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

The synthesis and surface-based self-assembly of thymine-functionalised porphyrins is described. Reaction of 1-formylphenyl-3-benzoyl-thymine with suitable pyrollic species leads to the formation of tetra( phenylthymine) porphyrin ( tetra-TP) or mono-thymine-tri-( 3,5-di-tert-butylphenyl) porphyrin ( mono-TP). Single crystal X-ray diffraction studies demonstrate the self-association of mono-TP in the solid state through thymine/thymine hydrogen-bonding interactions but in solution this interaction ( K-d = 6.1 +/- 3.0 M (-1)) is relatively weak in comparison to the heteromolecular interaction between mono-TP and 9-propyladenine ( K = 91.8 +/- 20.5 M (-1) 1). STM studies of the tetratopic hydrogen-bonding tecton, tetra-TP, deposited on an HOPG substrate reveal the formation of an almost perfectly square self-assembled lattice through thymine/thymine hydrogen-bonding. Co-deposition of tetra-TP with 9-propyladenine leads to the adoption of preferable thymine/adenine interactions leading to the formation of a heteromolecular tetra-TP/9-propyladenine hydrogen bonded array including both Watson-Crick thymine/adenine interactions and adenine/ adenine hydrogen-bonding. The studies demonstrate a pathway for the self-assembly of tetratopic hydrogen-bonding tectonsand the use of preferential heteromolecular thymine/ adenine interactions for the disruption of the homomolecular tetra- TP array. Studies of the self- assembly of tetra- TP and 9- propyladenine demonstrate a strong dependence on overall concentration and molar ratio of components indicating the importance of kinetic effects in surface self- assembly processes.