In this paper it is demonstrated that the stabilizing effect of linear alkanes can be utilized to achieve very high stability in the adsorption and assembly of planar organic molecules on inert surfaces under ambient conditions, by direct deposition from solutions. Using peripherally alkylated phthalocyanines and porphyrins as the examples, optimal resolutions can be achieved with complex molecular systems. Submolecular features of the molecular cores and the interdigitated alkyl parts are clearly visible. Distinctly different packing symmetries were also observed and could be attributed to the intermolecular and adsorbate−substrate interactions. Appreciable contrast variations were also recorded with changing bias voltages. This approach could be adapted to the studies of other molecules to observe submolecular features and could be helpful in obtaining two-dimensional assemblies of monodispersed molecules, especially planar molecules.

Hydrogen-bonded two-dimensional networks of 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) were formed on the surface of highly oriented pyrolytic graphite (HOPG). With these networks as host networks and copper(II) phthalocyanine (CuPc) and coronene as guest molecules, the host-guest architectures of CuPc/ TCDB and coronene/TCDB were achieved when host and guest molecules coadsorb on HOPG. The monolayer structure of the networks of TCDB and the inclusion structures of host-guest systems were investigated by STM.

Controlled regulation of the switchable behavior of the supramolecular network is central to the potential application in the molecular scale nanodevices. In this work, it is reported that the reversible accommodation of the guest molecules in the nanoporous supramolecular network can be regulated by the UV/visible light. The nanoporous complex template of TCDB/4NN-Macrocycle(trans,trans,trans,trans) with photosensitive units is well-defined. After the UV irradiation, the template can be switched on to encapsulate coronene molecules due to the formation of a new photoisomer(trans,cis,trans,cis) and switched off to expel coronene from the inner cavities under the visible light. The photoregulated switchable multicomponent supramolecular guest-host network provides a novel strategy for fabricating the functional nanodevices at the molecular scale.

Fullerenes have attracted a great deal of attention since their discovery [1] because of their unique physical and chemical properties and potential applications.[2] Many applications require the deposition of fullerenes onto a variety of surfaces including metals [3][4][5][6] or semiconductors. [7] The fabrication of ordered arrays of fullerenes on solid surfaces is of interest from both scientific and technological viewpoints. It has been demonstrated that fullerenes can form well-ordered arrays on metal or semiconductor surfaces under ultrahigh vacuum (UHV) conditions at low temperatures. [8][9][10][11][12] The arrangement is determined by the size and symmetry of the fullerenes and rigidly maintains its shape. On the other hand, C 60 is highly mobile at room temperature (RT) even when adsorbed on metal surfaces, and has no preferential orientation unless cooled to low temperatures. [13][14][15][16][17][18][19][20] Therefore, a well-decorated surface, which serves as a molecular template and provides binding sites, is important and necessary for the fabrication of highly ordered arrays of fullerenes at RT. Open porous networks obtained by metal-organic coordination, [21] the formation of hydrogen bonds, [8] or even van der Waals interactions [22][23][24] have been successfully used to direct the formation of ordered fullerene arrays. In this way the interfullerene distance and symmetry of the arrangement are solely determined by the molecular template and can be changed by adjusting its structure. More importantly, interactions between fullerenes can also be modified with this strategy.We have designed and synthesized a tetraacidic azobenzene molecule NN4A (Figure 1a) that exclusively forms KagomØ open networks with two types of cavities that have different size and symmetry at the liquid-solid interface. These cavities are capable of accommodating fullerene molecules as guest species. Herein, we examine the site selectivity of the networks for different fullerenes, a feature which has not been observed for other systems at liquid-solid interfaces. Azobenzene derivatives are typical photochromic compounds that have a wide range of potential applications, including for optical switching, holographic storage, light harvesting, long-term energy storage, and nonlinear optical materials. [25,26] The attractive photosensitive properties of azobenzene compounds have resulted in them being utilized as photoswitching units to control the structure and function of supramolecular systems. [27][28][29][30][31] Thus, the use of azobenzene units in the host matrix could allow for further control of the host-guest architectures.When deposited onto a graphite surface, NN4A forms a well-ordered open network with a KagomØ structure which is correlated to molecular geometry and network symmetry. [32,33]

The macrocyclic compounds consisting of photosensitive units as parts of the frame have been extensively studied to mimic photoregulated functions in nature. In this paper, controlled assembly of well-ordered arrays of photosensitive macrocyclic rectangles is demonstrated by using a host-guest molecular template. 4NN-Macrocycle molecules are observed to photoisomerize from trans-trans-trans-trans (t,t,t,t) to a range of isomers including trans-trans-trans-cis (t,t,t,c) and trans-cis-trans-cis (t,c,t,c) isomers after irradiation of UV light. The photoisomers are also observed to affect the guest-host network characteristic appreciably. In the STM observations we can distinguish three (t,t,t,t) conformational isomers, three (t,t,t,c) conformational isomers, and one (t,c,t,c) isomer, which self-assemble into different adlayers with TCDB on a HOPG surface. This study provides a facile approach to study the photoisomerization processes of the azobenzene groups and the conformational photoisomers.

Using CuPcOC8 and ZnPcOC8 as examples, we have demonstrated that metal phthalocyanines with covalently attached long alkyl chains can be immobilized at the interface of the organic solution and the basal plane of HOPG. Highly resolved images of the molecules can be obtained in a range of bias voltages. The high stability and close-packed assembly are attributed to the van der Waals interaction between the alkyl chains and the graphite substrate, which substantially increased the desorption barrier of the combined molecule. In addition, it is illustrated that the desorption barrier is further enhanced by the 2-D crystallization of alkane chains. It is hoped that this method could provide a complementary approach to prepare an ordered two-dimensional array of molecular films, and facilitate the STM studies of fine molecular structures.

Molecular structures are known to significantly impact the adsorption and assembling behavior of the adsorbates on surfaces. Precise control of the molecular orientation and ordering will enable us to tailor the physical and chemical properties of the molecular architectures. In this work, we present a strategy of attaching functional groups with dissimilar adsorption and assembling characteristics to the top and bottom phthalocyaninato moieties of a triple-decker complex, and orientational-dependent ordering of such molecules at the liquid/solid interface has been identified, which is attributed to the interaction of the intrinsic molecular dipole with the external electric field. In addition, isomerization of the noncentrosymmetric tris(phthalocyaninato) lutetium triple-decker complex has been revealed directly with STM and further confirmed by theoretical simulation. This approach provides a possible way for the preparation of organic films with switchable electronic and/or interface properties with external field.

Though moderate heating in a controlled environment is generally considered to be necessary, in this work we show that the most important prerequisite for obtaining high quality 2D imine polymers at the interface is the concentration and molar ratio of building blocks on the surface. With diverse monomers we have demonstrated that the concentration-in-control strategy is a general and powerful way to construct covalent single layer 2D imine polymers with high regularity at the solid/liquid interface.