Decay time of a molecule having charge transfer character shows decrease in life time with increasing amount of water in THF/Water system. Quantum yield also decrease along with red shift. But the molecule shows longer decay time with increasing solvent polarity (Tol.
As the water content increases, the first hydration shell of the molecule (where dynamical slow-down is experienced) gets filled-up and any additional water molecules adopt quasi bulk-like character. Dynamical analysis that include both hydration and these quasi bulk water molecules will tend to yield smaller decays times.
Thank you Dr John. Can you please provide me with some reference papers.
Have you observe the absorption band? Actually THF/water mixture may form aggregation also. It will eventually affect the quantum yield and life time.
Santanu sir i am actually doing aggregation studies.After aggregation life time increases but before aggregation it is decreasing. Life time of ICT molecules usually increases with increasing polarity (as seen in different solvents) but it decrease with increasing water fraction. I have some other ICT molecules also, but they show increased life time with increasing water fraction.
It is probably due to the different molecular arrangement in aggregated form for different ICT molecules. You should check the molecular structures as well as substituent pattern. May be it gives you better idea about the molecular arrangement in aggregated form. For your present molecules may be charge transfer is more prominent in aggregated form.
life time in aggregate state can be explained easily but the problem is the before aggregation life time.
Is it possible that the water molecule is simply a fluorescence quencher in your system?
A red shit of a CT band as solvent polarity incenses in normal but your solvent cant be a quencher or else you will have problems with a change in emission caused by the solvent.
Just an idea....
there is possibility of TICT in my molecule which is probably quenching the fluorescence, but why the life time is decreasing with increasing water content.
if it is a dynamic quenching process the lifetime will change as a function of the quencher concentration. look up Stern-Volmer plots
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