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  1. #1

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    Sensitizing dyes

    Hello,

    I would be very interested in a complete description of how the sensitizing dyes work. Is there a specific mechanism that they all use?

    Ben

    P.S. Erythrosine seems to have iodine which could be part of the mechanism.

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    Ben;

    I have posted a list of sensitizing dyes sold by EK from years ago, elsewhere in this forum.

    Here is the generic structure of one modern class and some results.

    Genearlly, they adsorb to the surface or make an actual salt with Silver. Sometimes they can do both.

    I hope that this is not too much organic chemistry for you.

    PE
    Attached Thumbnails Attached Thumbnails dye class vs wavelength.jpg   dye structure series.jpg   dye types.jpg  

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    Hello PE,

    it's slightly off topic, but was Tetracarbocyanine used for HIE?

    Thanks in advance.

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    Ron;
    I actually know quite a bit of organic, and I was looking looking for a more clear answer. If I had to guess, the resonance structure of those molecules absorbs some of the light outside the spectra of AgX sensitivity. Erythrosine is interesting because it has a nucleophillically substituted I, which probably affects the sensitivity range. It might be interesting to look at t e analogous molecule with an H instead.

    Ben

    P.S. my organic knowledge is self taught although it has some holes, hard to find people willing to teach a 16 y.o. organic, but I had to know, for the sake of curiosity and the NChO

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    Anony, IDK what was used in HIE. Sorry.

    Ben, the bottom line is that sensitizing dyes look very much like the dyes that sensitize human eyes to color, but they have an ionic tail end instead of a fatty tail end. The fatty tail end on human dyes help them adsorb on the receptor cells in the eye and the ionic tail ends help the sensizing dyes adsorb on the surface of the grain.

    The dyes do indeed absorb light outside of silver halide sensitivity which is primarily UV-Blue. So a Green sensitizer is Magenta in color (Erythrosine is a vivid Red-Magenta), and all of these dyes have huge molar absorption values. But, there is more to it than that. There is redox potential of the dye. The dye must transfer energy so being colored and adsorbing is not enough! If no energy is transferred then the dye is useless.

    As for helping you, I think that anyone not willing to teach a young person is foolish. Tell them I said so!

    PE

  6. #6

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    Ben - I appreciated your desire to learn! Especially Organic Chem! I took it (and passed it!), but it was never really my main interest.

    If you have a good library near by, see if they have or can get on loan "Spectral Studies of the Photographic Process" by Yu N Gorokhovskii. It was written in the early 1960s, but it will give you more info than you probably want. If you can't find a copy, try Google Books and searching there. You can often find some good texts that have previews there.

    If you want to play with some for making an emulsion, it's used as a food coloring. it's called FD&C Red #3, and like PE says, it's bright red.

    OK, so I gots to know, what's "NChO"?
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

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    Hi All,

    Another very good source of information is in The Photographic Emulsion, by Carroll, Hubbard, and Kretschman, pp 201-262. You can read those pages here:
    http://thelightfarm.com/cgi-bin/photoemulsion.py

    In addition, I recommend Photographic Emulsion Chemistry, by Duffin. The complete citations for Duffin and many other emulsion books is here:
    http://www.thelightfarm.com/Map/Lite...t/MapTopic.htm

    Good reading, Ben. I hope it leads to some great emulsion-making.
    Denise

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    Kirk; I've read up on erythrosine, I was looking for other dyes to use for adding red sensitivity, which is why I mentioned methyl violet, I however know nothing about its redox potential. NChO is the national chemistry olympiad, and it has some organic questions, but I was more motivated so that I could learn biochemistry, as becoming a molecular biologist is my eventual goal. I will definitely check out some of those books. I must have posted something I meant to posst in this thread somewhere else, I would be willing to look into the redox potential and sensitivities of other dyes, specifically those that can be found for cheap as cell stainers. I have access to a spectophotometer for measuring absorbance, and I can determine redox potential with an electrode and voltmeter setup.
    Ben

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    Mees and James have much information on sensitizing dyes Ben. And, the worlds greatest expert, Paul Gilman, is a friend of mine. I'm sure that between us we can answer most of your questions one way or another.

    As for adding red sensitivity, a good aggregating red sensitizer is available from H. W. Sands Corp. in Titusville Fla. This dye was discussed completely in another thread. It is a Green sensitizer on Bromide and Chloride emulsions and a Red sensitizer on Br/I emulsions due to "J" aggregation. It is used in Kodachrome film AAMOF. I have 0.9 grams of it here. I used 100 mg already. This dye runs about $300 / gram right now IIRC.

    PE

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    I was interested in finding cheaper alternatives more than using what's commercially available for highly inflated prices. What are the essentials for making your own emulsion and coating paper?

    Ben

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