Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 11, Issue 11, Pages 10768-10776Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.8b21568
Keywords
dihedral angle; thermally activated delayed fluorescence; organoboron emitter; deep-blue color; organic light-emitting diode
Funding
- Ministry of Science and Technology, Taiwan [MOST 107-2113-M-007-004]
- Instrumentation Center of Taiwan
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Five emitters CzAZB, tBuCzAZB, tmCzAZB, dmAcAZB, and PxzAZB based on dibenzo-1,4-azaborine as the electron acceptors and two identical amine groups as the donors were designed and synthesized. The dihedral angles between the planes of dibenzo-1,4-azaborine acceptors and amine-based donors greatly affect the thermally activated delayed fluorescence (TADF) property of these materials. A simple concept steric switching is introduced to predict whether the emitter possesses TADF property. CzAZB and tBuCzAZB, with very high photoluminescence quantum yields (PLQYs) but small dihedral angles, do not show TADF. In contrast, tmCzAZB reveals a PLQY of only 56% but with a large dihedral angle due to the presence of two methyl groups at Cl and C8 of the carbazole groups, the steric switching operates, and the compound shows TADF property with a deep-blue color having CIE coordinates of (0.14, 0.15). In a similar manner, in dmAcAZB and PxzAZB with high PLQYs and large dihedral angles between the donor and acceptor planes, the TADF steric switch readily operates to achieve device external quantum efficiencies as high as 20.8 +/- 1.2 and 27.5 +/- 1.9% with blue and green emissions, respectively.
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