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Surface-Confined Assemblies and Polymers for Molecular Logic

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Graham de Ruiter and Milko E. van der Boom*

Department of Organic Chemistry, The Weizmann Institute of Science, 76100 Rehovot, Israel

Acc. Chem. Res., Article ASAP

DOI: 10.1021/ar200002v

Publication Date (Web): June 16, 2011

Copyright © 2011 American Chemical Society

To whom correspondence should be addressed. E-mail: milko.vanderboom@weizmann.ac.il.

Biography

Graham de Ruiter obtained his B.Sc. (2006) and M.Sc. degrees (cum laude; 2008) in chemistry with Prof. Jan Reedijk at Leiden University, The Netherlands. He is currently a Ph.D. student in the group of Prof. Milko E. van der Boom at the Weizmann Institute of Science (Israel). He uses polypyridyl complexes as versatile platforms for optical devices, sensors, catalysis, and molecular logic gates.

Biography

Milko E. van der Boom received his B.Sc. degree (1992) from the University of Applied Sciences in Amsterdam, The Netherlands, and a M.Sc. degree (1994) in Inorganic Chemistry at the University of Amsterdam (with Prof. Kees Elsevier). He earned his Ph.D. degree with distinction in 1999 from the Weizmann Institute of Science in Israel (with Prof. David Milstein). After 3 years of postdoctoral research with Prof. Tobin J. Marks at Northwestern University in the United States, he became a Faculty member in the Weizmann Institute’s Department of Organic Chemistry.

Abstract

Stimuli responsive materials are capable of mimicking the 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 polymers and metal polypyridyl complexes on a solid support.

Metal polypyridyl complexes act as useful sensors to a variety of analytes in solution (i.e., H₂O, Fe^2+/3+, Cr⁶⁺, 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 input–output 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.