H-Bond Switching Mediated Multiple Flexibility in Supramolecular

Oct 30, 2007 - Two types of dramatically different host−guest architectures are identified for each MPc/TCDB systems, that is, the architecture MPc/...
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17382

J. Phys. Chem. C 2007, 111, 17382-17387

H-Bond Switching Mediated Multiple Flexibility in Supramolecular Host-Guest Architectures Xiang-Hua Kong,†,§ Ke Deng,‡ Yan-Lian Yang,‡ Qing-Dao Zeng,‡ and Chen Wang*,‡ Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100080, P. R. China, and National Center for Nanoscience and Technology, Beijing 100080, P. R. China ReceiVed: June 16, 2007; In Final Form: September 14, 2007

Two-dimensional (2D) self-assembled 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) networks connected by hydrogen bonds on highly oriented pyrolytic graphite (HOPG) surfaces are shown to accommodate a variety of unsubstituted metallophthalocyanine (MPc) molecules (such as H2Pc, CuPc, VOPc, and ClGaPc) and halogen-substituted MPcs (such as F16CuPc), which have been observed by scanning tunneling microscopy (STM) under ambient conditions. Two types of dramatically different host-guest architectures are identified for each MPc/TCDB systems, that is, the architecture MPc/TCDB (I) (with MPc monomers entrapped in the TCDB cavities) and the architecture MPc/TCDB (II) (with MPc dimers entrapped in the TCDB cavities). The intermolecular interactions are calculated by density functional theory (DFT), which demonstrates that the host-guest intermolecular interactions (including van der Waals forces and electrostatic interactions caused by asymmetrical electronic distribution of MPcs) are important in determining the on-and-off of hydrogen bonds in the host lattice. The STM study combined with the DFT calculations reveal that the hydrogen bond switching through O-H‚‚‚O bonds is responsible for the formation of TCDB cavities with multiple flexibility for guest molecule inclusion.

Introduction Constructing multicomponent host-guest architectures is an effective method to obtain well-ordered distributions with heterogeneous molecules/atoms on solid surfaces. By adopting various geometries and functionalities of molecular building blocks, a broad range of host structures could be obtained, providing us with a rich ground for explorations of composite molecular architechtures.1-19 For example, C60 molecules could be included in the PTCDI-melamine lattice to form the honeycomb networks,1 immobilized within hexagonal organic networks formed by the series of trimesic acid,2,3 and in the porous networks formed by porphyrin derivative,4 and even adsorbed on the specific sites formed by porphyrin derivatives or cyclothiophene C[12]T to form long range ordered assemblies.5,6 These observations have contributed to the understanding of intermolecular and adsorbate/substrate interactions. The weak noncovalent intermolecular interactions, such as van der Waals force and hydrogen bonding, are known to play essential roles in forming host-guest architectures.14-28 Recent studies reported that donor-acceptor interactions between host and guest molecules could also lead to the formation of C60/ cyclothiophene(C[12]T) or C60/macrocycle(1) composite architectures.6,7 However, it can be noticed that the mechanisms controlling the self-assembling phenomena have yet to be fully understood. Furthermore, host-guest interactions governing the characteristics of composite molecular architectures also keenly demand dedicated investigations. * Corresponding author. Tel: +86-10-62652700. Fax: +86-10-62562871. E-mail: [email protected]. † Institute of Chemistry, Chinese Academy of Sciences. ‡ National Center for Nanoscience and Technology. § Also in CAS Graduate School, Beijing 100080, P. R. China.

