Liu Guan-Cheng, Huang Tzu-Hao, Wang Hao-Wen, Hsu Chao-Hsien, Chou Pi-Tai, Hung Wen-Yi, Wong Ken-Tsung
Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
Department of Optoelectronics and Materials Technology, National Taiwan Ocean University, Keelung, 202, Taiwan.
Chemistry. 2023 Apr 13;29(21):e202203660. doi: 10.1002/chem.202203660. Epub 2023 Mar 8.
Two new 2,3-dicyanopyrazinophenanthrene-based acceptors (A) p-QCN and m-QCN were synthesized to blend with a donor (D) CPTBF for the exciplex formation. The energy levels of p-QCN and m-QCN are modulated by the peripheral substituents 4- and 3-benzonitrile, respectively. Exciplex-forming blends were identified by the observation of the red-shifted emissions from various D : A blends with higher ratios of donor for suppressing the aggregation of acceptor. The two-component relaxation processes observed by time-resolved photoluminescence support the thermally activated delayed fluorescence (TADF) character of the exciplex-forming blends. The device employing CPTBF : p-QCN and (2 : 1) and CPTBF : m-QCN (2 : 1) blend as the emitting layer (EML) gave EQE of 1.76 % and 5.12 %, and electroluminescence (EL) λ of 629 nm and 618 nm, respectively. The device efficiency can be further improved to 4.32 % and 5.57 % with CPTBF : p-QCN and (4 : 1) and CPTBF : m-QCN (4 : 1) as the EML, which is consistent with their improved photoluminescence quantum yields (PLQYs). A new fluorescent emitter BPBBT with photoluminescence (PL) λ of 726 nm and a high PLQY of 67 % was synthesized and utilized as the dopant of CPTBF : m-QCN (4 : 1) cohost system. The device employing CPTBF : m-QCN (4 : 1): 5 wt.% BPBBT as the EML gave an EQE of 5.02 % and EL λ centered at 735 nm, however, the weak residual exciplex emission remains. By reducing the donor ratio, the exciplex emission can be completely transferred to BPBBT and the corresponding device with CPTBF : m-QCN (2 : 1): 5 wt.% BPBBT as the EML can achieve EL λ of 743 nm and EQE of 4.79 %. This work manifests the high efficiency near infrared (NIR) OLED can be realized by triplet excitons harvesting of exciplex-forming cohost system, followed by the effective energy transfer to an NIR fluorescent dopant.
合成了两种基于2,3-二氰基吡嗪并菲的新型受体（A）对-QCN和间-QCN，将其与供体（D）CPTBF混合以形成激基复合物。对-QCN和间-QCN的能级分别由外围取代基4-苯甲腈和3-苯甲腈调节。通过观察不同供体比例更高的D : A混合物中红移发射来识别形成激基复合物的混合物，以抑制受体的聚集。通过时间分辨光致发光观察到的双组分弛豫过程支持了形成激基复合物的混合物的热激活延迟荧光（TADF）特性。采用CPTBF : 对-QCN（2 : 1）和CPTBF : 间-QCN（2 : 1）混合物作为发光层（EML）的器件，外量子效率（EQE）分别为1.76 %和5.12 %，电致发光（EL）波长分别为629 nm和618 nm。以CPTBF : 对-QCN（4 : 1）和CPTBF : 间-QCN（4 : 1）作为EML时，器件效率可进一步提高到4.32 %和5.57 %，这与其提高的光致发光量子产率（PLQYs）一致。合成了一种光致发光（PL）波长为726 nm、PLQY高达67 %的新型荧光发射体BPBBT，并将其用作CPTBF : 间-QCN（4 : 1）共主体体系中的掺杂剂。采用CPTBF : 间-QCN（4 : 1）: 5 wt.% BPBBT作为EML的器件，EQE为5.02 %，EL波长以735 nm为中心，然而，仍存在较弱的残余激基复合物发射。通过降低供体比例，激基复合物发射可完全转移到BPBBT上，以CPTBF : 间-QCN（2 : 1）: 5 wt.% BPBBT作为EML的相应器件可实现743 nm的EL波长和4.79 %的EQE。这项工作表明，通过激基复合物形成共主体体系的三线态激子捕获，随后有效地将能量转移到近红外荧光掺杂剂上，可以实现高效近红外（NIR）有机发光二极管（OLED）。
