ARTICLE pubs.acs.org/JPCC
Selective and Competitive Adsorptions of Guest Molecules in Phase-Separated Networks Yong-tao Shen,†,‡ Ke Deng,† Xue-mei Zhang,† Da Lei,‡ Ye Xia,‡ Qing-dao Zeng,*,† and Chen Wang*,† † ‡
National Center for Nanoscience and Technology (NCNST), Beijing 100190, P. R. China Department School of Materials Science and Engineering, Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University, Tianjin 300072, People’s Republic of China
bS Supporting Information ABSTRACT: The formation of crystalline multicomponent 2D lattices, containing more than two different organic molecular building blocks, has been rarely achieved because optimized recognition and selection processes require us to achieve the targeted multicomponent surface confined patterns. In this Article, we show that tetraacidic azobenzene (NN4A) and 1,3,5-tris(10-carboxydecyloxy)-benzene (TCDB) molecules can exclusively form 2D phase-separated nanoporous networks via hydrogen bonds between carboxyl groups at the liquidsolid interface, which have two types of cavities with different size and symmetry. These networks can serve as organic templates for the accommodation of fullerene (C60), coronene, and copper(II) phthalocyanine (CuPc) molecules. The experimental and calculated results indicate that coronene can be immobilized in the cavities formed by both NN4A and TCDB, whereas CuPc can be immobilized only in the cavity formed by TCDB and C60 can be immobilized only in the cavity formed by NN4A. Moreover, in the phase-separated networks, the coronene can be preferentially immobilized in NN4A. These results could benefit the studies on highly selectively molecular recognition and separation.
’ INTRODUCTION Self-assembly of nanoscaled building blocks at surfaces or interfaces is of increasing interest for nanoscience research because of their potential applications in surface templating, nanopatterning, sensing, and heterogeneous catalysis.16 Therefore, gaining control of molecular ordering on surfaces is an active field of research. Supramolecular chemistry is a powerful methodology to create such controlled assembly of nanostructures following bottom-up principles.7 Two-dimensional molecular crystals are typically formed by self-assembly at the liquidsolid interface8 or under ultra-high-vacuum conditions (UHV)9,10 on atomically flat conductive substrates, and their structures are frequently probed by scanning tunneling microscopy (STM). The formation of crystalline multicomponent 2D lattices, containing more than two different organic molecular building blocks, has been rarely achieved11,12 because optimized recognition and selection processes13,14 require us to achieve the targeted multicomponent surface confined patterns. Molecular assemblies of increasing complexity can be spontaneously formed based on a multitude of noncovalent interactions. Similarly, the spontaneous formation of multicomponent heteromeric 2D crystals requires efficient recognition and selection.1518 Such specific recognition is essential for the immobilization and study of functional molecules at the single-molecule level of precision, which can be applied in molecular sieves potentially. The confinement to two dimensions makes the self-assembly of multicomponent systems less problematic in terms of designing r 2011 American Chemical Society
and controlling intermolecular interactions. However, balancing moleculesubstrate interactions is absolutely crucial. At the liquidsolid interface, solventmolecule and solventsubstrate interactions must be also considered.
’ EXPERIMENTAL SECTION 1,3,5-Tris(10-carboxydecyloxy)-benzene (TCDB)1924 and tetraacidic azobenzene (NN4A)25 were synthesized according to the reported procedures. Copper(II) phthalocyanine (CuPc), coronene, and fullerene (C60) were purchased from Across, used without further purification, and synthesized by the reported methods, and the solvent was heptanoic acid (>98%). The sample was prepared in a two-step procedure. First, by depositing a droplet of the mixture solution of NN4A and TCDB (1:5) in heptanoic acid, phase-separated nanoporous networks were formed on a freshly cleaved HOPG surface. The concentration of the NN4A/TCDB solution was