A series of experimental studies have revealed that copper phthalocyanine (CuPc) molecules could be encapsulated within the tetragonal network of 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) to form a monomer-entrapped architecture CuPc/ TCDB (I).24 Whereas in a parallel study, vanadyl phthalocyanine (VOPc) molecules were found to form only the dimer-entrapped VOPc/TCDB (II) architecture when coadsorbed with TCDB molecules at relatively low temperatures (for example, below 26 °C). Additionally, it was observed that thermal annealing of the as-prepared adlayers could induce phase transition from VOPc/TCDB (II) to VOPc/TCDB (I).25 Common to the above studies is that an appreciable expansion or contraction of the host cavities could be induced by the guest molecule inclusion. TCDB provided us with an excellent host template that could readily self-adjust to accommodate guest molecules. In the previous reports, hydrogen bonding in host networks and van der Waals interactions between the substrates and the alkyl chains of TCDB networks were clearly the governing factors for controlling the detailed characteristics of the composite architectures.24,25 It can be envisioned that further insight on the impact of intermolecular interactions should be beneficial for the related studies on constructing novel heterogeneous molecular architectures. In this work, a series of MPcs (M ) H2, Cu, VO, and ClGa) and F16CuPc with various central metals or fluorin-substitution (see Scheme 1, parts a and b) are chosen as guest molecules or coadsorbates aimed for encapsulations in TCDB cavities. The on-and-off of hydrogen bond configurations and the distortion of host lattice according to various guest molecules are observed by using scanning tunneling microscopy (STM) under ambient conditions. The intermolecular interactions among host and guest molecules are calculated by density functional theory (DFT), and their effects on hydrogen bond switching of the host TCDB networks are discussed in detail.

10.1021/jp074682p CCC: $37.00 © 2007 American Chemical Society Published on Web 10/30/2007

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SCHEME 1: Chemical Structures of the Guest Molecules and the Host Moleculea

a (a) Metallophthalocyanines (MPc) (M ) H2, Cu, VO, ClGa). (b) Copper (II) hexadecafluoro-29H,31H-phthalocyanine (F16CuPc). (c) 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB).

Experimental Section TCDB was synthesized as previously reported.24,25,29 CuPc and H2Pc were purchased from Acros Co., VOPc and ClGaPc were purchased from Alfa, and F16CuPc was purchased from Aldrich. All MPcs were used as received. The guest species were introduced through a coadsorption approach, and STM observations were performed under ambient conditions. The solvent used in the STM experiments was toluene (HPLC grade, Acros). The concentrations of all of the solutions used were less than 1 mM. The molar ratio of TCDB to MPc was approximately 2:1. It should be noted that we had tried other concentrations and molar ratios and found that the above

conditions were optimal. When the molar ratio of TCDB to MPc was much higher than 2:1, most regions were occupied with unfilled TCDB networks. When the molar ratio of TCDB to MPc was far lower than 1:1, most regions were occupied with dimer-entrapped architectures along with only a few regions occupied with monomer-entrapped architectures. We have not found any other types of MPc/TCDB host-guest architectures. When the ratio was in the range from 2:1 to 1:1, both dimerentrapped and monomer-entrapped architectures could be easily observed simultaneously. The samples were prepared by depositing a droplet of the solution containing the host and the guest species on the freshly cleaved highly oriented pyrolytic graphite (HOPG) surfaces at room temperatures (about 30 °C). After the solvent was completely evaporated, the STM measurements were performed with a Nanoscope IIIA system (Veeco Metrology, USA). The tips were mechanically formed Pt/Ir wires (80/20). All of the STM images were recorded using constant current mode. The specific tunneling conditions are given in the figure captions. We performed theoretical calculations using DFT provided by the DMol3 code.30 The Perdew and Wang parametrization31 of the local exchange-correlation energy is applied in the local spin density approximation (LSDA) to describe the exchange and correlation. We expand the all-electron spin-unrestricted Kohn-Sham wave functions in a local atomic orbital basis. In such double-numerical basis set polarization is described. All calculations are all-electron ones and are performed with the extra-fine mesh. A self-consistent field procedure is done with a convergence criterion of 10-5 a.u. on the energy and electron density. Results and Discussion As previously reported, TCDB molecules (see Scheme 1c) could self-assemble into large-area and homogeneous networks with nearly tetragonal cavities when deposited on HOPG surfaces,24 as shown in Figure 1a. The proposed molecular model illustrating the packing arrangements of TCDB molecules is displayed in Figure 1b. We have performed DFT calculations and the calculated parameters of the unit mesh agree well with

TABLE 1: Measured and Calculated Unit Mesh Parameters, the Calculated Hydrogen Bonding, and the Unit Mesh Binding Energies of the Original Unfilled TCDB Networks and the Two Types of MPc/TCDB Architectures (MPc ) H2Pc, CuPc, F16CuPc, VOPc, and ClGaPc)a

type (I)

