CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] [Not Applicable]

FIELD OF THE INVENTION

[0003] This invention relates to memory devices. In particular this invention provides a nonvolatile electronic memory device capable of storing information in extremely high density.

BACKGROUND OF THE INVENTION

[0004] Basic functions of a computer include information processing and storage. In typical computer systems, these arithmetic, logic, and memory operations are performed by devices that are capable of reversibly switching between two states often referred to as “0” and “1”. In most cases, such switching devices are fabricated from semiconducting devices that perform these various functions and are capable of switching between two states at a very high speed using minimum amounts of electrical energy. Thus, for example, transistors and transistor variants perform the basic switching and storage functions in computers.

[0005] Because of the huge data storage requirements of modern computers, a new, compact, low-cost, very high capacity, high speed memory configuration is needed. To reach this objective, molecular electronic switches, wires, microsensors for chemical analysis, and opto-electronic components for use in optical computing have been pursued. The principal advantages of using molecules in these applications are high component density (upwards of 10¹⁸ bits per square centimeter), increased response speeds, and high energy efficiency.

[0006] A variety of approaches have been proposed for molecular-based memory devices. While these approaches generally employ molecular architectures that can be switched between two different states, the approaches described to date have intrinsic limitations making their uses in computational devices difficult or impractical.

[0007] For example, such approaches to the production of molecular memories have involved photochromic dyes, electrochromic dyes, redox dyes, and molecular machines. Each of these approaches, however, has intrinsic limitations that ultimately render it unsuitable for use in molecular memories. For example, photochromic dyes change conformation in response to the absorption of light (e.g. cis-trans interconversion of an alkene, ring opening of a spiropyran, interconversion between excited-states in bacteriorhodopsin, etc.). Typically, the molecular structure of the dye is interconverted between two states that have distinct spectral properties.

[0008] Reading and writing data with such photochromic dyes requires use of light, often in the visible region (400-700 nm). Light-mediated data storage has intrinsic diffraction-limited size constraints. Moreover, most photochromic schemes are limited to scanning and interrogating dyes deposited on a surface and are not amenable to 3-D data storage. Even with near-field optical approaches, which might allow reliable encoding/reading of data elements of 100×100 nm dimensions (Nieto-Vesperinas and Garcia, N., eds. (1996) Optics at the Nanometer Scale, NATO ASI Series E, Vol. 319, Kluwer Academic Publishers: Dordrecht) the inherent restricted dimensionality (2-D) limits data density to 10¹⁰ bits/cm² . Strategies for 3-dimensional reading and writing of photochromic systems have been proposed that rely on two-photon excitation of dyes to encode data, and one-photon excitation to read the data (Birge et al. (1994) Amer. Sci. 82: 349-355, Parthenopoulos and Rentzepis (1989) Science, 245: 843-845), but it is believed that no high-density memory cubes have reached prototype stage in spite of the passage of at least a decade since their initial proposition. In addition, it is noted that these dyes often exhibit relatively slow switching times ranging from microsecond to millisecond durations.

[0009] Electrochromic dyes have been developed that undergo a slight change in absorption spectrum upon application of an applied electric field (Liptay (1969) Angew. Chem., Int. Ed. Engl. 8: 177-188). The dyes must be oriented in a fixed direction with respect to the applied field. Quite high fields (>10⁷ V/cm) must be applied to observe an altered absorption spectrum which can result in heat/power dissipation problems. In addition, the change in the absorption spectrum is typically quite small, which can present detection difficulties. The dyes revert to the initial state when the applied field is turned off.

[0010] Redox dyes have been developed that undergo a change in absorption spectrum upon chemical or electrochemical reduction (typically a 2-electron, 2-proton reduction) (Otsuki et al. (1996) Chem. Lett. 847-848). Such systems afford bistable states (e.g., quinone/hydroquinone, azo/hydrazo). Redox dyes have only been examined in solution studies, where they have been proposed for applications as switches and sensors (de Silva et al. (1997) Chem. Rev. 97: 1515-1566). On a solid substrate, electrochemical reduction would need to be accompanied by a source of protons. The latter requirement may be difficult to achieve on a solid substrate. Furthermore, any optical reading scheme would pose the same 2-D limitations as described for photochromic dyes.

