Patent Application
20070189058
The present disclosure relates generally to molecular systems, and more particularly to methods of reversibly switching the molecular systems between four states.
Molecular electronics is a relatively new field that includes the use of individual molecules and molecular systems to perform a variety of functions (e.g., switching) at the micro- and nano-scale level. The use of molecules to perform such functions enables the fabrication of devices having micrometer-scale or nanometer-scale dimensions, thus extending technology to sizes not easily achievable with present semiconductor technology.
Using the interplay of chemical, electrical, and/or optical signals, the molecules may be designed to execute three basic logic operations (AND, NOT, OR) and simple combinations thereof. Under the influence of an appropriate input stimulation, chemical systems may switch from one form to another, thus producing a change in detectable output. The detectable output is often exhibited by a color change. These molecular switches may exhibit dye-like optical properties and are capable of switching between two colors. The two colors that are exhibited by these systems,. may, in some instances, limit the use of such systems.
As such, it would be desirable to provide a molecular switch capable of switching between more than two states, thus exhibiting more than two colors.
A molecular system that is reversibly switchable between four states is disclosed. The molecular system includes two or more ends. At least three rotors and at least two stators are located between the ends. Each of the rotors is capable of rotating when under the influence of an electric field having a predetermined strength. The predetermined strength of the electric field for rotating one of the rotors is different than that of the predetermined strength of the electric field for rotating each of the other rotors. One or more conjugated connecting units link at least one of the three rotors and at least one of the two stators. The rotation of at least one of the three rotors switches the molecular system to one of the four states.
Features and advantages of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though not necessarily identical components. For the sake of brevity, reference numerals or features having a previously described function may not necessarily be described in connection with other drawings in which they appear.
Embodiments of the present disclosure advantageously provide a new type of molecular system that is switchable between four states and is capable of exhibiting different colors. Generally, the availability of multi-colors with the molecular system may make the display devices in which the system is used simpler and thus more cost efficient. Embodiments of the molecular system disclosed herein are capable of both optical and/or electrical switching. The molecular systems have a functional length measured in nanometers, or larger (e.g. micrometers), and thus are suitable for use in a variety of optical and/or electronic devices.
Referring now to
Each of the rotors ROTOR1, ROTOR2, ROTOR3 is capable of rotating when under the influence of an electric field having a predetermined strength. It is to be understood that the predetermined strength of the electric field suitable for rotating one of the three rotors ROTOR1, ROTOR2, ROTOR3 is different than that of the predetermined strength of the electric field for rotating each of the other of the rotors ROTOR1, ROTOR2, ROTOR3. As such, the strength of the electric field depends, at least in part, on the rotors ROTOR1, ROTOR2, ROTOR3 in the molecular system 10. In an embodiment, the electric field used to rotate one rotor ROTOR1 ranges from about 0.004 eV to about 0.008 eV (0.1 to 0.2 kcal/mole); the electric field used to rotate a second rotor ROTOR2 is equal to or greater than about 0.02 eV (about 0.5 kcal/mole); and the electric field used to rotate a third rotor ROTOR3 is equal to or greater than about 0.04 eV (0.9 kcal/mole).
Generally, the rotors ROTOR1, ROTOR2, ROTOR3 are rotatable segments that have a large dipole moment and that link other portions of the molecular system 10 that are immobilized (e.g., the stators). Under the influence of an applied electric field, the vector dipole moment of the rotor(s) ROTOR1, ROTOR2, ROTOR3 attempts to align parallel to the direction of the external field. Each of the rotors ROTOR1, ROTOR2, ROTOR3 has a large dipole moment in a different environment. As such, an electric field that is capable of aligning the first rotor ROTOR1 is different than the electric field that is capable of aligning the second rotor ROTOR2, and both of these electric fields are different than the electric field that is capable of aligning the third rotor ROTOR3.
It is to be understood that the molecular system 10 is designed such that there are inter- and/or intramolecular forces, such as hydrogen bonding or dipole-dipole interactions as well as steric repulsions, which substantially stabilize the rotor(s) ROTOR1, ROTOR2, ROTOR3 in particular orientations with respect to the stator(s) STATOR1, STATOR2, STATOR3, STATOR4. Thus, different, relatively large fields may be used to unlatch the rotor(s) ROTOR1, ROTOR2, ROTOR3 from its initial orientation and rotate with respect to the stator(s) STATOR1, STATOR2, STATOR3, STATOR4, if the direction of the applied field is opposite to that of the dipole of the rotor ROTOR1, ROTOR2, ROTOR3.
