Hi,
I am currently studying some fluorophores and wanted to check that they don't show solvent dependency. When I change the solvent there is not a change in absorption/fluorescent spectrum by eye but there are changes picked up by spectroscopy.
I have attached the spectra and the solvent details are on the plot.
So my question is, would you consider this molecule's spectroscopy to be unaffected by solvent polarity or would you consider it to be polarity dependent?
Thanks
although the change is small but still it will be called polarity dependent. If you use some more polar solvents like DMSO, methanol or ethanol, you may observe large spectral shift. There is blue shift with increasing polarity, so your dye is showing negative solvatochromic behavior. Moreover your absorption spectrum is showing more blue shift with increasing polarity than your fluorescence spectrum (also shows that you ground state is more polar than excited state). Even small changes in absorption spectra are considered as significant.
although the change is small but still it will be called polarity dependent. If you use some more polar solvents like DMSO, methanol or ethanol, you may observe large spectral shift. There is blue shift with increasing polarity, so your dye is showing negative solvatochromic behavior. Moreover your absorption spectrum is showing more blue shift with increasing polarity than your fluorescence spectrum (also shows that you ground state is more polar than excited state). Even small changes in absorption spectra are considered as significant.
Dr. Singh had a good answer. He is right and all of the fluors I've ever worked with have a spectra which is at least slightly different in each solvent, at some level. However, the level of effect is dependent on your goals. Before you make any claims of solvent dependency make sure you run a few replicates to determine if the changes between solvents are significant. But again, in general fluors are dependent on polarity of solvent.
No doubt, solvent dependency presents. Blue shift with increase of solvent polarity can be considered as n-pi transition but second argument you can get from the molar coefficient value: if it less than 1000 it belongs to n-pi, if more than 3000 it is a result of pi-pi transition. Follow also to Dr. Singh advice and test influence of more polar solvents.
Most dyes I've worked with had a degree of solvent dependency, although those with strong EWG/EDG groups had stronger dependency - in the form of wavelength shifts and intensity changes.
Be careful as polarity is a complex term and covers several different interactions. Choose your solvents wisely to distinguish shift caused by H-bounding or polarizability. For more details check the book "Solvents and Solvent Effects in Organic Chemistry" by Ch. Reichardt.
Bonus points for Jose Kaneti! I am indeed looking at some BODIPY derivatives
The spectra look the same in all solvents. However, there is a "solvatochromic shift" which is happening if you change the solvent for the fluorescent dye. Sometimes you might see a 10nm difference in the wavelength (absorption lambda) and it is still normal. For further details please refer to one of the most wonderful book in this area:
Principles of Fluorescence Spectroscopy by Lakowicz.
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