Pyrene-appended calix[4]crowned logic gates involving normal and reverse PET: NOR, XNOR and INHIBIT

As a novel sensing system, N-(1-pyrenylmethyl) amide-appended calix[4]crown-5 (2) and crown-6 (3) have been newly synthesized. Judging from the fluorescence changes upon the addition of cations, 3 having crown-6 ring showed the Pb²⁺ ion selectivity over other cations tested regarding fluorescence quenching. Upon the Pb²⁺ ion coordination to two amide oxygen atoms with aid of crown ring, a reverse-photo-induced electron transfer (PET) occurs in such a way that electrons transfer from the pyrene groups to the electron deficient amide oxygen atoms to give a quenched fluorescence. By the addition of either HClO₄ or triethylamine in the solution of 3, the fluorescence intensity decreased because of the reverse-PET from pyrene groups to protonated amide oxygen atoms and because of normal PET from the nitrogen anion formed by triethylamine to pyrene groups, respectively. For 3, NOR logic gate in which the strong fluorescence signal appears at 395 nm (output: 1) is operated only when neither of triethylamine nor Pb(ClO₄)₂ (inputs A and B) is added (A=B: 0). XNOR gate is also operated only when both of two inputs are added (triethylamine and HClO₄, A=B: 1) or when neither of two inputs is added (A=B: 0). Then, for 3, new INHIBIT gate system was also designed using such combinational inputs as HClO₄, Pb(ClO₄)₂ and triethylamine.