Imaging Inhibition

Taking into account the fact that most of the hydrophilic dendrimers described up to now in the literature have been proposed as tools for various biological applications (e.g., transfection, medical imaging, inhibition of viruses, see below) it is important to have not only water-soluble, but also water-stable compounds. This is the case of most of the phosphorus-containing dendrimers reported in this review, some of them being stable for months and even years in water, demonstrating the very high stability toward hydrolysis of both the internal and external hydrazone units and the whole skeleton of the dendrimer. 

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. 

Figure 3 Migration inhibition assessment of ECRF24 and MDA-MB-231 cells after exposure to compound 1 and 3. Wound closure in ECRF24 cultures after 7 h of incubation with concentration ranges of 1 (A) and 3 (B). (C) Typical images of the wound at the beginning of the experiment (culture medium as a control) and after 7 h of incubation with 3, 60 pM. Error bars represent standard error of the mean. P < 0.05.

The workhorse of the VLSI industry today is a composite novolac-diazonaphthoquinone photoresist that evolved from similar materials developed for the manufacture of photoplates used in the printing industry in the early 1900 s (23). The novolac matrix resin is a condensation polymer of a substituted phenol and formaldehyde that is rendered insoluble in aqueous base through addition of 10-20 wt% of a diazonaphthoquinone photoactive dissolution inhibitor (PAC). Upon irradiation, the PAC undergoes a Wolff rearrangement followed by hydrolysis to afford a base-soluble indene carboxylic acid. This reaction renders the exposed regions of the composite films soluble in aqueous base, and allows image formation. A schematic representation of the chemistry of this solution inhibition resist is shown in Figure 6. 

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