M-L charge transfer spectra - flurosecense spectroscopy by using Stern- Volmer equation to estabslish a PR- Ligand bi-molecur quenching . But for a better queching or bathochromic shift the amino-acids residues of protein should have an extended Pie-Pie# conjugation .

By mechanism, if you mean whether static or dynamic, then since you are getting a change in uv-spectra, you can infer the interaction is static i.e. the interaction is due to the formation of an associative complex of protein-ligand in the ground state. However, to be absolutely sure, you need to perform temperature varied steady state fluorescence or time-resolved fluorescence.

@prayasee Baruah, thanks!