Soft-Cavity-type HostâGuest Structure of Cocrystals with Good

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Soft-Cavity-type Host-Guest Structure of Cocrystals with Good Luminescence Behavior Assembled by Halogen Bond and Other Weak Interactions Wei Jun Jin, Rui Liu, and Hui Wang Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 15 May 2017 Downloaded from http://pubs.acs.org on May 15, 2017

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Crystal Growth & Design

Soft−Cavity−type Host−Guest Structure of Cocrystals with Good Luminescence Behavior Assembled by Halogen Bond and Other Weak Interactions Rui Liu,† Hui Wang,*‡ and Wei Jun Jin*† The first and second authors contributed equally to this work. †College of Chemistry, Beijing Normal University, Beijing, Beijing, 100875, People's Republic of China ‡College of Chemistry & Material Science, Shanxi Normal University, Linfen, Shanxi, 041004, People's Republic of China Correspondence email: [email protected], [email protected]

KEYWORDS Halogen Bond, Host−Guest Cocrystals, Soft Cavity, Luminescence

ACS Paragon Plus Environment

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ABSTRACT The host cocrystal 1 with soft−cavity−type structure unit has been assembled by the 1,4−DITFB and PPNO molecules mainly using the robust C−I···−O−N+ halogen bond. The results indicate that the host cavity has the capacity to envelope functional guests, Car, Nap, Phe and BhQ molecules, to further form the host−guest cocrystals 2−5 by halogen bond, hydrogen bond and other weak noncovalent interactions. The supramolecular cavity can be adjusted in size or shape to a certain degree by the bound guest molecule, reflecting its softness, openness and inclusiveness. Moreover, compared to the pristine PPNO and guest molecules, the prepared cocrystals 1−5 display tunable luminescence behaviors at room temperature. The present work may pave a new platform for developing host−guest solid materials which have potential application in the fields of luminescent sensor, light-emitting displays, pharmaceutical encapsulation, as well as separation chemistry.

INTRODUCTION As the center of supramolecular chemistry, host−guest chemistry has advanced enormously during the past decades in organic chemistry and other related fields.1−3 To date, the deliberate design of host molecules with highly sensitive and guest−selective properties is a continuously major effort for host−guest chemistry, and various types of noncovalent interactions have been employed to constructed host−guest systems, such as hydrogen bond (HB),4,5 metal−ligand coordination bond6 as well as halogen bond (XB),7,8 etc. At present, the host−guest systems based on XB have received a lot of attention for its potential utility in encapsulation of guest molecules and separation of analytes, etc.7,8 Of which the molecular capsule is the most representative

example,

which

can

encapsulate

small


solvent

molecules

such

as 2

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1,4−dioxane.9,10−17 Also, some other kinds of host self−assembles by XB or with HB together are frequently reported, such as organic framework or channel,18−20 helicate,21 anionic cages,22,23 to name a few. However, these host systems possess small inside space and relative rigid structure. So, it is necessary to develop one kind of host assembles with relative larger or tunable inner size and shape for more widespread use of host−guest interaction. Compared with the hard or rigid cavity, such as resorcinarenes, cyclodextrins, and cucurbit[n]uril, a soft or flexible cavity can be described as a host unit with adjustable size or shape depended on the bound guest molecule under maintaining the stability of its basic framework structure. Herein, inspired by the report that the extremely strong −N−X+···−O−N+ XB can occur between an oxygen atom of pyridine N−oxide, for example, 4−phenylpyridine N−oxide (PPNO), and N−iodosuccinimide or its derivatives,24 an unusual host cocrystal with soft−cavity−type structure