(measured) (calculated)

type (II)

dimer O-H‚‚‚O TCDB dimer interaction TCDB dimer with MPc cell binding energy (measured) (calculated) MPcsMPc distance dimer O-H‚‚‚O TCDB dimer interaction TCDB dimer with MPcs cell binding energy

a

a b R a b R

a b R a b R

unit

TCDB

nm nm ° nm nm ° nm kcal mol-1 kcal mol-1 kcal mol-1 nm nm ° nm nm ° nm nm kcal mol-1 kcal mol-1 kcal mol-1

3.9 ( 0.1 2.2 ( 0.1 73 ( 2.0 3.80 2.25 73.0 0.253 25.26 71.09 3.9 ( 0.1 2.2 ( 0.1 73 ( 2.0 3.80 2.25 73.0 0 0.253 25.26 71.09

TCDB/ H2Pc

TCDB/ CuPc

3.0 ( 0.1 2.3 ( 0.1 86 ( 1.0 3.15 2.44 87.0 0.255 30.05 12.86 107.36 4.6 ( 0.1 2.0 ( 0.1 84 ( 1.0 4.55 2.00 85.0 1.62 0.259 9.57 17.63 69.27

2.9 ( 0.1 2.2 ( 0.1 87 ( 1.0 3.10 2.44 87.5 0.255 24.09 7.79 98.64 4.7 ( 0.1 2.0 ( 0.1 83 ( 1.0 4.60 2.00 84.0 1.66 0.266 7.25 14.96 56.96

TCDB/ F16CuPc 3.1 ( 0.1 2.4 ( 0.1 75 ( 1.0 3.20 2.40 78.0 0.250 20.69 11.76 39.70 4.6-5.6 2.0 ( 0.1 82-74 4.90 2.00 80.0 1.70 0.267 4.75 8.95 33.13

Bold and italic fonts emphasize the dimensions and energies mentioned in the text, respectively.

5.60 2.00 74.0 1.52 0.266 5.04 10.58 42.27

TCDB/ VOPc

TCDB/ ClGaPc

3.0 ( 0.1 2.3 ( 0.1 82 ( 1.0 3.15 2.38 83.0 0.250 48.42 12.45 130.38 5.1 ( 0.1 2.0 ( 0.1 80 ( 1.0 5.00 2.10 81.0 1.24 0.249 18.15 23.80 96.46

3.1 ( 0.1 2.2 ( 0.1 82 ( 1.0 3.20 2.40 78.0 0.250 44.81 14.59 128.06 4.9 ( 0.1 2.0 ( 0.1 84 ( 1.0 4.80 2.00 85.0 1.85 0.251 21.58 30.06 112.44

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Figure 1. (a) Typical high-resolution STM image of 2D self-assembled TCDB molecules adsorbed on HOPG surfaces. The unit mesh is superimposed with black lines. Tunneling conditions are 472.9 mV and 782.9 pA. (b) The proposed molecular model of TCDB networks. The neighboring rows are donated to rows I and II. The two black ellipses and the black square drawn in Figure 1b point out the hydrogen bonds of host networks.

the experimental values, which are listed in Table 1. Within the assembled molecular architecture, every two TCDB molecules form a cavity and the observed TCDB dimer structure is considered to be connected via hydrogen bonds between the carboxyl groups. This is also confirmed by the DFT calculations, which reveal that two TCDB molecules interact through double pairs of O-H‚‚‚O hydrogen bonds (as pointed out by the two black ellipses drawn in Figure 1b) to form a cavity with the alkyl chains. The calculation also suggested that O-H‚‚‚O hydrogen bond length is ∼ 2.53 Å, and the interaction of a TCDB dimer is about 25.3 kcal mol-1. It is noticed that the cavity in row I is connected with another one in the neighboring row II through another pair of O-H‚‚‚O hydrogen bonds (as pointed out by the black square drawn in Figure 1b) to construct the network. Our previous report demonstrated that CuPc (or VOPc) molecules could be immobilized in the TCDB cavities to form the CuPc/TCDB (or VOPc/TCDB) host-guest architectures.24,25 Further study herein shows that both dimer-entrapped (designated as MPc/TCDB (II)) and monomer-entrapped (designated as MPc/TCDB (I)) composite architectures could be obtained when the samples were prepared under ambient conditions. The particular interest is that, in spite of varying the central metal ions or halogen-substitution to MPcs, a variety of MPcs (such as H2Pc, CuPc, VOPc, ClGaPc and F16CuPc) could be incorporated into both types of the host-guest architectures when coadsorbed with TCDB molecules on HOPG surfaces. Mol-