Once switched into a particular orientation, the molecular system 10 remains in that orientation until exposure to an external field. Further, the molecular system 10 may include a steric repulsion that substantially prevents the rotors ROTOR1, ROTOR2, ROTOR3 from rotating through a complete 180° half cycle. The rotors' ROTOR1, ROTOR2, ROTOR3 rotation may be halted by the steric interaction of bulky groups on the rotors ROTOR1, ROTOR2, ROTOR3 and stators STATOR1, STATOR2, STATOR3, STATOR4 at an angle of approximately 90° from the initial orientation. Furthermore, this 90° orientation may be stabilized by a different set of inter- and/or intramolecular hydrogen bonds or dipole interactions, and is thus latched into place even after the applied field is turned off.
In
As depicted, the state of the molecular system 10 may be altered by applying a different strength of applied external e-field. Additionally, the colors of the molecular system 10 may be tuned to be substantially transparent, blue, green, or red by selectively rotating the rotor(s) ROTOR1, ROTOR2 and/or ROTOR3.
It is to be understood that the labels STATE1, STATE2, STATE3 and STATE4 are merely illustrative of the four states that the molecule 10 may switch between. It is to be further understood that the labels are not necessarily indicative of the molecule's particular configuration. For example, a first state of the molecule 10 may be the co-planar state (labeled STATE 4 in
Generally, the molecular system 10 tends to have all of the rotors ROTOR1, ROTOR2, ROTOR3 aligned with each other in an out-of-plane orientation with respect to the stators STATOR1, STATOR2, STATOR3, STATOR4, as shown in STATE 1. In this state, the molecular system 10 is strongly blue-shifted, is in a highly localized state, and exhibits a substantially colorless or transparent property.
Under the influence of an applied external field, one of the rotors ROTOR3 rotates to be substantially co-planar with the stators STATOR1, STATOR2, STATOR3, STATOR4, as shown in STATE 2. In this state, the rotor ROTOR3 aligns itself with the applied external electric field, while the other rotors ROTOR1, ROTOR2, remain in their out-of-planar orientation with the rest of the molecular system 10. With the rotation of the rotor ROTOR3, the molecular system 10 exhibits a blue color, due, at least in part, to the red-shifted absorption induced by partial delocalization of the molecular system 10. It is to be understood that the electric field applied to rotate one of the rotors ROTOR3 is generally smaller than the electric field applied to rotate the other rotors ROTOR1, ROTOR2.
In STATE 3, the applied electric field is capable of rotating two rotors ROTOR2, ROTOR3 such that they are co-planar with stators STATOR1, STATOR2, STATOR3, STATOR4. One of the rotors ROTOR1 remains out-of-plane with respect to the stators STATOR1, STATOR2, STATOR3, STATOR4. In STATE 3, the molecular system 10 exhibits another color, for example, a green color. It is to be understood that the electric field applied to achieve the rotation of two rotors ROTOR2, ROTOR3 is generally larger than that applied to rotate one of the rotors ROTOR3.
When a higher electric field is applied, the molecular system 10 is in STATE 4 where all three rotors ROTOR1, ROTOR2, ROTOR3 rotate to be co-planar with the stators STATOR1, STATOR2, STATOR3, STATOR4. In STATE 4, the molecular system 10 is completely conjugated and has the smallest band gap of all the states. The absorption of the molecular system 10 is red-shifted and a red color is exhibited.
It is to be understood that the terms “red shifted” and “blue shifted” as referred to herein are not meant to convey any relationship to hue, but rather to the direction in the electromagnetic energy spectrum of the energy shift of the gap between the HOMO and LUMO states.
Referring now to
In this embodiment, connecting groups CG are located at the ends 12, 14 of the molecular system 10. The connecting groups CG may be configured to connect the molecular system 10 to another molecular system 10 or to a suitable substrate. It is to be understood that the connecting groups CG may be a single unit or multiple units linked together. Non-limitative examples of suitable connecting groups CG include hydrogen; hetero atoms including at least one of C, N, O, S, and P; functional groups containing at least one of the hetero atoms; saturated hydrocarbons; unsaturated hydrocarbons; substituted hydrocarbons; and combinations thereof.