[0011] Yet another approach involves the design of molecular machines (Anell et al. (1992) J. Am. Chem. Soc. 114: 193-218). These elegant molecular architectures have moving parts that can be switched from one position to another by chemical or photochemical means. The chemically induced systems have applications as sensors but are not practical for memory storage, while the photochemically induced systems have the same fundamental limitations as photochromic dyes. Moreover, methods have not yet been developed for delineating the conformation/structure of the molecular machine that are practical in any device applications. ¹H NMR spectroscopy, for example, is clearly the method of choice for elucidating structure/conformation for molecules in solution, but is totally impractical for interrogating a molecular memory element. None of the current architectures for molecular machines has been designed for assembly on a solid substrate, an essential requirement in a viable device.

[0012] In summary, photochromic dyes, electrochromic dyes, redox-sensitive dyes, and molecular machines all have fundamental limitations that have precluded their application as viable memory elements. These molecular architectures are typically limited by reading/writing constraints. Furthermore, even in cases where the effective molecular bistability is obtained, the requirement for photochemical reading restricts the device architecture to a 2-dimensional thin film. The achievable memory density of such a film is unlikely to exceed 10¹⁰ bits/cm² . Such limitations greatly diminish the appeal of these devices as viable molecular memory elements.

SUMMARY OF THE INVENTION

[0013] This invention provides novel high density memory devices that are electrically addressable permitting effective reading and writing, that provide a high memory density (e.g., 10¹⁵ bits/cm³ ), that provide a high degree of fault tolerance, and that are amenable to efficient chemical synthesis and chip fabrication. The devices are intrinsically latchable, defect tolerant, and support destructive or non-destructive read cycles.

[0014] In a preferred embodiment, this invention provides an apparatus for storing data (e.g., a “storage cell”). The storage cell includes a fixed electrode electrically coupled to a “storage medium” having a multiplicity of different and distinguishable oxidation states where data is stored in the (preferably non-neutral) oxidation states by the addition or withdrawal of one or more electrons from said storage medium via the electrically coupled electrode. In certain embodiments, the storage medium comprises a storage molecule having a plurality of different and distinguishable oxidation states where the storage molecule comprises a first triple-decker sandwich coordination compound covalently linked to a second triple-decker sandwich coordination compound, and where the first compound and the second compound are different triple-decker sandwich coordination compounds. In various embodiments, the storage molecule comprises a heteroleptic sandwich coordination compound or a homoleptic sandwich coordination compound. Particularly preferred storage molecules comprise a triple decker sandwhich coordination compound having a formula selected from the group consisting of Por¹M¹Por²M²Por³, Por¹M¹Pc¹M²Por², Pc¹M¹Pc²M²Por¹, Pc¹M¹Pc²M²Pc³, Pc¹M¹Por¹M²Por², and Pc¹M¹Por¹M²Pc², where M¹, and M² are the same or different and each is a metal, e.g. as described herein; Por¹, Por², and Por³ are the same or different and each is a porphyrinato species; and Pc¹, Pc², and Pc³ are the same or different and each is a phthalocyaninato species. Particularly preferred storage molecules have at least 8 different and distinguishable non-zero oxidation states. In various embodiments, the two triple-decker sandwich molecules comprising a storage molecule of this invention are linked together (directly or indirectly) by a bond or linker joining a porphyrinato species of one triple-decker sandwich molecule to a phthalocyaninato species of another triple-decker sandwich molecule and/or by a bond or linker joining a porphyrinato species of one triple-decker sandwich molecule to a porphyrinato species of another triple-decker sandwich molecule and/or by a bond or linker joining a phthalocyaninato species of one triple-decker sandwich molecule to a phthalocyaninato species of another triple-decker sandwich molecule.

[0015] Particularly preferred storage molecules include, but are not limited to the molecules of formulas I-X, XIV-XXI, dyad1 through dyad 5,etc., and particular species identified herein.

