The invention relates to organometallic coordination complexes that exhibit photoswitching behavior and their methods of use.
A molecule that could act as a switch would be extremely useful for a variety of applications including information storage. A photochromic molecule having two or more forms could be used in binary (e.g., 0 or 1) or higher-order applications for optically storing bits of information. Furthermore, a photochromic molecule that also exhibited changes in electrochemical characteristics could be used as an optical interconnect or as a transducer to perform electrical/optical conversions.
A photochromic molecule could be used to detect and indicate the presence or introduction of light in an area in which light leakage was undesirable. If the photochromic change in the molecule corresponded to a change in reduction potential, the change in color could be monitored electrically from a remote location. This could be useful in security applications to signal a security breach.
A molecule that did exhibit a change in reduction potential upon irradiation could also be used in the field of solar energy. Such a complex could be used in dye-sensitized solar cells to absorb light and convert it into electricity.
Another way in which molecules can act as molecular switches is by changing color upon heating, or exhibiting thermochromic behavior. Thermochromic molecules can be used in applications similar to those in which photochromic molecules are used. Thermochromic molecules can be used to visually and/or electrically indicate that a certain temperature has been reached by monitoring a change in color and/or reduction potential. This type of indicator may be used to demonstrate exposure of heat-sensitive materials such as film and medicines to elevated temperatures.
Few examples exist of metal-containing molecules that exhibit switching behavior. Where it has been observed, switching has been observed almost exclusively in solution. These reactions are generally ground-state and are too slow for most applications. One example of a compound in which a photochromic change occurs as an excited-state reaction is sodium nitroprusside (Na2[Fe(CN5)NO]; xe2x80x9cSNPxe2x80x9d). Recent work has shown that photochromic sodium nitroprusside can be used for holographic information storage.1-3 Crystallographic studies indicate that two metastable states of SNP are involved: the first (MS I) is an isonitrosyl (Oxe2x80x94 bonded NO), whereas the second (MS II) is an xcex72-NO (side-on) complex.4,5 However, the metastable states in SNP can only be observed at low temperature ( less than 100 K) and thus are of limited utility.
Although many devices such as semiconductors already exist for information storage, molecules have not previously been used for this task. The advantage of using molecules is most apparent in optical computing applications. The primary advantage of using molecules is in information density. The small size of molecules would permit more information to be stored per unit volume.
The design of molecular coordination complexes exhibiting two separate, stable forms is described. Reaction from one form to the other is intramolecular, reversible, light-activated (a molecular switch) and occurs both in the solid and in solution. The two forms differ in photochemical and electrochemical characteristics, having different colors and reduction potentials. These differences allow use of such complexes in information storage and for sensing and detecting applications.
Accordingly, it is a primary object of the invention to provide novel metastable organometallic coordination complexes comprising an imine-containing ligand and a photoisomerizable ligand, along with additional ligands to complete the complex. Upon photoexcitation, an electron is passed from the metal to the imine-containing ligand via metal to ligand charge transfer; the photoisomerizable group also photoisomerizes and changes its bonding mode to the metal in the photoexcited state. The photoexcited state then decays to a metastable state exhibiting altered electrical and optical characteristics.
It is another object of the invention to provide articles comprising such complexes. The complexes can be incorporated into a polymer, which can be a semiconducting organic polymer. This incorporation can either provide or alter light emission from the polymer upon passing electricity through the polymer. The complexes can be incorporated into light-emitting diodes, optical interconnects, in transducers, and in dye-sensitized solar cells.
It is still another object of the invention to provide methods for using such complexes or the ground state of such complexes. The complexes can be utilized in detection methods to detect the presence of light; photoisomerization of the complex can be detected either optically or electrically. The complexes can also be used in methods of data storage and retrieval. A light source can be directed to an addressed location comprising the complex to photoexcite it and thereby store a bit of information in its metastable ground state. That information can be retrieved either optically or electrically by sampling for a change in the complex resulting form photoexcitation. The complexes can also be used in thermal applications to detect changes in temperature by any increase in decay of the metastable state to the ground state, which can also be detected by changes in color or reduction potential.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.