The rotors ROTOR1, ROTOR2, ROTOR3 are molecules that include an electron-accepting group A1, A2, A3 and an electron-donating group D1, D2, D3. It is to be understood that the electron-accepting group A1, A2, A3 is an electron-withdrawing group. In an embodiment, the electron-accepting group A1, A2, A3 is at least one of hydrogen; hetero atoms including at least one of N, O, S, P, F, Cl, and Br; functional groups containing at least one of the hetero atoms; saturated hydrocarbons; unsaturated hydrocarbons; substituted hydrocarbons; carboxylic acids; carboxylic esters; carboxylic amides; nitro groups; nitrites; carbonyls; cyano groups; imines; azo groups; sulfuric acids; sulfuric esters; sulfuric amides; phosphoric acids; phosphoric esters; phosphoric amides; and combinations thereof.
The electron-donating group D1, D2, D3 is at least one of functional groups containing at least one hetero atom including at least one of B, Si, I, N, O, S, and P; hydrogen; amines; OH; SH; ethers; saturated hydrocarbons; unsaturated hydrocarbons; substituted hydrocarbons; and combinations thereof. It is to be understood that the electron-donating group D1, D2, D3 is less electronegative, or more electropositive, than the electron-accepting group A1, A2, A3.
Specific non-limitative examples of rotors ROTOR1, ROTOR2, ROTOR3 include aromatic hydrocarbons, poly-aromatic hydrocarbons, substituted aromatic hydrocarbons, poly-aromatic hydrocarbons, aromatic heterocycles, poly-aromatic heterocycles, substituted aromatic heterocycles, poly-aromatic heterocycles, or the like, or combinations thereof.
The stator(s) STATOR1, STATOR2, STATOR3, STATOR4 are generally geometrically fixed conjugating systems. In the embodiment as depicted in
The stator STATOR1, STATOR2, STATOR3, STATOR4 hydrocarbon units may contain conjugated rings and/or at least one hetero atom including S, N, and/or O. The conjugated rings may contribute to the extended conjugation of the molecular system 10 when it is in its ON state. The conjugated rings of the stator(s) STATOR1, STATOR2, STATOR3, STATOR4 may include spacing group(s) (not shown). In an embodiment, the spacing group may be linked to any position on the conjugated ring, such as the 2, 3, 5, and 6 positions of a substituted benzene derivative. In a non-limitative example, the spacing group is located at the ortho, para or meta position of the stator STATOR1, STATOR2, STATOR3, STATOR4 in relationship to the connection site of the rotor ROTOR1, ROTOR2, ROTOR3.
Non-limitative examples of spacing group(s) include phenyls, diphenylmethyl groups, substituted diphenylmethyl groups (non-limitative examples of which include di(2-methylphenyl)methyl groups, di(2-ethylphenyl)methyl groups, di(2-propylphenyl)methyl groups, di(2-butylphenyl)methyl groups, di(2-tert-butylphenyl)methyl groups, di(3-methylphenyl)methyl groups, di(3-ethylphenyl)methyl groups, di(3-propylphenyl)methyl groups, di(3-butylphenyl )methyl groups, di(3-tert-butylphenyl )methyl groups, di(4-methylphenyl)methyl groups, di(4-ethylphenyl)methyl groups, di(4-propylphenyl)methyl groups, di(4-butylphenyl)methyl groups, di(4-tert-butylphenyl)methyl groups, di(5-methylphenyl)methyl groups, di(5-ethylphenyl)methyl groups, di(5-propylphenyl)methyl groups, di(5-butylphenyl)methyl groups, di(5-tert-butylphenyl)methyl groups, di(6-methylphenyl)methyl groups, di(6-ethylphenyl)methyl groups, di(6-propylphenyl)methyl groups, di(6-butylphenyl)methyl groups, di(6-tert-butylphenyl)methyl groups, and combinations thereof), arylalkyl groups, substituted arylalkyl groups (non-limitative examples of which include halogen substituted arylalkyl groups, and arylalkyl groups substituted with one or more of phenylmethyl groups, (2-methyl)phenylmethyl groups, (2-ethyl)phenylmethyl groups, (2-propyl)phenylmethyl groups, (2-butyl)phenylmethyl groups, (2-tert-butyl)phenylmethyl groups, (3-methyl)phenylmethyl groups, (3-ethyl )phenylmethyl groups, (3-propyl)phenylmethyl groups, (3-butyl)phenylmethyl groups, (3-tert-butyl)phenylmethyl groups, (4-methyl)phenylmethyl groups, (4-ethyl)phenylmethyl groups, (4-propyl)phenylmethyl groups, (4-buthyl)phenylmethyl groups, (4-tert-butyl)phenylmethyl groups, (5-methyl)phenylmethyl groups, (5-ethyl)phenylmethyl groups, (5-propyl)phenylmethyl groups, (5-buthyl)phenylmethyl groups, (5-tert-butyl)phenylmethyl groups, (6-methyl)phenylmethyl groups, (6-ethyl)phenylmethyl groups, (6-propyl)phenylmethyl groups, (6-buthyl)phenylmethyl groups, (6-tert-butyl)phenylmethyl groups, and combinations thereof), diaryl alkyl groups, substituted diaryl alkyl groups (non-limitative examples of which include halogen substituted diaryl alkyl groups, and diaryl alkyl groups substituted with diphenylmethyl groups, such as those previously described), alkyl groups, substituted alkyl groups (non-limitative examples of which include halogen substituted alkyl groups, and alkyl groups substituted with diphenylmethyl groups, such as those previously described), isopropyl groups, tert-butyl groups, tri-alkyl groups, and/or combinations thereof.
