Synthesis of Photoactive Dendrimers

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Dendrimers having a photochromic or a fluorescent chromophore in the core group were synthesized. The dendrimers were prepared by the convergent synthetic method developed by Frechet et al. Two equivalent of the bromo substituted dendric fragments were reacted with on equivalent 1,2-bis[2,4- dimethyl-5-(4'-hydroxyphenyl)thiophen-3-yl] perfluorocyclopentene or one equivalent 9,10- dihydroxymethylanthracene. The dendrimers were purified by flash chromatography and repetitive preparative TLC.We introduced bulky dendric groups into the dithienylethene in an attemp to change the ratio of two conformers, parallel and anti-parallel, and to increase the cyclization quantum yield. However, the dendric groups (even the third generation) did not alter the ratio of the two conformers. This result indicates that the free volume of the core part is large enough for the rotaion of the aryl groups. Fluorescence quenching of the core anthracene by N,N-diethylaniline was examined. Fluorescence quenching constants were dramatically decreased with the increasing generation. The quenching mechanism was studied in detail.