Diastereodifferentiation of novel naphthalene dyads by fluorescence quenching and excimer formation.

Four new bichromophoric naphthalene dyads in form of diastereomeric pairs are synthesized and photophysically characterized. For a closely related group of compounds (NAP-NAP, MNAP-NAP, MNAP-MNAP), systematic variation of the urea linker led to the observation of intramolecular fluorescence quenching for tertiary urea, but not for secondary urea. Chiral information contained in the dyads has an impact on the efficiency of this process. Furthermore, for the case of (R,R)-MNAP-MNAP, excimer formation in the pre-organized dyad was noted, while being absent in the corresponding (R,S) diastereomer. These differences in photophysical behavior are ascribed to the geometry of the linker and to the chiral information contained in the diastereomeric compounds. Other dyads, such as NPX-NPX, included naproxen as the chromophore. For these compounds strong excimer emission is obtained, however, only very small diastereodifferentiation is observed for the two investigated stereoisomers.