As the phenomena is taking place after the absorption of photon or you can say it is an excited state phenomena, so probably it may not be possible to use it in uv-visible studies. As far as mechanism is concerned, the following attachment may be of some help to you.

For my knlowedge you cannot use PeT in Uv-vis spectroscopy, as it regards a phenomena of quenching of an excited state, a process which can be followed by a  spectrofluorimeter, but not with a UV-vis absorption spectrophotometer

Hi Mohamed,

Yes, the previous answers are correct, a PET mechanism involves dyes in their excited state and can only be measured by fluorescence techniques. However, I'd like to point out that, if you do see changes happening in your UV/vis absorption studies following the addition of your target anion to your probe, then you should consider the presence of other mechanisms as well. The PET is just one 'sensing' mechanism among others, like Charge Transfer or Energy Transfer processes etc. You should find lots of literature I'd recommend doing a UV/Vis titration in order to mechanism. If you find and an isosbestic point (where the different lines of the spectra cross) then you should use this wavelength for future fluorescence measurements to exclude intensity changes resulting from an increased absorption.

http://pubs.acs.org/doi/abs/10.1021/cr960386p

I've made the titration and I found that the isosbestic point as mentioned. But, I didn't conducting any fluorescence study, so, does it means I can't assume that the mechanism of the receptor as PET mechanism?