Fluorinated Benzylphosphonic Acid Derivatives for Work Function Modification

Abstract

Methodology for the synthesis of polyfluorinated biphenyl benzylphosphonic acids was developed and various highly fluorinated phosphonic acid derivatives may be synthesised from the corresponding fluorobenzene system. Synthesis of analogous benzylphosphonic acids from corresponding benzyl bromides is also described. The use of these systems as self-assembled monolayers on AlOx was assessed by a range of surface-sensitive analytical techniques.
The surface energy and work function of aluminium oxide (AlOx) may be altered upon the adsorption of monolayers formed of partially fluorinated benzylphosphonic acids. Replacement of surface hydroxyl groups by hydro- and fluorocarbon modifiers significantly lowers the surface energy of AlOx, increasing its compatibility with suitable organic layers for applications such as organic light emitting diodes (OLEDs) and organic thin film transistors (OTFTs). Fluorinated self-assembled monolayers can alter the work function of AlOx by inducing a surface dipole upon adsorption. Depending on the nature of the dipole, the work function can either be increased or decreased over a total range of 0.91 eV.
In addition, the synthesis of related, highly polar, piperazine based biaryl benzylphosphonic acids, and their biphenyl counterparts, is described.