Chemical Control of the Photoluminescence of CdSe Quantum Dot−Organic Complexes with a Series of Para-Substituted Aniline Ligands

摘要

Abstract: Replacement of the native (as-synthesized) ligands of colloidal CdSe QDs with varyingnconcentrations of a series of para-substituted anilines (R-An), where R ranges from strongly electron-nwithdrawing to strongly electron-donating, decreases the PL of the QDs. The molar ratio of R-An to QDn([R-An]:[QD]) at which the PL decreases by 50% shifts by 4 orders of magnitude over the series R-An. Thenmodel employed to describe the data combines a Freundlich binding isotherm (which reflects the dependencenof the binding affinity of the amine headgroups of R-An on the substituent R) with a function that describesnthe response of the PL to R-An ligands once they are bound at their equilibrium surface coverage. Thenlatter function includes as a parameter the rate constant, knr, for nonradiative decay of the exciton at a sitento which an R-An ligand is coordinated. The value of this parameter reveals that the predominant mechanismnof QD ligand interaction is passivation of Cd2 surface sites through σ-donation for R-An ligands with RnH, Br, OCF3, and reductive quenching through photoinduced hole transfer for R MeO, (Me)2N.