is

assembled

by

C−I···−O−N+

XB

and

C−H···F

HB

using

bidentate

1,4−diiodotetrafluorobenzene (1,4−DITFB) and PPNO, which has the capacity to envelope some functional guest molecules, such as carbazole (Car), naphthalene (Nap), phenanthrene (Phe) and benzo[h]quinoline (BhQ) molecules, to further form the host−guest cocrystals 2−5. Moreover, the cocrystals 1−5 display good luminescent behaviors with different emission at room temperature. In general, the novelty of this work is designed from two aspects. One is the construction of host−guest cocrystals by the rational selection and design of the intermolecular noncovalent interactions (e.g., XB, HB, π−hole···π−hole bond and π−π stacking); the other is the modulation of the emission properties of host−guest cocrystals through changing the guest molecules and the corresponding crystal packing modes. It is expected that this study should be significant in the design of molecular solid materials, molecular recognition, pharmaceutical encapsulation, or even as a separation tool of easily sublimated guest such as Nap.


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EXPERIMENTAL SECTION Reagents.

1,4−Diiodotetrafluorobenzene

(1,4−DITFB,

98%)

was

purchased

from

Sigma−Aldrich Co. 4−Phenylpyridine N−oxide (PPNO, 98%), naphthalene (Nap, 99%), carbazole (Car, 99%), phenanthrene (Phe, 99%), benzo[h]quinoline (BhQ, 98%) were purchased from J&K Scientific Ltd. The solvents of analytical grade (ethanol and acetone) were purchased from Beijing Company of China National Medicals. The structures of these XB donors/acceptors and guests are shown in Scheme 1.

Scheme 1. Structures of XB donor (D) and acceptor (A) as well as the guest molecules. Growth of Cocrystals. Cocrystal 1. 1,4−DITFB and PPNO in 1:1 molar ratio were dissolved in the mixed solvent of ethanol and acetone (1:1) in a glass vial. The vial was kept in the dark at room temperature for slow evaporation of solvent. Well−formed cocrystal suitable for XRD measurement appeared within approximately two weeks. Cocrystal 2−5. 1,4−DITFB, PPNO and Nap, Car, Phe or BhQ in 1:1:1 molar ratio were dissolved in the mixed solvent of ethanol and acetone (1:1) in a glass vial. The vial was kept in the dark at room temperature for slow evaporation of solvent. Well−formed cocrystals suitable for XRD measurement appeared within approximately two weeks.


4

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X−Ray Diffraction (XRD) Crystallography. The single crystal diffraction data of cocrystals 1−5 were collected with a Rigaku oxford diffraction with Mo−Kα radiation (λ = 0.71073 Å) and a graphite monochromator operating in the multi−scan mode. The structures were resolved by direct methods and refined by full−matrix least−squares on F2 using the Olex2 program with anisotropic thermal parameters for all non−hydrogen atoms.25,26 Hydrogen atoms were included at estimated positions and refined using the calculated positions. The major crystal structure data were summarized in Table 1. Powder X−ray diffraction (PXRD) patterns were obtained at 293 K on an XPert Pro MPD diffractometer with a Cu−Kα Enhance Ultra source (λ 1.5418 Å). The ground cocrystal powders were dried for 24 h under vacuum at room temperature. Table 1. Crystal data and structure refinement. Reference

1

2

3

4

CCDC no.

1524273

1524275

1524274

1524276

1524277

Formula

C23H9F8I4NO

C14.5H9F2INO0.5

C22H13F4I2NO

C48H28F8I4N2O2

C47H27F8I4N3O2

Weight

974.91

370.13

637.13

1324.32

1325.32

Crystal size/mm

0.2×0.1×0.1

0.2×0.2×0.1

0.3×0.3×0.2

0.22×0.13×0.1

0.3×0.3×0.1

Crystal system

monoclinic

triclinic

orthorhombic

triclinic

monoclinic

Space group

C2/c

P−1

Pccn

P−1

P2/n

a/Å

7.4416(3)

9.275(6)

14.020(7)

10.728(11)

14.283(15)

b/Å

28.9654(12)

9.837(6)

15.882(8)

13.141(13)

18.89(2)

c/Å

12.0008(5)

15.718(10)

19.423(9)

16.958(17)

16.507(17)