Figure 2. Typical large-scale STM images of the host-guest architectures of MPc/TCDB on HOPG sufaces. Parts a-e are H2Pc/ TCDB, CuPc/TCDB, F16CuPc/TCDB, VOPc/TCDB, and ClGaPc/ TCDB, respectively. Tunneling conditions are as follows: (a) 649.7 mV, 399.8 pA; (b) -527.9 mV, 555.4 pA; (c) 474 mV, 423 pA; (d) 800 mV, 359 pA; (e) 566 mV, 568 pA.

ecules were adsorbed with high stability under ambient conditions, and high-quality STM images could be readily obtained. The large-scale STM images of MPc/TCDB architectures are exhibited in Figure 2. As shown in Figure 2, each long-range STM image can be classified into mainly two kinds of regions, marked as A and B. In region A, MPc monomers are entrapped in the TCDB cavities to form a nearly quadratic lattice with bright spots, whereas in region B, MPc dimers are included in the TCDB cavities to form a stripe structure with aligned bright spots. Although similar architectures can be observed, the hydrogen bond configurations of TCDB host lattice are varied according to different guest molecules in a sensitive way for both types of MPc/TCDB composite architectures. Hydrogen Bond Configurations of Host Lattice in Monomer-Entrapped MPc/TCDB (I) Architectures. The H2Pc/ TCDB (I) architecture is presented as an example. The detailed packing arrangement of H2Pc/TCDB (I) is shown in Figure 3a. One white square and two white circles are drawn in Figure 3a to represent H2Pc and the benzene cores of TCDB, respectively. The long alkyl chains of TCDB are not labeled here for simplification. On the basis of the adlayer symmetry and

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Figure 3. Typical high-resolution STM images of the monomer-entapped H2Pc/TCDB (I) architecture (a) and F16CuPc/TCDB (I) architecture (c). Panels b and d schematically illustrate the proposed molecular models for H2Pc/TCDB (I) and F16CuPc/TCDB (I), respectively. The unit meshes are superimposed with black lines. The white squares and the white circles in panels a and c represent the MPc molecules and the benzene cores of TCDB molecules, respectively. The black ellipses and the square drawn in panels b and d point out the hydrogen bonds of host networks, and the rectangle in panel d indicates that the distance of the carboxyl groups are too large to form hydrogen bonds. Tunneling conditions are as follows: (a) 649.7 mV, 399.8 pA; (c) -573 mV, 470 pA.

intermolecular distances, a unit mesh is superimposed with a ) 3.0 ( 0.1 nm, b ) 2.3 ( 0.1 nm, and R ) 86 ( 1.0°. The value of a is much smaller and the R is larger than those of the original unfilled TCDB unit mesh (with a ) 3.9 ( 0.1 nm, b ) 2.2 ( 0.1 nm, and R ) 73 ( 2.0°). The suggested molecular model to illustrate the assembling structure is shown in Figure 3b. Comparing with the molecular model of the unfilled TCDB network shown in Figure 1b, the area of the unit mesh (denoted as S, S ) ab sin R) (about 6.9 nm2) of TCDB host networks is shrunk significantly as the result of structural distortion. In addition, the hydrogen bonds connecting TCDB dimers and those linking the cavities have sustained the impact of the coadsorbate (as pointed out by the two black ellipses and the black square drawn in Figure 3b, respectively). Theoretical analysis shows that the O-H‚‚‚O hydrogen bond length connecting a TCDB dimer is ∼2.55 Å, resulting in similar interactions (about 30.0 kcal mol-1) for the host lattice to the original unfilled TCDB dimers. Similar high-resolution STM images of other MPc/TCDB (I) and the corresponding molecular models are shown in Figure S1. The calculated intermolecular interactions in MPc/TCDB (I) architectures are listed in Table 1. The interaction between a TCDB dimer and the included H2Pc is rather weak (only about 12.9 kcal mol-1), which is similar to other MPc/TCDB (I) systems. Herein, the intermolecular interaction between host molecules and guest molecules is mainly attributed to van der Waals forces. It is noted that the unit mesh binding energies of MPc/TCDB (I) (M ) H2, Cu, VO, and ClGa) are much higher than that of an unfilled TCDB unit mesh because of the guest molecule inclusion. Contrarily, the unit mesh binding energy

