Absorbance, near infrared

Porous silicon has been under evaluation as both a photosensitizer and a photothermal agent against eancer. Photodynamie therapy approaches exploit the ability of mesoporous silicon to generate reactive oxygen speeies under illumination photothermal therapy exploits its ability to absorb near-infrared light and the low thermal conductivity. Both the in vitro and in vivo data acquired to date are reviewed. 

Phthalocyanine compounds which absorb near-infrared radiation are available from Yamamoto Chemicals, a subsidiary of Mitsui Chemicals. Figure 17—4 shows the absorption spectra of a series of their products. Currently, they have 23 near infrared radiation-absorbing phthalocyanine compounds and eight absorbents composed of other materials. The absorption maxima of such phthalocyanine near-infra-red radiation absorbents are between 670 nm and 1000 nm. They may cost between one thousand and ten thousand dollars a kilogram Films of poly(vinyl chloride) and polyolefins containing phthalocyanine near-infrared absorbents are also commercially available. 

Phthalocyanines typically exhibit absorption in the red region of the spectrum. It is therefore relatively easy to make phthalocyanine compounds absorb near infrared radiation by molecular modification. For example, the introduction of elec-... 

Phthalocyanine compounds which absorb near infrared radiation are available from Yamamoto Chemicals, a subsidiary of Mitsui Chemicals. Figure 17.4 shows the absorption spectra of a series of their products. Currently, they have 23 near... 

As it is well known, calculations on the solar spectrum impinging on the Earth surface demonstrate that the ideal photosensitizer for a system that would absorb the maximum fraction of energy (somewhat above 1000 nm) would absorb near infrared photons, and of course, all of the photons above that limit. Thus, new sensitizers are continuously prepared with a maximum in the NIR for the use in solar cells. However, organic light absorbers have relatively narrow bandwidths separated by deep minima, which makes it difficult to obtain panchromatic absorption in a single organic semiconductor. 

Higher in energy than the mid-infrared, from 14,000 to 4000 cm , is the near infrared. Molecules vibrate when they absorb near infrared radiation, but the spectral features are fewer, broader, and more difficult to interpret than in the mid-infrared. Because of certain instrumental advantages, near infrared radiation is frequently... 

Ai- 4-(bis[4-(phenylamino)phenyl]methylene)-2,5-cyclohexadien-l-ykdene -3-methyl-ben2eneaminesulfate [57877-94-8] (20) have been claimed as positive CCAs (65). The absorption spectra of the triaryknethane dyes can be extended into the near-infrared region. The use of triaryknethane dyes as infrared absorbers for optical information recording media (66) and as infrared color formers in carbonless copy paper has been claimed. 

Reaction with vatious nucleophilic reagents provides several types of dyes. Those with simple chromophores include the hernicyanine iodide [16384-23-9] (20) in which one of the terminal nitrogens is nonheterocyclic enamine triearbocyanine iodide [16384-24-0] (21) useful as a laser dye and the merocyanine [32634-47-2] (22). More complex polynuclear dyes from reagents with more than one reactive site include the trinuclear BAB (Basic-Acidic-Basic) dye [66037-42-1] (23) containing basic-acidic-basic heterocycles. Indolizinium quaternary salts (24), derived from reaction of diphenylcyclopropenone [886-38-4] and 4-picoline [108-89-4] provide trimethine dyes such as (25), which absorb near 950 nm in the infrared (23). 

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. 

Table 12. Examples of Near-Infrared Absorbing Dyes...

Photo-thermal tumor ablation in mice using near infrared-absorbing nanoparticles. Cancer Letters, 209, 171-176. 

Benzo[l,2-fl]-8-methyl-9-azaphenothiazinone (14) was reduced to a leuco form 15 which was too unstable to be isolable.10 The leucos 16 and 18 obtained from thionation of iV,iV-diphenyl-p-phenylenediamine and j9,//-dianilinodiphenylamine, respectively, are also air sensitive. 11 They are oxidized to thiazine dyes 17 and 19 which are reported to absorb in the near infrared. 

The reaction of keto acids (79) having no amino group with 3-alkoxy-diphenylamines (80) is used to synthesize 3 -anilinofluorans (81), especially near-infrared-absorbing fluoran compounds (Eq. 6). 

Table 7 shows melting points of a few near-infrared-absorbing fluoran compounds (81) thus prepared. 

The first chapter of the book deals with leuco-spiropyrans and related spiro compounds, which constitute one of the classes of leuco compounds not of the redox type. Such materials are photochromic, and are of major technical importance. The author, Hiroyuki Nakazumi of the Department of Applied Chemistry at the University of Osaka Prefecture, is well known for his researches in functional dye chemistry, particularly photochromic materials, and he provides a very useful update of the field, covering mechanisms, synthesis, spectra and applications, together with a useful section on approaches to near-infrared absorbing photochromic dyes. 

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