α/°

90.00

108.178(10)

90.00

68.302(15)

90.00

β/°

98.579(4)

90.941(10)

90.00

79.588(16)

101.217(17)

γ/°

90.00

106.855(9)

90.00

86.613(15)

90.00

V/Å3

2557.82(19)

1294.9(14)

4325(4)

2185(4)

4369(8)

ρcalcd/g cm−1

2.552

1.899

1.957

2.013

2.015

Z

4

4

8

2

4

T/K

150.00(10)

296(2)

296(2)

296(2)

293(2)


5

5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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µ/mm−1

4.950

2.484

2.956

2.930

2.931

F(000)

1784.0

712.0

2416.0

1260.0

2520

Reflections collected

7113

9151

30021

11806

26228

Independent reflections

3087

6841

6137

7843

10317

Rint

0.0270

0.0324

0.0684

0.0549

0.1184

R1 (I>2σ(I))

0.0291

0.0701

0.0788

0.0579

0.0680

wR(F2) (I>2σ(I))

0.0576

0.1906

0.2027

0.1646

0.1764

R1 (all data)

0.0350

0.0804

0.1303

0.0658

0.1270

wR(F2) (all data)

0.0606

0.1975

0.2347

0.1762

0.2250

Goodness−of−fit on F2

1.063

1.084

1.141

1.011

0.939

Spectroscopic Measurements. The phosphorescence and total luminescence (fluorescence and phosphorescence) spectra, as well as luminescence quantum yields were recorded on a FLS980 fluorescence spectrometer (Edinburgh Instruments Ltd) equipped with an integrating sphere. The width of both excitation and emission slits were set at 15 nm, the step and dwell time were set at 1.00 nm and 0.05 s, respectively. In addition, a 1 × 10 mm quartz cuvette in 30/60° angle was used for the cocrystals.

RESULTS AND DISCUSSION Structures of Cocrystals. Host Cocrystal 1, 1,4−DITFB:PPNO (2:1). PPNO molecule is an innovative XB acceptor due to its highly polarized N−oxide moiety in which N and O atoms exist in N+−O− form. More importantly, the O atom in the N−oxide moiety can interact with certain XB donor to form extremely strong XB.24 In addition, the bidentate XB donor 1,4−DITFB has strong σ−hole on I atoms and π−hole, as well electronegative F atoms as good


6

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HB acceptor. These characters enable them to assemble XB−based cocrystal with special structure more easily. XRD analysis reveals that the cocrystal 1 with close supramolecular cavity network is successfully assembled by 1,4−DITFB and PPNO with a 2:1 stoichiometry. The PPNO molecule exhibits one conformation with a torsion angle of 22.5o between the phenyl and pyridyl units. As shown in Figure 1, it can be seen that PPNO molecule adopts the erect stance along the c−axis direction. Each 1,4−DITFB node connects two adjacent PPNO molecules via robust C−I···−O−N+ XB to produce a 1D infinite zigzag chain in which PPNOs as pendants alternatively located in the two sides of each chain. The resultant C1−I1···O1 separation [for the O1 atom at (x, y, z)] is 2.7646(14) Å, and the C1−I1···O1* angle is 176.95(13)o (cf. Figure S1b). The adjacent 1D chain are further interlocked by interchain C−H···F HBs between phenyl−H in PPNO and F in 1,4−DITFB to form the 2D network structure. On this basis, the 2D network is further cross−linked by C−H···F HBs to give a 3D supramolecular structure (cf. Figure 1a and S1c). It is observed that 3D structure triggers the close cavity structures which are connected by the above noncovalent interactions. In order to demonstrate the capacity of host cavity to envelope guest molecules, several two− or three−ring aromatic molecules, for example, the well−documented Nap, Phe, Car and BhQ, are chosen to assemble cocrystals with 1,4−DITFB and PPNO together, because of the potential important of these guests in developing luminescent materials or environmental interests. In addition, it is necessary to mention that the basic principle to choose the guest molecules is that the possible XB formed by 1,4−DITFB and guest molecule is much weaker than the C−I···−O−N+ XB in host cocrystal. The following experimental results validate that the initial


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design is reasonable, and the host cocrystal 1 can be able to encapsulate some functional guest molecules.

