Purely Organic Dyes

Motivated by the great potential of electrodeposition as a technology (Section 4.2) and for the preparation of active ZnO semiconductor electrodes in particular (Section 

ZnO electrodes prepared by these means from 02-saturated solutions showed photoelectrochemical sensitization characteristics towards ZnO in standard iodine-containing electrolytes of 2.3 mAcm under illumination by 200mWcm  

it was oriented with its c-axis perpendicular to it in the case of C343/ZnO. 

Porous Crystalline Networks of ZnO as Starting Material for Dye-Sensitized Solar Cells 

The good accessibility of EY incorporated in the porous ZnO crystalline network detected in the photoelectrochemical characteristics was used to desorb the dye 

---

The organometallic sensitizer can be replaced by a purely organic dye such as eosin Y that acts as a photoredox catalyst after excitation with visible light and gives rise the more stable triplet state [26]. In the presence of eosin Y and MacMillan s trons-methyl imidazolidinone catalyst 10 and substrates (aldehyde and a-bromocarbonyl compounds) the alkylation reaction performed similarly while requiring somewhat longer reaction times at the optimal -5 °C temperature. 

The terms FD C, D C, and External D C (Ext. D C), which are part of the name of colorants, reflect the FDA s colorant certification. FD C dyes may be used for foods, dmgs, and cosmetics D C dyes are allowed in dmgs and cosmetics and Ext. D C dyes are permitted only in topical products. Straight colorants include both the organic dyes and corresponding lakes, made by extending the colorant on a substrate such as aluminum hydroxide or barium sulfate. The pure dye content of these lakes varies from 2 to 80% the organic dyes contain over 80% pure dye. Colorants certified for cosmetic use may not contain more than 0.002% of lead, not more than 0.0002% of arsenic, and not more than 0.003% of heavy metals other than lead and arsenic. 

In general, coordination complexes and metallized dyes exhibit higher photochemical stability than purely organic molecules so it is clear that coordination chemistry has a major role to play in the future development of ODS media. 

The present author has developed a novel method called ion-association method. This is also a simple and versatile method for the preparation of ion-based organic dye nanoparticles in pure aqueous solution by the ion association approach [23]. It utilizes the control of hydrophilicity/hydrophobicity of the ionic material itself via ion-pair formation for example, addition of a cationic target dye solution into aqueous solution containing a certain kind of hydrophobic anions forms an electrically neutral ion-pair because of the strong electrostatic attraction, followed by aggregation of ion-pair species originated from van der Waals attractive interactions between them to produce nuclei and the subsequent nanoparticles (Fig. 3). In this case, hydrophobic but water-soluble anions, such as tetraphenyl-borate (TPB) or its derivatives (tetrakis(4-fluorophenyl)borate (TFPB), tetrakis [3,5-... 

Fig. 3 Concept of the ion-association method for fabricating ion-based organic dye nanoparticles in pure aqueous media. The approach is based on ion-pair formation between the ionic dye (for example, cationic dye) and the hydrophobic counterion that is soluble in water [for example, tetraphenylborate (TPB) or its derivative anion], which gives rise to a hydrophobic phase in water. For preparation, organic cosolvent is unnecessary. The size of the dye nanoparticles can be controlled by adjusting the interionic interaction between the dye cation and the associative hydrophobic counteranion...

In this chapter, we describe the design and important properties of supra-molecularly organized dye molecules in the channels of hexagonal nanocrystals. We focus on zeolite L as a host. The principles, however, hold for other materials as well. As an example, we mention ZSM-12 for which some preliminary results have been reported [55], We have developed different methods for preparing well-defined dye-zeolite materials, working for cationic dyes, neutral dyes, and combinations of them [3, 22, 25, 52], The formula and trivial names of some dyes that so far have been inserted in zeolite L are reported in Section II.C. The properties of natural and commercially available zeolites can be influenced dramatically by impurities formed by transition metals, chloride, aluminiumoxide, and others. This fact is not always sufficiently taken care of. In this chapter, we only report results on chemically pure zeolites, the synthesis of which is described in [53]. 

Traditionally, the sol-gel process has been used for the preparation of silica nanoparticles via the hydrolysis of alkoxides in organic solvents [52,53]. Similar hydrolysis and condensation carried out in w/o microemulsion offers robust control over the synthesis process. W/o emiflsion-mediated sol-gel synthesis is currently used for the fabrication of pure sihca, as well as inorganic and organic dye-doped silica nanoparticles. The synthesis of sihca and dye-doped nanoparticles is classified in the following sections on the basis of the classification of the head group fimctionahty of the major surfactant used. 

It is well known that the aqueous phase behavior of surfactants is influenced by, for example, the presence of short-chain alcohols [66,78]. These co-surfactants increase the effective value of the packing parameter [67,79] due to a decrease in the area per head group and therefore favor the formation of structures with a lower curvature. It was found that organic dyes such as thymol blue, dimidiiunbromide and methyl orange that are not soluble in pure supercritical CO2, could be conveniently solubihzed in AOT water-in-C02 reverse microemulsions with 2,2,3,3,4,4,5,5-octafluoro-l-pentanol as a co-surfactant [80]. In a recent report [81] the solubilization capacity of water in a Tx-lOO/cyclohexane/water system was foimd to be influenced by the compressed gases, which worked as a co-surfactant. 

Artificial Organic Dyes.—Indigo carmine may be adulterated with artificial organic dyes, especially aniline blue. If silk is dyed with an acidified solution of the carmine and then washed and boiled with water, the fibre will become colourless if the carmine is pure, but remains blue if aniline blue is present. 

Also by oxidising the carmine solution with permanganate for the determination of the mdigotin, many artificial organic dyes may be detected thus, pure indigo carmine solution remains yellow, whereas it may be bluish, violet, grey or reddish in presence of artificial organic dyes. 

Then, Dimroth and Reichardt proposed a solvent polarity parameter, Ey(30), based on transition energy for the longest-wavelength solvatochromic absorption band of the pyridynium N-phenolate betaine dye, which is dye No. 30 in a table constructed by these authors. The x(30) values have been determined for more than 360 pure organic solvents and many binary solvent mixtures. 

It was originally thought that lead azide existed in two allotropic forms a and 0 (VoL 111, p. 169). Now it is accepted that tlie substance is polymorphic and exists in four forms o, 0, y and 6. The a-orthorhombic is the only one acceptable for technical application. It is the main product of precipitation with traces of the other forms present [89]. The monoclinic jS-fomi is stable when dr>. but recrystallizes as the a-form. Tlie presence of some organic dyes (e.g. eosin) enhances the fomiation of form and hydrophile colloids inhibit its formation. Breaking a needle of Torm may produce an explosion (contrary to the views of some authors Vol. Ill, p. 173). The monoclinic y-form is less stable than a and jS [90]. It can be obtained from pure reagents at pll 3.5—7.0 or in the presence of vinyl alcohol. The triclinic 6-form precipitates from pure reagents at pH values of between 3.5 and 5.5 [90]. Both forms yand 6 are usually precipitated simultaneously and can be separated (with care ) by hand. 

---