Pyrene-based amphiphile regulated C60 aggregation in monolayers and Langmuir–Blodgett films

Abstract

The advantage of using Langmuir–Blodgett (LB) method in assembling thin films is mainly the effective controlling the orientation of the molecules and deposition of mono- and multilayer films with an organized and ordered layer structure. In this paper, we have studied the interactions between C60 and a kind of pyrene-based amphiphile, N, N’-bis(octadecyl)-L-(1-pyrenebutyric acid)-glutamic diamide (abbreviated as LPG) in monolayers and in LB films by surface-pressure isotherms, CD spectroscopy, fluorescence spectroscopy, and atomic force microscopy (AFM). It has been found that the existing state of C60 was closely related to the mixing ratio of C60 to LPG. Miscibility and AFM image investigation revealed that C60 molecules were embedded into the LPG monolayer as monomers when the mole fraction of C60 was below 0.33 (molar ration of LPG to C60 is 2:1). Meanwhile, the inserting of C60 disturbed the packing of LPG. As a result, the magnitude of supramolecular chirality, which was derived from the self-assembly of LPG, decreased with the addition of C60. When more C60 molecules were mixed with LPG, they have to form three dimensional aggregates due to high adhesive energy. The donor-acceptor interaction between pyrene moieties and C60 was supposed to be the driving force to disperse C60 in LPG monolayer. A reasonable mechanism of the transition from C60 monomers to aggregates in LPG monolayer was also proposed.