Figure 1. Structural details of cocrystal 1 as supramolecular host (distance in Å). (a) Ball and stick model of 3D supramolecular cavity structure constructed by C−I···−O−N+ and C−H···F bonds; (b) Space filling representation of the 3D supramolecular cavity structure.


8

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Host−guest cocrystals 2−5. As expected, the targeted guest molecules are effectively “trapped” as a part of crystalline lattice using the C−H···F and C−H···π HBs to produce new crystalline solids, i.e., host−guest cocrystals 2−5, which have similar basic skeleton structure with cocrystals 1. But interestingly, the cavity of cocrystals 2−5 in size or shape varies with guest molecules, which reflects the softness of the cavity structure. Cocrystal 2 1,4−DITFB:PPNO:Car (1:1:1). Figure 2 shows the expected self−assembly structure of the host with Car molecule. It can be seen that the robust C−I···−O−N+ XBs and C−H···F HBs maintain the 2D structure. The resultant C1−I1···O1 and C4−I2···O1 separations [for the O1 and O2 atom at (x, y, z)] are 2.728(6) and 2.714(6) Å, and the corresponding C−I···O* angles are 175.2(2)o and 174.0(2)o, respectively. Moreover, it is observed that the phenyl and pyridyl units in PPNO molecule are approximatively plane, with a torsion angle of 4.4o, and PPNO molecule also presents the erect stance. In addition, the 2D network triggers two alternating cavity−type structure. Of which, one is a broaden octamer cavity−type structure with two reversed guest Car molecules trapped obliquely by C−H···F and N−H···π HBs, the other one is an empty tetramer cavity−type structure. On these bases, the split−level 2D network crosslinks together to generate the complicated 3D supramolecular host−guest structure using the above HBs.


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Figure 2. The extracted supramolecular host−guest structural units of cocrystal 2 constructed by C−H···F and C−H···π bonds with two reversed Car molecules trapped in the broaden octamer cavity by C−H···F and N−H···π bonds (distance in Å). Cocrystal 3−5 1,4−DITFB:PPNO:Nap/Phe/BhQ (2:2:1). The cavity structures of cocrystals 3−5 formed by host with Nap, Phe and BhQ molecules are similar with that of cocrystal 1 (cf. Figure 3, S3b, S4b and S5b), but different from the cocrystal 2. In general, the molecules self−organize into the closed−packed layers (2D structure) using C−I···−O−N+ XBs and C−H···F HBs in cocrystals 3−5. The layered 2D frameworks are further extended by π−π stackings of interlamellar PPNOs and π−hole···π−hole bonds of planar 1,4−DITFBs to give rise to a 3D supramolecular host−guest structures, as shown in Figure 3 and Figure S3−S5. As a result, four 1,4−DITFBs and four PPNOs construct an octamer host cavity and every two cavities share a pair of 1,4−DITFB molecules. The targeted guest, Phe, reversed Nap or BhQ molecule, is trapped perpendicularly and hung in the host cavity by C−H···F and C−H···π HBs. Due to the existence of C−H···π HBs between PPNO and guest molecules, PPNO molecules in theses


10

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cocrystals adopt horizontal alignment along the a−axis direction in cocrystal 3 and 5, and the oo’ direction in cocrystal 4, which is different from that in cocrystal 1 and 2. In addition, due to the higher electronegativity of N atom than C atom, the H atom in N−H moiety of Car is much more acidity than that in C−H, thus it is easier to form stronger N−H···π HB rather than C−H···π HB. This should be one of the reasons for the different cavity property between cocrystals 2 and 3−5.

