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 red-shifted (λ_max = 772 nm and 748 nm, respectively). Charge delocalization in the cations is evident from the low-field shifts of the ^¹³C 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.

Key words

stilbene - charge delocalization - Wittig-Horner reaction - olefination - dendrimers - dyes

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12

Due to the equilibration, the intensity of the band depends on the ratio of 3/CF₃COOH. The λ_max values are somewhat blue-shifted by a high CF₃COOH concentration. We assign this effect to a decrease of push-pull character due to increasing protonation of the alkoxy groups.