I am interested in making a theoretical calculation of a charge transfer (CT) interaction between dicationic 4,4'-bipyridinium ("viologen") moiety as charge acceptor and nucleobases (i.e. thymine or adenine) as charge donor? Does anybody know a methodology to do this? The goal of such a calculation is to show a "degeneration" of the molecular orbitals in viologen as a consequence of the CT interaction with the charge donor. Also, some changes in the HOMO-LUMO gap that can be derived from theoretical calculation are expected.
Any expertise and advices regarding CT of viologens and theoretical calculations are appreciated. Thank you!
I will tell you the procedure how to calculate the charge transfer, i am not sure about the type of semi empirical calculation, since we use ab-initio methodologies.
First take the two molecules which you are interested in calculating the charge transfer, and optimize both together.
charge on neutral molecules will be zero, now taking the charges of individual atoms on the molecule, you determine the charge of your molecule.
Dear Vikram, Thanks for your answer! One molecule of interest is looking like in the document attached. An inter or intramolecular charge transfer between 4,4'bipyridinium moiety and thymine groups take place. In the case of intramolecular CT it will be expected that the thymine groups will fold via propylene spacer in order to interact in a co-facial manner with the 4,4'-bipyridinium core. I do not have experience in molecular modeling but I believe It should be chose a pre-defined geometry of the molecule for which the calculation will be done. What do you think? On the other hand, as you can see, the molecule is not neutral. It has 2 positive charges.
Using g09 software, i have carried out a semi-empirical pm6 calculation, you just find the attachment, i have highlighted Mulliken charges calculated on individual atoms in the molecule, if you add all the individual charges you can get the total charge as zero, since it is a neutral molecule.
As far as your case is concerned, as the molecule is not neutral, you just do a sample calculation using any semi-empirical methodology you wish build the molecule and submit the optimization calculation and look into the Mulliken charge analysis of your molecule and see how the charge is determined, make a note of it.
Do the same for the other molecule note down the charge.
Now you optimize together both the molecules of interest and see how the charges are being varied in the individual molecules from the output file and see the difference between individual calculation charges and the calculation done together.
I am not aware of exactly how you calculate intramolecular charge transfer, but since i work on solar cells and oleds, there is a procedure to evaluate photon induced charge transfer.
All the best.
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