I have a compound under investigation for its photophysical characteristics, and during investigation of its emission spectra with varying polarity I observed a red shift from low to high polar solvent which can be attributed to intramolecular CT. But when emission lifetimes were investigated it was seen that in low polar solvents like dioxane, dcm there is monoexponential decay, also in high polar solvent like acetonitrile similar decay was observed, however in high polar dmso biexponential decay was observed. Could this 2nd time constant in dmso be attributed to solvent to solute CT, as in high polar acetonitrile only one lifetime was observed?
Any expert advise is grateful.
Dear Bidyut Das the first thing to check is if your DMSO is pure (free from impurities which might fluoresce in the same region). if your solvent is pure, then chekc for possible exciplex formation between your sample and DMSO. best of luck!
In addition to Ephriem Mengesha suggestions, check for impurities of the fluorescent molecule that could be revealed in DMSO only...
Biexponential decays can be due to impurities http://dx.doi.org/10.1016/j.jphotochem.2021.113170
but also to stable conformers of the fluorescent molecule http://dx.doi.org/10.1039/A900584f
.
Another potential scenario is that the DCM and Acetonitrile do not have the capability to create a hydrogen bond, while DMSO can form a hydrogen bond depending on the structure of your solute. If there is a complex formed in the ground state, it is likely that you will observe multiple lifetimes.
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