Self-Assembled Monolayers of Perfluoroanthracenylaminoalkane Thiolates on Gold as Potential Electron Injection Layers

Abstract

As a material with relatively small band gap and low lying valence orbitals, perfluoroanthracene (PFA) is of interest for the modification of electrode surfaces, for example, as charge injection layers for n-type organic semiconductors. To covalently attach PFA in the form of self-assembled monolayers (SAMs), we developed a synthesis of derivatives with a sulfur termination, linked to the 2-position of the PFA moieties by an -NH- group and a short alkane chain with two and three methylene groups, respectively. Spectroscopic characterization of the SAMs reveals that the molecules adopt an almost upright orientation on the gold surface, with the packing density mostly determined by the steric demands of the PFA units. The number of the methylene groups in the -NH-alkyl linker has only a minor impact on the SAM structure because of the nonsymmetric attachment of the PFA units, which permits the compensation of the orientational constraints imposed by the bending potential. The investigated SAMs alter the work function of gold by +(0.59-0.64) eV, suggesting comparably strong depolarization effects, affecting the extent of the work function modification.

Structure–Property Relationship of Phenylene-Based Self-Assembled Monolayers for Record Low Work Function of Indium Tin Oxide

“…Because SAM formation is highly sensitive to a large variety of parameters, this angle is an estimation of how the molecules in this work relate to tilt angles of literature-known SAM molecules. Additionally, the dimethyl headgroup and the fluorine substitution increase the molecular dimension, and thus a larger tilt angle is to be expected. ,, In correlation to our findings, Gliboff et al show that short phenyl-based molecules exhibit larger tilt angles if fluorinated, whereas longer alkyl-chain-based molecules follow the opposite trend due to stronger intermolecular forces.…”

“…The very low value for PhFPA compared with all other molecules leads to the assumption of a possible lower coverage. Fluorinated molecules are known to have a reduced coverage down to only half of that of the unfluorinated ones, , possibly explaining the smaller nominal thickness. With the help of the F 1s emission peak, this can be further clarified: The signal of the longer molecule XFPA with the tilt angles calculated above and at roughly the same coverage should reveal a weaker signal due to a stronger damping of the fluorine signal for XFPA.…”

Side‐Group‐Induced Polymorphism in Self‐Assembled Monolayers: 3,5‐Bis(trifluoromethyl)benzenethiolate Films on Au(111)

“…First, the intensities of the F 1s peak in the F 1s spectrum (Figure c) and the CF 3 ‐related feature in the C 1s spectrum (Figure b) are noticeably lower, which suggests a lower molecular coverage. Second, the peak at 284.6 eV ( 1 ) in the latter spectrum is now accompanied by an intense shoulder at 286.3 eV ( 3 ), which can be tentatively assigned to CF species, which appears upon partial decomposition of the CF 3 groups or in the presence of a contamination (e.g., CO) . Finally, the S 2p spectrum of the TFBT SAM with an IT of 24 h is dominated by the signal of atomic sulfur, with the thiolate‐related doublet being comparatively weak.…”

A dithiocarbamate anchoring group as a flexible platform for interface engineering

“…Finally, the fluorination of the terminal phenyl ring in FP-Pz/Au does not result in a noticeable disturbance of the molecular inclination, which again appears to be a general trend for SAMs containing perfluorinated aromatic moieties. 45,86…”