The one electron excitation is response for the activity of the molecule. Then how these HOMO-1, -2 and LUMO+1, +2 molecular orbitals and its band gaps favor the activity. Then what is the phenomena behind these type of excitation's and its band gap.
Hi Dhandapani,
Your question is very though because is very General. To have a precise answer you will have to look at each molecule in some more Detail.
In General a molecule could be excited by an external source (i.e. photons) and an electron can jump from an occupied state to an unoccupied state. By doing that you create an excited molecule. Sometimes this molecule reacts differently than the ground state molecule.
For example in Ir 3+ complexies, often used as catalyst, you can have an "unspinning" process. By Irradiation with light, an electron pair (spin +1/2 -1/2) in the highest occupied d orbital is excited and the electron jump in the unoccupied d orbital. By doing this you create 2 singlets with +1/2 spin. This now can relax also by transfering (or taking) one of this electrons to a Ligand (or the molecule attached to the catalytic Center). The process is not completely well understood, as these active Transition states, are very hot, so they have a short life, but with DFT could be simulated quite well.
As I said what will happend will depend a lot on the specific electronic structure of the molecule, and on the allowed/not allowed transitions. I suggest to look at some photochemistry literature, as there the transitions are often well described.
Dear Giulio Lolli,
First I like to thank you for your valuable answer.... Hope it helps me a lot. and everyone struggled on some fundamentals and am also one among them. Now i clarified sir. Thanks for your response......
The HOMO and LUMO and their energy difference are possibly the most important things for thinking about optical excitations of and chemical reactions of molecules and give approximations for the lowest lying excited state, which is commonly most important for both optical excitations and chemical reactions. However:
Electrons interact and so HOMO and LUMO are only approximate ideas in the first place
Electrons interact so thinking that "all" that happens in the first excited state is that one electron is excited from the HOMO to the LUMO is a VERY serious approximation. Generally, there is a very significant change to such excite states from electron-electron interactions (depending on the molecule and the calculation scheme.
Molecular properties do not depend only on the first excited state. Sometimes higher excited states also matter.
Sometimes, even, the first excited state is degenerate and the terms HOMO and HOMO+1 e.g. can not be give clear distinctions.
- Badges
- Science topic
- Similar topics
- Biological Science
- Physiology
- Physiological Processes
- Stress