Synthesis and Characterization of New Amphiphilic And Chiral Squaraines

Abstract

Squaraines are a class of dye molecules obtained through reaction of mostly electron-rich molecules with squaric acid. It is an intriguing class of molecules, which has a wide field of applications and seemingly endless possibilities for future endeavors, especially in the field of optoelectronics. With its tunable properties and the many synthetic routes developed, certain characteristics with regards to the employment in photodiodes were deemed especially desirable. As previous works have beautifully shown the introduction of chirality on to the squaraine framework, which is often described as a quadrupolar D-A-D type rigid-rod –like geometry, is highly fascinating. It was discovered that the inherent central chiral information of the chirality source introduced to the framework was translated to the supramolecular level upon aggregation of the dye, resulting in measurable macroscopic circular dichroism both in colloidal solution and in thin films. <br/> In the presented thesis the synthetic route to a new highly versatile class of squaraine was successfully developed. This class is a hybrid combining chiral information introduced by the naturally occurring amino acid alanine with additional alkyl-chains, which were found to be beneficial for the aggregation behavior of squaraines, but could not be introduced to the previous chiral squaraine class due to the nature of the chirality source. The developed synthetic route allows for various substitution patterns for this new family of chiral squaraines. As a result, it also lays the ground stone for further investigation towards other naturally occurring amino acid based squaraines. These newly obtained compounds were characterized and investigated regarding their (chiro-)optical properties in solution. <br/> Beyond the classical field of application, optoelectronics, another ambitious combination was successfully achieved. Here the goal was the synthesis of a squaraine-based stimuli-responsive designer surfactant that could be used for micellar catalysis. It envisioned the combination of the squaric acid core with different solubilizing groups to tune the final solubility of the then amphiphilic squaraine-based surfactant. <br/> In the presented thesis a new amphiphilic squaraine-based surfactant was synthesized, which not only combined the desired squaric acid core with a pH-indicative functional group as originally desired. Additionally, the assembly of micelles and the disassembly thereof were reliably visualized by a color change. Most importantly a new so far unique feature of the newly synthesized squaraine based surfactant results in an attractive advantage during the post-reaction purification process for the new designer surfactant compared to conventional surfactants for micellar catalysis.