A Taco Complex Derived
from a Bis-Crown Ether Capable of Executing Molecular Logic Operation
through Reversible Complexation
- Publication date
- Publisher
Abstract
As learned from natural systems, self-assembly and self-sorting
help in interconnecting different molecular logic gates and thus achieve
high-level logic functions. In this context, demonstration of important
logic operations using changes in optical responses due to the formation
of molecular assemblies is even more desirable for the construction
of a molecular computer. Synthesis of an appropriate divalent as well
as a luminescent crown ether based host <b>1</b> and paraquat
derivatives, <b>2</b>(PF<sub>6</sub>)<sub>2</sub> and <b>3</b>(PF<sub>6</sub>)<sub>2</sub>, as guests helped in demonstrating
a reversible [3](taco complex) (<b>1</b>·{<b>2</b>(PF<sub>6</sub>)<sub>2</sub>}<sub>2</sub> or <b>1</b>·{<b>3</b>(PF<sub>6</sub>)<sub>2</sub>}<sub>2</sub>) formation in nonpolar
solvent. Detailed <sup>1</sup>H NMR studies revealed that two paraquat
units were bound cooperatively by the two crown units in <b>1</b>. Because of preorganization, the flexible host molecule <b>1</b> adopts a folded conformation, where each of two paraquat units remain
sandwiched between the two aromatic units of each folded crown ether
moiety in <b>1</b>. Disassembly of the “taco”
complex in the presence of KPF<sub>6</sub> and reassembly on subsequent
addition of DB18C6 was initially demonstrated by <sup>1</sup>H NMR
spectral studies, which were subsequently corroborated through luminescence
spectral studies. Further, luminescence spectral responses as output
signals with appropriate and two independent molecular inputs could
be correlated to demonstrate basic logic operation like OR and YES
gates, while the results of the three molecular inputs could be utilized
to demonstrate important logic operation like an INHIBIT gate