Hi:
You have 2 liquids where both are forced to transfer electrons from their ground states to their first energy state via UV light, for example. One liquid returns to a vibrational level of the ground state, emitting a photon whose wavelength is longer than UV, say emitting red light (within picoseconds usually). The second liquid doesn't fluoresce at all after UV light injection.
1. Why doesn't it undergo fluoresce (or phosphorescence), returning electrons to the ground state?
2. Does the second liquid remain in this meta-stable state indefinitely or are the energized electrons 'lost' into the vibrational energy levels of the first state? Or do radiationless transfers occur between the first and ground vibrational states?
I guess I'm puzzled about the physics or chemistry that prevents one material from undergoing fluorescence or phosphorescence while another does.
Thanks,
David
Hi,
please have a look at the following webpage:
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Reactions/Reactivity/Part_V%3A__Reactivity_in_Organic%2C_Biological_and_Inorganic_Chemistry_3/PC._Photochemistry/PC3._Fluorescence_and_Phosphorescence
You will find some clues there...
Good luck,
Aleksander
Hi David, the efficency of the fluorescence depends on the relative speed of the processes involved. An excited molecule in solution can undergo a radiationless deactivation to the electronic groundstate (energy goes to vibrational states), a radiative deactivation to the electronic groundstate (=fluorescence), and a transfer to the so-called triplet state (called intersystem crossing). That latter is the most important path of deactivation.
May be it is clearer if you google Jablonski Diagram
Best regards
Frank
David,
Excited State Proton Transfer Reaction (ESPT) is an complicated phenomenon. The excited state can be deactivated via radiative way or non-radiation way. In the case of non-radiative deactivation you have either Intersystem Crossing or Internal Convertion. Internal Convertion means direct transition between excited singlet state and ground state.
If you want to solve the problem you should read about proton transfer reactions. Good point to start are keywords: "proton transfer Grabowska", "proton transfer Zachariasse", "proton transfer Grabowski". Grabowska, Zachariasse, Grabowski are the name of the scientists who did a lot of research in the field of PT.
With best.
Pawel Borowicz
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