Energy transport in CdSe nanocrystals assembled with molecular wires

Continuous-wave photoluminescence studies on CdSe nanocrystals assembled with oligo-p-(phenyleneethynylene),-dibenzylthiols (n = 0,1,3) indicate long-range resonant energy transfer can be tuned by size-dependent control of the weak electromagnetic dipole-dipole coupling of the donor (molecular wire) and the acceptor (nanocrystal). These micron-scale free-standing inorganic-organic composite structures are composed of CdSe in the strongly confined regime with diameters between 2.8 nm to 8.0 nm assembled with rigid molecular wire lengths of 1.3 nm, 1.9 nm, and 3.1 nm. Evidence is presented which supports the possibility that interchain interactions of molecular wires within the assembly form two additional species that participate in the energy transfer process, dimers and aggregate excitons. Dimer states act as intermediate states for the migrating molecular exciton, and are selectively quenched by quantized CdSe electronic transitions (1S(3/2)-1S(e), 1P(3/2)-1P(e) while aggregate excitons act as emissive excitation traps.