Photosensitizers chemistry

In explaining the photodetection process in vision, there remains the every present problem of clashes in nomenclature as two previously separate fields of chemistry become more entwined. In this case, they are the field of photosensitization chemistry as used in photography and the field of dye chemistry as used in the textile industry. The reader is cautioned to review Section 5.2.4 before proceeding beyond that section. 

So far, only the mercury-photosensitized chemistry, discussed above, allows direct functionalization of alkanes with a Si substituent under mild conditions (equation 36). ... 

Commercial photosensitive SBC formulations are available from several suppliers and provide a range of materials differentiated by wavelength photosensitivity, chemistry type, and film properties. A list of commercial photosensitive SBC formulations is shown in Table 5 (29,30,32,61-63). Table 6 shows a compilation of selected film physical property data selected from those listed in Table 5. 

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Fig. 4. Chemistry of poly(vinyl cinnamate) negative-acting resist. Initial light absorption by the photosensitizer is followed by energy transfer to produce a pendant cinnamate group in a triplet electronic state. This combines with a second cinnamate on another polymer chain, forming a polymer—polymer...

Dry-Film Resists Based on Radical Photopolymerization. Photoinitiated polymerization (PIP) is widely practiced ia bulk systems, but special measures must be taken to apply the chemistry ia Hthographic appHcations. The attractive aspect of PIP is that each initiator species produced by photolysis launches a cascade of chemical events, effectively forming multiple chemical bonds for each photon absorbed. The gain that results constitutes a form of "chemical amplification" analogous to that observed ia silver hahde photography, and illustrates a path for achieving very high photosensitivities. 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

The impact on negative-CA resists of airborne base contamination differs qualitatively from their positive tone counterparts. Suppression of acid-catalyzed chemistry at the surface of a negative resist results in some film erosion at the top of the exposed fields and in some cases an apparent loss of photosensitivity, but in general the reUef images formed exhibit the expected cross-sectional profile. This is in sharp contrast with the typical behavior seen with positive-tone CA resists, where suppression of acid-catalyzed chemistry at the surface causes an insoluble surface skin. 

The main suppHers and manufacturers of polymethine dyes are Aldrich Chemical Company, Eastman Organic Chemicals (U.S.), Japanese Institute for Photosensitizing Dyes, NK Dyes (Japan), Riedel deHaen (Germany), Institute of Organic Chemistry of the National Academy of Sciences (Ukraine), and NIIKhim-EotoProekt (Russia). 

V. Zehavi, Applications of Photosensitive Protecting Groups in Carbohydrate Chemistry, Adv. Carbohydr. Chem. Biochem., 46, 179-204 (1988). 

Photosensitive functions are in many cases also heat sensitive, so the preparation of photosensitive polyimides needs smooth conditions for the condensations and imidization reactions. Some chemical reactants, which can be used for polyamide preparation, have been patented for the synthesis of polyimides and polyimide precursors. For example, chemical imidization takes place at room temperature by using phosphonic derivative of a thiabenzothiazoline.102 A mixture of N -hydroxybenzotriazole and dicyclohexylcarbodiimide allows the room temperature condensation of diacid di(photosensitive) ester with a diamine.103 Dimethyl-2-chloro-imidazolinium chloride (Fig. 5.25) has been patented for the cyclization of a maleamic acid in toluene at 90°C.104 The chemistry of imidazolide has been recently investigated for the synthesis of polyimide precursor.105 As shown in Fig. 5.26, a secondary amine reacts with a dianhydride giving meta- and para-diamide diacid. The carbonyldiimidazole... 

Lu, C. Lin, W. Wang, W. Han, Z. Yao, S. Lin, N. (2000). Riboflavin-(VB2) photosensitized oxidation of 2 -deoxyguanosine-5 -mono-phosphate (dGMP) in aqueous solution A transient intermediates study. Physical Chemistry Chemical Physics, Vol.2, 0anuary 2000), pp.329-334, ISSN 1463-9076. 

Kndr, G. (2001) Intramolecular charge transfer excitation of meso-tetrakis (1-pyrenyl) porphyrinatogold(lll) acetate. Photosensitized oxidation of guanine. Inorganic Chemistry Communications,... 

Asa study of spin chemistry at solid/liquid interfaces, we have examined M F Es on the photoelectrochemical reactions of photosensitive electrodes modified with nanoclusters containing CgoN and MePH (Figure 15.4), intended for utilization of C o as photofunctional nanodevices. 

It will not be lost on the reader that, while PHOTOFRIN and compounds (3), (5) and (6) contain no metal, they would be expected to be excellent ligands. Are metal complexes useful as PDT photosensitizers Indeed, they are, and may be expected in the future to become more important. The rest of this chapter is about this aspect it will emphasize metal complex formation and properties in relation to PDT. The synthesis of ligands, while of crucial importance, will not usually be treated here in detail, but leading references to relevant synthetic organic chemistry will be provided. The synthesis of porphyrins and related compounds has been considered in several monographs and reviews (porphyrins,46 47 phthalocyanines48). 

Of the following amine-reactive and photoreactive crosslinkers, the overwhelming majority use an aryl azide group as the photosensitive functional group. Only a few use alternative photoreactive chemistries, particularly perfluorinated aryl azide, benzophenone, or diazo compounds. For general background information on photoreactive crosslinkers, see Das and Fox (1979), Kiehm and Ji (1977), Vanin and Ji (1981), and Brunner (1993). 

While the majority of the chemistry strategies and synthesis design is equivalent to standard analogue producing approaches, a unique feature can be taken into account based on the relative photosensitivity of the probes. The introduction of the radio or other types of labels can also modify the reaction sequences. 

Kessel D, Thompson P, Musselman B, Chang CK (1987a) Chemistry of hematoporphyrin-derived photosensitizers. Photochem Photobiol 46 563-568. 

APPLICATIONS OF PHOTOSENSITIVE PROTECTING GROUPS IN CARBOHYDRATE CHEMISTRY... 

The first modern day negative photoresists were developed by the Eastman Kodak Company which utilized cyclized rubbers and cinnamic acid derivatives as photosensitive crosslinking agents (42). The first commercially important photoresist based on this chemistry was known as KPR, which was of a cinnamate ester of polyvinyl alcohol. It was introduced by Kodak in 1954. 

Chemistry and Structure of the Principal Tumor-Localizing Porphyrin Photosensitizer in Hematoporphyrin Derivative... 

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