In situ synthesis of semiconductor nanocrystals at the surface of tubular J-aggregates†
Hybrid nanostructures consisting of dye molecules and semiconducting nanocrystals are currently much investigated because they can benefit from the strong absorption of organic dyes and the chemical stability of inorganic components, a combination of properties that is promising for various optoelectronic applications. Here, we report an in situ synthesis method to design hybrid nanotubes by growing metal sulfide (MeS) nanocrystals at the surface of tubular J-aggregates of amphiphilic carbocyanine dyes. In this method, metal cations (Me2+ = Cd2+, Zn2+, and Ni2+) are enriched at the negatively charged surface of J-aggregates via electrostatic attraction, giving rise to a diffuse Helmholtz layer. Subsequent addition of thioacetamide and ammonium hydroxide leads to the formation of a dense layer of MeS nanocrystals exclusively close to or at the surface of J-aggregates. Typically, a shell of CdS nanocrystals (size ∼ 3 nm) is formed at the surface of tubular J-aggregates without significantly affecting the aggregate morphology. The crystal structure is analyzed by electron diffraction revealing a sphalerite structure. The coverage of CdS nanocrystals on J-aggregates can be tuned by varying the concentration of the sulphur source. Efficient energy transfer from CdS nanocrystals to J-aggregates results in the quenching of the CdS photoluminescence. Structurally and morphologically similar hybrid systems of tubular J-aggregates and semiconductor nanocrystals (e.g., ZnS and NiS) are synthesized by analog chemical reactions.