Dipole-Controlled Self-Assembly of 2,7-Bis(<i>n</i>-alkoxy)-9-fluorenone: Odd–Even and Chain-Length Effects

Abstract

Fluorenone derivatives (F–OCn) 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–OCeven 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–OCodd 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–OC16 and F–OC14. However, F–OC17 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.