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Silverless Photography Based on Racemization

IP.com Disclosure Number: IPCOM000088538D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Aviram, A: AUTHOR [+3]

Abstract

The silver halide photography system is a high gain (10/9/-10/10/ noiseless amplifier. To date many attempts have been made to develop a new system that will come close to the silver halide gain and speed without real success. The purposes of those proposed schemes were (a) to record an image based on color change or index of refraction change or induce an opaque image in a transparent medium; in other words, to induce an observable change; (b) to provide amplification of 10/6/ or more; and (c) to provide fixing (eliminate the sensitivity after the development stage).

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Silverless Photography Based on Racemization

The silver halide photography system is a high gain (10/9/-10/10/ noiseless amplifier. To date many attempts have been made to develop a new system that will come close to the silver halide gain and speed without real success. The purposes of those proposed schemes were (a) to record an image based on color change or index of refraction change or induce an opaque image in a transparent medium; in other words, to induce an observable change; (b) to provide amplification of 10/6/ or more; and (c) to provide fixing (eliminate the sensitivity after the development stage).

This article describes a new photographic concept which answers all the requirements listed in (a), (b) and (c). It is based on changing the state of matter from optically active to racemic, the driving force thus being entropic. The basic chemistry involved is that of "free radical chemistry" and in particular that of the trityl free radical. In general, free radicals tend to (i) combine, (ii) abstract a hydrogen as a free radical, leaving another free radical behind, (iii) add to double bonds and (iv) are very short lived. In contrast the trityl free radical (1) does not combine but exists in an equilibrium of 2 free radicals and a dimer 2R. /<-/(->) R- R, (2) does abstract other groups from different molecules, (3) does not add to double bonds, (4) is very long lived (months) and (5) is extremely sensitive to oxygen with which it combines to form Phi(3) C-O-O-C Phi(3).

Another principle in the chemistry of asymmetric molecules, the so called "chiral molecules", is that in order to racemize a sample of chiral molecules one should pass through an intermediate that is planar. Examine the chiral molecule A

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behind a "trityl" radical that is planar. This free radical is subject to rules 1,2,3,4 and 5 described above. Thus, as long as oxygen is excluded, the free radical will live in the solution and the only thing it could do is abstract a hydrogen from a molecule A with which it would collide. But in the process, the newly made A can be recreated in either the d or the l stereochemistry depending on the way the free radical collided with an A molecule:.

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Thus, the free radical propagates in the sample leaving behind it nothing but optical activity destruction.

In order to have this process sensiti...