The 1,3,5-triazine derivatives 1−4 having styryl or higher oligo(phenylenevinylene) chains in the 2-, 4-, and 6-positions represent star-shaped push-pull compounds. Alkoxy or dimethylamino groups on the peripheral benzene rings, which act as electron donors, and the central 1,3,5-triazine ring, which acts as an electron acceptor, cause intramolecular charge transfer (ICT) to occur in the absorption S 0 ǞS 1 . Protonation of the 1,3,5-triazine core enhances the effect, as demonstrated by a bathochromic shift; a secondary protonation on the dimethylamino groups, however, leads to the
Keywords: Oligomers / Conjugation / Push-pull effect / Chromophores Five oligo(2,5-thienyleneethynylene) series (OTE, n = 1-5), namely the push-pull substituted compounds 1b-5b and 1c-5c, the purely donor substituted compounds 1a-5a and two precursor series with protected and deprotected ethynyl endgroups, respectively, were obtained by a convergent synthetic strategy. The extension of the conjugated chromophores in the donor-acceptor OTE (DAOTE) series is super-
The fluorescence quantum yields φ F (n) of oligo[2,5-bis(propyloxy)-1,4-phenylenevinylene]s (1b) reach for the trimer (n = 3) in solution a maximum of 86 %, which is almost twice as high as for the monomer (n = 1) and the octamer or undecamer (n = 8, 11). The latter represent the convergence limit of 46 %. 4-Mono-, 3,4-di-or 3,4,5-trisubstituted terminal phenyl rings in the trimers 6a-f do not lead to calamitic or phasmidic liquid crystals; however, 2,3,4-trisubstitution with
IntroductionDue to their interesting electrical, optical and optoelectronic properties, oligo-and poly(1,4-phenylenevinylene)s [OPV and PPV] are a highly attractive class of compounds in organic chemistry and materials science.[1] Already with n Ͼ 3, the parent system 1a is insoluble in organic solvents, so solubilizing alkyl or better alkoxy side chains have to be introduced. Some time ago we prepared the series 1b (n = 1-8, 11, 15) with 2,5-dipropoxy-substituted phenyl rings (Scheme 1). [2][3][4] Increasing numbers n of repeating units in conjugated oligomers lead for various properties P to limiting values which can be matched by the corresponding polymer. This approach can be monotonous, as for the λ max values of absorption and fluorescence of 1b, [2][3][4] but the approach P(n) Ǟ P ϱ can also pass for a certain number nЈ through a maximum and/or a minimum. [1l] An important example is given for the electroluminescence efficiency of 1b which reaches a maximum for n = 3. [5] Earlier studies indicated that the photoluminescence quantum yields φ F should also have a maximum for a certain repeat number n of 1b since φ F = 0.82 for the dimer n = 2 measured in CH 2 Cl 2 is much higher than φ F of a long oligomer chain (φ F ≈ 0.5 for n = 11). [6,7] We determined now the fluorescence quantum yields φ F (n) for the whole series 1b (n = 1-8, 11) and tried to obtain liquid crystals (LC) for those oligomers that have the highest φ F value.[
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