| Abstract
| - Zeolite-Y (Y), zeolite-L (L), mordenite (M), and ZSM-5 exchanged with methyl viologen C1VC12+ andN‘,N‘ ‘-trimethylenebis(1-methyl-4,4‘-bipyridinium) (henceforth bisviologen) C1V2+-C3-VC12+ were prepared.Treatment of the dried, viologen-doped zeolites with solvated electrons in diethyl ether readily yields thecorresponding viologen radical cation, i.e., C1VC1•+ and C1V•+-C3-VC1•+ within the zeolite pores. AlthoughC1V•+-C3-VC1•+ readily folds to its intramolecular dimer C3[C1V•+]2 in solution, it remains in the open formin the four zeolites. C1VC1•+ readily dimerizes to [C1VC1•+]2 at high concentrations in L but not in otherzeolites. However, C1V•+-C3-VC1•+ does not dimerize by itself in any of the four zeolites even at highconcentrations. C1VC1•+ readily dimerizes in Y, L, and M when the pores are filled with water. The hydration-induced dimerization also works well for C1V•+-C3-VC1•+ in L and M. This leads to selective formation ofthe unprecedented intermolecular dimer of bisviologen radical cation, i.e., [C1V•+-C3-VC1•+]2 in L and M.The intramolecular analogue C3[C1V•+]2 can also be dispersed into Y, L, and M by direct occlusion of itsbisperchlorate salt from the acetonitrile solution. The broad ∼530 nm band of the viologen radical dimersplits into two when the viologen radical moieties are forced to juxtapose in the collinear conformationwithin the narrow and straight channels of L and M. The near-infrared band of the viologen radical dimerprogressively blue shifts with decreasing the interannular distance. This paper thus demonstrates a noveluse of zeolites to selectively disperse inter- and intramolecular dimers of diradical dication and to lock theviologen radical dimers into the collinear conformation which allows us to delineate the spectral variationof viologen radical dimers with changing the interannular conformation and distance.
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