Page 4 - Surface-Confined Assemblies and Polymers for Molecular Logic

Surface-Confined Assemblies and Polymers de Ruiter and van der Boom

FIGURE 3. Representative milestones in molecular logic. The timeline does not include bioinspired systems. 24

FIGURE 5. (A) Schematic representation of gate-to-gate communication
between Os and Ru-based monolayers, mediated by Fe 2þ as messenger
and operating with three chemical inputs I 1 =Fe 3þ , I 2 =H 2 O, and
I 3 =Ce 4þ . (B) Corresponding logic circuit operating according to:
F =[A þ B]C. Adapted with permission from ref 27. Copyright 2008
Wiley-VCH Verlag GmbH & Co. KgaA.
FIGURE 4. Representation of the information transfer, mediated by a
3þ
messenger component (Fe 2þ/3þ ), between Os- and Ru-based monolayers. by Fe , whereas the concurrently formed Fe 2þ reduces a series
Adapted with permission from ref 27. Copyright 2008 Wiley-VCH Verlag of Ru -based monolayers. The simultaneous readout of the
3þ
GmbH & Co. KgaA. 2þ
light absorption intensities of the Ru -based monolayers,
which are placed in parallel to each other, provides the output.
The metal center is only reduced (logical 1) when water or Fe 2þ
2þ
The gain can be controlled by the addition of a Fe -chelating
2þ
(generated by the Os -based monolayer) is present and in the
ligand such as 2,2 -bipyridine.
0
4þ
absence of Ce , which is a strong oxidizing agent that keeps
both the osmium and ruthenium in an oxidized state. The OR IV. Sequential Logic and Memory
2þ
gate present in the circuit is generated partly by the Os -based In sequential logic, the output is determined by the current
monolayer, which communicates its output as Fe , toward the state of the system and the input currently present. The current
2þ
AND gate, represented by the Ru -based monolayer. This state is usually a function of the previous input, and hence, the
3þ
corresponds to the logic circuit shown in Figure 5B. These molecular-based system behaves as a basic memory element.
findings have been extended by us to a system that amplifies In contrast, in combinatorial logic, the output solely depends
its optical signature upon reaction with FeCl 3 . 28 Covalently on the current inputs. Consequently, sequential logic systems
immobilized Os 2þ complexes on a glass substrate are oxidized arecommonlyusedinmemorydevices as wellasinfinite state
566 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 563–573 ’ 2011 ’ Vol. 44, No. 8