The spacing groups may generally be used to provide a desired three-dimensional scaffolding which advantageously allows the molecules to consolidate together while providing space for each rotor(s) ROTOR1, ROTOR2, ROTOR3 to rotate over a desired range of motion.
The molecular system 10 may further include conjugated connecting units (i.e. bridging group(s)) Gn (where “n” is an integer) that connect the stators STATOR1, STATOR2, STATOR3, STATOR4 to the rotors ROTOR1, ROTOR2, ROTOR3, the stators STATOR1, STATOR2, STATOR3, STATOR4 and/or rotors ROTOR1, ROTOR2, ROTOR3 to the connecting groups CG, and/or two or more conjugated rings connected to each other or to the connecting groups CG to achieve desired optical and/or electrical properties.
Non-limitative examples of suitable conjugated connecting units Gn include hydrogen, hetero atoms including one or more of C, N, O, S, and P, acetylenes, substituted acetylenes, ethylenes, substituted ethylenes, amides, imides, imines, azo groups, and combinations thereof. The conjugated connecting units Gn may alternately include a single atom bridge, such as an ether bridge with an oxygen atom, or a direct sigma bond between the rotors ROTOR1, ROTOR2, ROTOR3 and the stators STATOR1, STATOR2, STATOR3, STATOR4.
Generally, in embodiments of the molecular system 10 disclosed herein, each of the rotors ROTOR1, ROTOR2, ROTOR3 may have angularly offset sides to which the conjugated connecting unit(s) Gn may be attached, and the stators STATOR1, STATOR2, STATOR3, STATOR4 may have angularly offset positions to which the conjugated connecting unit(s) Gn may be attached. The angularly offset sides or positions may be at any suitable angle relative to each other, including, but not limited to 90° apart and/or 180° apart. In an embodiment, such as those depicted in
Referring now to
The stators STATOR1, STATOR2, STATOR3, STATOR4 in the molecular system 10 are substituted naphthalene rings. The substitution groups are depicted as Rn (where “n” is a number, e.g., R1, R2, R3, R4, R5 ,R6 ,R7 and R8). It is to be understood that the substitution groups Rn may be alkyl groups, substituted alkyl groups, aryl groups, substituted aryl groups, or the like, or combinations thereof.
The rotors ROTOR1, ROTOR2, ROTOR3 in the molecular system 10 are nitro-substituted benzene rings. The nitro group (N2O) functions as the electron-accepting group A1, A2, A3. One of the hydrogen groups (H) functions as the electron-donating group D2, D2, D3.
In this non-limitative example, one rotor ROTOR1 is bonded to two stators STATOR1, STATOR2 with acetylene conjugated connecting units G1, G2. The acetylene conjugated connecting units G1, G2 have a free rotational nature, which allows the rotor ROTOR1 to feel less steric and electronic repulsion from the stators STATOR1, STATOR2. The energy barrier for the rotor ROTOR1 to switch in-plane or out-of-plane with the stators STATOR1, STATOR2 is minimal (about 0.1-0.2 kcal in a vacuum). As such, in this example molecular system 10, ROTOR1 is the rotor that switches the easiest, or with the weakest applied electric field.
The second rotor ROTOR2 is bonded to two stators STATOR2, STATOR3 via an ethene conjugated connecting unit G3 and an acetylene conjugated connecting unit G4. The steric and electronic repulsion between the rotor ROTOR2 and the stator STATOR2 is greater than that between the rotor ROTOR1 and the stators STATOR1, STATOR2 due to the nature of the ethene conjugated connecting unit G3. The energy barrier for the rotor ROTOR2 to switch in-plane or out-of-plane with stator STATOR2 is higher (at least about 0.5 kcal or more in a vacuum) than the energy barrier for rotor ROTOR1. Generally, the rotor ROTOR2 prefers to be in an out-of-plane orientation with respect to the stators STATOR1, STATOR2, STATOR3, STATOR4 in the absence of an external aligning force (e-field). In this example molecular system 10, ROTOR2 requires a higher external electric field than ROTOR1 to switch between states.
