Most organic radical species are unstable and extremely reactive. However, their unique electronic and magnetic properties suggest they have potential as organic semiconductors in electron transfer materials and spintronics. Potential applications of these materials include organic light-emitting diodes (OLEDs), photovoltaics, and data storage. Thus, designing new stable organic radical species are extremely important for the development of these fields. Methyl viologen (MV), a bipyridine derivative, has shown to incorporate itself in a 2:1 ratio within cucurbit[8]uril (Q8) when it is mono-reduced. The binding constant of this interaction is on the magnitude of 107. Q8 is able to protect and stabilize both MV radicals from rapid reoxidation. The effectiveness of this radical encapsulation strategy can be increased by synthetically linking the two MV units, causing a decrease in lost entropy when binding to Q8. With this in mind, I have synthesized an ortho-linked MV dimer (ortho-dimer), which carries a permanent 4+ charge. When the ortho-dimer is reduced, the 3+ radical state is significantly stabilized by Q8, as shown by a binding constant of 109. This is about 100x stronger binding than the two individual mono-reduced MV with Q8. This dimerization strategy can be extended to other similar cationic materials. One such example is 2,5-Bis(4-pyridyl)thiazolo[5,4,d]thiazole (Py2TTz), which contains a slightly longer conjugated p-system than MV. The design of radical cationic dimers encapsulated in Q8 presents a unique method for stabilizing radicals for potential use in organic electronics.

Synthesis of novel linked viologen and Py2TTz dimers to enhance radical stability in cucurbit[8]uril

2019 Spring National Meeting

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