Cation-induced self-assembly of an amphiphilic perylene diimide derivative in solution and Langmuir–Blodgett films

Abstract

A novel amphiphilic perylenetetracarboxylic diimide (PDI) derivative, N-(4′-benzo-15-crown-5-ether)-N-hexyl-1,7-di(4-tert-butyl-phenoxy)perylen-3,4,9,10-tetracarboxylic diimide (15C5PDI), has been synthesized and characterized. Dimerization of 15C5PDI is induced in CHCl3 solution with the present of K+, resulting in the formation of the slipped co-facial J-aggregates, as revealed by absorption and fluorescence spectroscopies. Analysis of the surface pressure–area (π–A) isotherms and spectral change for the monolayer formed at the air/water interface, disclosed that 15C5PDI molecules adopted the H-type aggregation mode with a face-to-face configuration and edge-on orientation on both the surface of pure water and K+ aqueous solution. Consequently, a particularly interesting fluorescence emission change from “switch-on” to “switch-off” could be observed upon aggregation that was accompanied by a transformation from strongly fluorescent J-type into non-fluorescent H-type packing of the 15C5PDI dyes. Depending mainly on the coordination bonding between 15-crown-5-ether groups and K+ ions, one dimensional nanofibrils formed on the surface of the K+ aqueous solution with a more closely arrangement of 15C5PDI molecules relative to those on pure water subphase revealed by the π–A isotherms and atomic force microscopy (AFM) images. X-ray diffraction studies indicate that the film crystallinity and general molecular order in the Langmuir–Blodgett (LB) films deposited from the KCl solution are improved effectively in comparison with those from pure water subphase. Furthermore, the conductivity of the LB films prepared in K+ solution is more than ca. 1 order of magnitude higher than those from water.