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Methylated bis-triethylene glycolic crown-5-calix[4]arene (M-BTC5A) as a phase-transfer catalyst showed the best performance among other analogues and even conventional Kryptofix 222 in the nucleophilic aromatic 18F-fluorination of diaryliodonium tosylate precursors owing to (i) the efficient release of reactive "naked" [18F]fluoride, (ii) the high stabilization of the precursor in the reaction, and, presumably, (iii) the ease of access between the precursor and the K18F/M-BTC5A complex facilitated by π-π interactions. [18F]Flumazenil wa