Making blue light from green light

[dsli_jon]

Time for another clue: The system is very sensitive to oxygen. If a little air gets in no blue light is generated.

Hrmm, well, I was going to submit something in the 'optical brightener'-family, common in 'brite-white' papers and detergents, or possibly, acridine yellow...till I saw the 'sensitivity to O2'... so, now I'm

...Umm, Tinkerbell pee?
j

[DjMagnus]

Just a guess here, could it be some kind of ET primer like the ones used in dna sequencing?

[Vidal Wolf]

is it the stuff from a glowstick?

[tocket]

Just a guess here, could it be some kind of ET primer like the ones used in dna sequencing?

Don't know what is used for DNA sequencing, but are they really capable of upconversion at low intensities?

is it the stuff from a glowstick?

One of the dyes in this system can actually be found in blue glowsticks. Namely, the super-efficient fluorophore, 9,10-diphenylanthracene (DPA).

Now comes the interesting part. DPA only absorbs UV light, which is not present here. Yet, it is clearly emitting light in my little vial. Well, there must be another dye in the solution. However, the other dye will not be able to transfer its energy to DPA in a FRET-like manner, simply because green light is less energetic than blue. That would violate a bunch of laws of nature.

[andythemechanic]

It's getting more and more interesting! You actually brought me to searching for literature on the effect. I found this: http://pubs.acs.org/doi/abs/10.1021/ja075014k
There the trick is to excite a red flourophore (e.g. PdOEP) which then enters it's triplet state and can transfer energy radiationless via triplet-triplet anihilation (didn't even know before that such a process exists ). That also explains why oxygen hinders this process, since oxygen will lower the lifetime of the triplet state and not allow for energy transfer anymore.

[tocket]

It's getting more and more interesting! You actually brought me to searching for literature on the effect. I found this: http://pubs.acs.org/doi/abs/10.1021/ja075014k
There the trick is to excite a red flourophore (e.g. PdOEP) which then enters it's triplet state and can transfer energy radiationless via triplet-triplet anihilation (didn't even know before that such a process exists ). That also explains why oxygen hinders this process, since oxygen will lower the lifetime of the triplet state and not allow for energy transfer anymore.

Yep, triplet-triplet annihilation is the secret here! I use a different triplet dye, but the principle is the same.

It's quite a beautiful process. The first key step is triplet-triplet energy transfer from the excited triplet dye to the triplet acceptor, in this case DPA. The magic then happens when two DPA triplets collide and undergo triplet-triplet annihilation. In that process you end up with one DPA molecule in an excited singlet state and the other in the ground state. The excited DPA will then decay giving the blue light.

[andythemechanic]

Thanks Tocket for showing this nice effect! I just realized that quite a lot of work on this topic was done in the institute where I did my PhD (MPI for Polymer Reasearch, Germany). I worked however on a completely different topic, so I had no Idea.

Greetings
Andreas

[dsli_jon]

...thanks for the dual chem and laser-research lesson...

triplet-triplet annihilation

Hah, that would be a killer name for a punk-band... ...and 'Tinkerbells' Pee' could open for them...

cheers...
j

[dar303]

Educational AND funny thread, very nice!