Hi, everyone!
I am currently studying molecules with fluorescent properties which strongly depend on the viscosity of the medium it is dissolved (fluorescent viscosity sensors).
I have calculated the absorption properties, orbital contributions, rotational barrier of the portion of the chromophores that depends on the viscosity and some other stuff.
Experimental meassurements are carried out in mixtures of MeOH/Glycerol to gradually increase viscosity.
My question is, whether it is possible to include in Gaussian or Materials Studio the effect of viscosity on absorption/emission calculations.
Because the viscosity of the MeOH/Glycerol mixtures can be determined and I wish trying to calculate the absorption/emission properties but using different values of viscosity.
Is that kind of study possible? If so, could you tell me a summary of how this could be done or lend me some references where to find such computational methodolgy?
Thank you so much
DFT is a microscopic method and therefore doesn't "know" macroscopic properties such as the viscosity. What causes the fluorescence shift is the solvatation, the coordination by the solvent. Thus, in order to investigate the effects of your solvent mixtures on the fluorescence, you will have to calculate the fluorescence with different solvent molecule compositions around it. Since this might esceed the number of atoms that you can calculate with a reasonable amount of CPUs/GPUs/RAM, you might require some sort of embedding, either QM/MM or QM/semiempirical. I have never done that myself, but there is a tutorial by Gaussian developer Bernhard Schlegel:
http://chem.wayne.edu/schlegel/Software/oniomtoolTAO/TAOtutorial.html
Jürgen Weippert, thanks so much for your answer. I'll dig into the tutorial to check those alternatives.
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