Light blue and green thermally activated delayed fluorescence from 10H-phenoxaborin-derivatives and their application to organic light-emitting diodes

Abstract

New luminescent compounds consisting of 10H-phenoxaboryl group as an electron-accepting unit and carbazole (9), 9,9dimethylacridane (10), or phenoxazine (11) as an electron-donating unit have been synthesized. Compounds 10 and 11 showed thermally activated delayed fluorescence (TADF) with light blue and green emissions, respectively, with very high PL quantum yields (PLQYs), however, compound 9 exhibited only a prompt emission and no delayed component. Photoluminescence studies and quantum chemical calculation based on density functional theory (DFT) and timedependent density functional theory (TD-DFT) revealed that in comparison with compound 9, HOMO and LUMO for compounds 10 and 11 are well separated, resulting in lowering ∆EST and effective reverse intersystem crossing (RISC) between a lowest triplet excited state (T1) and a lowest singlet excited state (S1). Organic light-emitting diodes (OLEDs) using compounds 10 and 11 exhibited light blue and green emissions with very good maximum ηext of 15.1% and 22.1%, respectively.

Thermally Activated Delayed Fluorescence Emitters for Deep Blue Organic Light Emitting Diodes: A Review of Recent Advances

“…Triarylboron derivatives are also characterized by their bulkiness and these materials are also strong electron withdrawing groups. Interestingly, triarylboron derivatives have often been opposed to donors, such as 9,10-dihydroacridine, triphenylamine of the popular carbazole group [91][92][93]. Some of them even show CIE coordinates of (0.15, 0.09) and (0.15, 0.08) for the PL of emitters in toluene but none of them gave OLEDs with colour coordinates satisfying or being close to the NTSC blue standard of CIE coordinates (0.14, 0.08) [94].…”

Pyridyl Pyrrolide Boron Complexes: The Facile Generation of Thermally Activated Delayed Fluorescence and Preparation of Organic Light‐Emitting Diodes

“…On this basis,w ep repared as eries of novel boron complexes bearing electron deficient pyridyl pyrrolide and electron donating phenylcarbazolyl fragments or triphenylamine.The new boron complexes show strong solvent-polarity dependent chargetransfer emission accompanied by as mall, non-negligible normal emission. We report herein an ew approach to the TADF emitters.T he boron-containing fragment was chosen for its high rigidity and good electronaccepting ability, [7] which then serves as ah ub for anchoring both the donor and acceptor groups without affecting their electronic properties.Consequently,under solution-processed conditions, [8] we demonstrate for the first time the boroncomplex-based OLEDs,t hese give external EL quantum efficiencies (h ext )o f1 3.6 %, ar esult attributed to the TADF characteristics.These organoboron compounds inherited the traditional designs of pyrazolate-and pyrrolide-substituted boron complexes, [9] except for incorporation of electron-donating triphenylamine or carbazolyl fragments. [2] However,the issue of costs becomes amajor obstacle for these phosphors.O ne promising approach is to employ am etal-free luminophore that shows efficient thermally activated delayed-fluorescence (TADF).…”

“…[2] However,the issue of costs becomes amajor obstacle for these phosphors.O ne promising approach is to employ am etal-free luminophore that shows efficient thermally activated delayed-fluorescence (TADF). We report herein an ew approach to the TADF emitters.T he boron-containing fragment was chosen for its high rigidity and good electronaccepting ability, [7] which then serves as ah ub for anchoring both the donor and acceptor groups without affecting their electronic properties.Consequently,under solution-processed conditions, [8] we demonstrate for the first time the boroncomplex-based OLEDs,t hese give external EL quantum efficiencies (h ext )o f1 3.6 %, ar esult attributed to the TADF characteristics. [4] This tactic not only promotes the singlet-triplet mixing, but also facilitates the reverse intersystem crossing from T 1 to S 1 and hence harvesting the delayed fluorescence via thermal activation.…”

“…[5] As ar esult, numerous systems that displayed notable TADF behaviors have been investigated, the associated electron transfer properties can be categorized being intra-and intermolecular type of donor-acceptor composites; the intermolecular type is ascribed to the exciplex formation. We report herein an ew approach to the TADF emitters.T he boron-containing fragment was chosen for its high rigidity and good electronaccepting ability, [7] which then serves as ah ub for anchoring both the donor and acceptor groups without affecting their electronic properties.Consequently,under solution-processed conditions, [8] we demonstrate for the first time the boroncomplex-based OLEDs,t hese give external EL quantum efficiencies (h ext )o f1 3.6 %, ar esult attributed to the TADF characteristics. We report herein an ew approach to the TADF emitters.T he boron-containing fragment was chosen for its high rigidity and good electronaccepting ability, [7] which then serves as ah ub for anchoring both the donor and acceptor groups without affecting their electronic properties.Consequently,under solution-processed conditions, [8] we demonstrate for the first time the boroncomplex-based OLEDs,t hese give external EL quantum efficiencies (h ext )o f1 3.6 %, ar esult attributed to the TADF characteristics.…”

Recent progress of green thermally activated delayed fluorescent emitters

“…Carbazole, acridine, and phenoxazine were the donor units of the (11) with the phenoxaborin acceptor, respectively. The weak carbazoledonor-based compound 9 did not show any TADF property, while the strong acridine-and phenoxazine-based compounds 10 and 11 exhibited efficient TADF emission, along with high EQE values of 15.1 and 22.1%, respectively [73]. In the case of the compounds 10 and 11, the steric hindrance between the phenoxaborin acceptor and the phenyl linker induced the distortion of the molecular structure and a strong CT character.…”