Spectral sensitizing dyes

[OzJohn]

I read somewhere else that the poor man's way of making a spectroscope is to use the silvered surface of an ordinary CD as a diffraction grating. Never had the urge or need to try it but they do reflect a rainbow effect in certain light. For what it's worth. OzJohn

 

[holmburgers]

John, that's a great idea. I do recall seeing some DIY spectroscope before. (here it is)

The design would obviously have to be a bit different than this example since you'd want to have a reference light source and to project the spectrum onto a film sample. I would think that if you're messing around with spectral sensitizing you'd really want to have some way to qualify what you're doing.

Ron, who made monochromators designed for this kind of thing?

Maybe we should make Bill one so he doesn't have to keep pounding his pud all day...

 

[Photo Engineer]

Now all you need is a step wedge perpendicular to the horizontal spectral lines.

PE

 

[holmburgers]

I thought the idea was that you projected them obliquely onto a surface and the spectral beams naturally decrease in intensity as they travel, no step wedge needed.

Or a step wedge works too.

 

[wildbillbugman]

Holmburgers,
Seeing a spectrum is one thing. Reading-interpriting one is another. I know from first hand experience that one can get so caught up in analysis that you frind yourself doing nothing but analysis. An organized multi-person effort is about the only way to go here. I have known photographers who do nothing but curves on graph paper. Thats fine. It obviously makes them happy. So, I let you make the spectrometer. Then I will send you samples to read!
Bill

 

[Photo Engineer]

I thought the idea was that you projected them obliquely onto a surface and the spectral beams naturally decrease in intensity as they travel, no step wedge needed.

Or a step wedge works too.

Nope. You need a step wedge. You also should know the frequency in nanometers if you are to read a B&W spectrogram. With color, it is a bit easier.

PE

 

[holmburgers]

Well well... that's ok Bill.

Maybe instead of quantifying the results, we should be content with qualifying them. I would think that by comparing one emulsion to a manufactured film you could tell a lot from that. A piece-of-junk shoebox monochromator might be surprisingly illuminating (that's not a pun), and building it sounds like not a bad way to spend an afternoon either.

But anyways, I'm not about to go testing emulsions when I get home, I'm just enjoying the discussion.

 

[Hexavalent]

I made such a contraption (shoe box, grating etc.,) many many moons ago based on a "Amateur Scientist" article in Scientific America. (You might find the article in a web search). IIRC, I used a grating from Edmund Scientific.
Of course, for any real accuracy, one needs to know the profile of the light source and all the optics.

 

[Kirk Keyes]

One of my many unfinished projects is to make a recording spectrograph for testing films/emulsions. I've got a really beautiful 3" concave diffraction grating waiting for the project.

 

[Kirk Keyes]

This is a completely foreign language to me, but I'd like to learn it. What do you call these kinds of diagrams?

You're going to U Kansas aren't you? You should sign up and take General Chem and the Organic Chem. Don't think of it as two long years of work, just think of it as a great way to learn more about an aspect of emulsion making!

I'd say the problem with the Rhodamines is that oxygen molecule right in the middle of the molecule. The cyanines have carbon atoms that are conjugated (google it) between the nitrogens. It's that conjugation that allows the dye to have electron resonance and be good dye. The oxygens don't allow the resonance as well being in the middle of the chain of conjugated carbons.

I believe (PE correct me if I get it wrong) it's the electron orbitals projecting up from the nitrogens on the ends of the cyanines are the source of the electrons for the resonance and also allow the dye to attach to the silver halide crystal.

 

[holmburgers]

Hi Kirk,

Well I'm a graduate of KU, but I honestly have been toying with the idea of auditing some chemistry courses next semester.

I understand acoustic resonance of course, but in this context it's unclear how to conceptualize it. It sounds like the key to a good sensitizing dye is that it "becomes one" with the silver-halide crystal? What's the other option, that they're just sitting next to each other? Simplified, I know...

 

[Photo Engineer]

The dye "becomes one" with the crystal is a good way to put it!

The resonance of the electrons and the plus charge on the Nitrogens help in this. In the eye, similar dyes cause color vision, but they have fat tails to anchor them to the retina although they still have the charged Nitrogen IIRC.

PE

 

[holmburgers]

Is this the kind of resonance we're talking about? -> http://en.wikipedia.org/wiki/Electron_Spin_Resonance

 

[Photo Engineer]

No, try this: http://en.wikipedia.org/wiki/Resonance_(chemistry)

 

[holmburgers]

ahh.. thanks!

