This dissertation is concentrated on the theoretical studies of pyrrole-based macrocycles by using quantum mechanics and molecular mechanics methods. Several systems, that are, neutral metal complexes of porphyrin isomers, heteroporphyrins, calix[4]arenes, and calix[4]pyrroles are investigated.
In chapter 2, systematic theoretical studies of the geometrical features, metal binding properties and electronic features of a variety of neutral metals (Ni, Cu, Zn, Cd, Mg, Ca) complexes of porphyrin isomers are presented. For various metals, the parent metal-porphyrin-( l,l,l,l) is the most stable. It has been found that the N
4-core size of the porphyrin isomers is an important factor for the metal-binding stabilization. Generally, large-sized metals prefer to bind large N
4-core ligands; while small-sized metals favor to bind small N
4-core macrocycles. Natural bond orbital analysis shows that the electron configuration of Ni, Cu, Zn, Cd are d[superscipt 8], d
9, d
10, and d
10, respectively. Moreover, the redox behaviours of these metal porphyrins can be qualitatively predicted. In chapter 3, the β-octasubstituent effect on the Z/E preference of metalloisoporphycenes is studied. Our study showed that the introduction of eight β-ethyl groups would destabilize the (Z)-isomers more than the (E)-isomers in each case of metal complexes. The effect is qualitatively correlated to the size of the metal cation: Ni > Cu > Zn > Pt. In chapter 4, our study is focused on the structural properties, aromaticity, and two electron oxidation potentials of heteroporphycenes (N,O,S). According to our calculated results, heteroatoms prefer to occupy the trans-position in the N
4-core of porphycene either in 20 π-electron or 18 π-electron structures. Calculated NICS values demonstrate that all 18 π-electron structures are aromatic that obeys the Huckel 4n+2 rule. Meanwhile, most 20 p-electron structures are predicted to be anti-aromatic. Some exceptional cases are also found owing to the non-planarity of the structures. Frontier orbital energy analysis shows that Pyc-S
4 is difficult to be oxidized. However, structures 7a, 10a and 13a are easier to be oxidized to their 18 π-electron structures. The prediction of UV-Vis spectra indicates that 4b, 7b, l0b, llb, 12b and 13b have considerable absorption near IR region ([is more than]700nm).
Another objective of this thesis is to investigate the conformational features and binding properties of calix[4]pyrrole and its related structures. In chapter 6, a comparison of conformational features of calix[4]aromatics including parent calix[4] arene, O-tetramethyl calix[4]arene, calix[4]benzene, calix[4]furan, calix[4]thiophene, and calix[4]pyrrole is carried out. Results show that calix[4]arene favors the cone conformation due to four hydrogen bonds. On the contrary, calix[4]furan, calix[4]thiophene, and calix[4]pyrrole all prefer a 1,3-alternate conformation, while the cone conformation is least stable. In chapter 7, the conformational feature and anion-binding properties of calix[4]pyrrole in the gas phase and dichloromethane solution are studied. The stability sequence is predicted to be 1,3-altemate [is more than] partial cone [is more than] 1,2-alternate [is more than] cone either in the gas phase or in CH
2C1
2 solution. Anion binding analysis reveals that 1:1 calix[4]pyrrole-F
- binding pattern with the cone structure is more favourable than 1:2-pattern with the 1,2-alternate structure. N-H---F
- hydrogen bond strength and anion binding energies are also established in the work. Finally, the β-substituent effects on the conformational preference and anion-binding abilities of three series of substituted calix[4]pyrroles are investigated. It reveals that the introduction of electron-withdrawing groups at β-positions enhances the anion binding of calix[4]pyrroles.
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