of F16CuPc/TCDB (I) is only about 39.7 kcal mol-1, much lower than that of an empty TCDB unit mesh (about 71.1 kcal mol-1). This is attributed to the breakage of the hydrogen bonds linking the cavities based on DFT calculations (as pointed out by the black rectangle drawn in Figure 3d). The typical high-resolution STM image of F16CuPc/TCDB (I) architecture and the proposed molecular model are shown in Figure 3, panels c and d, respectively. A unit mesh is superimposed in Figure 3c with a ) 3.1 ( 0.1 nm, b ) 2.4 ( 0.1 nm, and R ) 75 ( 1.0°. In order to accommodate the guest molecules F16CuPc which have larger size due to fluorin-substitution, the host structure had to open the weaker hydrogen bonds linking the cavities, which reveals the strong effect of guest molecules to the host lattice. Above all, in the composite architectures MPc/TCDB (I), the host structures were observed to contract appreciably due to the guest molecule inclusion. Theoretical analysis suggested that hydrogen bonding among TCDB molecules is crucial to stabilize the host networks, and van der Waals forces are the dominant intermolecular interactions between the host and the guest molecules. The architectures MPc/TCDB (I) are subject to the balance between the hydrogen bonding of host lattice and all of the intermolecular interactions between the host and the guest molecules. Hydrogen Bond Configurations of Host Lattice in DimerEntrapped MPc/TCDB (II) Architectures. The H2Pc/TCDB (II) architecture is presented as an example for dimer-entrapped architecture. The detailed adsorption structure of H2Pc/TCDB (II) is shown in Figure 4a. Two white squares and four white circles are drawn in Figure 4a to represent H2Pc molecules and the benzene cores of TCDB, respectively. A dimer formed by

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Figure 4. (a and c) Typical high-resolution STM images of the dimer-entrapped H2Pc/TCDB (II) and F16CuPc/TCDB (II) architectures, respectively. The unit meshes are superimposed with black lines. The white squares and the white circles in panels a and c represent the MPc molecules and the benzene cores of TCDB molecules, respectively. The length of the blue lines in panel c shows the central distance between two F16CuPc molecules in one cavity. Tunneling conditions are as follows: (a) 865 mV, 489 pA; (c) 631 mV, 530 pA. (b) The proposed molecular model of H2Pc/TCDB (II) structure. Panels d and e are the suggested molecular models illustrating the two proposed architectures of F16CuPc/TCDB (II) with R ) 74° and 80°, respectively. The black ellipses and the squares in panels b, d, and e point out the hydrogen bonds of host networks, and the rectangle in panel e indicates that the distance of the carboxyl groups are too large to form hydrogen bonds.

a pair of H2Pc molecules is entrapped in one TCDB cavity. The two H2Pc molecules in one cavity are positioned nearly side-by-side to achieve the most stabilized arrangement. Choosing a cavity including a H2Pc dimer as a repeating unit, a unit mesh is superimposed in Figure 4a and the parameters are a ) 4.6 ( 0.1 nm, b ) 2.0 ( 0.1 nm, and R ) 84 ( 1.0°. The resulted area of the unit mesh S (about 9.2 nm2) of TCDB host networks is expanded greatly when the guest molecules are entrapped in them. Herein, one can observe that the TCDB cavity is totally different from the original unfilled cavity and the one filled with monomer, both in size and conformation. Seen from Figure 4a, there are four TCDB molecules associated with one cavity instead of two TCDB molecules. One can also identify that there are still two TCDB molecules involved in each unit mesh considering the neighboring unit mesh shares these four molecules. The hydrogen bond configurations of the host lattice in H2Pc/TCDB (II) architecture are illustrated in the proposed molecular model in Figure 4b. The TCDB dimer could form only a single pair of hydrogen bonds in a unit mesh (as pointed out by the black ellipse drawn in Figure 4b), resulting in relatively weak interaction (about 9.6 kcal mol-1) and larger cavity size. As the result, the host TCDB networks show high flexibility attributed to the reduced number of hydrogen bonds. Herein, the hydrogen bonds linking the cavities still exist to stabilize the composite architecture (as pointed out by the black square drawn in Figure 4b). Compared with the host-guest interaction in H2Pc/TCDB (I) architecture, the total host-guest