Figure 3. Structural details of cocrystal 3 as an example of supramolecular host−guest systems (distance in Å): (a) and (b) The extracted 3D supramolecular host−guest structural along the a−axis and c−axis directions constructed by C−I···−O−N+ XBs, C−H···F, C−H···π HBs, π−π stacking, as well as π−hole···π−hole bonds. Specifically speaking, for cocrystal 3, the PPNO molecule exhibits one conformation with a torsion angle of 19.2o between phenyl and pyridyl group, thus corresponding to one π−π stacking mode (cf. Figure S3b−1). It is observed that all octamer host cavity structures are same, which are connected mainly by strong C15−I1···O1 and C12−I2···O1 XBs. While for cocrystal 4 and 5, the PPNO molecules exhibit two conformations with the torsion angle of 3.5o and 13.1o, 16.3o and 26.1o, thus presenting two π−π stacking patterns, respectively (cf. Figure S4b−1, S4b−2,


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S5b−1 and S5b−2). All octamer cavity structures in cocrystal 4 are also same, and each cavity is held together mainly by strong C1−I1···O1, C10−I4···O1, C4−I2···O2 and C7−I3···O2 XBs (cf. Figure S4b and S4c). But there are two kinds of octamer cavity structures in cocrystal 5 (cf. Figure S5b and Figure S5c), one is connected mainly by C1−I1···O1 and C4−I2···O2 XBs, the other one by C7−I3···O1 and C10−I4···O2 XBs. Table S1 listed all the interactions and geometrical parameters, and it is useful for a further understanding of the principle behind the design of the cocrystal 1 and 2−5. From Table S1 and above description, it can be noticed that all cocrystals maintain a basic 1D infinite zigzag chain by strong C−I···−O−N+ XB between 1,4−DITFB and PPNO molecules. The resultant bond lengths dI···O are about 20% shorter than the sum of vdW radii of interacting atoms, which can be comparable with the XB strength in Ref 24. The interlock/intersection of the 1D chains constructs the special soft cavity by weak interactions, such as C−H···F HB, π−π stacking and π−hole···π−hole bond, of which the contact distances are more or less 5% shorter than the sum of vdW radii of interacting atoms. The guest molecule as weaker and non−competitive C−I···π/N XB acceptor is trapped in the host cavity via weak C−H···F and C−H···π HBs. Furthermore, the host cavity is modulated in shape or size to a certain degree by guest properties, which preferably exhibits the openness and inclusiveness of the supramolecular host structure by XB. PXRD. PXRD patterns were measured at room temperature for confirming the homogeneity and phase purity of the cocrystals. Figure S6 shows that the peak position of experimental PXRD pattern is in agreement with that of simulated one by XRD data, indicating a good phase purity of the crystal product. In addition, the few discrepancies in intensity between experimental and simulated values may be the consequence of preferred orientations of the crystal powder samples.


12

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The luminescent behaviors of cocrystals. In general, the pristine aromatic molecules with rigid planar structure and π-conjugation system can easily produce fluorescence, whereas their hidden potential to produce phosphorescence can be released when they are hybridized with other molecules, especially in the assemble of color−tunable luminescent materials.27−31 At present, σ−hole bond (XB) and π−hole bond as effective strategies have been adopted to modulate the emission colors of solid materials. PPNO and the selected guest molecules, Car, Nap, Phe, emit only strong UV/blue fluorescence with well−defined vibrational structures in solid phase, BhQ molecule emits strong fluorescence and relatively weak phosphorescence. But, after introducing 1,4−DITFB molecule, the as−obtained host and host−guest cocrystals 1−5 exhibit different luminescent (fluorescent and phosphorescent) behaviors at room temperature (cf. Figure 4, Figure 5 and Figure S7), which are different from that of pristine PPNO and guest molecules, as well as the binary cocrystal of 1,4−DITFB with Car, Nap, Phe or BhQ.32−34 The total luminescent spectra of cocrystals measured under fluorescent mode go from 400 nm to near 800 nm with well−defined vibrational bands when excited at 380 nm, which can be divided into two bands, one between 400 and 500 or 550 nm from fluorescence and another one more than 500 or 550 nm from phosphorescence (cf. Figure 4), the corresponding spectral characteristics are summarized in Table 2. The host cocrystal 1 has the maximum emission (λemmax) at 586 nm (S1−S0) giving color coordinates of (0.4266, 0.4119). And the emission colors varied obviously when the guest molecules are enveloped in the host. The as−obtained host−guest cocrystals 2−5 possess the λemmax at 587, 455, 447 and 652 nm, and the corresponding


