Spiropyran Derivatives

The contribution of computational chemistry to the study of mechanistic problems in photochromism is increasing since information on intermediates, transition states, and conical intersections is often very difficult to obtain experimentally. As a list of all such studies is beyond the scope of the present chapter, our discussion will focus on representative molecules such as spiropyran derivatives and fulgide derivatives, but will also include examples of other recent work. 

The investigation of the colored form of spiropyrans by theoretical calculations started at the dawn of studies on photochromic compounds. The pioneering studies of a benzothiazolinic spiropyran were published by Guglielmetti and coworkers, who investigated the different planar forms of the open-form stereoisomers by calculations of the atomic interaction energies,31 the extended Hiickel method,3133 the PPP method,32 and theCNDO/2 method.34 The results of molecular mechanical (MM) calculations on spiropyrans and spirooxazines were compared with the X-ray structures and used to explain H NMR data.35 

Semiempirical MO studies were also reported by other research groups.23 36 1 Recently, a systematic comparison of the various computational techniques for predicting the geometry and electronic spectra of spiropyrans and spirooxazines has been published.42 The validity of various semiempirical methods has been checked. This may provide a useful aid for practical uses of semiempirical methods.42 Molecular dynamics (MD) has also found use for these series of derivatives.43 5 

It is relevant to cite here two more examples of the application of molecular calculations to spiropyran derivatives. First, in a study of the relationship between photochromism and second-order nonlinear optical (NLO) properties in spiropyran- and spirooxazine-doped polymer films, dipole moments, polarizabilities, and hyperpolarizabilities were estimated by the MNDO method.46 Second, the relative stabilities of the radical anions as well as their spin density distributions for a spiroindolinic series were calculated by an ab initio method in a combined electron paramagnetic resonance (EPR)/electrochemistry study.47 

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In the following, a number of examples are presented with emphasis on how such amplified imaging device can be built in self-supporting polymer materials. The present photochromic compounds (azobenzene and spiropyran derivatives) are rather common and have been used many times in molecular assemblies without touching upon the concept of image amplification. The most recent references are given(4. - 6). 

The spiropyran derivative incorporated RMs showed good photo-controUed extraction of zwitter-ionic amino acid under UV irradiation and release under visible irradiation Unlike native enzyme, the modified counterpart tended to form reversible oligomeric structures in RMs, which allowed in realizing the role of carbohydrate moieties in the functioning of glycoproteins... 

We have also demonstrated self-held ultrafast parallel optical switching based on the same geometry and using photochromic compounds instead of phthalocyanines [81-84], Absorption spectra of spiropyran derivative (SP) dispersed in polystyrene with a weight ratio of 1 10 are shown in Fig. 28 before and after UV irradiation for 5 sec. Strong absorption in the visible region due to photomerocyanine (PM) can be held for a long time and be reverted to that of... 

Fig. 5 Smart UV-responsive coating on silica nanoparticles with PNIPAM brushes functionalized with FRET donors, 4-(2-acryloyloxyethylamino)-7-nitro-2,l,3-benzoxadiazole (NBDAE), and photoswitchable acceptors, l -(2-methacryloxyethyl)-3, 3 -dimethyl-6-nitro-spiro(2//-l-benzo-pyran-2,2 -indoline) (SPMA). The UV radiation induces the change from colorless spiropyran derivatives in the outer part of the coating (7) to the fluorescent merocyanine form (2). Thus, FRET with the benzoxadiazole moieties in the inner part of the coating is enabled and the fluorescence color changes from green to red. By variation of the temperature and induction of a collapse of the PNIPAM chains (3), the FRET efficiency can be tuned (4). Reprinted, with permission, from [70], Copyright (2009) American Chemical Society...

Spiropyran Derivatives Possessing a Molecular Recognition Site. 402... 

N. Kubo, N. Kobayashi, K. Ikeda, and R. Hirohashi, Control of ion conductivity in solid polymer electrolyte containing spiropyran derivative by photoirradiation, Nippon Kagakuu Kaishi 1992, 1148-1153. 

For any application of photochromic molecules, a discussion of the thermal stability of the colored form is in order. We will discuss two types of photochromic molecules (1) those that operate by a photon-heat mode (photochemical forward reaction and a thermal reverse reaction), such as spiropyran derivatives, and (2) those that exhibit a photon-photon mode, such as diarylethene derivatives. 

