F− and OH− induced monodeprotonation of a lacunar cationic dibenzotetraaza[14]annulene: experimental evidence of tautomerism in a monoanionic macrocycle

A search for selective receptors of anions resulted in a new lacunar cationic derivative of dibenzotetraaza[14]annulene (DBTAA) being synthesized and its crystal structure determined. UV–vis, fluorescence and preliminary 1H NMR studies of anion binding abilities revealed that under the influence of F− and OH−, deprotonation of the macrocycle takes place leading to a zwitterionic species containing a monoanionic DBTAA core and a positively charged quaternized amine nitrogen. The tautomerism of the remaining single NH hydrogen is discussed on the basis of 1H NMR experiments and DFT calculations.