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color coordinates are (0.4704, 0.4099), (0.3266, 0.2601), (0.2265, 0.1487) and (0.4142, 0.3154), respectively. Overall, the main contribution to luminescence is derived from phosphorescence for cocrystals 1, 2, 5, and fluorescence for cocrystals 3, 4. In addition, the photographs of cocrystals under UV−365 radiation at ambient condition are taken (cf. Figure 5), which are fitted to their total luminescent spectra. And the corresponding color coordinates calculated by CIE1931 Chromaticity Coordinate Calculation are also shown in Figure 5. The such luminescent behaviors can be ascribed to the heavy atom effect of iodine, local molecular environment, as well as the interaction pattern existed in cocrystals. For the host cocrystal 1, the robust C−I···−O−N+ XB in cocrystal must lead to the lowest lying exited triplet state with ππ* property, by which the host cocrystal emits phosphorescence. For the host−guest cocrystals 2−5, the guests are enveloped in the cavity by C−H···F and N−H···π or C−H···π HBs to effectively limit their rotation. Although there are no XB formed between 1,4-DITFB and guests, iodine atom also plays a perturbing role in a certain degree to lower the exited triplet state of guests, so as to produce phosphorescence with certain fluorescence.


14

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Figure 4. The normalized total luminescent spectra of pristine monomers and the corresponding cocrystals 1−5 when excited at 380 nm, and the fluorescence decay curves at the emission monitoring wavelength measured under fluorescent mode (cf. Table 2).

Figure 5. Photographs of cocrystals 1−5 under UV−365 radiation and the color coordinates.

Table 2. The total luminescent properties of cocrystals 1−5. Cocrystals

1

2

3

4

5

Quantum yield

Spectra/λ, nm

Decays/τ, ns

λex

λem

τ1(f1, %)

τ2(f2, %)

τ3(f3, %)

τaverage/ns

(Φ)

380

417, 443, 472 545,

0.53

4.45

43.11

2.94

1.40%

585

(86.3%)

(8.9%)

(4.8%)

413, 433, 585, 671,

0.49

5.00

---

0.73

6.13%

742

(94.8%)

(5.2%)

455, 602, 654, 710

0.68

4.46

34.16

3.21

2.87%

(78.4%)

(15.8%)

(5.8%)

428, 447, 465, 601,

0.91

3.48

50

1.62

3.21%

667, 684, 754

(93.0%)

(5.9%)

(1.1%)

463, 497, 599, 652,

0.68

4.36

33.82

2.94

3.27%

716

(76.3%)

(19.0%)

(4.7%)

380

380

380

380

Notes: λ: the emission monitoring wavelength; τ1, τ2 and τ3: the lifetime of each components; f1, f2 and f3: the fractional contribution of each components.


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In addition, the luminescent decays are analyzed from two parts, i.e., fluorescence and phosphorescence decays. For the fluorescence component, the decay curves of cocrystals obey the tri−exponential model except for the cocrystal 2 which obeys the bi−exponential model. The average lifetimes are 2.94, 0.73, 3.21, 1.62 and 2.94 ns, respectively, as listed in Table 2. While for the phosphorescence component, all decay curves obey the bi−exponential model with the average lifetime of 0.857, 2.991, 0.232, 0.975 and 0.331 ms, respectively (cf. Table S2). The dependence of luminescent behaviors and decays on the structural characters of luminophores as well as various interactions in the cocrystal environment is interested and the accurate reasons are exploring currently.

