Quantum dot and π -conjugated molecule hybrids: Nanoscale luminescence and application to photoresponsive molecular electronics

Hybrid nanoparticles (NPs) consisting of an n-type CdSe/ZnS quantum dot (QD) as a core and p-type π -conjugate molecules as a shell were fabricated, and their nanoscale photoluminescence (PL) and photoresponsive molecular electronic characteristics were investigated. π-Conjugated macromolecular dioctyloxybenzodithiophene-based polythiophene (P3000) or a single carbazole (CB) molecule with insulating molecular blocks were attached to the QD surface. The nanoscale PL characteristics for the single QD were drastically changed through close contact with P3000 owing to energy and charge transfer effects. However, for the hybrid QD-CB NP, the PL of the QD was dominant because of weak energy transfer resulting from the relatively longer insulating molecular block between the QD and the CB molecule. From time-resolved PL spectra, the exciton lifetimes of the QD in the hybrid QD-P3000 and QD-CB NPs were clearly different because of a variation in the energy transfer rate. The photocurrents of the single hybrid QD-P3000 NP were considerably higher and actively responded to both forward and reverse biases due to the energy and charge transfer effects, while those of the single QD-CB NP exhibited diode characteristics. The QD-based hybrids show distinct nanoscale PL features and photoresponsive molecular electronic characteristics depending on the structures of π -conjugated molecules.