interaction in H2Pc/TCDB (II) is a little higher (about 17.6 kcal mol-1), which is considered the result of the addition of one H2Pc molecule per cavity. The van der Waals force is still proposed to be the main intermolecular interaction between the host molecules and the guest molecules. Similar structures were observed in dimer-entrapped CuPc (or VOPc, ClGaPc)/TCDB (II) architectures (see Figure S2). However, the composite architecture F16CuPc/TCDB (II) was different from the other four MPc/TCDB (II) structures mentioned above. The central distance between two F16CuPc molecules in one cavity was not definite but variable ranging from 1.5 to 1.7 nm, as denoted with blue lines in Figure 4c. The length of the blue lines shows clearly the change of the distance. Two molecular models are demonstrated in Figure 4, panels d and e to illustrate the adsorbed structures of F16CuPc/ TCDB (II) under the two proposed conditions. The O-H‚‚‚O hydrogen bonds linking TCDB cavities are on when the PcPc distance is about 1.5 nm (as shown in Figure 4d) while they are off when the distance is about 1.7 nm (as shown in Figure 4e), resulting in the fact that the unit mesh binding energy of the latter (about 33.1 kcal mol-1) is lower than that of the former (about 42.3 kcal mol-1). It is considered that the electronegative characteristics of fluorin groups lead to a higher dipole moment and enhance the intermolecular interactions (especially electrostatic mutual repulsion) between two adjacent F16CuPc molecules in each cavity. The intermolecular repulsion leads to the increase of the Pc-Pc distance and subsequently

H-Bond Switching Mediated Multiple Flexibility expansion of the cavities. The architectures of F16CuPc/TCDB (II) are the result of a delicate balance mainly between the hydrogen bond of TCDB dimers and the intermolecular interactions including molecule-molecule electrostatic interactions (homo) and van der Waals forces (homo and hetero). Herein, the hydrogen bond configurations of the host lattice were tuned sensitively according to the total size of the entrapped MPc dimers. The theoretical simulation of MPc/TCDB (II) architectures are also presented in Table 1. It can be recognized that the unit mesh binding energies for VOPc and ClGaPc systems are dramatically stronger than those for H2Pc (or CuPc and F16CuPc) systems in both monomer-entrapped and dimer-entrapped types. Such difference could be attributed to the dipole moments of VOPc and ClGaPc. As nonplanar molecules, further theoretical results show that the dipole moments of VOPc and ClGaPc are perpendicular to the Pc ring planes (about 2.4 and 3.5 debye, respectively), which enhance the electrostatic interaction between VOPc (or ClGaPc) molecules in each TCDB cavity. Simultaneously, the increased molecular interactions lead to the change (expansion or contraction according to the horizontal (or perpendicular) percentage in dipole-dipole interactions) of the Pc-Pc distance and subsequently changed the hydrogen bond configuration of host lattice and the unit mesh parameters of the composite architectures. This further proves the sensitivity of hydrogen bonds in the host lattice to the size and symmetry of guest molecules, and confirms that a size matching requirement is an important factor for constructing host-guest architectures. Conclusion In summary, a variety of MPcs could be observed to form two dramatically different types of composite architectures when coadsorbed with TCDB molecules on HOPG surfaces. Theoretical analysis suggests that O-H‚‚‚O hydrogen bonds play essential roles in stabilizing the host network. The host lattice could self-adjust its conformations to accommodate the guest molecules. Such host structure flexibility is achieved by the alkyl chain distortion and the hydrogen bond switching of host networks. Theoretical calculations also reveal that van der Waals forces are the dominant intermolecular interactions for H2Pc (or CuPc)/TCDB architectures, whereas there also exists electrostatic interaction for F16CuPc and dipole-dipole interaction for VOPc (or ClGaPc) in MPc/TCDB (II) systems. In all, the MPc/TCDB composite architectures are the result of a delicate balance mainly between the hydrogen bonds of TCDB lattice and the MPc-TCDB interactions including van der Waals forces and electrostatic interactions. This study provides a good example in studying the flexibility of host lattice in 2D selfassembled host-guest architectures. Because of the well-known optoelectronic properties of MPc molecules, the heterogeneous architectures obtained in this work are of interest in the potential applications of molecular devices and nanoelectronics. Acknowledgment. Financial support from the National Natural Science Foundation of China (Grant Nos. 90406019,

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