Photoswitching photochromic molecules

The occurrence of two different structures that can be interconverted through the agency of an external light stimulus can be the basis of a molecular switch. Moreover, when photochromic molecules are incorporated into polymeric compounds, their photoisomerization can affect the structure and the physical properties of the attached macromolecules. Therefore, photochromic polymers may be highly promising materials for application in optical technologies, as well as in the design of photoswitchable devices. 

PHOTOASSISTED POLING AND PHOTOSWITCHING OF NLO PROPERTIES OF SPIROPYRANS AND OTHER PHOTOCHROMIC MOLECULES IN POLYMERS AND CRYSTALS... 

Fulgides and related diarylethenes have been investigated extensively because of the long-term thermal stability of their photocyclized colored forms, which could lead to this application in erasable optical recording materials and photoswitchable optical elements. The entrapment of these photochromic molecules in polymer films is necessary for these practical applications. Picosecond laser photolysis was employed to study the electrocyclic reaction of a furylfulgide (18, Figure 8) in polymer solids and revealed that the colored structure was formed with a time constant of ca. lOps irrespective of the nature of the polymer matrix.49... 

Interest in photochromic systems other than those based on the hexa-fluorocyclopentene moiety continues to grow. The photochemical reactivity of the two photoswitches (35) is similar, and irradiation is efficient with conversions of 85% and quantum yields of around 0.6. The novel photo-chromic systems (36) undergo reversible ring closure in a reaction analogous to that observed in the bisthienyl system. Qin et al. have studied the novel pyridyl substituted cyclopentene system (37). This undergoes photocyclization with an enhanced quantum yield when the reactions are carried out in the presence of a metal. The pyridine units are capable of co-ordinating with the metal. The photochromic dithienylethene unit tethered to 3-cyclodextrin (38) has been used as a photoswitch to control the uptake of porphyrin. A series of new photochromic molecules (39) have been synthesized and studied. These exhibit the usual cyclization on irradiation. " The terthiophene derivatives (40) exhibit reversible photochemical cyclization (at 313 nm) and reversion (at wavelengths >460 nm) reactions. The cycles can be carried out many times... 

J.A. Delaire, E. Ishoy K. Nakatani, Photoassisted Poling and Photoswitching of NLO Properties of Spiropyrans and other Photochromic Molecules in Polymers and Crystals, in Z. Sekkat, W. Knoll (eds.), Photoreactive Organic Thin Films, Academic Press, Amsterdam (2002). 

Nonadiabatic transitions definitely play crucial roles for molecules to manifest various functions. The theory of nonadiabatic transition is very helpful not only to comprehend the mechanisms, but also to design new molecular functions and enhance their efficiencies. The photochromism that is expected to be applicable to molecular switches and memories is a good example [130]. Photoisomerization of retinal is well known to be a basic mechanism of vision. In these processes, the NT type of nonadiabatic transitions play essential roles. There must be many other similar examples. Utilization of the complete reflection phenomenon can also be another candidate, as discussed in Section V.C. In this section, the following two examples are cosidered (1) photochromism due to photoisomerization between cyclohexadiene (CHD) and hexatriene (HT) as an example of photoswitching molecular functions, and (2) hydrogen transmission through a five-membered carbon ring. 

Lim S-J, An B-K, Jung S-D, Chung M-A, Park SY (2004) Photoswitchable organic nanoparticles and a polymer film employing multifunctional molecules with enhanced fluorescence emission and bistable photochromism. Angew Chem Int Ed 43 6346-6350... 

The photoreactivity of DTE derivatives in the crystalline state is of special interest because of their potential usefulness for holographic and three-dimensional memories. In crystals, molecules are regularly oriented and packed in fixed conformations. In many cases, free rotation is inhibited. Therefore, the photoreactivity in the crystalline phase is dependent on the space for free rotation of the thienyl rings and the conformation formed in the crystal lattice. Several reports on the synthesis of metal complexes of photochromic diarylethenes and their photo-reactivity in the single-crystalline phase or the photoswitching of the coordination structure have been reported. These studies demonstrate that complexation to metal ions does not prohibit the photochromic reactions of the diarylethene units in the single-crystalline phase. 

A photochromic dianthryl molecule can act as a triplet energy transfer quencher when combining with a ruthenium diimine complex [123]. UV excitation of the systems (X = CH2O, C(O)O) results in a photoinduced cycloaddition of the dianthryl unit, leading to an increase of the luminescence intensity. Near-field optical addressing of this luminescent photoswitcheable system (X = CH2O) as a dopant in PMMA films has been demonstrated [124] (Fig. 14). 

Sol 7. Photochromism is the reversible transformation of a chemical species between the two forms by the absorption of light, where the two forms have different absorption spectra. It can be described as a reversible change of color upon exposure to light. Such molecules find use as photoswitches in optoelectronic devices. For example, the given diarylethene derivative is capable of undergoing reversible chemical changes. They operate by means... 

T. Fukaminato, T. Sasaki, T. Kawai, N. Tamai, M. Me, Digital photoswitching of fluorescence based on the photochromism of diarylethene derivatives at a single-molecule level, J. Am. Chem. Soc, 126, 14843-14849... 

Some selected examples of 1,2-diarylethenes were shown in this review. Miyasaka and Irie et al. revealed the three-photon cyclization and two-photon cycloreversion of diarylethens (223) by a near-infrared femtosecond laser pulse at 1.28 pm. They also found single-molecule fluorescence photoswitching of a diarylethene-perylenebisimide dyad (225)." " Photomechanical effects of two-component cocrystal (226) composed of 1,2-diarylethene derivative and perfluoronaphthalene or hydrogen-bonded diarylethene-imidazoline crystalline (227) were examined. A variety of photochromic reactions of 1,2-diarylethenes in crystalline states were reported by Iiie et al. ... 

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