Hosted dyes

Zeolite-hosted dyes can be prepared by ion-exchange of cationic dye molecules or by incorporation during hydrothermal crystallization [100]. Optical absorption bands of molecular sieve-accomodated dyes can be... 

Phthalocyanine and naphthalocyanine are guest dye dopants suitable for the near infrared (IR) region. PVK is used as usual, as the hole transport polymer, Alqs, or a sulforamide derivative (Al(qs)3) is used as the host dye. The absorbance spectra of the guest dyes are significantly different from the emission spectra of the host dyes. However, the high molar absorption of the host dye dopants result in such efficiencies of energy transfer that are comparable to quinacridone or rubrene dopants. 

Fig. 6. Computed dependence of perceived contrast ratio on cell thickness for a reflective display with three different guest-host dyes having the indicated dichroic ratios R. Dye concentration adjusted to maintain an on-state brightness of 50%. Concentration of chiral dopant adjusted to maintain 3 turns of the cholesteric helix in the cell.

Fig. 7. Reflected display brightness versus perceived contrast ratio for three guest-host dyes having the indicated dichroic ratios. Increasing the concentration of the dye generally decreases the display brightness and increases the contrast ratio. Values used for this computation ng=1.76, nQ=1.50, d/p 3.0 and d=10.0 ym.

A completely new class of guest-host dyes based on the anthraquinone structures has recently been reported.The chemical structures of these dyes are of the two types illustrated in Fig. 13 where R denotes a general substituent R -OCqHiqCl) for the dye D16 (blue) and -C2H5(II) for the dye D35 (rose). 

Fig 13. Two classes of guest-host dyes that are based on the... 

Furthermore, upon encapsulation and formation of dendrimer-encapsulated dyes, new fluorescence properties which were different from each constituent were observed and assigned to quenching/sensitization processes. The fluorescence of peripheral dansyl groups of the dendrimer was totally quenched through energy transfer by the encapsulated dyes while hosted dyes experienced partial quenching. 

Friedel G (1922) The mesomorphic states of matter. Ann Phys 18 273 74 Fuh AYG, Tsai MS, Huang LJ, Liu TC (1999) Optically switchable gratings based on polymer-dispersed liquid crystal films doped with a guest-host dye. Appl Phys Lett 74 2572-2574 Han JW (2000) Effects of composition, curing-time, and temperature on the electro-optical characteristics of polymer-dispersed liquid crystal films. J Korean Phys Soc 36 156-163 Han JW (2002) Effect of the nematic-isotropic phase transition on the electro-optical characteristics of polymer-dispersed liquid crystal films. J Korean Phys Soc 40 849-855 Im SJ, Jin YW, Sung JH, Park WY, Sakong DS (1995) A study of electro-optical property and VHR of PDLC depending on the molecular structure of monomer and preparation process. Synth Met 71 2203-2204... 

For two-photon memories, a number of media types and reading mechanisms have been used (165). Generally, media comprise two photon-absorbing chromophores dissolved within a soHd polymer matrix. Suitable reversible photochromic dyes are, for example, spiropyrans. Although photochromic materials often suffer from photobleaching, as well as from instability leading to self-erasure, new materials and host environments are under development (172). Bacteriorhodopsin (BR) also has been proposed as a two-photon memory material. 

In order to develop the dyes for these fields, characteristics of known dyes have been re-examined, and some anthraquinone dyes have been found usable. One example of use is in thermal-transfer recording where the sublimation properties of disperse dyes are appHed. Anthraquinone compounds have also been found to be usehil dichroic dyes for guest-host Hquid crystal displays when the substituents are properly selected to have high order parameters. These dichroic dyes can be used for polarizer films of LCD systems as well. Anthraquinone derivatives that absorb in the near-infrared region have also been discovered, which may be appHcable in semiconductor laser recording. 