CONCLUSIONS The cocrystals with soft cavity host unit have been assembled successfully by main driving force, very strong C−I···−O−N+ XB. The cavity can be adjusted in size or shape depended on the bound guest molecule under maintaining stability of its basic 1D structure. As a new supramolecular platform constructed by XB and other intermolecular noncovalent interactions possessing the openness and inclusiveness, the host−guest cocrystals 1−5 exhibit good luminescent behaviors with different emission at room temperature. This work will allow the luminescent properties of molecular solid materials to be applied in light−emitting diodes and chemical sensors, etc., and should be significant in the design of molecular recognition, pharmaceutical encapsulation, or even as a separation tool of easily sublimated guest such as Nap, which is similar with the work by Aakeröy.35 The further studies are ongoing to elaborate on these perspectives, particularly with regard to the luminescent materials and the regulation mechanism of the soft−cavity in size and shape by guest molecule.


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ASSOCIATED CONTENT Supporting Information. The following files are available free of charge on the ACS Publications website. Structures of cocrystals, interactions and geometrical parameters and luminescent behaviors of cocrystals (PDF) Crystallographic data (CIF) AUTHOR INFORMATION Corresponding Author *E−mail: [email protected]; [email protected] Notes The authors declare no competing financial interests. ACKNOWLEDGMENT The authors thank the National Natural Science Foundation of China (No. 21675013) for the support. REFERENCES (1) Vögtle, F.; Weber, E. Host Guest Complex Chemistry/Macromolecules: Synthesis, Structures, Applications, Springer, Berlin, 1985.


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(2) Lehn, J.-M. Supramolecular Chemistry: Concepts and Perspectives, VCH, Weinheim, 1995. (3) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry, 2nd ed., John Wiley Sons, Chichester, 2009. (4) Wyler, R.; de Mendoza, J.; Rebek, Jr., J. Angew. Chem. Int. Ed. Engl. 1993, 32, 1699–1701. (5) Prins, L. J.; Reinhoudt, D. N.; Timmerman, P. Angew. Chem. Int. Ed. 2001, 40, 2382–2426. (6) Smulders, M. M. J.; Riddell, I. A.; Browne, C.; Nitschke, J. R. Chem. Soc. Rev. 2013, 42, 1728–1754. (7) Cavallo, G.; Metrangolo, P.; Milani, R.; Pilati, T.; Priimagi, A.; Resnati, G.; Terraneo, G. Chem. Rev. 2016, 116, 2478−2601. (8) Gilday, L. C.; Robinson, S. W.; Barendt, T. A.; Langton, M. J.; Mullaney, B. R.; Beer, P. D. Chem. Rev. 2015, 115, 7118−7195. (9) Dumele, O.; Trapp, N.; Diederich, F. Angew. Chem. Int. Ed. 2015, 54, 12339−12344. (10) El-Sheshtawy, H. S.; Bassil, B. S.; Assaf, K. I.; Kortz, U.; Nau, W. M. J. Am. Chem. Soc. 2012, 134, 19935−19941. (11) Aakeröy, C. B.; Rajbanshi, A.; Metrangolo, P.; Resnati, G.; Parisi, M. F.; Desper, J.; Pilati, T. CrystEngComm 2012, 14, 6366−6368. (12) Sarwar, M. G.; Ajami, D.; Theodorakopoulos, G.; Petsalakis, I. D.; Rebek, J. J. Am. Chem. Soc. 2013, 135, 13672−13675.


