Revealing the Electronic Structure of Organic Emitting Semiconductors at Single-Molecule level

Revealing the electronic structure of organic emitting molecules is instructive for tuning electron-hole balance, one of the key factors in regulating the organic light emitting diodes (OLED) performance. Herein, we introduced single molecule conductance measurement (SMCM) technology to probe the conductance of three model emitting molecules on Au surface, finding their hole transporting ability across the metal-molecule interface can be suppressed after electron-withdrawing arms are connected to the center component. This observation would benefit the electron-hole balance of the film in large scale (OLED devices)  whose holes are excessive relative to electrons. I-V modeling reveals that the conductance drop between molecules is owing to reduced metal-molecule coupling rather than the impaired energy level alignment. The electronic structure variation between molecules could also be revealed by photophysical measurement, electrochemical analysis, and density functional theory (DFT) simulation, which give supportive evidence to the SMCM result.