Assembly of T-Shaped Amphiphilic Thiazoles on the Air-Water Interface: Impact of Polar Chromophore Moieties, as Well as Dipolarity and π-Extension of the Chromophore on the Supramolecular Structure

in: Langmuir (2019)
Hupfer, Maximilian L.; Kaufmann, Martin; Preiß, Julia; Weiß, Dieter; Beckert, Rainer; Dietzek, Benjamin; Presselt, Martin
The supramolecular structure essentially determines the properties of organic thin films. In this work, we systematically investigate the influence of the chromophore on the supramolecular structure formation at air−water interfaces by means of the Langmuir−Blodgett technique. Therefore, we focus on the recently introduced class of double-anchor Tshaped amphiphilic dyes, namely, 4-hydroxy-thiazole chromophores that are centrally equipped with an amphiphilicityinducing hexanoic acid. The thiazoles contain hydrophilic subphase-anchor groups in the 2-position (4-N,N-dimethylaminophenyl (Am), 2-pyridyl (Py), and 4-nitrophenyl (Ni)), whereas the chromophores are systematically extended in the 5-position with various substituents. The combination of the Langmuir technique with online fluorescence measurements revealed that the π−π interactions that are pronounced in the case of 4-methoxybiphenyl derivatives yield the most distinct supramolecular structures. Whereas in the case of Py and Ni derivatives ordered J-type supramolecular structures in microdomains are formed, the Am derivative forms ordered supramolecular structures that are more homogeneous, which are, however, not stabilized by J-type dipolar interactions. Because of the synergetic π−π and dipolar stabilizations, the Ni derivative bearing the 4-methoxybiphenyl unit forms exceptionally stable quasi-two-dimensional Langmuir monolayers reaching very high surface pressures beyond 60 mN/m without any sign of disturbance of the Langmuir monolayer.

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