Supramolecular Reorientation During Deposition Onto Metal Surfaces of Quasi-Two-Dimensional Langmuir Monolayers Composed of Bifunctional Amphiphilic, Twisted Perylenes

Abstract

Supramolecular dye structures, which are often ruled by π−π interactions between planar chromophores, crucially determine the optoelectronic properties of layers and interfaces. Here, we present the interfacial assembly of perylene monoanhydride and monoimide that do not feature a planar chromophore but contain chlorine substituents in the bay positions to yield twisted chromophores and hence modified π-stacking. The assembly of the twisted perylene monoanhydride and monoimide is driven by their amphiphilicity that ensures proper Langmuir layer formation. The shielding of the hydrophilic segment upon attaching an alkyl chain to the imide moiety yielded a more rigid Langmuir layer, even though the degrees of freedom were increased due to this modification. For the characterization of the Langmuir layer's supramolecular structure, the layers were deposited onto glass, silver, and gold substrates via Langmuir−Blodgett (LB) and Langmuir−Schaefer (LS) techniques and were investigated with atomic force microscopy and surface-enhanced resonance Raman spectroscopy (SERRS). From the similarity between all SERR spectra of the LS and LB layers, we concluded that the perylenes have changed their orientation upon LB deposition to bind to the silver surface of the SERRS substrate via sulfur atoms. In the Langmuir layer, the perylenes, which are πstacked with half of the twisted chromophores, must already be inclined and cannot achieve full parallel alignment because of the twisting-induced steric hindrance. However, upon rotation, the energetically most favorable antiparallel aligned structures can be formed and bind to the SERRS substrate. Thus, we present, to the best of our knowledge, the first fabrication of quasi-twodimensional films from twisted amphiphilic perylene monoimides and their reassembly during LB deposition. The relation between the molecular structure, supramolecular interfacial assembly, and its adoption during adsorption revealed here is crucial for the fabrication of defined functionalizations of metal surfaces, which is key to the development of organic (opto)electronic devices.

Embedding an Amphiphilic 4-Hydroxy Thiazole Dye in Langmuir Matrices: Studying Miscibilities with Arylic and Alkylic Matrix Amphiphiles via Langmuir Isotherms and Photo-induced Force Microscopy

“…For Π LB = 12 mN/m, where the excess area starts rising, phase-separated domains similar to the 10:SA system are observed, hence showing phase separation. Consequently, although the c ( 10 ) TPCA = 80% Langmuir layer featured the most negative excess area (Figure ) as compared to other blending ratios and as compared to SA matrices (Figure ), TPCA tends to show two-dimensional crystallites, possibly formed during the deposition process . According to our findings for the SA blends discussed above, the spherical features of the opposing phase (blue in Figure B) as compared to the surroundings are assigned to dye 10 .…”

“…Such phase separations are not obvious from the excess areas for low dye concentrations or for the TPCA matrix. Therefore, we conclude that the deposition process influences phase separation . Using PiFM to assign the segregated domains to the matrix or dye, we also found that phase separation of identically composed Langmuir monolayers deposited at high surface pressures (Π LB > 8 mN/m) differs between deposition onto glass and onto gold, thus highlighting the influence of the substrate on phase separation kinetics.…”

“…Therefore, we conclude that the deposition process influences phase separation. 71 Using PiFM to assign the segregated domains to the matrix or dye, we also found that phase separation of identically composed Langmuir monolayers deposited at high surface pressures (Π LB > 8 mN/m) differs between deposition onto glass and onto gold, thus highlighting the influence of the substrate on phase separation kinetics. In case of deposition onto the gold phase, separation of SA and dye 10 could actually not be detected via AFM but was revealed via the chemical fingerprint contrast at nanometer scales provided by PiFM.…”

Tailoring the Weight of Surface and Intralayer Edge States to Control LUMO Energies

“…The highest rigidity of the MPEGC 60 Langmuir layer at mma C (C −1 S,max ) = 68 Å 2 corresponds to the inflection point in the Π(mma) isotherm being referred to as the collapse point of the monolayer. [ 17 ] Consequently, the Langmuir technique provides a tool to systematically tune the mma from loose to dense and rigid packing at the collapse point of the monolayer.…”

Supramolecular Control of Photonic Response and Sensing of Nitricoxide using Iron(III) Corrole Monolayers and Their Stacks

“…The Langmuir layers are deposited using the LB technique at different packing densities, specifically at areas A LB = 35, 32, 31, 29, 28 Å 2 , corresponding to Π LB = 5, 10, 15, 20, 25 mN/m, as indicated by the dotted lines in Figure 1. Exemplarily, Figure 2A shows atomic force microscopy images of an imperfect layer section [45] to determine the resulting film thickness (B and C) for a LB monolayer deposited at Π LB = 25 mN/m (see Figure S2 in the Supporting Information for larger areas of a perfect LB layers). Figure 2C shows the height distribution of the region shown in panel A.…”