SPIROPYRAN DERIVATIVES POSSESSING A MOLECULAR RECOGNITION SITE... 

In section 9.3.1, various spiropyran derivatives possessing a molecular recognition site were described. The coloration results from the structural change in the spiropyrans. Hence these artificial receptors have two conjugated functions, structural change and signaling based on molecular recognition. This is the reason why the spiropyrans are called multifunctional artificial receptors.58... 

Kato and coworkers combined a very peculiar mesogen, fan-shaped spiropyran derivatives, 43, to a poly(styrenesulfonate) main chain, 44 [100,101]. 

Spiropyrans are an important class of materials that show interesting properties such as photochromism and acidichromism. Similar to azo compounds, photoirradiation or the addition of acidic molecules to spiropyrans lead to drastic changes in physical and chemical properties due to spiro-merocyanine isomerization. Hexagonal columnar LC complexes of a spiropyran derivative with 4-methylbenzenesulfonic acid were formed due to the acid-induced spiro-merocyanine isomerization [100], The columnar LC mixture aligned uniaxially on a substrate can serve as one-dimensional ion conductors. When poly(styrenesulfonate) was employed as a complexing agent for spiropyran, no mesophase was observed. 

Tan B, Yoshio M, Watanabe K et al (2008) Columnar liquid-crystalline assemblies composed of spiropyran derivatives and sulfonic acids. Polym Adv Technol 19 1362-1368... 

Secondly, a stabilization of the color has been observed when the polymer film is rapidly cooled below the glass-transition temperature Immediately after irradiation with UV light. A quantitative study of the thermoreversion of the co-polyester film at 293°K is shown in Figure 18, where the process can be compared with the thermoreversion of the photochromic spiropyran derivative III in poljmiethylmethacrylate matrix. 

Spiropyran derivatives are very well known for their photochromlc properties. The lifetime of the colored form is not long enough for adequate use in data-storage systems. On the other hand, it is well known that a stable coloration of the spiropyrans can be obtained if halogen acid is added to the systems. 

A spiropyran derivative with an amine linker was synthesized and coupled to grafted brushes of PGMA and of PMAA activated with perfluorophenyl trifluoroacetate. Exposure of the modified brushes to UV light, which converts the attached moieties from the uncharged transparent spiropyran to the zwitterionic merocyanine form, rendered the brushes deep purple in color, fluorescent, and hydrophilic. The properties switched back by thermal or visible light-induced relaxation. The kinetics of the switching was found to be dependent on the chemical environment provided by the polymer brushes as well as on the polarity of added solvent. 

In another example, a different chromophore, a spiropyrane derivative, is attached at the free y-carboxyl group of an E-containing ELP either chemically synthesized or genetically engineered. Figure 14 represents the photochromic... 

Another application of a photochromic reaction involves the reversibile size control of gold aggregates in nanoparticles by using 5-functionalized spiropyran derivatives. In the dark, the merocyanine form associates with each other, which suppresses the thermal rearrangement. Irradiation, on the contraiy, accurately tunes the dimension of the aggregates due to the different electrostatic properties of spiropyran and merocyanine (Fig. 3). In photocatalysis the effect of changing parameters is often limited, because the process of photon absorption photoexcitation of adsorbate -metal bond occur at some distance. It has recently been shown that when sub 5 nm metal particles are used, the hybridized absorbate-metal ions is excited preferentially. This results is an increased proportion of CO oxidation in H2 rich streams (Fig. 4). ... 

In addition, a versatile route to benzodiazocine and spiropyran derivatives via chalcones was reported (13JCS517). The synthesis of spiro[o-thiophene-5, 6 -diphenyl-2H-pyran-4, 3 ] -5-methylbenzo [b] thio-phene-2-one from thioisatins is shown below. The broad scope of usable substrates of industrial relevance is discussed. 

Photocontrol of affinity chromatography provides a novel means of regulating binding and release of the desired molecule from an affinant, as has been demonstrated for L-asparaginase using an L-aspartic acid-spiropyran derivative of agarose (36). The enzyme is bound in visible light and released in the dark. 

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