[0016] The storage medium is electrically coupled to the electrode(s) by any of a number of convenient methods including, but not limited to, covalent linkage (direct or through a linker), ionic linkage, non-ionic “bonding”, simple juxtaposition/apposition of the storage medium to the electrode(s), or simple proximity to the electrode(s) such that electron transfer (e.g. tunneling) between the medium and the electrode(s) can occur. The storage medium can contain or be juxtaposed to or layered with one or more dielectric material(s). Preferred dielectric materials are imbedded with counterions (e.g. Nafion). The storage cells of this invention are fully amenable to encapsulation (or other packaging) and can be provided in a number of forms including, but not limited to, an integrated circuit or as a component of an integrated circuit, a non-encapsulated “chip”, etc. In some embodiments, the storage medium is electronically coupled to a second electrode that is a reference electrode. In certain preferred embodiments, the storage medium is present in a single plane in the device. The apparatus of this invention can include the storage medium present at a multiplicity of storage locations, and in certain configurations, each storage location and associated electrode(s) forms a separate storage cell. The storage present on a single plane in the device or on multiple planes and said storage locations are present on multiple planes of said device. Virtually any number (e.g., 16, 32, 64, 128, 512, 1024, 4096, etc.) of storage locations and/or storage cells can be provided in the device. Each storage location can be addressed by a single electrode or by two or more electrodes. In other embodiments, a single electrode can address multiple storage locations and/or multiple storage cells.

[0017] In preferred storage cells, the storage medium stores data at a density of at least one bit, preferably at a density of at least 2 bits, more preferably at a density of at least 3 bits, and most preferably at a density of at least 5, 8, 16, 32, or 64 bits per molecule. Thus, preferred storage media have at least 2, 8, 16, 32, 64, 128 or 256 different and distinguishable oxidation states. In particularly preferred embodiments, the bits are all stored in non-neutral oxidation states. In a most preferred embodiment, the different and distinguishable oxidation states of the storage medium can be set by a voltage difference no greater than about 5 volts, more preferably no greater than about 2 volts, and most preferably no greater than about 1 volt.

[0018] In another embodiment, this invention provides an information storage medium comprising a storage molecule having at least eight different and distinguishable non-zero oxidation states where the storage molecule is a multimeric molecule comprising two or more triple-decker sandwich compounds. Preferred storage molecules include, but are not limted to the molecules of formulas I-X, XIV-XXI, dyad1 through dyad 5, etc.

[0019] This invention also provides a method of storing data. The method typically involves providing an apparatus for storing data as described herein and applying a voltage to an electrode comprising such a device at sufficient current to set an oxidation state of the storage medium. In certain embodiments, the voltage ranges up to about 5 volts, preferably up to about 3 volts, more preferably up to about 2 volts, and most preferably up to about 1 volt. The voltage can be the output of an integrated circuit. The method can further involve detecting the oxidation state of said storage medium comprising the apparatus and thereby reading out the data stored therein. Detecting the oxidation state can additionally comprise refreshing the oxidation state of the storage medium. In various embodiments, dececting involves analyzing a readout signal in the time domain or the frequency domain (e.g. by performing a Fourier transform on the readout signal). In various embodiments, the detection method utilizes a voltammetric method (e.g. sinusoidal voltammetry).

[0020] This invention also provides a porphyrin half-sandwich complex comprising a cis-A₂BC porphyrin complexed with a metal. The half-sandwich complex can be used to synthesize/assemble a triple-decker sandwich dyad.

[0021] Also provided is a method of making a triple-decker sandwich dyad. The method involves providing a metal-porphyrin half-sandwich complex comprising a cis-A₂BC porphyrin complexed with a metal or an ABCD porphyrin complexed with a metal; and reacting the half-sandwich complex with a double-decker sandwich complex to form a triple-decker sandwich compound.

[0022] In still another embodiment, this invention provides a computer system comprising a memory device, where the memory device comprises an apparatus for storing data as described herein. In certain embodiments, the computer system comprises a central processing unit, a display, a selector device, and a memory device, where the memory device comprises a data storage molecule as described herein.

[0023] Definitions

[0024] The terms “sandwich coordination compound” or “sandwich coordination complex” refer to a compound of the formula LⁿMⁿ⁻¹, where each L is a heterocyclic ligand (as described below), each M is a metal, n is 2 or more, most preferably 2 or 3, and each metal is positioned between a pair of ligands and bonded to one or more hetero atom (and typically a plurality of hetero atoms, e.g., 2, 3, 4, 5) in each ligand. Thus sandwich coordination compounds are not organometallic compounds such as ferrocene, in which the metal is bonded to carbon atoms. The ligands in the sandwich coordination compound are generally arranged in a stacked orientation, i.e., they are generally cofacially oriented and axially aligned with one another, although they may or may not be rotated about that axis with respect to one another (see, e.g., Ng and Jiang (1997) Chem. Soc. Rev., 26: 433-442).