The third rotor ROTOR3 is bonded to two stators STATOR3, STATOR4 via an acetylene conjugated connecting unit G5 and a single carbon-carbon sigma bond conjugated connecting unit G6. The steric and electronic repulsion between the rotor ROTOR3 and the stator STATOR4 is greater than that between the rotor ROTOR2 and the stator STATOR2 due to the nature of the single carbon-carbon sigma bond conjugated connecting unit G6. The energy barrier for the rotor ROTOR3 to switch in-plane or out-of-plane with stators STATOR3, STATOR4 is the highest (at least about 0.9 kcal or more in a vacuum) among the three rotors ROTOR1, ROTOR2, ROTOR3 in the molecular system 10. Generally, this rotor ROTOR3 prefers an out-of-plane orientation with respect to the stators STATOR1, STATOR2, STATOR3, STATOR4 in the absence of a strong external aligning force (e-field). In other words, in this molecular system 10, ROTOR3 is the hardest of the three rotors ROTOR1, ROTOR2, ROTOR3 to switch between the states.
Generally, this particular molecular system 10 has all of the rotors ROTOR1, ROTOR2, ROTOR3 aligned with each other in an out-of-plane orientation with respect to the stators STATOR1, STATOR2, STATOR3, STATOR4, as shown in STATE 1. Each of the rotors ROTOR1, ROTOR2, ROTOR3 is in an OFF state. The molecular system 10 is strongly blue-shifted, is in a highly localized state, and exhibits a substantially colorless or transparent property.
Under the influence of an applied external field, the first rotor ROTOR1 rotates to be substantially co-planar with the stators STATOR1, STATOR2, STATOR3, STATOR4, as shown in STATE 2. Two of the rotors ROTOR2, ROTOR3 remain in an OFF state (out-of-plane), while ROTOR1 switches to the ON state by aligning itself with the applied external electric field. As previously described, the electric field applied to rotate ROTOR1 is smaller than that applied to rotate ROTOR2 and ROTOR3. With the rotation of the rotor ROTOR1, the molecular system 10 in STATE 2 exhibits a different color from that exhibited in STATE 1, for example, a blue color. The shift in color may be due, at least in part, to the red-shifted absorption induced by partial delocalization of the molecular system 10.
An electric field is applied to the molecular system 10 to switch from STATE 2 to STATE 3. The electric field is capable of rotating two rotors ROTOR1, ROTOR2, as such the electric field is larger than that applied to rotate one rotor ROTOR1. The rotors ROTOR1, ROTOR2 rotate so they are co-planar (ON state) with the stators STATOR1, STATOR2, STATOR3, STATOR4. One of the rotors ROTOR3 remains out-of-plane (OFF state) with respect to the stators STATOR1, STATOR2, STATOR3, STATOR4. With the rotation of the rotors ROTOR1, ROTOR2, the molecular system 10 in STATE 3 exhibits a different color from that exhibited in both STATE 1 and STATE2, for example, a green color.
When a higher electric field is applied, the molecular system 10 switches to STATE 4, where all three rotors ROTOR1, ROTOR2, ROTOR3 rotate to be co-planar with the stators STATOR1, STATOR2, STATOR3, STATOR4. In this co-planar or ON state, the molecular system 10 is completely conjugated and has the smallest band gap of all the states. The absorption of the molecular system 10 is red-shifted and a color is exhibited (e.g., red) that is different from the colors exhibited in all the other states.
While wires 112, 114 are depicted as having substantially circular cross-sections in
Further, the wires 112, 114 may be modulation-doped by coating their surfaces with appropriate molecules—either electron-withdrawing groups (Lewis acids, such as boron trifluoride (BF3)) or electron-donating groups (Lewis bases, such as alkylamines) to make them p-type or n-type conductors, respectively.
Embodiments of the molecular system 10 are advantageously switchable between four states and are capable of exhibiting different hues. The molecular system 10 is versatile in that it is capable of optical and/or electrical switching. Furthermore, the size of the molecular systems 10 may range from nanometers to micrometers, making them suitable for use in a variety of optical and/or electronic devices.
While several embodiments have been described in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting.
