I am doing fluorescence studies of two molecules (one containing dibenzothiophene-S,S-dioxide and other benzothiadiazole) in THF/ water mixture. Fluorescence intensity decreases with increasing water content in both cases. But fluorescence decay time increases in case of the first molecule having dibenzothiophene-S,S-dioxide while decreases in other case. It appears to me that oxygen atoms of dibenzothiophene-S,S-dioxide might be playing some role in this.
Increasing solvent polarity increases the decay time in both cases (Tol.
Does the molecule where you observe increased lifetime have dual fluorescence? Polar solvents stabilize TICT state, and in case of this state being formed (and fluorescent), I would generally expect increase in observed lifetime (note that this state might have lower radiative rate constant, though). Furthermore, H-bonding might have significant influence. You'd have to investigate this case by dissolving your molecule in non H-bonding solvent, and add very tiny amounts of H-bonding solvent. Then check fluorescence intensity change and TCSPC and you might be well on your way to having the right answer. Good luck!
both the molecules show single fluorescence band and the decay time increases with increasing solvent polarity(Tol.
I should have mentioned it earlier, but you need to add very small amount of H2O. Definitely not more than 5%(v/v). See how emission and excitation spectra changes by making 0,1%(the smaller the starting quantity the better), 0.5%, 1%... 5% solutions of H2O/THF (for instance). If there are specific interactions, you will notice reasonably large changes in spectral shape. You can measure lifetimes of these solutions for complete picture. Main idea in this experiment is not to change dielectric properties of the solvent (since CT and ICT chromophores are very sensitive to solvent's dielectric properties), while introducing H2O. If there are specific interactions, shape of the spectrum will change and Stoke's shifts will behave unpredictably (e.g. very tiny amounts of H2O will make huge Stokes shifts, and after adding some more of H2O shifts will become smaller and smaller). Bands of TICT states and LE might overlap. It is even possible that LE goes almost completely to TICT at rt if barrier is small enough. Do some simple calculations to get the general idea about the potential energy surfaces (simple calculations might and might not help, depends from one system to another... it is much more difficult when you have CT/TICT chromophores to be honest...).
I am not actually going for hydrogen bonding effect but doing aggregation studies. My molecules are not soluble in water, methanol or ethanol so they can just act as bad solvent or will promote aggregation at their higher ratio in mixture.As i keep on adding water my molecules begin to form aggregates (above 60% water). But upto 60% water, my molecules are showing similar fluorescence behavior (decreasing intensity as the polarity of medium is increasing) but the decay time is showing different trend and that is the thing i want to know, why?
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