 

[Kirk Keyes]

In addition to PE's link to resonance, follow up with this on on conjugation - the resonance is needed to get an photon absorbed into the molecule, which then needs this property:
http://en.wikipedia.org/wiki/Conjugated_system

Resonance is needed to help absorb a photon and allow an electron to move about the molecule. The conjugation helps distribute the charge of the electron about the area of conjugation. The longer the area of conjugation, the more the charge is distributed. Also, the length of the conjugated chain the longer the wavelength of light that can be absorbed. That is, a blue dye will be shorter in length than a red dye. And IR dye will be longer yet.

Then check this:
http://en.wikipedia.org/wiki/Cyanine

And look at the molecules PE showed in Post #33. You can see how the longer the chain of conjugated carbons in those molecules affect the wavelength of absorption.

 

[Photo Engineer]

Kirk;

Thanks for the clarification and extension. It really will help everyone understand this stuff which otherwise is arcana to most.

PE

 

[holmburgers]

Thanks to both you guys. I'm gonna catch up on this reading today.

Kirk's description is just the kind of thing for someone such as myself. My understanding of chemistry is basically nil, but I do, like most, have an understanding of physics and can conceptualize systems like this. It takes someone who gets it to say it in such an illuminatory manner.

 

[holmburgers]

A thought occurred to me.. can we just recycle the dyes that get washed out of a commercial film in a pre-wash?

When I was looking at my discolored developer the other night this quote came back to my memory.

The next post was PE saying, well how the heck are you gonna separate out the sensitizing dyes? A fair question, but what if it's not necessary to do that? Then there were a fair number of intelligent people saying, what seemed to me, to be intelligents things, but I'd rather fly in the face of all of that a re-assert this proposition!

:munch:

So lets say we do a really thorough pre-wash in distilled water and evaporate all the liquid. The remaining powder should contain sensitizing dyes, along with other dyes and _________. (what else?)

You guys say that the dyes are ionic, so does that mean they're easily destroyed?

I don't know, maybe I'm just spinning wheels, but it seems like such a good idea. And of course who can really say whether it works or not until somebody actually tries it... but "what ifs", "how comes" and "why nots" aside, what do you guys think?

GO!

 

[Photo Engineer]

Chris;

That mix will be about 90% absorber dyes and 10% sensitizing dyes, if that. The sensitizing dyes were designed to stick to the grains and that is why some films end up pink! The dyes (some of them) come out slowly or in the fix or final wash.

Other things present in the pre-wet are tetra-aza-indede or similar compounds, metal complexes (very low concentration), antifoggants and surfactants.

PE

 

[holmburgers]

Thanks for the answer Ron.

I wonder if there's something one could add to the pre-wash (that's not detrimental to the process) that would leach out more of the dye.

Who knows... probably a hare-brained idea. But let's say you find a bunch of old panchromatic film that's way too old to use... might be worth it then.

 

[Photo Engineer]

A desensitizer will remove sensitizing dyes from the crystals.

These include the Pynacryptols or Pinacryptols, as there are spelling differences. Today's PINA numbers for dyes derives from this earliest class.

It will probably do bad things to speed and contrast. Experiments will have to be done.

PE

 

[BobCrowley]

Pardon me if this has already been posted. We used several of these for lasers and also absorption targets when we were working on optical spectroscopy for cancer detection. All of these dyes are stable and the concentrations, secondary emissions and extinction coefficients are available. The question that comes to mind is how to efficiently go about trying these as spectral sensitizers in an emulsion. It looks like it could take a long time.

http://www.exciton.com/wavelength_chart.html

 

[Photo Engineer]

Bob;

Just a quick look but about 25% of them look interesting but the rest are not suitable. The time is not a problem, the cost is. And, I can pretty much identify an emulsion sensitizer by structure which is how I figured out that some might work.

How to get some samples? Can an ordinary human get some?

PE

 

[BobCrowley]

I don't know if they would take a credit card order, but we can order any of them for you if you want through Soundwave Research if they won't. Some are very expensive but usually not much of it is needed. Not all of the dyes are of the centrosymmetric type, and I only have experience with a few of them that we used as precise spectral markers for development of ratiometers and spectrometers. Like this one http://new55project.blogspot.com/2011/05/first-spectrometer-on-chip-osa-poster.html

Maybe, just maybe, that company would be interested in an organized exploration of other applications addressable with their product line, if conducted by a qualified scientist. In return for sharing the information, they could supply samples to be used in a planned experiment, something like that. Depends on who asks. If it was the GEH and PE I would think they would be honored, or at least polite.