I synthesized a new material analogue to PCBM and I need to know which is the best way to calculate the HOMO/LUMO energy from Cyclic Voltammetry data
I think you cannot do that using cyclic. You need a software
http://www.jmaterenvironsci.com/Document/vol1/10-JMES-15-2010-bouachrine.pdf
You can do this relatively easily using cyclic voltammetry. The one thing you need to do is to use a reference material (or electrode), such as ferrocene. Once you perform the CV and rescale the potential to be vs. that reference system (you assume that the redox potential of your reference is equal to 0.0V), find the onset potential (Eox) of the first oxidation peak of your investigated species. Do the same for the onset potential of your first reduction peak (Ered).
At this point, it is best to find the values separately in two experiments, as the products of oxidation/reduction will likely undergo reduction/oxidation closer to neutral potentials than your species will, obscuring your true onset potential.
Once you have the two onset potentials (let us assume you are using the ferrocene redox pair as reference), the following empirical equations can be used:
HOMO = 4.8 + Eox(vs.ferrocene) [eV]
LUMO = 4.8 + Ered(vs. ferrocene) [eV]
The experimental constant reported for ferrocene redox is -4.8eV (I have seen them reported as -5.1eV, however).
You might be interested in the following paper, as it details the procedure some more:
https://www.researchgate.net/publication/264269067
EDIT: Another freely available paper, this time giving the ferrocene value as -4.4eV:
https://www.scientificbulletin.upb.ro/rev_docs_arhiva/rezdd1_869282.pdf
you cannot do that using cyclic voltammetry , you can use GAUSSIAN program, using B3LYP functional and O3LYP methods with 6-31+G(d), 6-31G+(d,p) and 6-31+G(d,p) basis set. you can use cyclic Voltammetry in order to calculate number of electrons , No.of proton and study electro chemical behavior (oxidation reduction) , .......
Tomasz Jarosz Hello, do you have any idea how about the experimental setup? For example if I have my material as a powder, how should I run my experiment? i.e., should I dissolve it and run CV?, .. its a porous coordination polymer... how could I find out which electrolyte to use?
Thank you.
M. L. Gonzalez-Juarez : Regarding the form of the electroactive species that you want to investigate, it should be either in solution or in the form of a uniform coating (e.g. film) on your working electrode - any way that does not significantly hinder charge transfer between this species and the working electrode should be fine.
Regarding the choice of solvent and supporting electrolyte, the only truly crucial consideration is that they should not show redox signals (and not be electroactive) in the range of potentials, in which you will be investigating your polymer. A porous polymer might be a bit tricky and require some measures to deal with its (possible) high electric resistance (not sure how easily it is soaked by your solvent and how easilyare gas bubbles removed from within), but essentially, you will want an electrolyte with relatively small ions.
If you can provide a bit more details, I might be able to point you in a more specific direciton, but you might need to do some trial and error experiments to see what the best setup is.
Does changed the equation of calculation HOMO-LUMO energy by changing the solvent? My compounds are not soluble in Acetonitrile but soluble in DCM. if i do perform the cyclic voltammetry analysis in DCM solvent, then the equation will be same or not
HOMO = 4.8 + Eox(vs.ferrocene) [eV]
LUMO = 4.8 + Ered(vs. ferrocene) [eV]
Yes, i also used this equation in my compound, which is also soluble in DCM
Shamsa Munir, while the cited link does provide some information, it sadly contains errors that make it unreliable.
One thing that should be set straight immediately is that the dependence "EHOMO = ELUMO - EG(optical)" is incorrect, as the band gap values determined using different methods (electrochemical and spectroscopic) are neither equivalent nor equal (see e.g. DOI: 10.1016/j.synthmet.2006.02.013 for a comparison of the two).
While we might roughly estimate the value of EHOMO based on the value of ELUMO and the value of optical EG, depending on the experimental set-ups, this approximation may range from fairly accurate to wildly inaccurate (see e.g. Fig. 13 in DOI: 10.1021/om500604z ), as we are de facto comparing two somewhat related parameters (an exaggerated analogy would be having a mass of water at 4*C and using the density of water at 80*C to calculate the volume of the former - the result will be "approximately correct" but be flawed in terms of physical sense).
Another issue of the above-cited video is that it identifies the absorption signal of the HOMO-LUMO transition as "lying at the highest wavelength" or "the most bathochromically shifted one". This is unfortunately a gross over-simplification, as for a given molecule we can have a variety of transitions, including ones with an energy lower than that of the band gap. As such, it may lead to the signal corresponding to the HOMO-LUMO transition being misinterpreted. If I were to give advice on identifying the relevant absorption signal, I would suggest utilising UV-Vis spectroelectrochemical methods - the absorption peak that diminishes upon doping (oxidation or reduction) of the molecule and is restored upon dedoping *typically* corresponds to the HOMO-LUMO transition.
Regarding the previous question, while the "4.4", "4.8" and "5.1" values given in the equations cited in my original answer are determined based on what reference electrode was used (see e.g. DOI: 10.1007/s10008-002-0289-0 ), the solvation effect does also contribute (see e.g. Fig. 5 in DOI: 10.1021/om500604z ) to the observed EG value, hence a change of solvents may require the equations to be reevaluated, depending on investigated molecule and employed solvent.
Dear All experts, I want to calculate HOMO LUMO values using VASP as well as Quantum Espresso, so can you guys help me ?
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