Chromic effect

A study of the effect of substitution patterns in oxadiazoles and isoxazoles and their effect on the UV spectra in the lO -lO M concentration range was performed. Hypso-chromic effects and deviations from Beer s law were observed and were believed to be associated with antiparallel, sandwich-type self-association via dipole-dipole interactions. Beer s law is followed when the molecular dipole moments are small or when self-association is sterically hindered. 

Applications of titania nanotube arrays have been focused up to now on (i) photoelectrochemical and water photolysis properties, (ii) dye-sensitized solar cells, (iii) photocatalysis, (iv) hydrogen sensing, self-cleaning sensors, and biosensors, (v) materials for photo- and/or electro-chromic effects, and (vi) materials for fabrication of Li-batteries and advanced membranes and/or electrodes for fuel cells. A large part of recent developments in these areas have been discussed in recent reviews.We focus here on the use of these materials as catalysts, even though results are still limited, apart from the use as photocatalysts for which more results are available. 

These compounds (297) have interesting thermochromic and solvato-chromic effects. Ethanolic solutions of 4-(2, 4, 6 -triphenylpyridinium)-... 

Which structural features may produce a bathochromic or a hypso-chromic effect in an organic compound. 

The peak shift due to aggregation is observed not only in LBK films containing azobenzene chromophores, but also for other chromophores with extended Ji-systems, such as viologen polymers. For monolayers of the poly(p-phenylene sulfonate) 9/ dioctadecyldimethylammonium bromide (DODA) complex, the peak shift due to aggregation results in a piezo-chromic effect—that is, upon compression of the monolayer, a significant shift of the poly(p-phenylene sulfate) A band is observed (see Figure 6.9). This photochromic effect has been shown to be based on the improved 7t-Jt interaction upon compression of the monolayer. ... 

Here the introduction of polar substituents disrupts the chromic effects due to strong association of these groups with chromic units. 

On the other hand, when the formation of the triplet signal of the radical pair and the growth of the absorption of the colored species were simultaneously monitored, they were found to occur at different rates, as did their decay, thus providing an indication that the radical pair was not responsible for the photo-chromic effect.43... 

It is also possible to choose substituents that reduce the sterical hindrance. This approach has been used by Leclercs group in studies of polymers of 3-alkoxy-thiophenes [41]. The oxygen of the alkoxy group offers less steric hindrance than the methyl or methylene of the alkyl group therefore there is smaller steric hindrance in the poly(3-octyloxythiophenes), and much less thermochromism. Therefore, the chemical structure and size of the substituent side chain is of major importance in determining the character of the thermo-chromic effect. 

The shapes of the absorption, fluorescence and phosphorescence spectra of the homopolymers are basically unchanged from those of the monomers and for the most part only minor shifts are noted in the wavelengths. The molar extinction coefficients of the polymers indicate a ochromic effect in poly-L-tr3q)tophan and poly-L-tyrosine 120) but a Ay e chromic effect in poly-L-phenylalanine 121). 

The causes of these chromic effects are listed in Table 2.2. 

Hotta, S., S.D.D.V. Rughooputh, A.J. Heeger, and F. Wudl. 1987. Thermochromic and solvato-chromic effects in poly(3-hexylthiophene). Macromolecules 20 212. 

Although the process is readily reversible and can be repeated a large number of times by applying anodic and cathodic pulses in alternate sequence, a careful inspection of the voltammetric response reveals some slight differences between the first initial cycle and the following subsequent cycles (Figure 8.2), this suggesting that the development of the electro-chromic effect requires a sort of preliminary activation process. Such a process, which is commonly encountered in insertion compounds [13], may be described as an initial and permanent uptake of ions which some-... 

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