Two-Dimensional Porous Molecular Networks of Dehydrobenzo[12]annulene Derivatives via Alkyl Chain Interdigitation

摘要

The self-assembly of a series of hexadehydrotribenzo[12]annulene (DBA) derivatives has been scrutinized by scanning tunneling microscopy (STM) at the liquid-solid interface.First,the influence of core symmetry on the network structure was investigated by comparing the two-dimensional (2D) ordering of rhombic bisDBA 1a and triangular DBA 2a (Figure 1).BisDBA 1a forms a Kagome network upon physisorption from 1,2,4-trichlorobenzene (TCB) onto highly oriented pyrolytic graphite (HOPG).Under similar experimental conditions,DBA 2a shows the formation of a honeycomb network.The core symmetry and location of alkyl substituents determine the network structure.The most remarkable feature of the DBA networks is the interdigitation of the nonpolar alkyl chains: they connect the pi-conjugated cores and direct their orientation.As a result,2D open networks with voids are formed.Second,the effect of alkyl chain length on the structure of DBA patterns was investigated.Upon increasing the length of the alkyl chains (DBAs 3c-e) a transition from honeycomb networks to linear networks was observed in TCB,an observation attributed to stronger molecule-substrate interactions.Third,the effect of solvent on the structure of the nonpolar DBA networks was investigated in four different solvents: TCB as a polar aromatic solvent,1-phenyloctane as a solvent having both aromatic and aliphatic moieties,n-tetradecane as an aliphatic solvent,and octanoic acid as a polar alkylated solvent.The solvent dramatically changes the structure of the DBA networks.The solvent effects are discussed in terms of factors that influence the mobility of molecules at the liquid-solid interface such as solvation.