Star-Shaped Push-Pull Compounds Having 1,3,5-Triazine Cores

The 1,3,5‐triazines 9–11 having OPV chains in the 2‐, 4‐ and 6‐position represent star‐shaped compounds which exhibit strong push‐pull effects. Their long‐wavelength absorption S0 → S1 is characterized by an intramolecular charge transfer (ICT) from the dialkylamino group as electron donor D via the conjugated chain to the 1,3,5‐triazine core as electron acceptor A. Protonation of the dialkylamino group removes the donor capability, whereas protonation of the 1,3,5‐triazine ring enhances the acceptor strength. Thus, the prevailing protonation site has a crucial influence on the push‐pull effect and the ICT. The transition energies ΔE (S0 → S1) pass through a minimum for the second generation 10 in the electroneutral series 9–11; on the contrary they pass through a maximum for 10b in the protonated series 9a, 10b, 11b. These unexpected results are explained by the superposition of different effects, namely the extension of the conjugation from 9 to 11, the decreasing ICT for growing distances of D and A, the aggregation, and the positions of the protonation in the presence of increasing amounts of CF3COOH. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)