I wonder, what is the equation of HOMO and LUMO if I used ferrocyanide as a reference electrolyte?
is the equation Ehomo/lumo = e (Eox/red – E1/2) + 4.8 eV still valid?
because as far as I know, the value of 4.8 is the value from HOMO energy level of ferrocene in vacuum.
Yes, you are right that 4.8 eV is due to the ferrocene redox couple. This could be used as a standard for calibrating the CV curves. You can use any other supporting electrolyte (definitely not ferrocyanide couple) to determine the HOMO-LUMO energy level of your compound.
The above equation given by Prof. John is the simplified version of the below equation where the value – 4.8 eV is the HOMO energy level of ferrocene against vacuum.
EHOMO (eV) = - (Eox onset - E Fc/Fc+onset) - 4.80 eV
and it is found that E Fc/Fc+onset is close to 0.4 V vs Ag/AgCl.
where Eox onset and E Fc/Fc+onset are the onset oxidation potentials for the polymer sample and the ferrocene against the Ag/AgCl reference electrode,
Ref:
(a) M. Kumada and K. Tamao, Adv. Organomet. Chem.1968, 6, 19.
(b) J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bassler, M. Porsch and J. Daub, Adv. Mater. 1995, 7, 551.
(c) B. W. D. Andrade, S. Datta, S. R. Forrest, P. Djurovich, E. Polikarpov and M. E. Thompson, Org. Electron. 2005, 6, 11.
(d) Y. Liu, M. S. Liu and A. K.-Y. Jen, Acta Polym., 1999, 50, 105–108.
what should be value instead 4.8 if we are using KOH as an electrolyte?
Please could you explain more clear about your reply? I meant I have seen many papers but most of them mentioned about using ferrocene as internal reference or external reference and calculate them with formular HOMO (LUMO) = -4.8 - (Eonset - E1/2 ferrocene) or second way, tried to measure UV-VIS absorbance and emission spectra and get the Eo-o transition energy from the intersection between them, get the HOMO value from oxidation potential and LUMO=HOMO-Eo-o.
Adilah Roslan, I know that now your question might be deprecated but I will still answer it as someone else might step upon the same problem in the future.
The equation You've given will be no longer valid if you use other reference than ferrocene. Nevertheless You can conduct measurments using ferrocyanide and then calibrate Your measurments by testing Your reference (ferrocyanide) against ferrocene. This way You simply take ferrocyanide's potential into account in the given equation. You can also get ferrocyanide's electron affinity (in vacuum) from literature and include it in the equation instead of value of ferrocene's, which is 4,8 eV.
To answer Reetu Sharma's question: electrolyte has no effect on this equation, as value of 4,8 is reference compound's electron affinity, which has originally been measured by other, direct method. Electrolyte has effect on reduction and oxidation potential of the whole setup, which is Ered and Eox. You should always measure the reference compound, which is compound of known E1/2 potential from literature.
- Badges
- Science topic