Optical properties and electronic structure of terminal group-perturbed ethynyl-linked dendrimers

Three ethynyl-linked dendrimers with terminal carbazole, namely the electronic donor–acceptor compounds 1–3, the symmetric compound 9-(3-(2-(1-(2-(3-(9Hcarbazol-9-yl)-9-p-tolyl-9H-carbazol-6-yl)ethynyl)pyren-6-yl)ethynyl)-9-p-tolyl-9H-carbazol-6-yl)-9H-carbazole (1), the unsymmetric compounds 6-pyren-1-ylethynyl-9-p-tolyl-9H-[3,9′]bicarbazolyl (2) and 3,6-di-tert-butyl-9-(4-pyren-1-ylethynyl-phenyl)-9H-carbazole (3), respectively, were well investigated by experimental and theoretic methods. Good reversible oxidation and reduction processes of these compounds were observed, and the corresponding HOMO and LUMO levels could be well tuned by the different terminal group, which was proved by the theoretical calculation. In addition, they showed bright blue-green emission in dichloromethane solution and in the solid state, and exhibited efficient solvatochromism, suggesting that their electron transition may be considered as π–π* transition, charge–transfer transition and the coeffect of the former two, respectively.