Thymine functionalised porphyrins, synthesis and heteromolecular surface-based self-assembly

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Self-assembly is a fundamental process in nature and materials science.
• Hydrogen bonding plays a crucial role in molecular recognition and the formation of ordered structures.
• Porphyrins are versatile macrocyclic compounds with applications in various fields.

Purpose of the Study:

• To synthesize thymine-functionalized porphyrins.
• To investigate their self-assembly behavior in solution and on surfaces.
• To explore the role of thymine-thymine and thymine-adenine interactions in directing self-assembly.

Main Methods:

• Synthesis of tetra-(phenylthymine)porphyrin (tetra-TP) and mono-thymine-tri-(3,5-di-tert-butylphenyl)porphyrin (mono-TP).
• Single crystal X-ray diffraction for solid-state structural analysis.
• Solution-based studies to determine binding constants (Kd).
• Scanning Tunneling Microscopy (STM) for surface self-assembly studies on HOPG substrates.

Main Results:

• Mono-TP self-associates via thymine-thymine hydrogen bonding in the solid state.
• In solution, thymine-thymine interactions are weak (Kd = 6.1 M⁻¹), while thymine-adenine interactions are stronger (K = 91.8 M⁻¹).
• Tetra-TP forms square lattices on HOPG via thymine-thymine hydrogen bonding.
• Co-deposition with 9-propyladenine leads to preferential thymine-adenine interactions, forming heteromolecular arrays and disrupting the tetra-TP lattice.

Conclusions:

• Thymine-functionalized porphyrins can be synthesized and self-assemble on surfaces.
• Preferential heteromolecular thymine-adenine interactions can control and disrupt self-assembled porphyrin arrays.
• Surface self-assembly is influenced by concentration and molar ratios, highlighting kinetic effects.