystal Growth & Design, Vol. 9, No. 8, 2009 3813 (20 mL), dissolved in acetone, and then treated with an acetone solution of G[BF4]. The G2BSPE · (acetone)n precipitate was filtered and dried under vacuum to give 4.73 g (9.6 mmol) of pure, white G2BSPE (60% yield). 1H NMR (dimethyl sulfoxide-d6, 400 MHz, J/Hz): δ 7.52 (d, 4H, 2J ) 8, 2-H), 6.92 (s, 12H, G), 6.87 (d, 4H, 2J ) 8, 3-H), 4.32 (s, 4H, O-CH2). Fluorescence. Fluorescence measurements were performed using a Hitachi F-2500 fluorescence spectrophotometer, equipped with a 150 W xenon light source. Several single crystals of a given compound were placed at the bottom of a glass NMR tube cut to fit into the cuvette holder of the spectrophotometer. The excitation slit width was set at 2.5 nm. The emission slit widths (2, 5, or 10 nm) were adjusted to enhance intensity values. Data were collected at a scan speed of 300 nm/min and a photomultiplier (PMT) detector voltage of 400 V. Reflectance Absorption. Reflectance absorption measurements were performed using a Perkin-Elmer Lambda 950 UV/vis spectrometer. Measurements were performed in total reflectance mode by attaching an 8° wedge to the sample port of a 60 mm integrating sphere. All crystalline samples were lightly ground into polycrystalline powders, loaded into a 1.25 in. diameter sample cup, mixed with BaSO4 (95% by weight) as a diluent, and pressed firmly to create a smooth sample surface. The sample cup was then attached onto the sample port of the integrating sphere. The UV/vis slit width was fixed at 2 nm. The photomultiplier detector gain was 30, and its integration (response) time was 0.20 s. Absorbance values (A) were converted from % reflectance (% R) according to A ) -log(% R). Crystallography. Experimental parameters pertaining to the singlecrystal X-ray analyses are given in Table 3 (see Supporting Information). Data were collected on either a Siemens or Bruker SMART APEX II CCD platform diffractometer with graphite monochromated Mo KR radiation (λ ) 0.71073 Å) at 100(2) K, 173(2) K, or 200(2) K. The structures were solved by direct methods and refined with full-matrix least-squares/difference Fourier analysis using the APEX2 (fully integrated with SHELX-97) suite of software.65 Crystals 1a and 2 were additionally refined using the PLATON/SQUEEZE program. All nonhydrogen atoms were refined with anisotropic displacement parameters, and all hydrogen atoms were placed in idealized positions and refined with a riding model. Data were corrected for the effects of absorption using SADABS.

Acknowledgment. The authors thank Mr. Victor G. Young of the University of Minnesota X-ray Crystallographic Laboratory and Samuel Hawxwell, Ph.D., and Chunhua (Tony) Hu, Ph.D., of the New York University Molecular Design Institute for their assistance in crystal structure determinations. This work was supported in part by the National Science Foundation Division of Materials Research (DMR-0720655/0906576). Supporting Information Available: Key intermolecular distances of the coumarin guests in the inclusion compounds and the pure coumarin crystals, absorption and emission measurements of the inclusion compounds, and X-ray experimental details in the form of a crystallographic information file (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.

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