Near-infrared sensitizers

Mecher, E., Gallego-Gomez, F., Tillmann, H., Horhold, H.H., Hummelen, J.C., and Meerholz, K. (2002) Near-infrared sensitivity enhancement of photorefractive polymer composites by pre-illumination. 

In the chemiluminescent detection of nitrogen oxides, a constant source of ozone reacts with a metered air sample containing nitric oxide. Fontijn et al. suggested that this method could also be used for ozone detection by using a constant nitric oxide source for reaction with ozone in the air sample. The ozone-nitric oxide reaction is carried out at reduced pressure, to avoid quenching the chemiluminescent reaction. Detection of the emission in the spectral r on involved (600-3,000 nm) requires using a near-infrared-sensitive photomultiplier tube. The noise of such a photomultiplier tube is reduced by cooling it to about - 20 C. ... 

Due to their high near-infrared sensitivity, pigments have been widely used as generation layers. Pigment layers can be prepared by vapor deposition or solvent coating techniques. 

Naphthalocyanines (Nc) are of interest for applications involving near-infrared sensitivity. Nikles et al. (1992) used an w-butanol soluble derivative, [RO(CH3)2SiO]2 SiNc, and prepared the generation layers by solution coating. Hayashi et al. (1992) made generation layers from -SiO SiNc as dispersions and as vapor-deposited layers. The best results were obtained with a vapor-deposited generation layer and a transport layer containing bis(p-diethyl-aminophenyl-4,4-diphenyl)-l,3-butadiene. 

Photoactivation can further allow release of entrapped materials from aqueous space. The liposomes may carry materials of low toxicity that are converted to more potent materials upon radiation (e.g., prodrugs). The methods applied for photoactivation of liposomes are based on reactions that destabilize the liposomal bilayer. The mechanisms can be direct or mediated by oxygen, heat, specific ions, or a change in pH (Table 15.1). Many efforts are underway to develop two-photon schemes or near-infrared-sensitive liposomes to optimize the effectiveness of the system. The toxicity of the photosensitive units is a problem that must be looked into to improve the utility of these phototriggered systems. 

Figure 1 Absorption and fluorescence spectra of Cgg and Cyg in room-temperature hexane. The fluorescence spectra were obtained by using a regular detector and small slit (-----) and a near-infrared-sensitive detector and large slit (-------).

Near-infrared-active materials such as phthalocyanines are becoming especially important in materials of this type, because they permit the use of infrared diode lasers (which are compact, inexpensive, and easily modulated) for electronic printing applications such materials can have quantum efficiencies (electron-hole pairs produced per photon absorbed) near unity and near-infrared sensitivities (for 50% discharge) of about 1 erg/cm. There are worldwide efforts underway, however, to produce usable visible-light diode lasers. 

He, M., and Twieg, R.J. (2003) High-performance photorefractive organic glass with near-infrared sensitivity. Appl. Phys. Lett., 82 (21), 3602-3604. 

Ma, B. and Sun, Y.-R, Fluorescence spectra and quantum yields of [60]fullerene and [70]fiillerene under different solvent conditions. A quantitative examination using a near-infrared-sensitive emission spectrometer, /. Chem. Soc., Perkin Trans. 2, 2157,1996. 

Observation, in the laboratory, of the a-X system of O2 represents a greater challenge because it is much weaker than the b-X system. It has been observed using CRDS, a 1.5 m cavity and O2 at atmospheric pressure. Because the transition is in the near infrared, mirror reflectivity is very high thereby increasing the sensitivity. 

Sucrose quantitation has also been performed by colorimetric methods. However, in recent years, automated enzymatic analyzers and instmmental methods (eg, ion chromatography and hplc) have become increasingly popular, as they provide greater sensitivity and accuracy. Near infrared (nir) spectroscopy is currendy under evaluation as a tool for sucrose quantitation in sugar mills and food processing operations. 

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

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