Controlled preparation of CdS nanoparticle arrays in amphiphilic perylene tetracarboxylic diimides: organization, electron-transfer and semiconducting properties

Abstract

Langmuir monolayers of two amphiphilic perylene tetracarboxylic diimide (PDI) derivatives, PDI-1 and PDI-2, which are modified with different numbers of hydrophilic polyoxyethylene/hydrophobic alkoxy side-chains, have been used as not only organic templates but also good functional organic materials to produce the first examples of rose- and petal-like nano-particle arrays of cadmium sulfide (CdS)–PDI composites with a controllable and tunable size (from 40, 60 to 80 nm for nano-roses; from 20 to 30 nm for nano-petals), respectively. These newly fabricated CdS–PDI hybrid nanostructures were comparatively studied using a wide range of methods including SEM, TEM, electronic absorption, fluorescence emission and X-ray diffraction analysis. The crystalline regions for CdS were identified to be hexagonal wurtzite with (101) and (001) face preferred growth on the PDI-1 and PDI-2 monolayers, respectively, associated with the polyoxyethylene side chains architecture changing from parallel to the subphase surface for PDI-1 to perpendicular to the subphase surface for PDI-2. Furthermore, electron-transfer from PDI molecules to CdS nanocrystals is established by both quenching the photoluminescence intensity and changing the lifetime of photoluminescence emission of PDI in the hybrid nanoparticle arrays. In particular, a significantly enhanced conductivity for both nano-roses and nano-petals of CdS–PDI nanocomposites was achieved, relative to that of the individual component, due to the existence of the densely packed molecular architecture in the film matrix and the large interfacial area between the two components that removed the charge transporting bottleneck by creating an interpenetrating network of the hybrid materials, implying the potential of providing synergetic semiconducting properties of the present hybrid organic–inorganic nanomaterials.