[0025] The term “triple-decker sandwich coordination compound” refers to a sandwich coordination compound as described above where n is 3, thus having the formula L¹—M¹—L²—M²—L³ , wherein each of L¹, L² and L³ may be the same or different, and M¹ and M2 may be the same or different (see, e.g., U.S. Pat. No. 6,212,093 B1; Arnold et al. (1999) Chem. Lett. 483-484).

[0026] The term “homoleptic sandwich coordination compound” refers to a sandwich coordination compound as described above wherein all of the ligands L are the same.

[0027] The term “heteroleptic sandwich coordination compound” refers to a sandwich coordination compound as described above wherein at least one ligand L is different from the other ligands therein.

[0028] The term “heterocyclic ligand” as used herein generally refers to any heterocyclic molecule consisting of carbon atoms containing at least one, and preferably a plurality of, hetero atoms (e.g., N, O, S, Se, Te), which hetero atoms may be the same or different, and which molecule is capable of forming a sandwich coordination compound with another heterocyclic ligand (which may be the same or different) and a metal. Such heterocyclic ligands are typically macrocycles, particularly tetrapyrrole derivatives such as the phthalocyanines, porphyrins, and porphyrazines (see, e.g., Tran-Thi (1997) Coord. Chem. Rev., 160: 53-91).

[0029] The term “oxidation” refers to the loss of one or more electrons in an element, compound, or chemical substituent/subunit. In an oxidation reaction, electrons are lost by the element, compound or chemical substituent/subunit(s) involved in the reaction. The charge on these species then becomes more positive. The electrons are lost from the species undergoing oxidation and so electrons appear as products in an oxidation reaction. An oxidation takes place in the reaction Fe²⁺(aq)→Fe3(aq)+e⁻ because electrons are lost from the species being oxidized, Fe²⁺ (aq), despite the apparent production of electrons as “free” entities in oxidation reactions.

[0030] Conversely the term reduction refers to the gain of one or more electrons by an element, compound, or chemical substituent/subunit.

[0031] An “oxidation state” refers to the electrically neutral state or to the state produced by the gain or loss of electrons to an element, compound, or chemical substituent/subunit. In a preferred embodiment, the term “oxidation state” refers to states including the neutral state and any state other than a neutral state caused by the gain or loss of electrons (reduction or oxidation).

[0032] A “non-zero” or “non-neutral” oxidation state refers to an oxidation state other than an electrically neutral oxidation state.

[0033] The term “multiple oxidation states” means more than one oxidation state. In preferred embodiments, the oxidation states may reflect the gain of electrons (reduction) or the loss of electrons (oxidation).

[0034] The term “different and distinguishable” when referring to two or more oxidation states means that the net charge on the entity (atom, molecule, aggregate, subunit, etc.) can exist in two or more different states. The states are said to be “distinguishable” when the difference between the states is greater than thermal energy at room temperature (e.g. 0° C. to about 40° C.).

[0035] The term “electrode” refers to any medium or material capable of transporting charge (e.g. electrons) to and/or from a storage molecule. Preferred electrodes are metals, conductive organic molecules, or semiconductors. The electrodes can be manufactured to virtually any 2-dimensional or 3-dimensional shape (e.g. discrete lines, pads, planes, spheres, cylinders, etc.).

[0036] The term “fixed electrode” is intended to reflect the fact that the electrode is essentially stable and unmovable with respect to the storage medium and/or storage molecule(s). That is, the electrode and storage medium and/or storage molecule(s) are arranged in an essentially fixed geometric relationship with each other. The relationship can alter somewhat due to expansion and contraction of the medium with thermal changes or due to changes in conformation of the molecules comprising the electrode and/or the storage medium. Nevertheless, the overall spatial arrangement remains essentially invariant. In a preferred embodiment this term is intended to exclude systems in which the electrode is a movable “probe” (e.g. a writing or recording “head”, an atomic force microscope (AFM) tip, a scanning tunneling microscope (STM) tip, etc.).

[0037] The term “working electrode” is used to refer to one or more electrodes that are used to set or read the state of a storage medium and/or storage molecule.

