Short and long-range electron transfer compete to determine free-charge yield in organic semiconductors

Electronic Mechanism of In Situ Inversion of Rectification Polarity in Supramolecular Engineered Monolayer

This Communication describes polarity inversion in molecular rectification and the related mechanism. Using a supramolecular engineered, ultrastable, binary-mixed self-assembled monolayer (SAM) composed of an organic molecular diode (SC₁₁BIPY) and an inert reinforcement molecule (SC₈), we probed a rectification ratio (r)-voltage relationship over an unprecedentedly wide voltage range (up to |3.5 V|) with statistical significance. We observed positive polarity in rectification at |1.0 V| (r = 107), followed by disappearance of rectification at ∼|2.25 V|, and then eventual emergence of new rectification with the opposite polarity at ∼|3.5 V| (r = 0.006; 1/r = 162). The polarity inversion occurred with a span over 4 orders of magnitude in r. Low-temperature experiments, electronic structure analysis, and theoretical calculations revealed that the unusually wide voltage range permits access to molecular orbital energy levels that are inaccessible in the traditional narrow voltage regime, inducing the unprecedented in situ inversion of polarity.