Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-07-26
2003-04-01
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S010000, C556S115000, C556S116000
Reexamination Certificate
active
06541645
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to three dimensional metal ion complexes containing chromophores that can be manipulated by valence changes to result in a change in differential absorption of light.
BACKGROUND OF THE INVENTION
Chiral coordination complexes are frequently used in asymmetric synthesis and chiral discrimination technologies (Eliel et al., 1994). Recently, C
3
-symmetric chiral ligands have shown great potential for enantioselective reactions, yet few such compounds are available (Burk et al., 1990).
A recent and exciting prospect in the area of information technology lies in the development of molecular switches that operate with efficiency, reversibility, and resistance to fatigue (Lehn, 1995). The development of electrochemical switches has recently attached much attention due to applications such as data storage (Huck et al., 1996).
Redox switches require:
(A) components whose structures and physical properties can be turned on or off electrochemically (Fabbrizzi et al., 1995); and
(b) sufficiently different optical spectra that allow the individual states to be addressed (Huck et al.).
(Feringa et al., 1991) have used isomerism in thioxanthenes to obtain chiroptical switches. Lights of different wavelengths was used to switch between M and P isomers. The difference in chirality/helicity leads to a different response in the circular dichroism (CD), where &Dgr;&egr;&Dgr;=45(M)vs &Dgr;&egr;=49(P)). The enantiomers 1 and 2 in
FIG. 1
were found to be stable at room temperature. Thermal racemization of isomer
1
a
showed first-order reaction kinetics with a barrier to racemization of 26.4 kcal/mol. Cis-trans isomerization was not observed under ambient conditions. On the other hand, irradiation of pure
1
a,
presumably at ambient temperature, yielded 64%
1
a
and 36%
2
a,
with no observable racemization, while irradiation at 250 nm gave 68%
1
a
and 32%
2
a.
Furthermore, alternate irradiation of 1a at 250 and 300 nm caused a modulation of the circular dichroism (CD) signal for 1a at 232 and 262 nm for a switching time of three seconds. Similar behavior was observed for switching times of 0.5 to 60 seconds. Compound 1 could be cycled between cis and trans forms a minimum of 10 times without racemization of changes in the UV and CD spectra. Feringa added his racemate mix to a nematic liquid crystal and then irradiated them with circularly polarized light. The resulting excess of one enantiomer was enough to switch the liquid crystal into its chiral cholesteric phase.
Shining ordinary light on the mix will convert the liquid crystal and the racemate back again (Feringa et al., op. cit.). Important problems that remain to be solved are improved thermal stability, increased fatigue resistance, and structural modification to achieve switching with visible light.
A different approach towards an optical switch was published by Schuster et al. Schuster recognized that in an opto-optical switch, where the position of the switch is transposed with light and sensed with light by change in its absorption spectrum, a fundamental problem is the destructive readout. That is, reading the position of the switch ultimately erases it. To overcome this potential problem, Schuster developed a system consisting of a photochromic fulgide dissolved in a photochemically inert cholesteric liquid crystal that is bistable and switchable by repetitive application of ultraviolet and visible light. In the course of the experiment, he showed that the pitch of a cholesteric liquid crystal can be controlled photochemically by the photochromic fulgide dopant. The pitch changes were measurable at reasonable fulgide concentrations, and both states of the liquid crystal/fulgide mixture are thermally stable under the conditions tested. The change of the pitch was bi-directional and reversible, and is controlled with light of suitable wavelength. According to Schuster, the pitch of the liquid crystal can be read optically without affecting the record information (Janicki et al., 1995). This is shown in FIG.
2
. Daub et al. reported a dihydroazulene/vinylheptafulvene photochroism system in which the information is stored and read with light. Besides the disadvantage of both storing and reading with light, the system possesses several chemical modification sites that might permit the tuning and optimization of the switching behavior (Spreitzer et al., 1996). This system is shown in FIG.
3
.
Coordination complexes featuring iron in its two distinct oxidation states embedded in a triple stranded ligand were inter-converted by chemical means. This system took advantage of a “hard” binding cavity and a “soft” binding cavity present within the system. The iron literally translocated within the strand depending upon its oxidation state. The process was monitored by the UV (d-d transitions of the Fe(II) as well as the Fe(III) species). The system did not display reversible behavior. In fact, oxidation of the Fe(II) species had to be facilitated at 50° C. in order to obtain the Fe(III) complex (Zelikovich et al., 1995).
Another version of this redox switch inter-converts between two distinct states by ligand exchange. At the heart of this switch is a molecule that possesses two sets of binding groups: one set of hard and one set of soft ligating groups. The two sets are anchored on a calix[4]arene ring in an alternating fashion, such that they can form either a hard or a soft ion biding cavity. One cavity is formed at the exclusion of the other, according to the authors. When loaded with Fe(III), the hard binding groups, hydroxamates, converge to embrace the hard metal ion, while soft groups diverge. Upon reduction, the ligand rearranges to engulf Fe(II) with its soft bipyridyl groups, while the hard groups diverge. Subsequent oxidation reversed the process. This switch action was again followed by UV (Canavet et al., 1996). Stoddart et al. developed a synthetic methodology based on the idea of assembling carefully designed small molecular components in a template-directed manner. The molecular subunits are not held together by classical covalent bonds, but rather by twinning and interlocking, the mechanical interactions responsible for the presence of catenanes, rotaxanes, and knots. They described a synthesis of catenanes and a rotaxane which were able to function as “molecular trains” and a “molecular shuttle.” As seen in
FIG. 6
, the [2]-rotaxane 1, which can operate as a molecular shuttle, consists of a molecular assembly in which a tetracationic bis-pyridinium cyclophane moves back and forth like a shuttle (1<-->2) between two “stations” which are situated symmetrically in a polyether terminated at the ends by large groups that acct as “stoppers.” The positively charged cyclophane ring will be attracted equally by the two identical electron-rich hydroquinol groups and therefore jump back and forth between the two stations. Temperature dependent H-NMR spectra indicated that this process occurred 500 times a second (Stoddart et al., 1992).
Lehn et al. reported a molecular switching device 1→2 shown in
FIG. 7
that effects the redox on/off switching of luminescence and combines an electroactive component with a light-emitting center. Both the oxidized and reduced forms are isolatable and stable. The reduced form 2 is luminescent, whereas the oxidized form 1 is quenched. The electrochemical interconversion of the two species was reported to be reversible (Goulle et al., 1993).
Another approach by Lehn et al. featured 1,2-diarylethenes that can undergo reversible ring closure. The open form can be converted almost quantitatively into a closed form by UV light at 365 nm. The reverse process can be effected thermally or photochemically, at 600 nm, as shown in FIG.
8
. The process was followed by UV (Giltam et al., 1995).
Sauvage et al. reported electrochemically triggered swinging of a [2]-catenate, taking advantage of the principle of bi-stability, as many systems have before. This is shown in
FIG. 9. A
transition meta
Canary James W.
Zahn Steffen
Browdy and Neimark , P.L.L.C.
Nazario-Gonzalez Porfirio
New York University
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