Star-shaped compounds having 1,3,5-triazine cores

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-->S-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 breakdown of the ICT. Thus, the yellow compound 1d first becomes violet and then colorless upon the addition of trifluoroacetic acid. In neutral solution, the long-wavelength absorption of the series 1f, 2b, 3, and 4 converges lambda(x) = 427 nm (with an effective conjugation length n(ECL) = 7). The absorption of the corresponding protonated compounds approaches lambda(infinity) = 515 mn (nECL = 6). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).