Date of Award
2-1-2025
Publication Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry and Biochemistry
Supervisor
Holger Eichhorn
Rights
info:eu-repo/semantics/embargoedAccess
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Abstract
Controlling the orientation of polycyclic aromatic dyes in thin films is critical for tuning their optical, electronic, mechanical, and reactive properties. In this study, we engineered the supramolecular assembly of macrocyclic dyes by converting them into amphiphilic structures. Two octaalkylthio-substituted tetraazaporphyrins (TAPs), each with a 5-carboxypentyl chain and either a pentyl or dodecyl chain per pyrrole ring, were synthesized as statistical mixtures of four regioisomers. The unsymmetrically substituted maleodinitrile precursors were prepared in good yields using a flow reactor. Neither the tetra-ester precursors nor the tetra-acid TAPs exhibited mesomorphism, and both were classified among the rare porphyrin derivatives that form isotropic liquid phases at or near room temperature. The interfacial properties of these amphiphilic tetra-acids were investigated using Langmuir and Langmuir-Blodgett (LB) films. Langmuir films were prepared on aqueous subphases at varying pH levels and characterized by surface pressure-area isotherms, compressibility, Brewster angle microscopy, ellipsometry, and grazing incidence X-ray diffraction (GIXD). LB films were transferred to mica substrates and analyzed using atomic force microscopy (AFM). The dodecyl-substituted tetra-acid (4b) formed condensed Langmuir monolayers at 15 mN/m surface pressure and at pH values of 4.0 and 6.5, but higher surface pressures and a pH of 11 induced the formation of 3D structures. In contrast, the LB films of the pentyl-substituted tetra-acid (4a) produced a homogeneous monolayer at 15 mN/m surface pressure and pH 6.5. AFM measurements and packing correlations derived from GIXD indicated that compound 4a adopts a spider-like conformation, with its macrocycle oriented parallel to the substrate (face-on) and organized in a tightly packed hexagonal unit plane. This difference in molecular packing is attributed to intramolecular mixing of the 5-carboxypentyl and pentyl chains in 4a, which provides a better match between the footprints of the macrocycle, acid groups, and alkyl chains. In contrast, the longer dodecyl chains in 4b are either too large to fit between the 5-carboxypentyl chains or too small to fill the footprint of the TAP macrocycle. Amphiphilic dyes are technologically significant due to their tunable properties, which can be adjusted through self-organization and assembly at interfaces. Here, we report the synthesis, thermal properties, and Langmuir monolayer behavior of amphiphilic tetraazaporphyrin (TAP) derivatives, which feature four terminal carboxylic acid groups attached via pentamethylenethio spacers and four dodecylthio side chains. The metal-free tetra-ester TAP was synthesized first and subsequently metalated with Ni(II), Cu(II), Co(II), and Zn(II) acetates, yielding stable products. Hydrolysis of the esters to form the tetra-acid TAPs was achieved in moderate yields. The TAP esters are isotropic liquids at room temperature, an unusual property for porphyrins of this size, while the tetra-acid derivatives form isotropic solids with glass transitions between 40-80 °C. All tetra-acid TAPs formed Langmuir monolayers, but only the Ni(II)-containing TAP exhibited a mean molecular area consistent with a flat-on molecular orientation and could be compressed to pressures above 35 mN/m. The metal-free and Cu(II)-metalated TAPs showed similar properties, though only at pH 11, and not at pH values of 6.5 or 3. TAPs typically adopt an edge-on orientation in Langmuir films due to strong cofacial interactions between macrocycles, especially at high surface pressures. Achieving a face-on orientation is rare but would enhance applications in sensing and catalysis by improving electronic interactions with the substrate. In this study, we functionalized Ni(II)-metalated TAPs with four carboxylic acid groups via flexible aliphatic spacers and four alkyl chains, promoting face-on assembly at polar interfaces. The impact of different methylene spacers and alkyl chain lengths on monolayer formation was evaluated in Langmuir films. Di-acid NiTAP derivatives with shorter chains (C1) and longer chains (C12) were synthesized for comparison as edge-on references. The linear alkyl chains of these NiTAPs enhanced monolayer stability, with chain length and branching critically influencing interfacial behaviour. These findings contribute to the optimization of TAPs' optical and electronic properties through controlled molecular orientation, with broad implications for materials science applications. Lastly, fluorescent probes are indispensable for studying membrane dynamics via fluorescence microscopy in the context of biological membranes. However, the disruption of membrane behavior by standard probes necessitates their use in low concentrations. This research introduces two diketopyrrolopyrrole (DPP) derivatives designed to mimic cholesterol, allowing for higher dye concentrations without compromising membrane integrity. DPP-1 contains one phenyl and one cyclohexyl group attached to the DPP core, while DPP-2 has two phenyl groups, simplifying its synthesis and yielding a bathochromic shift in absorption spectra. The most significant challenge in the synthesis of DPP-1 lies in the cyclic condensation reaction involving the cyano-cyclohexyl group, which is complicated by side reactions attributed to the C-H acidic proton and geminal carbocation. Subsequent studies will thoroughly examine the fluorescence properties, amphiphilicity, and interactions with the lipid membranes of DPP-1 and DPP-2.
Recommended Citation
Abdulhamied, Elmahdy, "Controlling Interfacial Interactions of Amphiphilic Organic Dyes by Molecular Design" (2025). Electronic Theses and Dissertations. 9641.
https://scholar.uwindsor.ca/etd/9641