Photochromism in polymer matrices

Ct break point at 54°C. This temperature may correspond to the transition temperature (Tg) attributable to the local mode relaxation of polymer main chains. A long alkyl substituent at the nitrogen atom of the indoline moiety enhances the effect of local mobility of polymer chains on the thermal reversion. 

Negative photochromic polymers were obtained by introducing a spiroben-zoselenazolinobenzopyran (SSeP) moiety onto PMMA backbones. Monomers (7) 

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This paper reviews experimental work done on the NLO properties of photochromes other than azo derivatives, which have been described in the preceding chapters of this book. In the first part, the molecular second-order NLO polarizabilities will be given the NLO properties of the materials will indeed depend on these values. In the second part, photoassisted poling of different photochromes in polymer matrices will be described. The photo-switching of second-order NLO properties of poled polymers or crystals will then be described in the third section. Both second and third parts will end with some applications of these optical phenomena. We will conclude with the prospectives of these materials in NLO. 

In a polar polymer, i.e., cellulose acetate (CA) or nitrocellulose (NC) 35E, 35Z, and 36 had a relatively longer absorption maximum wavelength than in less polar matrices. In NC the of 36 shifts to 528 nm, which is also longer than in organic solvents. The role of polymer films in the quantum yields of photoreactions is not clear. In a comparison of the photochemical properties of 35 in polymer films and in solvents, it was found that the E c in polymer matrices was substantially smaller than that in the corresponding solvent with similar polarity. However, the decoloration quantum yield Oc e in a polymer film was larger than that in solvents. In conclusion, the polymer matrix properties, such as polarity, viscosity, and glass transition temperature (Tg) are quite important for photochromic reactions and applications. The coloration, E — Z and Z —> E isomerizations were suppressed in polymer matrices. 

The study of the efficiency of photochromic transformations for a series of aryloxy-substituted anthraquinones in polymer matrices showed that the quantum yields of phototransformations in a polymer were large and somewhat dependent on the compound s structure (Table 7.15).29... 

Photochromic Organic Compounds in Polymer Matrices, J. C. Crano, C. N. Welch,... 

A third book, edited by C. B. McArdle3, should be added to the list, which focuses on the very important topic of the behavior of photochromic systems in polymer matrices. 

Where possible, photochromic behavior (spectrokinetic parameters, photostability) in solution or in polymer matrices, and potential applications are described. 

As concerns photochromes in a solid matrix, a question that immediately arises is to what extent the nature of the matrix impedes the photochromic reaction. This problem has been studied in detaih but it is beyond the scope of this review. There is a general rule that states photochromic reactions are sluggish in polymer matrices compared to fluid solutions. This statement is true for some stilbene derivatives, but it is not true for azo derivatives, especially for push-pull azobenzene derivatives like DRl, for which the trans->cis quantum yield equals 0.11 in PMMA at 20°C compared to 0.24 in a liquid hydrocarbon mixture at -110°C. Photochromism of spiropyrans shows an important matrix effect as the quantum yield for the conversion between the spiropyran and the photomerocyanin is equal to 0.8 in ethyl acetate and decreases to 0.102 in PMMA at room temperature. The same decrease is observed for the back photochemical reaction efficiency 0.6 in ethyl acetate, compared with 0.02 in PMMA at room temperature. Conversely, the matrix effect is much less for furylfulgides the quantum yields are almost the same in solutions as in polymer matrices. Although most of photochromic molecules exhibit photochromism in polymers and sol-gels, few of them exhibit this property in the crystalline state, due to topochemical reasons. However, some anils and dithienylethenes are known to be photochromic in the crystalline state. 

Because photochromic reactions in polymer matrices deviate in general from first-order kinetics of both photochemical and thermal isomerization below the Tg (vide infra), polymers with Tgs lower than room temperature are of interest in order to perform photochromic reactions smoothly even in the solid state. In this respect, polysiloxanes17 and polyphosphazenes18 with flexible main chains are attractive. 

Organic Photochromic and Thermochromic Compounds, of which this book is the second volume, is the fourth major treatise on photochromism involving organic molecules and derived systems. The first such book, edited by G. H. Brown, was published in 1971 as a volume in the Weissberger series, and the second, edited by H. Durr and H. Bouas-Laurent, was published in 1990 in the Elsevier series.2 To this list should be added a third book, edited by C. B. McArdle,3 which focuses on the very important topic of the behavior of photochromic systems in polymer matrices. 

In conclusion it can be stated from these general studies that photochromic processes in polymer matrices can be described by the free volume theory moreover, these processes are controlled by the kind of local environment around the photochromes,... 

Yang, X., Yang, B., Liu, Y., Zhu, H., 2012. Microwave-assisted synthesis of novel spiroox-azines and their photochromic behaviors in polymer matrices. Optoelectronics and Advanced Materials-Rapid Communications 6 (11—12), 1146—1152. 

S. Irie, M. Irie, Radiation-induced coloration of photochromic dithienylethene derivatives in polymer matrices. 

Thermal backward reactions of photochromic spiroindolinon hthoxazine (SN05Q and salicylidenaniline in polymer matrices were found to be dispersive processes with an exp (—1 ) dependence. The dispersion parameter a is plotted against T/T in... 

Fig. 10.5. Photochromic fatigue in polymer matrices with differing oxygen permeabilities. Relative oxygen permeability A, 1-0 B, 6 7 C, 33 3 D,...

The incorporated SP exhibited photochromism in both of the immobilized bilayer complexes with montmorillonite and PSS. Kinetic measurements of the thermal isomerization (decoloration) were carried out for the annealed film. The decoloration reaction rate is dependent on the mobility of the surroundings and, in polymer matrices, is influenced by the glass transition. It was found that the reaction rates abruptly increased near the gel-to-liquid-crystal phase-transition temperature (54°C) of the immobilized bilayer due to increased matrix mobility in this system. The film prepared with montmorillonite gives more homogeneous reaction environments for the chromophore than those with the linear polymer (PSS). This leads to drastic changes in the reaction rate at the crystal-to-liquid-crystal phase transition of the bilayer, showing the effect of the phase transition of immobilized bilayers to be more pronounced than that of the glass transition of amorphous polymer matrices. 

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