Studies of optical and structural properties of CdSe/polymer nanocomposites: evidence of charge transfer and photostability

In this work, the role of conducting [poly (p-phenylinevinylene) (PPV)] and nonconducting (polystyrene) polymers on the properties of their respective composites with CdSe quantum dots of varied sizes has been investigated. The emission and structural properties of polymer–CdSe composites are found to be dependent on the crystallite size and morphology of CdSe nanocrystallites. Smaller CdSe quantum dots (size, ∼5 nm) ensures efficient charge transfer process across polymer–CdSe interface as evident by almost complete quenching of photoluminescence (PL) emission as compared to larger CdSe quantum dots (size, ∼7 nm). Presence of residual trioctylphosphine (TOP)/ tri-n-octylphosphine-oxide (TOPO) species and agglomeration of particles act as a hindrance for quenching of emission and hence charge transfer for larger CdSe nanocrystallites. Emission studies indicated an increased conjugation length for PPV polymers in different solvents (toluene, pyridine) and in solid state. Nonconducting polymer polystyrene shows charge transfer across polymer–CdSe interface as well. However, polystyrene polymer has a shorter chain length, which ensures maximum coverage on the surface of CdSe nanocrystallites and provides better photostability to CdSe QDs within the polymer matrix as compared to that for PPV–CdSe nanocomposites.