[0038] The term “reference electrode” is used to refer to one or more electrodes that provide a reference (e.g. a particular reference voltage) for measurements recorded from the working electrode. In preferred embodiments, the reference electrodes in a memory device of this invention are at the same potential although in some embodiments this need not be the case.

[0039] The term “electrically coupled” when used with reference to a storage molecule and/or storage medium and electrode refers to an association between that storage medium or molecule and the electrode such that electrons move from the storage medium/molecule to the electrode or from the electrode to the storage medium/molecule and thereby alter the oxidation state of the storage medium/molecule. Electrical coupling can include direct covalent linkage between the storage medium/molecule and the electrode, indirect covalent coupling (e.g. via a linker), direct or indirect ionic bonding between the storage medium/molecule and the electrode, or other bonding (e.g. hydrophobic bonding). In addition, no actual bonding may be required and the storage medium/molecule can simply be contacted with the electrode surface. There also need not necessarily be any contact between the electrode and the storage medium/molecule where the electrode is sufficiently close to the storage medium/molecule to permit electron transfer (e.g. tunneling) between the medium/molecule and the electrode.

[0040] The term “redox-active unit” or “redox-active subunit” refers to a molecule or component of a molecule that is capable of being oxidized or reduced by the application of a suitable voltage.

[0041] The term “subunit”, as used herein, refers to a component (e.g. a redox-active component) of a molecule.

[0042] The terms “storage molecule” or “memory molecule” refer to a molecule having one or more oxidation states that can be used for the storage of information (e.g. a molecule comprising one or more redox-active subunits). Preferred storage molecules have two or more different and distinguishable non-neutral oxidation states. In addition to the compounds illustrated by the formulas herein, a wide variety of additional molecules can be used as storage molecules (see, e.g., U.S. Pat. Nos. 6,272,038, 6,212,093, 6,208,553, and international patent applications WO 01/51188 and WO 01/03126) and hence further comprise the storage medium. Preferred molecules include, but are not limited to a porphyrinic macrocyclce, a metallocene, a linear polyene, a cyclic polyene, a heteroatom-substituted linear polyene, a heteroatom-substituted cyclic polyene, a tetrathiafulvalene, a tetraselenafulvalene, a metal coordination complex, a buckyball, a triarylamine, a 1,4-phenylenediamine, a xanthene, a flavin, a phenazine, a phenothiazine, an acridine, a quinoline, a 2,2′-bipyridyl, a 4,4′-bipyridyl, a tetrathiotetracene, and a peri-bridged naphthalene dichalcogenide. Even more preferred molecules include a porphyrin, an expanded porphyrin, a contracted porphyrin, a ferrocene, a linear porphyrin polymer, and porphyrin array. Certain particularly preferred storage molecules include a porphyrinic macrocycle substituted at a beta-position or at a meso-position. Molecules well suited for use as storage molecules include the molecules described herein.

[0043] The term “storage medium” refers to a composition comprising a storage molecule of the invention, preferably juxtaposed to and/or bonded to a substrate.

[0044] An “electrochemical cell” typically consists of a reference electrode, a working electrode, a redox-active molecule (e.g. a storage molecule or storage medium), and, if necessary, some means (e.g., a dielectric, a conductive linker, etc.) for providing electrical conductivity between the electrodes and/or between the electrodes and the molecule/medium. In some embodiments, the dielectric is a component of the storage medium.

[0045] The terms “memory element”, “memory cell”, or “storage cell” refer to an electrochemical cell that can be used for the storage of information. Preferred “storage cells” are discrete regions of storage medium addressed by at least one and preferably by two electrodes (e.g. a working electrode and a reference electrode). The storage cells can be individually addressed (e.g. a unique electrode is associated with each memory element) or, particularly where the oxidation states of different memory elements are distinguishable, multiple memory elements can be addressed by a single electrode. The memory element can optionally include a dielectric (e.g. a dielectric impregnated with counterions).

[0046] The term “storage location” refers to a discrete domain or area in which a storage medium is disposed. When addressed with one or more electrodes, the storage location can form a storage cell. However if two storage locations contain the same storage media so that they have essentially the same oxidation states, and both storage locations are commonly addressed, they can form one functional storage cell.

