Arylic versus Alkylic—Hydrophobic Linkers Determine the Supramolecular Structure and Optoelectronic Properties of Tripodal Amphiphilic Push–Pull Thiazoles

Abstract

The supramolecular structures and their constituents essentially determine the optoelectronic properties of thin films. The introduction of amphiphilicity to the constituents and interface assembly is one established technique to control supramolecular structures and resulting material properties. To yield amphiphilicity, rather hydrophobic chromophores are linked to hydrophilic head groups via flexible alkyl chains. In the present work, we investigate whether replacement of the alkyl linkers by a phenylene linker, that is, replacing an electrically isolating moiety with a potentially semiconducting one, increases the conductivity through the resulting layers. After investigating the influence of the linker on molecular properties of the 2-(4-N,N-dimethylaminophenyl)-4-hydroxy-5-nitrophenyl-1,3 thiazoles exemplarily used in this work, we produce supramolecular structures by means of the Langmuir–Blodgett (LB) technique. Atomic force microscopy (AFM) and UV–vis absorption spectroscopy reveal that thin films made from the more rigid thiazole bearing the arylic linker feature a more homogeneous and stable supramolecular structure as compared to those made from the thiazole dye containing the flexible alkylic linker. Finally, conductive AFM (cAFM) results disclose that the LB films made from the thiazole bearing the π-conjugated arylic linker are less conductive than their counterparts based on the alkylic linkers. In the latter layers, the alkylic linkers provide sufficient motional degrees of freedom to allow for supramolecular rearrangement upon electrical operation during cAFM measurements, hence yielding supramolecular structures featuring increased conductivity with successive cAFM measurements. This work highlights the importance of supramolecular structures for optoelectronic properties by presenting a case where supramolecular effects excel the property changes introduced by molecular modifications.

Autonomous Supramolecular Interface Self‐Healing Monitored by Restoration of UV/Vis Absorption Spectra of Self‐Assembled Thiazole Layers

“…This red‐shift indicates a supramolecular structure constituted by J‐aggregates, cf . spectrum of the corresponding Langmuir–Blodgett (LB) film in Figure C ( λ max (LB)=450 nm) …”

“…For dyes constituting the SAMs we focus on amphiphilic thiazoles because their supramolecular structures, surface activities, and optical properties have been extensively studied in literature . The amphiphilicity und weak solubility of thiazole 1 in water (see Figure A, electrostatic potential ( φ ) distribution) renders 1 predestined for SAM formation and self‐healing to restore both, structure and function of the SAM.…”

“…(C) Absorption spectra of self‐assembled monolayer of the amphiphilic push‐pull‐thiazole 1 in saturated solutions (solid) with different nonpolar (heptane, cyclohexane) and polar (water) solvents on hydrophilic (dotted) and hydrophobized (dashed) quartz glass substrate in comparison to the spectrum of the LB film of 1 reported in Ref. . (D) Sketch of device‐implementation of the model system shown in (B).…”

“…(B) Scheme of setup to detect self-healing of self-assembled structures in situ by means of photothermal deflection spectroscopy (PDS). (C) Absorptionspectra of self-assembled monolayer of the amphiphilic push-pull-thiazole 1 in saturated solutions (solid) with different nonpolar(heptane, cyclohexane)and polar (water) solvents on hydrophilic (dotted) and hydrophobized (dashed) quartz glass substrate in comparison to the spectrum of the LB film of 1 reported in Ref [25]…”

“…Absorbtance versus time kinetic of the initial assembly (a), together with the healing (left, b, d, f) and damage(right;c,e, g) of self-assembled monolayer of the amphiphilic push-pull-thiazoles 1 on hydrophilic quartzglass from as aturated solutiono fh eptane determined at l max = 450 nm.Chem.E ur.J 2019,25,…”