Oligotriarylamine-Extended Organoboranes with Tunable Electron-Donating Strength by Changing the Number of Donor Units.

Triarylborane (Ar 3 B) and triarylamine (Ar 3 N) have been widely employed to construct electronically different donor-acceptor (D-A) systems. Herein, we describe a series of A-D-A-type luminescent organoboranes L-B 2 N n ( n = 1, 3, 5) that show an increased number of Ar 3 N units as electron donors and two terminal Ar 3 B as acceptors. When the Ar 3 N moieties were extended from one to five units, their electron-donating strength was gradually enhanced and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps could also be tuned, which was further reflected in the red-shifted emissions from blue (λ em = 458 nm) to orange (λ em = 595 nm) with a decrease in E gap(elect) from 3.19 to 2.61 eV. L-B 2 N 5 showed a huge Stokes shift (∼14 057 cm -1 ) and a considerably bright emission with an enhanced solid-state quantum efficiency (Φ S = 98%) compared with the other members. L-B 2 N 3 and L-B 2 N 5 exhibited aggregation-induced emissions (AIEs), and an apparent solvatochromic shift was also observed in the emission spectra as the solvent was changed from hexane to tetrahydrofuran (THF) (430 → 595 nm). In addition, the donor-acceptor charge-transfer character in these organoboranes caused a thermally responsive emission over a broad range.