Guest-Host Mode LCD Systems. Guest-host hquid crystal display systems consisting of dichioic dyes (guest) and hquid crystal media... 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

Heterocyclic chemistry is of the utmost practical and theoretical importance. Heterocyclic compounds are in use as pharmaceuticals, dyes, pesticides, herbicides, plastics, and for many other purposes the industries producing and researching into these products provide employment for a large fraction of all chemists. On the theoretical side, heterocyclic chemistry has provided a host of interesting concepts and structures. Yet, the subject is often deprived of the importance it deserves it is said that it is possible to complete work at graduate schools of some universities without having attended a lecture course dealing specifically with heterocyclic chemistry. 

Not all carbon compounds are derived from living organisms, of course, and chemists over the years have developed a remarkably sophisticated ability to design and synthesize new organic compounds. Medicines, dyes, polymers, food additives, pesticides, and a host of other substances are now prepared in the laboratory. Organic chemistry touches the lives of everyone. Its study is a fascinating undertaking. 

Using a stable dopant as the emissive dye has been shown to greatly enhance the lifetime of small molecule LEDs. Rubrene doped into the Alq, electron transport layer ] 184] or into the TPD hole transport layer 1185] can extend the lifetime by an order of magnitude. Similarly, dimclhylquinacridone in Alq has a beneficial effect ]45 ]. The likely mechanism responsible for this phenomenon is that the dopant acts as a trap for the excilon and/or the charge. Thus, molecules of the host maLrix are in their excited (cationic, anionic or cxcitonic) states for a smaller fraction of the time, and therefore have lower probability to undergo chemistry. 

PMMA finds ordn usage in several areas in ballistic or impact shields for missiles or airplanes also as windows, windshields or canopies in aircraft (Refs 7 and 22) as a Laser Q switch host using an organic Ni complex dye (Ref 22) and in proplnts as fuel (with A1 and NG as cofuels — Ref 20) and Amm perchlorate or K perchlorate as oxidizers (Refs 2, 4, 8—11, 13,14 16—20). Also see under Aeroplex Propellants in Vol 1, A108-R and under Composite Propellants in Vol 3, C464-L to C474-L Refs 1) Beil 2, [398] and (1279 1283 ... 

Quantitative analysis of the results obtained has shown that a single eosin guest is sufficient to completely quench the fluorescence of any excited dansyl unit of the hosting dendrimer. Fluorescence lifetime measurements indicated that the dye molecules can occupy two different sites (or two families of substantially different sites) in the interior of the dendritic structure. 

Dye molecules can also be hosted into poly(propylene amine) dendrimers peripherally modified with OPV units [71]. In these systems, energy transfer from the OPV fluorescent units nm) to the enclosed dye molecules is... 

Oaks and especially Quercus coccifera are host plants for Kermes ilicis, producing the red kermes pigment. In Asia, the Laccifer lacca insects that grow on trees like Schleichera oleosa, Ziziphus mauritiana, and Butea monsperma are the sources of the red lac dye. - ... 

Unfortunately these and other existing quality control procedures do not answer aU problems. There remains a clear need for development of PCR reference materials that win provide information both on quality and quantity levels. For quality the reference materials should be host-specific and PCR primers, for positive control, may correspond to host specific house keeping genes e.g. b-actin. For quantitative analysis, fluorescence dyes in specific primers might be used in order to measure accurately the amount of DNA present. Such practices, and other as yet un-realized procedures, will be needed to achieve reliable results in the quantification of DNA analysis. 

Lasers produce spatially narrow and very intense beams of radiation, and lately have become very important sources for use in the UV/VIS and IR regions of the spectrum. Dye lasers (with a fluorescent organic dye as the active substance) can be tuned over a wavelength range of, for instance, 20-50 nm. Typical solid-state lasers are the ruby laser (0.05% Cr/Al203 694.3 nm) and the Nd YAG laser (Nd3+ in an yttrium aluminium garnet host 1.06 pm). 

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