Under basic conditions, the electron-deficient 3-nitro-3'-bromo-6,6'-difluorodicyanobiphenyl undergoes an uncom-mon nucleophilic aromatic substitution (S_NAr) reaction with 1 equiv. of carbazole, in which the nitro group on the ring is replaced by a 9-carbazolyl group, to afford compound 1. In contrast, in the same reactions with 2 equiv. of carbazole and di-tert-butylcarbazole, respectively, the nitro group and the fluorine atom on the same benzene ring are substituted by 9-carba-zolyl or 9-di-tert-butylcarbazolyl to produce 3',6'-bis(9H-carbazol-9-yl)-[1,1'-biphenyl]-2,2'-dicyanide (2a) and 3-bromo-6-fluoro-3',6'-bis(3,6-di-t-butyl-9H-carbazol-9-yl)-[1,1'-biphenyl]-2,2'-dicyanide (2b). Compound 2a undergoes a Pd-catalyzed Suzuki coupling with 3-formylphenylboronic acid to give 3,6-bis(9H-carbazol-9-yl)-6'-fluoro-3''-formyl-[1,1':3',1''-terphenyl]-2,2'-dicyanide (3). The structures and compositions of the products have been studied using spectroscopic methods, elemental analysis (2b), X-ray diffraction (2a and 3), as well as density functional theory (DFT) calculations, and the mechanism of the S_NAr reaction is discussed. Investigations on the emission properties show that compounds 1, 2a, 2b, and 3 exhibit thermally activated delayed fluorescence (TADF) properties. These results provide new ideas for the design and synthesis of asymmetric biphenyl TADF compounds.

Key words: biphenyl, nucleophilic aromatic substitution (S_NAr), electron-deficient, thermally activated delayed fluorescence (TADF)