Merocyanine molecules

These primary defects would relax rapidly and be transformed into secondary defects the volume of which is related with the local volume difference between the DIPS and their open-merocyanines. Assuming a non-uniform distribution of distances between the merocyanine molecules and these secondary defects, they found indeed a time-dependent concentration of the merocyanine given by the following equation... 

On the basis of this defect model the disappearance of 60-70% of the merocyanine molecules may be accounted for. Moreover, the constant K is a sensitive indicator of the glass transition temperature, as demonstrated on the basis of the Arrhenius plots. 

Tagaya et al. [205,206] studied the photoisomerization of photochromic molecules sulfonated indolinespirobenzopyran (SP-SOs") to merocyanine (MC) in the interlayer region of an Mg/Al LDHs. They found that the photo/-... 

The desire to increase P values above those of molecules used in the earliest materials has led to the exploration of organic compounds as the active components of second order NLO devices. Considerable effort has been expended in the synthesis and analysis of candidate molecules, which are largely donor-acceptor substituted conjugated n systems. (2) Examples of compound classes whose members display large nonresonant P include azo dyes, stilbenes, polyenes, merocyanines, stilbazolium salts, and quinoid... 

Unlike the still-unknown 277-pyran which exists exclusively in the ring-opened form, 277-thiopyran is a well-characterized molecule. Nevertheless, the S-C(2) bond can be cleaved and this is the basis of the photochromic properties observed with spirobenzothiopyrans. Irradiation at 365 nm of the spiro[2/7-l-benzothiopyran-2,2 -indoline] 273 in both the solid state and in solution results in opening of the thiopyran ring and the formation of a colored metastable zwitterionic merocyanine (Equation 21). The open form exhibits solvatochromism, with Amax 588 nm in methanol and 673 nm in acetone. In solution, the thiopyran unit reforms rapidly when irradiation ceases, but continuous irradiation leads to the growth of crystals of the open form <2002JOC533>. 

Chemically modified crowned spirobenzopyran 112, containing a pyrenyl fluorophore attached at the nitrogen atom, can function as a fluorescence emission switch <2004T6029>. This sensor displayed a quenching of the PET fluorescence emission of the fluorophore in the absence of metal ions (the merocyanine form was not produced). When, however, the spiro form of 112 was converted into the merocyanine form by metal ion complexation of the crown ether portion of the molecule, a fluorescence resonance energy transfer (FRET) from the pyrene to the merocyanine moiety took place, producing fluorescence emission. 

However, it is a truism in materials science that the pathway from vision to reality or from an idea to a marketable product is hardly ever as straightforward as it may seem. The field of organic materials for non-linear optics is no exception. Many problems are encountered when it comes to the translation of a molecular property into a bulk property. It has transpired that some of these problems are not easy to solve with classical NLO-phores that mostly belong chemically to the class of merocyanine dyes. New design strategies for organic molecules and their respective bulk structures, crystals or oriented composite materials like polymers, are needed. Only a more fundamental understanding of these issues will allow rational optimization of molecular and bulk properties. 

The negative entropy changes observed in all solvents are a result of an ordering of solvent molecules in the environment of the zwitterionic form. Since polar solvents are per se more structured than apolar solvents, proportionally less negative entropy changes are obtained in more polar solvents such as ethanol. The rate of the spiropyran/ merocyanine interconversion is also solvent-dependent, as is the position of the visible absorption band of (27a), which, as is typical for a merocyanine, exhibits a pronounced negative solvatochromism (see Section 6.2) [99c, 99d]. 

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