Synthesis characterization and redox properties of expanded isophlorinoids containing six seven eight nine and ten heterocyclic units

Abstract

Aromatic molecules as stated by Huckel are planar conjugated 4n 2 960 electronic systems Benzene is the simplest known example for the same On the other hand 4n 960 systems are anti aromatic and not so stable Isophlorinoids are typical examples for stable anti aromatic systems Such 960 conjugated macrocycles could be stabilized by changing the core of a porphyrin by substituting pyrrole with other heterocyclic units such as furan or thiophene Signature paratropic ring current effects from NMR spectroscopy is crucial to evaluate the extent of planarity and antiaromaticity of these macrocycles Such molecules are vulnerable to redox reactions similar to metal ions However large expanded porphyrins adopt figure of eight topology owing to their structural flexibility In this thesis synthesis characterization and redox properties of novel core modified expanded isophlorinoids with six seven eight nine and ten heterocyclic units will be discussed In attempts to stabilize a planar 32 960 heptaphyrin a novel asymmetric tristhiophene was designed to yield the macrocycle with four bridging carbons By virtue of its anti aromaticity it undergoes two electron reversible oxidation to yield the 30 960 dicationic species Adopting a similar approach to synthesize a 40 960 octaphyrin resulted in figure of eight conformation of the macrocycle hence rendering it non antiaromatic in nature However this molecule also displayed reversible oxidation and stable aromatic 38 960 dication could be isolated This strategy was modified to synthesize for 38 960 octaphyrin and 46 960 decaphyrin by reducing the number of bridging carbon atoms Interestingly two structural isomers of a 38 960 octaphyrin were isolated from the same reaction Details of synthesis characterization redox properties and quantum chemical calculations will be discussed in detail newline newline