[0047] Addressing a particular element refers to associating (e.g., electrically coupling) that memory element with an electrode such that the electrode can be used to specifically determine the oxidation state(s) of that memory element.

[0048] The term “storage density” refers to the number of bits per volume and/or bits per molecule that can be stored. When the storage medium is said to have a storage density greater than one bit per molecule, this refers to the fact that a storage medium preferably comprises molecules wherein a single molecule is capable of storing at least one bit of information.

[0049] The terms “read” or “interrogate” refer to the determination of the oxidation state(s) of one or more molecules (e.g. molecules comprising a storage medium).

[0050] The term “refresh” when used in reference to a storage molecule or to a storage medium refers to the application of a voltage to the storage molecule or storage medium to re-set the oxidation state of that storage molecule or storage medium to a predetermined state (e.g. the oxidation state the storage molecule or storage medium was in immediately prior to a read).

[0051] The term “E_1/2” refers to the practical definition of the formal potential (E°) of a redox process as defined by E=E°+(RT/nF)ln(D_ox/D_red) where R is the gas constant, T is temperature in K (Kelvin), n is the number of electrons involved in the process, F is the Faraday constant (96,485 Coulomb/mole), D_ox is the diffusion coefficient of the oxidized species and D_red is the diffusion coefficient of the reduced species.

[0052] A voltage source is any source (e.g. molecule, device, circuit, etc.) capable of applying a voltage to a target (e.g. an electrode).

[0053] The term “present on a single plane”, when used in reference to a memory device of this invention refers to the fact that the component(s) (e.g. storage medium, electrode(s), etc.) in question are present on the same physical plane in the device (e.g. are present on a single lamina). Components that are on the same plane can typically be fabricated at the same time, e.g., in a single operation. Thus, for example, all of the electrodes on a single plane can typically be applied in a single (e.g., sputtering) step (assuming they are all of the same material).

[0054] The phrase “output of an integrated circuit” refers to a voltage or signal produced by one or more integrated circuit(s) and/or one or more components of an integrated circuit.

[0055] A “voltammetric device” is a device capable of measuring the current produced in an electrochemical cell as a result of the application of a voltage or change in voltage.

[0056] An “amperometric device” is a device capable of measuring the current produced in an electrochemical cell as a result of the application of a specific potential (“voltage”).

[0057] A potentiometric device is a device capable of measuring potential across an interface that results from a difference in the equilibrium concentrations of redox molecules in an electrochemical cell.

[0058] A “coulometric device” is a device capable of measuring the net charge produced during the application of a potential field (“voltage”) to an electrochemical cell.

[0059] A “sinusoidal voltammeter” is a voltammetric device capable of determining the frequency domain properties of an electrochemical cell.

[0060] The term “porphyrinic macrocycle” refers to a porphyrin or porphyrin derivative. Such derivatives include porphyrins with extra rings ortho-fused, or ortho-perifused, to the porphyrin nucleus, porphyrins having a replacement of one or more carbon atoms of the porphyrin ring by an atom of another element (skeletal replacement), derivatives having a replacement of a nitrogen atom of the porphyrin ring by an atom of another element (skeletal replacement of nitrogen), derivatives having substituents other than hydrogen located at the peripheral (meso-, beta-) or core atoms of the porphyrin, derivatives with saturation of one or more bonds of the porphyrin (hydroporphyrins, e.g., chlorins, bacteriochlorins, isobacteriochlorins, decahydroporphyrins, corphins, pyrrocorphins, etc.), derivatives obtained by coordination of one or more metals to one or more porphyrin atoms (metalloporphyrins), derivatives having one or more atoms, including pyrrolic and pyrromethenyl units, inserted in the porphyrin ring (expanded porphyrins), derivatives having one or more groups removed from the porphyrin ring (contracted porphyrins, e.g., corrin, corrole) and combinations of the foregoing derivatives (e.g. phthalocyanines, porphyrazines, naphthalocyanines, subphthalocyanines, and porphyrin isomers). Preferred porphyrinic macrocycles comprise at least one 5-membered ring.

[0061] The term porphyrin refers to a cyclic structure typically composed of four pyrrole rings together with four nitrogen atoms and two replaceable hydrogens for which various metal atoms can readily be substituted. A typical porphyrin is hemin.

