Structurally rigid and optically active dendrimers

Novel rigid and optically active dendrimers containing cross-conjugated units are synthesized from the coupling of phenylacetylene-based dendrons with an optically pure diacetate of 4,4',6,6'-tetrabromo-1, 1'-bi-2-naphthol. The UV and fluorescence spectroscopic studies demonstrate that there is a very efficient energy migration from the cross-conjugated dendrons to the center core, leading to greatly enhanced fluorescences at higher generations. This is the first example of an efficient energy migration conducted in an optically pure dendritic system, which is potentially useful in developing an enantioselective fluorescence sensor. The generation 2 dendrimer has been used to catalyze the asymmetric reaction of diethylzinc with aldehydes and has shown high enantioselectivity in the presence of Ti(O-i-Pr)(4).