Page 3 - Surface-Confined Assemblies and Polymers for Molecular Logic

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

SCHEME 1. Polypyridyl Complexes (A,B) and Conductive Polymers (C) Used for MBLC on Solid Support (i.e., Silicon, Glass, and IndiumTin Oxide (ITO)
Coated Glass) 32,37,38,40

4þ
FIGURE 2. Logic circuit operating with three chemical inputs (I 1 =Ce ,
I 2 =H 2 O,andI 3 =NO 2 ), accordingtoF = A[B þ C]. Adaptedwithpermission
from ref 11. Copyright 2008 Wiley-VCH Verlag GmbH & Co. KgaA.

Physical integration of molecular logic gates has proven
to be difficult, especially because of inhomogeneity between
FIGURE 1. Representative absorption spectra of osmium-polypyridyl inputs and outputs. This is of critical importance, as homo-
complexes (Scheme 1A) covalently bound to a quartz substrate when (a)
geneity allows for communication between (different) logic
2þ
3þ
reduced (Os ; red trace) and (b) oxidized (Os ; blue trace). The dotted lines
gates. There are a few examples of communication through
indicate the threshold values that determine the value of the binary digits
(1 or 0) at two selected wavelengths (317 and 516 nm). Adapted with molecular intermediates. One of these is the three-phase test
permissionfromref11.Copyright2008Wiley-VCHVerlagGmbH& Co.KgaA. where messenger molecules are generated by a polymer-
bound material and detected by another polymer. 25 Credi
TABLE 1. Truth Table for the Combinatorial Logic Circuit (Figure 2) Oper- et al. reported another example where the communication
4þ
ating with Three Chemical Inputs (I 1 =Ce , I 2 =H 2 O, and I 3 =NO 2 ) 11 between a merocyanine derivative and an osmium terpyridyl
þ
chemical Inputs complexbymeans of H was demonstrated. 26 We explored
the communication between Os - and Ru -based mono-
3þ
2þ
entry Ce 4þ H 2 O NO 2 output
27
1 0 0 0 1 layersbymeansofaFe 2þ/3þ redoxcouple. Subsequently,we
2 0 0 1 0 used this to concatenate logic gates. 11,27,28 The electrochemi-
3 0 1 0 1
4 0 1 1 1 cal potential of Fe 3þ is high enough to oxidize Os 2þ but not
5 1 0 0 0 2þ 2þ 3þ
6 1 0 1 0 Ru . On the other hand, Fe is able to reduce Ru but not
7 1 1 0 0 Os 3þ ; therefore, the redox couple can be used to transfer
8 1 1 1 0
information from one monolayer to the other (Figure 4).
The communication was subsequently used to construct a
circuits were constructed with compounds that rely on the logic circuit that relies on physical integration rather than on
3þ
functional integration of logic gates; that is, one molecular functionalintegration.UsingOs -andRu -basedmonolayers
2þ
3þ
based assembly represents an entire logic circuit rather than as information processors, in combination with Fe ,H 2 O, and
a gate. 23 This is unprecedented in silicon technology and Ce 4þ as inputs, a logic circuit is constructed by monitoring the
3þ
underscores the potential power of MBLC. output of the Ru -based monolayer at λ = 463 nm (Figure 5A).
Vol. 44, No. 8 ’ 2011 ’ 563–573 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 565