is 2.558 A. Previously, tertiary or secondary amines were added as cosolvents to alkali metal enolates in order to study the interaction of the free base with the salt.[' -41 Compound 1 represents a new and important stage after full enolization has taken place: the enolate is immediately solvated by free amine. Although
Organic photochromic compounds display properties''] that make them attractive candidates for numerous applications. Their use in optical memory systems constitutes one of the main interests, since light as a trigger offers certain advantagesL2] over magnetism, which is mainly used in memory systems today. Among others, multiplexity and multifunctionality are two of the advantages of light-triggered systems. Although many new photochromic compounds with attractive properties have been synthesized, apparently only a few multicolor processes where light irradiation is the only trigger have been described (in the patent literatureP1). Such systems are of great interest since they may allow high-density storage as well as multiple addressing and readout. We report here two examples of multicolor systems based on mixtures of two dithienylethene compounds (mixtures of compounds 1 + 3 and 1 + 4). In addition, these systems show two different categories of states with respect to either fluorescence or redox properties.A number of thermally stable photochromic compounds of dithienylethene type which can be photoswitched reversibly between an open form o and a closed form c have been reported by our group in recent year^. [^-^] In order to achieve multiple-wavelength-triggered mixtures, photochromes with well separated, individually addressable absorption bands are required. The use of mixtures of compounds has certain advantages in comparison to single compounds containing several photochromic centers: a) the synthesis is much simpler, b) many combinations can be tested in a minimum of time, and c) changes in the relative intensity of the colors can easily be controlled by changing the molar ratio of the components.In the various perfluorocyclopentene dithienylethene compounds the i,,, of the absorption of the closed-ring forms varies from 425 to about 830 nm, whereas for the open forms it lies in a narrower range between 230 and -460 nm. This requires a careful choice of components so as to make selective photointerconversions possible. Also, complications arise from the fact that in the UV-visible ab- Table 1; the extension of the trailing edges of the absorption bands is also an important factor.
We have developed new transparent photochromic hybrid organic-inorganic materials in which the photochromic group belongs to the polymer network. These materials involving chemically bonded dithienylethene derivatives were prepared by the sol-gel process in the form of thin films a few microns thick. The thickness and refractive index of the sol-gel films either at 633 or 785 nm were determined both in the colored and discolored state by using the attenuated total reflection (ATR) method. Functionalized sol-gel films showed a large refractive index change in a nonabsorbing spectral region: ∆n ≈ 4 × 10 -2 at 785 nm. This important variation due to the high photochrome content allowed us to design optical components used in the field of wave guiding.
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