I measured the Nano-second transient absorption spectroscopy and singlet oxygen emission for a terephthalate based system (attached), in ACN it shows weak fluorescence emission intensity, strong triplet-triplet transient absorption (lifetime in micro second) and strong singlet oxygen emission as well. Same systems in toluene, shows strong fluorescence emission but no triplet-triplet absorption and singlet oxygen emission, i was wondering what might be possibly leading to such a different behavior in these two solvents?
I agree with the statements above.
However I may see another potential problem. Based on the structure of the compound that you provided I am assuming that you are pumping (exciting) your sample in the UV region of the electromagnetic spectrum.
Based on that I am wondering, is is possible that when you use toluene that you are exciting your solvent and that you are seeing a signal from you solvent as well as the sample. Maybe one signal blocks the other. (also a stimulated emission can sometimes be seen for toluene by transient absorption).
Acetonitrile absorbs much farther in the UV thank toluene does so it may bot cause re same problem.
You could always tru a solvent like Dichloromethane (DCM) which is far less polar than ACN but still absorbs far in the UV.
Good luck!
There is a big difference in polarity of the solvents: toluene has a dielectric constant of 2.4 and acetonitrile of 37.5. Depending on the dipole moment of the excited states, this can have a big effect on the relative position of the excited states.
Perhaps the solvent polarity would influence the singlet-triplet splitting and hence the intersystem crossing rate?
http://www.sciencedirect.com/science/article/pii/0009261489850985
Then maybe in toluene isc is slower, leading to stronger fluorescence.
I agree with the statements above.
However I may see another potential problem. Based on the structure of the compound that you provided I am assuming that you are pumping (exciting) your sample in the UV region of the electromagnetic spectrum.
Based on that I am wondering, is is possible that when you use toluene that you are exciting your solvent and that you are seeing a signal from you solvent as well as the sample. Maybe one signal blocks the other. (also a stimulated emission can sometimes be seen for toluene by transient absorption).
Acetonitrile absorbs much farther in the UV thank toluene does so it may bot cause re same problem.
You could always tru a solvent like Dichloromethane (DCM) which is far less polar than ACN but still absorbs far in the UV.
Good luck!
Adam, your point is well taken and while doing measurements that was confirmed that what we are seeing is not from solvent. I was exciting these systems at 300nm with laser pulse, you guess is right.
I suggest you to record your fluorescence, lifetime, and ns laser measurements in more solvents with different polarities e.g., THF, Dichlorobenzene, DMF. This will help to confirm if this change arise from the solvent polarity or something else. Good luck.
I suggest you carry out this experiment in series of polar aprotic solvent like as well as non polar solvent (at least five each). If this is happened again, there is solvent polarity effect.
file:///C:/Users/Anil/Downloads/Lakowicz-cap1.pdf
Thanks for suggestion on choosing different polarity solvents. However, solubility of these systems is very limited which makes the list of solvents very short.
Luminescent intensity dependence upon polarity solvents may be due to the charge transfer complex formation. Did you observe the red shift of luminescene band in ACN? Besides, thermodynamic strength of solvent influence on luminescent intensity.
http://kemia.unideb.com/pr/Principles%20of%20Fluorescence%20Spectroscopy.pdf
I would suggest dimerization of your compound in toluene?
The observed behavior would be expected if the intersystem crossing efficiency was much higher in acetonitrile than in toluene. Thus in toluene one would expect to see fluorescent emission from singlet terepthalate and in acetonitrile triplet terephthalate would be the predominant excited state which would excite oxygen to its singlet state. Very likely this is related to the higher polarity of acetonitrile but experiments with other polar solvents are needed to confirm this hypothesis.
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