Synthesis and Aggregation of a Conjugated Helical Molecule

Abstract

Described are an improved method to synthesize helicenebisquinone 1 and an efficient method to resolve its enantiomers and those of other helicenebisquinones by separating derived camphanate esters. The union of p-benzoquinone and the bis(triisopropylsilylenol ether) of a 2,7-diacetyl-4,5-dialkoxynaphthalene gives the helicene skeleton in 56% yield. Molecules of nonracemic 1 aggregate when their dodecane solutions are concentrated to 5 × 10-4 M or more. Chloroform dissociates the aggregates. Aggregation is characterized by enhanced circular dichroisms and g values, red-shifted UV−vis absorptions, increased specific rotations, increased light scattering at an absorption frequency, and, as reported previously, fluorescence emissions that shift to the red, 1H NMR resonances that shift upfield, and organization of the pure material into fibers. The CD and UV−vis absorption spectra of spin-coated films are similar to those of concentrated solutions in dodecane, but the g values are higher. The specific rotatio...