Novel Triindolo-Truxene Derivatives: Design, Synthesis, and FineTuning of Electronic Properties and Molecular Assembly through Molecular Engineering
Triindolo-truxene, a C3-symmetric molecule with a large π-conjugated plane, has six methylene carbon atoms and three aromatic carbon atoms which can be facilely functionalized. Herein, we introduce butyl, carbonyl, cyano, and/or malononitrile groups into six methylene carbon atoms (6-, 14-, 22-, or 8-, 16-, 24-positions) and/or three aromatic carbon atoms (2-, 10-, and 18-positions) of triindolo-truxene to produce eight derivatives. Their photophysical and electrochemical properties, and molecular assembly can be effectively modulated by substituents and substitution patterns. Incorporation of electron-deficient groups led to red shifts in both the absorption and the emission of these derivatives, and also lowered their HOMO and LUMO levels. Different substitution patterns resulted in the different intramolecular donor-acceptor interactions. The substitutions of electron-deficient groups at 6-, 14-, and 22-ethylene carbon atoms led to the intramolecular charge transfer from the fluorene arms to the truxene core, whereas the corresponding substitutions at 8-, 16-, and 24-methylene carbon atoms resulted in the converse intramolecular charge transfer from the truxene core to the fluorene arms. Their molecular packing in single crystals and molecular aggregation in solutions are also manipulated by their substituents and substitution patterns. This work provides a straightforward strategy to alter the properties of triindolo-truxene.