Spectral sensitizing dyes

[wildbillbugman]

"Some are very expensive."
Bob,
Could you define "very expensive"? One of the dyes that I use all the time costs over $600/gm. Are we talking more or less than that? A cheaper red-sensitive dye would be great!
Bill

 

[Photo Engineer]

Bob;

Even a 100 mg sample with a courtesy fee of $100 or so would be good. I can do a lot of work with 100 mg.

There are so many dyes though it is hard to pick one. They are not in the best format for review either. There must be a better way to present them such as by chemical class (best) and then spectral response (second best).

PE

 

[BobCrowley]

I think the way to proceed is to find out who the scientist is at that company and ask him/her about the various dyes. That person would possibly learn something too, and may be intrigued about the use of their product with silver halide sensitized materials for intellectual as well as business reasons.

There was a detailed spec sheet for each one on their website. We used PBD and got less than a gm of it which was 100 times what we needed. I don't think it does much good to speculate on cost until you select the one(s) you want and know how much coverage it could afford. I would not even approach the cost question when calling, as that alerts them in the wrong way. It could turn out that a substitute dye the photo industry has never used is right there in the catalog, and that could be valuable to Ilford, InovisCoat and others who may also have wondered about it, and not had the time yet to explore the dye laser space fully, though I am very sure they are well aware of it.

Let's find out about performance first because costs vary through R&D to manufacturing quantities. Let me know if I can help - I would not be as conversant as others like PE on the subject, but our lab could call and make inquiries, if we had a few good candidates picked out.

 

[Photo Engineer]

There are a few IR dyes there that look interesting. For those wanting to make IR sensitive materials that is probably the place to go. AFAIK, most of the rest of the dyes are unusable, and the usable ones, I have from my sources already.

Also, I would not recommend perchlorate salts to anyone for use with AgX emulsions.

PE

 

[BobCrowley]

We thought $100 a gm was quite expensive when we bought the material for spectroscopy. I get McDonald's $1 coffee and think that Dunkin Donuts coffee is very expensive.

 

[Photo Engineer]

Generic Sensitizing Dye Structures

Here are a few generic examples of what works best.

So far, I have only found 2 that suit in the visible region and 1 in the IR region.

PE

 

[Neanderman]

Here are a few generic examples of what works best.

I suspect the symmetry may be indicative?

Ed

 

[BobCrowley]

Centrosymmetric molecular structures are commonly seen in dyes and other colorants as they tend to have relatively narrow bulk EM resonances (lightwave resonance) The elongated, high length to diameter ratio, which is effectively doubled in the centrosymmetric structure, is responsible for what we term "antenna effect" today. The antenna (dye molecule) can be touching or attached to something else (like SiO2, or silver salt, or other metallic oxide) and the charge selectively transferred. Organic dyes used to be the only way to get these long-ish chains (100-500nm or more) but now there are other ways being developed and a ton left to explore.

Many "good" dyes absorb, fluoresce and reradiate at the same time, and there is a lot of what is referred to as excitonic activity. Lightwaves provide the energy and excitons, phonons, electrons all get into the act.

The only reason I learned of this was because I work in centrosymmetric structures like this
http://www.google.com/patents/US6038060

 

[BobCrowley]

PE, in your experience, do the dyes commonly used as sensitizers produce an extra sensitivity bump at 1/2 the absorption wavelength?

 

[Photo Engineer]

Bob;

No, AFAIK, they do not. Of course, that would put them into the UV region and we do not routinely measure there. My tests and ours at work normally ran from 400 - 700 nm. However, IR dyes that sensitize AgX at 800 - 900 nm do not show secondary peaks at 400 or so, and I am basing my assumption on these longer chain examples as well as the more common dyes.

Ed;

Symmetry is not needed as much as conjugation, that is the double bonds shown. Symmetry is often there because a given molecule is easy to make.

PE

 

[BobCrowley]

Looking again at Meese and James, favorite reading, trying to figure out the dye(s) used for a Pan X emulsion, and the representative dye absorption and emission spectra.

