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

This paper describes polarity inversion in molecular rectification and the related mechanism. Using supramolecular engineered, ultrastable binary mixed self-assembled monolayer (SAM) composed of organic molecular diode (SC11BIPY) and inert reinforcement molecule (SC8), we probed a rectification ratio (r)-voltage relationship in an unprecedently 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 four orders of magnitude in r. Low-temperature experiments, electronic structure analysis, and theoretical calculation revealed that the unusually wide voltage range permits access to molecular orbital energy levels, inaccessible in the traditional narrow voltage regime, inducing the unprecedented in-situ inversion of polarity. 

https://pubs.acs.org/doi/10.1021/jacs.2c02391