Photophysical Recognition of Chiral Surfaces

We report that R andS Quenchers [(R)-(+)- and (S)-(-)-N,N-dimethyl-1-phenethylamine, RQ and SQ] recognize differently an R excited-state chiral surface (silica derivatized with (R)-(-)-1,1-binaphthyl-2,2^'-dihydrogen phosphate, RS). This is revealed by a ~30% difference in Stern-Volmer constants between RQ/RS and SQ/RS. A similar recognition difference was obtained between these quenchers and the corresponding S-(+) surface. The surface derivatization enhances the chiral recognition; in solution, no difference between the constants was observed. It is suggested that what we believe to be the first observation of a photophysical recognition of a chiral surface can be explained in terms of an increase in the relative weight of an exciplex formation (over ion-pair formation) quenching route and in terms of the decrease in the dimensionality of the quenching process.