 

[Photo Engineer]

Dye Types

You want this then!

PE

 

[BobCrowley]

When I saw the UV/blue response at 1/2 lambda of the IR films, I thought there had to be either harmonic doubling, or instrument artifact.

 

[Photo Engineer]

I'll ask a world class expert!

PE

 

[holmburgers]

Mssr. Gillman perhaps?

 

[Photo Engineer]

Yes, Chris. Email sent to himself!

PE

 

[Photo Engineer]

And the answer is:

Any sensitizing dye will sensitize an emulsion wherever it has a peak. This does not have to occur at 1/2 Lambda max.

PE

 

[wildbillbugman]

PE,
To skip to another question on dye sensitization: Using dyes such as SDA3057, which are added at the end of the make. Once a dye has been sufficiently mixed, such that the dye has coated the silver-halide crystals, would washing wash out the dyes, or are they sufficiently bonded to the halide to withstand washing. I am thinking that this might be a way to optimize dye concentration and eliminate excessive dye. Of course, I could take a very small amount of dye sensitized emulsion and try it. But I hate to waste emulsion, if you already know the answere..
Bill

 

[andrew.roos]

When I saw the UV/blue response at 1/2 lambda of the IR films, I thought there had to be either harmonic doubling, or instrument artifact.

I suspect maybe the blue/UV sensitivity is merely the native sensitivity of the emulsion, without dyes. The dye absorbs in the IR region and emits in the Blue/UV region, giving the IR sensitivity but retaining the original sensitivity.

 

[BobCrowley]

The two blue peaks are quite pronounced and are at lambda/2. So this is actual response, and not an instrument artifact? Also, apparently a strong, broad absorber in the sensitizing target region has to do more than absorb, it has to exchange electrons with adjacent halides. Any absorber can produce something, like heat, but others are better at charge transfer to an adjacent molecule. Does that require a chemical bond?

 

[Photo Engineer]

Bob;

Remember that sensitizing dyes are also desnsitizers in the blue region and you can use enough such that the blue speed is strongly repressed. They are also, in some cases, development inhibitors.

Bill;

Yes, you can wash off excess dye, but that is NOT the way to go. You should do a dye series and then coat and test and pick the best level. Otherwise you introduce another variable.

PE

 

[Kirk Keyes]

The two blue peaks are quite pronounced and are at lambda/2.

If a diffraction grating is used in the design of a recording spectrograph, then care does have to be taken to eliminate 2nd order diffractions so that they do not show up when trying to measure a 1st order diffration. The second order pattern will be at 1/2 the wavelength of the 1st order, and when trying to record wide ranges of wavelengths, it can be a big problem.

It's not an issue if a prism is used.

 

[Kirk Keyes]

Here's a nice article on absorption of a cyanine dye and how it can be solved using Schroedinger's wave equation (the particle in a box analogy).
http://www.dartmouth.edu/~chemlab/chem6/dyes/full_text/chemistry.html

 

[wildbillbugman]

PE,
Would not a wahing of a pigmented emulsion be a more accurate way of eliminating excess pigment, as grain size may vary somewhat from batch to batch, regardless of how much care is given to temperature and rate off adition of Ag, and all that factors that influence grain size.Assumung one is not using an automated programed system? What if I were to hold off all washing untill the pigment had been added and dispersed? Could the same process be used for Au and S sensitization.
I do not want to sound stuborn here. But I want to make sure that this is a bad idea befor I abandone it completely.
Bill

 

[Photo Engineer]

Well, lets firsts not call the dyes pigments as they are entirely different, especially here and it can confuse casual readers.

Now, as to the question, the dyes adsorb at their preferred ratio if you add them to the emulsion. Since you stir, the dye is distributed and used up at the proper amount for each grain size. It is only when you have too much that the situation is as you describe. If you do a proper series, you see this actually take place.

And, I would add that your method would work if there was an excess of dye, but you would also change the vAg of the emulsion thereby changing its surface adsorption characteristics. It would therefor cause some sort of secondary problem IMHO.

PE