Synthesis, characterization, and photophysical properties of chiral dendrimers based on well-defined oligonaphthyl cores

Chiral dendrimers based on (R)-1,1′-bi-2-naphthyl and its oligomeric (R,R)-tetranaphthyl and (R,R,R)-hexanaphthyl chiral cores cores and Fréchet-type aryl-ether dendrons were synthesized using the Fréchet conditions or deprotonation of the chiral cores with NaH followed by nucleophilic attack on benzyl bromide moieties of the dendrons. These chiral dendrimers were characterized by ¹H and ¹³C{¹H} NMR spectroscopy and mass spectrometric analyses. The UV absorption of the chiral dendrimers steadily increases as the generation grows. These dendrimers show significantly enhanced fluorescence compared to (R)-1,1′-bi-2-naphthol, and the fluorescence intensity increases as the generation grows for most of the dendrimers. Both CD and optical rotation data suggest that the increased steric bulk of the dendrons leads to larger dihedral angles between the naphthyl rings through their 1,1′-linkages. The absolute configuration of the chiral dendrimers remains the same as their chiral cores.