[0062] A “porphyrinato species” refers to a porphyrin that has lost any core protons and is complexed to one or more metal cations.

[0063] A “phthalocyaninato species” refers to phthalocyanine that has lost any core protons and is complexed to one or more metal cations.

[0064] The term “multiporphyrin array” refers to a discrete number of two or more covalently linked porphyrinic macrocycles. The multiporphyrin arrays can be linear, cyclic, or branched.

[0065] A linker is a molecule used to couple two different molecules, two subunits of a molecule, or a molecule to a substrate.

[0066] A substrate is a, preferably solid, material suitable for the attachment of one or more molecules. Substrates can be formed of materials including, but not limited to glass, plastic, silicon, minerals (e.g. quartz), semiconducting materials (e.g. type IV, type V semiconductors, etc.), ceramics, metals, etc.

[0067] The term “aryl” refers to a compound whose molecules have the ring structure characteristic of benzene, naphthalene, phenanthrene, anthracene, etc. (i.e., either the 6-carbon ring of benzene or the condensed 6-carbon rings of the other aromatic derivatives). For example, an aryl group may be phenyl (C₆H₅) or naphthyl (C₁₀H₇). It is recognized that the aryl, while acting as substituent can itself have additional substituents.

[0068] The term “alkyl” refers to a paraffinic hydrocarbon group which may be derived from an alkane by dropping one hydrogen from the formula. Examples are methyl (CH₃—), ethyl (C₂H₅—), propyl (CH₃CH₂CH₂—), isopropyl ((CH₃)₂CH—).

[0069] The term “halogen” refers to one of the electronegative elements of group VIIA of the periodic table (fluorine, chlorine, bromine, iodine, astatine).

[0070] The term “nitro” refers to the —NO₂ group.

[0071] The term “amino” refers to the —NH₂ group.

[0072] The term “perfluoroakyl” refers to an alkyl group where every hydrogen atom is replaced with a fluorine atom.

[0073] The term “perfluoroaryl” refers to an aryl group where every hydrogen atom is replaced with a fluorine atom.

[0074] The term “pyridyl” refers to an aryl group where one CR unit is replaced with a nitrogen atom.

[0075] The term “cyano” refers to the —CN group.

[0076] The term “thiocyanato” refers to the —SCN group.

[0077] The term “sulfoxyl” refers to a group of composition RS(O)— where R is some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to methylsulfoxyl, phenylsulfoxyl, etc.

[0078] The term “sulfonyl” refers to a group of composition RSO₂— where R is some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to methylsulfonyl, phenylsulfonyl, p-toluenesulfonyl, etc.

[0079] The term “carbamoyl” refers to the group of composition R¹(R²)NC(O)— where R¹ and R² are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to N-ethylcarbamoyl, N,N-dimethylcarbamoyl, etc.

[0080] The term “amido” refers to the group of composition R¹ CON(R²)� �� where R¹ and R² are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group. Examples include, but are not limited to acetamido, N-ethylbenzamido, etc.

[0081] The term “acyl” refers to an organic acid group in which the OH of the carboxyl group is replaced by some other substituent (RCO—). Examples include, but are not limited to acetyl, benzoyl, etc.

[0082] In preferred embodiments, when a metal is designated by “M” or “Mⁿ” where n is an integer, it is recognized that the metal may be associated with a counterion.

[0083] The term “substituent” as used in the formulas herein, particularly designated by S or Sⁿ where n is an integer, in a preferred embodiment refer to redox-active groups (subunits) that can be used to adjust the redox potential(s) of the subject compound. Preferred substituents include, but are not limited to, aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, and carbamoyl. In preferred embodiments, a substituted aryl group is attached to a porphyrin or a porphyrinic macrocycle, and the substituents on the aryl group are selected from the group consisting of aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, and carbamoyl. Additional substituents include, but are not limited to, 4-chlorophenyl, 4-trifluoromethylphenyl, and 4-methoxyphenyl. Preferred substituents provide a redox potential range of less than about 5 volts, preferably less than about 2 volts, more preferably less than about 1 volt.

[0084] The phrase “provide a redox potential range of less than about X volts” refers to the fact that when a substituent providing such a redox potential range is incorporated into a compound, the compound into which it is incorporated has an oxidation potential less than or equal to X volts, where X is a numeric value.