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(25) Sheldrick, G. M. SHELXTL Version 5.1, Bruker Analytical X−ray Instruments Inc., Madison, Wisconsin, USA, 1998. (26) Sheldrick, G. M. SHELX−97, PC Version, University of Gottingen, Germany, 1997. (27) Yan, D. P.; Lin, Y. J.; Meng, Q. Y.; Zhao, M. J.; Wei, M. Cryst. Growth Des. 2013, 13, 4495−4503. (28) Yan, D. P.; Yang, H. J.; Meng, Q. Y.; Lin, H. Y., Wei, M. Adv. Funct. Mater. 2014, 24, 587–594. (29) Yan, D. P.; Evans, D. G. Mater. Horiz. 2014, 1, 46–57. (30) Ono, T.; Sugimoto, M.; Hisaeda, Y. J. Am. Chem. Soc. 2015, 137, 9519−9522. (31) Li, S. Z.; Lin, Y. J.; Yan, D. P. J. Mater. Chem. C 2016, 4, 2527–2534. (32) Gao, H. Y.; Shen, Q. J.; Zhao, X. R.; Yan, X. Q.; Pang, X.; Jin, W. J. J. Mater. Chem. 2012, 22, 5336−5343. (33) Shen, Q. J.; Pang, X.; Zhao, X. R.; Gao, H. Y.; Sun, H. L.; Jin, W. J. CrystEngComm 2012, 14, 5027−5034. (34) Wang, H.; Hu, R. X.; Pang, X.; Gao, H. Y.; Jin, W. J. CrystEngComm 2014, 16, 7942−7948. (35) Aakeröy, C. B.; Wijethunga, T. K.; Benton, J.; Desper, J. Chem. Comm. 2015, 51, 2425−2428.


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For Table of Contents Use Only Soft−Cavity−type Host−Guest Structure of Cocrystals with Good Luminescence Behavior Assembled by Halogen Bond and Other Weak Interactions Rui Liu,† Hui Wang,*‡ and Wei Jun Jin*† The first and second authors contributed equally to this work. †College of Chemistry, Beijing Normal University, Beijing, Beijing, 100875, People's Republic of China ‡College of Chemistry & Material Science, Shanxi Normal University, Linfen, Shanxi, 041004, People's Republic of China

The host cocrystal with soft−cavity−type structure unit has been assembled by 1,4−DITFB and PPNO molecules mainly using the robust C−I···−O−N+ halogen bond, which has the capacity to envelope functional guests, Car, Nap, Phe and BhQ molecules, and to further form the host−guest cocrystals displaying good luminescence behaviors.


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Scheme 1. Structures of XB donor (D) and acceptor (A) as well as the guest molecules. 139x57mm (300 x 300 DPI)


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Figure 1. Structural details of cocrystal 1 as supramolecular host (distance in Å). (a) Ball and stick model of 3D supramolecular cavity structure constructed by C−I•••−O−N+ and C−H•••F bonds; (b) Space filling representation of the 3D supramolecular cavity structure. 65x152mm (300 x 300 DPI)



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Figure 2. The extracted supramolecular host−guest structural units of cocrystal 2 constructed by C−H•••F and C−H•••π bonds with two reversed Car molecules trapped in the broaden octamer cavity by C−H•••F and N−H•••π bonds (distance in Å). 134x88mm (300 x 300 DPI)


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Figure 3. Structural details of cocrystal 3 as an example of supramolecular host−guest systems (distance in Å): (a) and (b) The extracted 3D supramolecular host−guest structural along the a−axis and c−axis directions constructed by C−I•••−O−N+ XBs, C−H•••F, C−H•••π HBs, π−π stacking, as well as π−hole•••π−hole bonds. 129x66mm (300 x 300 DPI)



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Figure 4. The normalized total luminescent spectra of pristine monomers and the corresponding cocrystals 1−5 when excited at 380 nm, and the fluorescence decay curves at the emission monitoring wavelength measured under fluorescent mode (cf. Table 2). 65x33mm (300 x 300 DPI)


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Figure 5. Photographs of cocrystals 1−5 under UV−365 radiation and the color coordinates. 150x56mm (300 x 300 DPI)


Soft-Cavity-type HostâGuest Structure of Cocrystals with Good

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