Dendritic Triphenylmethylium and Tetraphenylmethane Compounds

Abstract

Stilbenoid dendrimers possessing a methanol or methane core are prepared using Wittig-Horner reactions. The dendritic tris(stilbenyl)carbinols 3a-c are converted into the corresponding methylium salts 3'a-c on treatment with trifluoroacetic or tetrafluoroboric acid. The extended cross-conjugation in the dendritic methylium ion 3'c results in a long-wavelength absorption (λ max = 697 nm) whereas the conjugated model systems 3'a and 3'b are redshifted (λ max = 772 nm and 748 nm, respectively). Charge delocalization in the cations is evident from the low-field shifts of the 13 C NMR signals. In contrast to the dark-blue dyes 3'a-c, the tris(stilbenyl)carbinols and tetrakis(stilbenyl)methane derivatives 3a-c and 7 exhibit long-wavelength absorption bands in the UV region.