[rap35]

Hello,

I am optimising a long persistent luminescent material involving the recrystallisation of an organic species and introducing a dopant during this stage. As it crystallises, dopant becomes trapped within the crystal lattices which have an effect on the relaxation speed of the electron when excited via UV light.

The more dopant introduced during the re-crystallisation stage the material = a longer luminescence observed visually.

I have different dopant concentrations and I want to establish a correlation between the duration of emission and concentration of dopant added. Although I am adding x10 moles of dopant to crystal, I can't say for sure that x10 the amount of dopant is becoming trapped within the material, therefore, I wish to do proton NMR digestions to work out the degree of doping. The only issue is, I do not know where to start.

The dopant I am adding is dimethylaniline, how can I perform quantitative analysis to identify the concentration of dopant within crystals, formed under different conditions (mol ratio, recrystallisation method). As I do not have a known amount of dopant trapped within a crystal, how can I create a concentration gradient?

[Corribus]

By "duration" do you mean you are measuring the luminescence lifetime?

Can't you just filter off the crystals, then redissolve them and analyze the concentration of DMA using a more conventional analytical method, like mass spectrometry? Proton NMR is not a particularly good technique for concentration determination.

In general directly measuring concentrations of something dissolved in a solid is difficult, because it's hard to get reliable concentration standards.

[rap35]

Thanks for your reply.

Yes by duration I am measuring the lifetime of the luminescence.

I can certainly request to use MS as that would make more sense. The idea was to spike a dissolved amount of my crystal with a known amount of DCM - and then identify the ratio of DMA by comparing it to the peak made by DCM.

[wildfyr]

Is your luminescent crystal soluble? If so I don't think you need a quantitative analysis. All you need is is dissolve it, take NMR, and find some well identified peak in the luminescent compound, and another in dimethylaniline (I would choose the dimethyl, I imagine you have a pile of aryl groups on the luminescent material) and take the peak integration ratio. Easy as pie!

Say your luminescent material has a well defined peak at 6ppm that is 1 proton on the luminescent material. You set that integration value to 1. The dimethyl peak gives also gives you a value of 2, but it represents 6H. That means the ratio of moles of luminescent compound to aniline is 3:1!

If you want to use chromatography, I think straight up LC would be fine, no need for MS. Just need to know elution time of DMA and make a calibration curve for it to get concentration.

[Corribus]

Is your luminescent crystal soluble? If so I don't think you need a quantitative analysis.

We must have different definitions of quantitative? If he's getting a number, it's quantitative.
It really depends on needs for accuracy and precision. NMR certainly will work, as long as you can live with a large error/uncertainty. ~3 to 1? Sure. 2.92 to 1? No.

[wildfyr]

I meant it will only tell you a ratio, not actual concentrations!

For high accuracy LC is the way to go.

[rap35]

Is your luminescent crystal soluble? If so I don't think you need a quantitative analysis. All you need is is dissolve it, take NMR, and find some well identified peak in the luminescent compound, and another in dimethylaniline (I would choose the dimethyl, I imagine you have a pile of aryl groups on the luminescent material) and take the peak integration ratio. Easy as pie!

Say your luminescent material has a well defined peak at 6ppm that is 1 proton on the luminescent material. You set that integration value to 1. The dimethyl peak gives also gives you a value of 2, but it represents 6H. That means the ratio of moles of luminescent compound to aniline is 3:1!

If you want to use chromatography, I think straight up LC would be fine, no need for MS. Just need to know elution time of DMA and make a calibration curve for it to get concentration.

That clears it all up perfect for me, thanks for commenting!