A convenient synthesis and spectroscopic characterization of N,N '-bis(2-propenyl)-2,7-diazapyrenium quaternary salts

N,N'-Bis(2-propenyl)-2,7-diazapyrenium salts are synthesized in good yield from the reaction of 1,4,5,8-naphthalenetetracarboxylic dianhydride with al lylamine, followed by LiAlH4 reduction and subsequent oxidation with 2,3-di chloro-5,6-dicyano-1,4-benzoquinone (DDQ). The nature of the counteranion d epends on the solvent system used for recrystallization of the crude produc t from the final DDQ-oxidation step. X-ray analysis shows that if recrystal lization is carried out in boiling CH3OH/H2O (1:1, v/v), the counteranion i n the resulting deep-red crystals is always the alkoxy anion of 2-cyano-5,6 -dichloro-3-hydroxy-1,4-benzoquinone whether the final DDQ oxidation ends w ith addition of HClO4 or HCl; on the other hand, if recrystallization is ca rried out with anhydrous acetonitrile, the product is N,N'-bis(2-propenyl)- 2,7-diazapyrenium diperchlorate or dichloride depending on whether the DDQ oxidation is followed by addition of coned HClO4 or coned HCl, respectively . Importantly, if the DDQ oxidation is quenched with HBr, Br- is oxidized t o Br-2 by unreacted DDQ, and the resulting product is N,N'-bis(a,3-dibromop ropyl)-2,7-diazapyrenium dibromide. Comparative absorption and time-resolve d emission studies provide evidence for possible dimerization of N,N'-bis(2 -propenyl)-2,7-diazapyrenium diperchlorate in CH3CN.