Page 1 - Surface-Confined Assemblies and Polymers for Molecular Logic
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Surface-Confined Assemblies and Polymers
for Molecular Logic
GRAHAM DE RUITER AND MILKO E. VAN DER BOOM*
Department of Organic Chemistry, The Weizmann Institute of Science, 76100
Rehovot, Israel
RECEIVED ON JANUARY 5, 2011
CONSPECTUS
timuli responsive materials are capable of mimicking the
S operation characteristics of logic gates such as AND, OR, NOR,
and even flip-flops. Since the development of molecular sensors
and the introduction of the first AND gate in solution by de Silva in
1993, Molecular (Boolean) Logic and Computing (MBLC) has
become increasingly popular. In this Account, we present recent
research activities that focus on MBLC with electrochromic poly-
mers and metal polypyridyl complexes on a solid support.
Metal polypyridyl complexes act as useful sensors to a variety
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of analytes in solution (i.e., H 2 O, Fe 2þ/3þ ,Cr ,NO ) and in the gas
phase (NO x in air). This information transfer, whether the analyte is
present, is based on the reversible redox chemistry of the metal
complexes, which are stable up to 200 °C in air. The concurrent
changes in the optical properties are nondestructive and fast. In
such a setup, the input is directly related to the output and,
therefore, can be represented by one-input logic gates. These
inputoutput relationships are extendable for mimicking the
diverse functions of essential molecular logic gates and circuits
within a set of Boolean algebraic operations. Such a molecular
approach towards Boolean logic has yielded a series of proof-of-
concept devices: logic gates, multiplexers, half-adders, and flip-flop logic circuits.
MBLC is a versatile and, potentially, a parallel approach to silicon circuits: assemblies of these molecular gates can perform a
wide variety of logic tasks through reconfiguration of their inputs. Although these developments do not require a semiconductor
blueprint, similar guidelines such as signal propagation, gate-to-gate communication, propagation delay, and combinatorial and
sequential logic will play a critical role in allowing this field to mature. For instance, gate-to-gate communication by chemical wiring
of the gates with metal ions as electron carriers results in the integration of stand-alone systems: the output of one gate is used as
the input for another gate. Using the same setup, we were able to display both combinatorial and sequential logic.
We have demonstrated MBLC by coupling electrochemical inputs with optical readout, which resulted in various logic
architectures built on a redox-active, functionalized surface. Electrochemically operated sequential logic systems such as flip-flops,
multivalued logic, and multistate memory could enhance computational power without increasing spatial requirements. Applying
multivalued digits in data storage could exponentially increase memory capacity. Furthermore, we evaluate the pros and cons of
MBLC and identify targets for future research in this Account.
I. Introduction fabricating chips with 32 and 22 nm size transistors, which is
The increasing information load requires new approaches used in the latest computer processors. Further miniaturiza-
for data processing. The present methods are governed by tion, however, comes with additional problems. 1,2 For in-
a top-down approach in which one strives toward miniatur- stance, heat dissipation and electrical conductance are
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izing known (logic) devices. Current technology allows for problematic below certain size thresholds. 2 Molecular
Vol. 44, No. 8 ’ 2011 ’ 563–573 ’ ACCOUNTS OF CHEMICAL RESEARCH ’ 563
Published on the Web 06/16/2011 www.pubs.acs.org/accounts
10.1021/ar200002v & 2011 American Chemical Society