The self-assembly of 2,7-bis(10-ethoxycarbonyl-decyloxy)-9-fluorenone (BEF) has been investigated by scanning tunneling microscopy at the liquid/solid interface. The coexistence and reversible transformation of linear structure and cyclic network were observed. Solvents with different polarity had little effect on the self-assembly of BEF on the HOPG surface. The observed structural transformation was found to be driven by voltage pulses applied to the STM tips. The influence of dipoleÀdipole interactions and van der Waals (vdWs) interactions on the different packing patterns was scrutinized by comparing the two-dimensional self-assembly of 2,7-bis(10-ethoxycarbonyldecyloxy)-9-fluorene, 2,7-ditetradecyloxy-9-fluorenone, and 2,7-ditetradecyloxy-9-fluorene with that of BEF molecule. The formation of different morphologies depended critically not only on the molecular conformation, but the different dipoleÀdipole interactions of the fluorenone unit and two ester alkoxy chains. The computer simulation and calculation of different morphologies are useful tools to dissect and explain the formation mechanism. On the basis of the comparative experiments and calculation, we could conclude that for the linear structure, the vdWs forces between the molecules were more important than the dipoleÀdipole interactions; on the contrary, the intermolecular dipoleÀdipole interactions induced the cyclic network.

Fluorenone derivatives (F−OC n ) with various lengths of peripheral alkyl chains (with carbon numbers of n = 12−18) were synthesized, and their self-assembled adlayers were investigated in solvents with different polarities and functionalities by scanning tunneling microscopy (STM) on a highly oriented pyrolytic graphite (HOPG) surface. The chain-length effect on the self-assembly of F− OC even was observed in 1-phenyloctane. With the shortening of the side chain, the self-assembled pattern changed from a dense-and loose-packed structure to a pliers-like structure. Self-assembly of F− OC odd showed a uniform lamellar pattern. An even−odd effect was observed resulting from the direction of the end methyl group in the alkyl chain unit. Furthermore, when the samples using dichloromethane as solvent were observed within 3 h, a less ordered lamellar structure appeared in most cases. The pliers-like pattern was observed for self-assembly of F−OC 16 and F−OC 14 . However, F− OC 17 formed a zigzag structure. Observation of the odd−even and chain-length effects on the self-assembled adlayers might provide an analytical method for examining the structural and chemical homogeneities.

The supramolecular patterns of a thienophenanthrene derivative could be switched among dissimilar polymorphs with different halogen-bond densities by solution concentration, which is demonstrated through a combination of STM and density functional theory (DFT) calculations.

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Two-dimensional self-assembly of 2,7-ditridecyloxy-9-fluorenone (F-OC13) is investigated by scanning tunneling microscopy (STM) in solvents with different polarities and functional groups on a high oriented pyrolytic graphite surface. The STM images reveal that the self-assembly of F-OC13 is strongly solvent-dependent. 1-Phenyloctane can coadsorb on the self-assembly of F-OC13, and the structural transformation of the adlayer from the linear structure to alternate lamella can be observed with the decrease of the concentration. At the 1-octanol/HOPG interface, only a well-ordered linear pattern is obtained. The intermolecular hydrogen bonding between the 1-octanoic acid and the F-OC13 molecule is responsive for the formation of butterfly configuration. When n-tridecane or n-tetradecane is used as solvent, a regular alternate pattern is formed under high concentrations, and a coadsorbed lamellar structure is observed under low concentrations. Furthermore, when the sample with use of the methanol, dichloromethane, or toluene as solvent is observed within one hour, a denser-packed structure appears. After the sample is placed more than three hours, in methanol and dichloromethane, a regular alternate pattern is formed corresponding to the result using n-tridecane or n-tetradecane as a solvent under high concentration. In toluene, the alternated pattern is similar with that in 1-phenyloctane at low concentration. The solvent induced self-assembly polymorphism is discussed in terms of factors of the polarity of the F-OC13 molecule and the nature of the solvent. The results provide a new objective to fabricate and control molecular nanopatterns based on the polar group in the molecule.