Surface-Area-Dependent Electron Transfer between Isoenergetic 2D Quantum Wells and a Molecular Acceptor

We report measurements of electron transfer rates for four isoenergetic donor-acceptor pairs comprising a molecular electron acceptor, methylviologen (MV), and morphology-controlled colloidal semiconductor nanoparticles of CdSe. The four nanoparticles include a spherical quantum dot (QD) and three differing lateral areas of 4-monolayer-thick nanoplatelets (NPLs), each with a 2.42 eV energy gap. As such, the measurements, performed via ultrafast photoluminescence, relate the dependence of charge transfer rate on the spatial extent of the initial electron-hole pair wave function explicitly, which we show for the first time to be related to surface area in this regime that is intermediate between homogeneous and heterogeneous charge transfer as well as 2D to 0D electron transfer. The observed nonlinear dependence of rate with surface area is attributed to exciton delocalization within each structure, which we show via temperature-dependent absorption measurements remains constant.