Issue 39, 2022

Synthesis, self-assembly and optical properties of some rigid π-bridged triphenylene dimers

Abstract

The synthesis of an exclusive family of liquid-crystalline dimers consisting of two protomesogenic triphenylene moieties connected via a rigid, π-conjugated bridge, and the study of their mesomorphous, gel self-assembly and optical properties as a function of the nature of the bridge are reported. Various triphenylene bridged dimers were successfully prepared by either palladium-catalyzed Suzuki–Miyaura cross-coupling between pentakis(alkoxy)triphenylene nonaflates and various commercially accessible aryldiboronic acids (as bridges) or by FeCl3-promoted Scholl oxidative homo-coupling of thiophene/thienothiophene/furan-containing pentakis(alkoxy)triphenylene derivatives. All linear dimers are mesomorphous, and self-organize into large multi-columnar rectangular superlattices, with columnar pairs arranged according to a chevron-like pattern, as deduced from SWAXS and supported by STM. At high temperature, most compounds also display a nematic columnar mesophase (NCol), easily recognized by characteristic optical textures. The transition temperature and mesophase ranges show a high dependency on the bridge nature and, to a lesser extent, on the chain-lengths around the triphenylene moieties. The sole kinked bridged-dimeric homolog of this series exhibits a single, room-temperature hexagonal mesophase (Colhex), as do the monofunctionalized triphenylene precursors, whereas the dimeric triphenylene with no bridge is not mesomorphous. UV-visible absorption and fluorescence emission spectra were measured in both solvents and thin films. The π-conjugated bridged-dimers exhibit emission spanning from 400–700 nm, thus covering the full visible-light range, whose emission maxima are obviously influenced by the chemical nature of the bridge. Furthermore, fluorescence quantum yields as high as 64% were measured for some of them. DFT theoretical computing calculations fully support the experimental measurements. Most dimers also form gels in cyclohexane and emit blue-to-orange light when irradiated by UV light; the corresponding xerogels revealed that their gelation ability results from the 3D morphology of entangled ultra-long and thin microfibers. The facile synthesis of these unique, multifunctional rigid discotic dimers, their rich mesomorphism, strong gelation ability and fine-tuned photophysical properties make these materials very attractive for the active field of organic electronics.

Graphical abstract: Synthesis, self-assembly and optical properties of some rigid π-bridged triphenylene dimers

Supplementary files

Article information

Article type
Paper
Submitted
10 Jūn. 2022
Accepted
01 Sept. 2022
First published
02 Sept. 2022

J. Mater. Chem. C, 2022,10, 14453-14470

Synthesis, self-assembly and optical properties of some rigid π-bridged triphenylene dimers

H. Lin, K. Zhao, M. Jing, X. Long, K. Zhao, P. Hu, B. Wang, P. Lei, Q. Zeng and B. Donnio, J. Mater. Chem. C, 2022, 10, 14453 DOI: 10.1039/D2TC02441A

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