Executive Summary : | Stable and neutral radicals are synthetically challenging due to their highly reactive nature. Access to such neutral radical species are very limited and usually they are found unstable under ambient conditions. This project aims to synthesize a variety of stable and neutral 25pi radical species which can be stabilized by five heterocyclic units stitched in a cyclic fashion. Connecting them by sp2 carbon atoms induces effective pi delocalization. They represent example of intermediates that can be expected between (4n+2) and 4n pi-conjugated systems. Since this framework contains twenty-five carbon atoms, the odd electron will be delocalized and stabilized in the cyclic network. Such derivatives are stable enough to be isolated by column chromatography and characterized under ambient conditions. By virtue of bearing an unpaired electron, 25pi radicals are poised to behave and display metal like redox properties. In principle they can be either reduced or oxidized by one-electron to yield charged species and exhibit multiple oxidation states. They can be identified, isolated and studied by electrochemical and spectro-electrochemical methods to justify the redox process. Such redox active neutral radicals are most wanted materials for organic electronics. Due to their reversible redox active nature, 25pi radical species are potential candidates for applications in organic radical batteries and in other energy storage devices. Since the macrocyclic framework provides opportunities for substitution with different functional groups, it is easier to tune their structural features and their electronic and redox properties. Hence, it can be expected that these 25pi radicals can fine-tuned with redox potential suitable for applications in organic radical batteries. At the same time, they are also potential candidates for applications in organic magnets. In contrast to metal counterparts, the magnetic properties of these organic radicals can be tuned by suitable redox active substituents on the macrocycle. For ex., a ferrocene coupled to 25pi radical provides the option to selectively generate the ferrocenium cations which can couple with the unpaired electron from the macrocycle. Alternatively, a synthetic strategy is devised to generate a dimer radical through a phenylene bridge which can provide a possible access to triplet ground state which is proposed to be ideal for organic materials to exhibit magnetic properties. At the same time, the unpaired electron can impart better charge conducting property. In summary, the design and synthesis of novel 25pi radical species is of academic interest and holds promise for applications in organic electronics. |