Carbazol-benzothiadiazole based D-A-D mesogens: Self-assembly and photophysical characteristics

By:Mo, Miaoshui ; Guo, Zilong ; Chen, Shibo ; Ma, Tao ; Duan, Yuantang ; Yang, Yu ; Cheng, Xiaohong

Journal  of Molecular Liquids

DOI：https://doi.org/10.1016/j.molliq.2024.124619

Published：2024-05-01

Abstract

Three carbazole(C)-benzothiadiazole(B) based D -A -D mesogens CBC/n (n = 12, 16) and CTBTC/16 containing terminal N-trialkoxylbenzyl carbazoles at both side of central benzothiadiazole core have been designed and synthesized. By inserting thiophene (T) unit between B and C units, the rigid core was elongated and the molecular conformation changed from twist to planar one, thereby the liquid crystal (LC) phase changed from SmA to Col/hex phase. Such molecular packings caused by inserting T unit remained in their organogels formed in organic solvents. The long -core compound CTBTC/16 containing T unit with a more planar and tighter pi-pi packing structure showed a significant optical red shift and a stronger intramolecular charge transfer (ICT) effect than the short -core compounds CBC/n without thiophene unit. These compounds are all strong fluorescent in solution with fluorescence quantum yields (OF) ranging from 38 % to 86 %. But their solid fluorescence quantum yields (OFs) differ greatly with values of 43 %, 11 % and 0.6 % for CBC/12, CBC/16 and CTBTC/16 respectively. Further, short core compound CBC/12 with the highest OFs showed different OFs in its three different solid aggregation states. The application of the short twist core compound CBC/12 as white light -emitting diodes (LEDs) has been realized. The influence of the thiophene unit as well as the terminal alkyl chain length on selfassembly and OFs of these compounds is discussed.