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Synthesis and Self-Association, Absorption, and Fluorescence Properties of Differentially Functionalized Hexakis(p-substituted-phenylethynyl)benzenes

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journal contribution
posted on 02.04.2004, 00:00 by Kenji Kobayashi, Norifumi Kobayashi
The dual Sonogashira coupling reactions of 1,3,5-tribromo-2,4,6-triiodobenzene with p-X-phenylacetylene followed by another p-Y-phenylacetylene (X, Y = OSiMe2Bu-t or CO2Et) produced a series of differentially functionalized hexakis(p-substituted-phenylethynyl)benzenes with D3h symmetry (3h:  1,3,5-X-2,4,6-Y) and C2v symmetry (3g,i:  1,2,3,5-X-4,6-Y; 3f,j:  1-X-2,3,4,5,6-Y). In a similar manner, 1,3,5-tris(p-X-phenylethynyl)-2,4,6-tris(p-Y-phenylethynyl)benzenes and 1,2,3,5-tetrakis(p-X-phenylethynyl)-4,6-bis(p-Y-phenylethynyl)benzenes (3l:  X = OSiMe2Bu-t, Y = NO2; 3m,n:  X = N(n-octyl)2, Y = NO2; 3o,p:  X = N(n-octyl)2, Y = CH(OCH2CH2O); 3q,r:  X = N(n-octyl)2, Y = CHO; 3s,t:  X = N(n-octyl)2, Y = CHC(CN)2) were prepared. Compounds 3 with electron-withdrawing groups self-aggregated by a π−π stacking interaction and solvophobic effect. In the absorption and fluorescence spectra of 3, λmax(abs) and λmax(em) showed red shifts as the donor−acceptor dipole at the end functional groups of the para position was increased. In the absorption spectra, λmax(abs) showed red shifts upon increasing the number of combination of electron-donating and -withdrawing groups on the diagonal line in a molecule, whereas λmax(em) in the fluorescence spectra exhibited red shifts upon decreasing the molecular symmetry.