F−V/SMS:  A New Technique for Studying the Structure and Dynamics of Single Molecules and Nanoparticles

We recently introduced a new technique for semiconductor nanoparticle research that involves simultaneous single molecule spectroscopy (SMS) and controllable oxidation/reduction in an electronic device. This paper shows that the new technique, denoted by fluorescence-voltage single molecule spectroscopy (F−V/SMS), is analogous to current vs voltage ( I − V ) measurements for devices and electrochemical cells. F−V/SMS data are reported for single molecules (nanoparticles) of the conjugated polymer MEH−PPV as a function of bias voltage on the device and bias sweep rate to obtain information on both the energetics and kinetics of the charge transfer (oxidation/reduction) process in situ on the nanoscale. The extensive F−V/SMS data presented herein reveal that the dynamics for oxidation/reduction of MEH−PPV nanoparticles are controlled by various factors including filling of deep hole traps in the charge transporting layer of the device, the oxidation/reduction chemical “state” of the MEH−PPV molecule, and the molecular scale heterogeneity of the device.