Functionalized Tetrapodal Diazatriptycenes for Electrostatic Dipole Engineering in n-Type Organic Thin Film Transistors

Abstract

A diazatriptycene-based tetrapodal scaffold with thiol anchors enforces a nearly upright orientation of functional groups, introduced to its quinoxaline subunit, with respect to the substrate upon formation of self-assembled monolayers (SAMs). Substitution with electron-withdrawing fluorine and cyano as well as electron-rich dimethylamino substituents allows tuning of the molecular dipole and, consequently, of the work function of gold over a range of 1.0 eV (from 3.9 to 4.9 eV). The properties of the SAMs are comprehensively investigated by infrared reflection absorption spectroscopy, near edge X-ray absorption fine structure spectroscopy, and X-ray photoelectron spectroscopy. As prototypical examples for the high potential of the presented SAMs in devices, organic thin-film transistors are fabricated.