Electrically addressable multistate volatile memory with flip-flop and flip-flap-flop logic circuits on a solid support.

Molecules that can perform complex mathematical operations are a potential alternative for transistor-type semiconductors. Since a molecular AND gate was demonstrated in 1993, logic gates, circuits, and even molecular memory elements have been reported. Most systems feature solution-based chemistry that inherently suffers from amassing chemical entities, thus compromising on operability and reversibility. Nevertheless, molecular information processing is becoming increasingly popular, since molecules are versatile synthetic building blocks for a bottom-up approach for information transfer and storage. In particular, the field of molecular logic has attracted much attention. 7] The behavior of molecules as logic gates that respond to specific inputs has found potential applications in sensors, medical diagnostics, molecular memory devices, and molecular computational identification (MCID) tags. To date, the applied logic is almost exclusively based on the underlying principle of mathematical operations performed on a system that can exist exclusively in two stable states, as introduced by George Boole. The ease of fabrication and wide variety of applications of binary systems has made them the status quo for (molecular) information processing technology. However, in order to cope with an ever-increasing information density, the viability of the binary numeral system also has to be considered. It is well-established that base three is the most efficient numeral system for transferring and storing information (see the Supporting Information). For instance, the information density in a ternary system is approximately 1.6 times higher than in a binary system. Therefore, exploration of molecular-based systems that are capable of existing in multiple states is highly desirable. The exploration of ternary memory devices is of particular interest, since it is expected that they eventually will replace the conventional flip-flop architecture in static random access memory (SRAM). Multivalue logic or multistate memory has rarely been demonstrated with molecular-based systems. 15] Herein we present a reconfigurable binary memory, and the first example of a ternary memory device constructed from a molecular-based assembly on a solid support. Fascinatingly, the assembly mimics both the well-known flip-flop logic circuit, commonly found in SRAM, and the even more interesting ternary flip-flap-flop logic circuit. The latter system enabled the storage of bits (binary digits) and trits (ternary digits) on a reconfigurable molecular-based assembly on a solid support. Furthermore, fourand five-state memory devices could be constructed for applications in dynamic random access memory (DRAM). The electrical addressability ensures chemical reversibility and stability, whereas the optical readout is fast and nondestructive. This result unequivocally demonstrates the proof-of-principle that the electrically addressable assemblies are capable of performing complex mathematical operations, and as such, brings us one step further towards the development of alternatives for transistor-type memory devices. The molecular memory was constructed from an assembly formed by alternating deposition of 1 and PdCl2 on indium tin oxide (ITO) coated glass functionalized with a pyridylgroup terminated monolayer (Scheme 1). Because the optical output is a precise function of the applied potential, the optical properties can be accurately controlled (Figure S1 in the Supporting Information). Therefore, multivalued information can be written on to the assembly by applying specific potential biases (vs. Ag/AgCl). The read–write cycle is completed by monitoring the metal-to-ligand charge-transfer (MLCT) band at l = 510 nm, which can be read out by a conventional UV/Vis spectrophotometer. Interestingly, the read–write operations are fundamentally different, that is, optical and electrochemical, respectively. The optical readout is nondestructive and allows for instantaneous data transfer.