Donor–Acceptor Type of Fused-Ring Thermally Activated Delayed Fluorescence Compounds Constructed through an Oxygen-Containing Six-Membered Ring

Abstract

Nowadays, thermally activated delayed fluorescence (TADF) compounds with a fused-ring core skeleton are getting increasing research interest because of their use in high-performance organic light-emitting diodes (OLEDs). In this study, TADF compounds featuring a D–A-type fused-ring core skeleton are developed. The challenging compatibility of a planarized D–A arrangement and the TADF property is achieved through linking the D and A moieties with two oxygen atoms within a six-membered ring. Compared with a single-oxygen analogue possessing a flexible skeleton and a twisted D–A arrangement, these fused-ring compounds with higher skeleton rigidity show higher photoluminescence quantum yields and narrower emission spectra in toluene and in doped thin films. Their electroluminescent devices achieve high external quantum efficiencies (up to 19.4%), suggesting the potential of rarely achieved D–A-type fused-ring TADF systems to serve as high-performance emitters of OLEDs.

Progresses and Perspectives of Near-Infrared Emission Materials with “Heavy Metal-Free” Organic Compounds for Electroluminescence

“…The hybridization of energy level after donor and acceptor bonding could make the energy level of HOMO higher than that of donor, while the energy level of LUMO is lower than that of acceptor, resulting in abnormally small HOMO-LUMO separation. ( Figure 4 a) [ 68 , 69 ]. For example, Skene et al [ 70 ] synthesized azomethines compound with the maximal absorption and emission are 440 and 534 nm.…”

Design and Synthesis of a Y-Type Thioxanthone-Carbazole for the Application in Blue and Yellow Organic Light-Emitting Diodes

“…Particularly, emitters with donor-acceptor (D-A) structure were the most anticipated that have been developed rapidly and the internal quantum efficiency the-oretically achieved 100% through effective reverse intersystem crossing. [1][2][3][4] However, it is still a great challenge to establish the relationship between structure and performance. Nowadays, novel design strategies were proposed to optimize and improve the photophysical properties.…”

Highly Efficient Luminescence from a Red Thermally Activated Delayed Fluorescence Emitter with Flexible Conformation of Ancillary Groups

“…[2][3][4][5][6][7] The twisted donor-acceptor (DÀ A) configuration was typically applied for the construction of TADFs, where the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were separated largely due to the interrupted electronic communication between D and A units. Rigid donors [8,9] /acceptors [10,11] /bridges [12,13] and robust configuration [14] were usually employed in TADF to minimize the vibrational and rotational motions, thus reducing the non-radiative decay. For example, Zhang and coworkers reported a fused-ring (double-oxygen-linked) TADF [PA-(OO)Q] with higher rigidity, higher PLQY (53 %) and narrower emission spectra (FWHM of 74 nm) than the flexible (singleoxygen-linked) analogue [PA(O)Q with PLQY of 3 % and FWHM of 92 nm].…”

“…Rigid donors [8,9] /acceptors [10,11] /bridges [12,13] and robust configuration [14] were usually employed in TADF to minimize the vibrational and rotational motions, thus reducing the non‐radiative decay. For example, Zhang and coworkers reported a fused‐ring (double‐oxygen‐linked) TADF [PA(OO)Q] with higher rigidity, higher PLQY (53 %) and narrower emission spectra (FWHM of 74 nm) than the flexible (single‐oxygen‐linked) analogue [PA(O)Q with PLQY of 3 % and FWHM of 92 nm] [14] . It is worth mentioning that the rigid and planar D/A units could result in the energetically close‐lying charge transfer (CT) states and locally excited (LE) states, and the inefficient reverse intersystem crossing (RISC) from the lowest triplet state (T 1 ) to the lowest singlet state (S 1 ) can be improved by the intervention of 3 LE between 1 CT and 3 CT [15–18] .…”

“…For example, Zhang and coworkers reported a fused-ring (double-oxygen-linked) TADF [PA-(OO)Q] with higher rigidity, higher PLQY (53 %) and narrower emission spectra (FWHM of 74 nm) than the flexible (singleoxygen-linked) analogue [PA(O)Q with PLQY of 3 % and FWHM of 92 nm]. [14] It is worth mentioning that the rigid and planar D/A units could result in the energetically close-lying charge transfer (CT) states and locally excited (LE) states, and the inefficient reverse intersystem crossing (RISC) from the lowest triplet state (T 1 ) to the lowest singlet state (S 1 ) can be improved by the intervention of 3 LE between 1 CT and 3 CT. [15][16][17][18] In addition, the rigid molecular structure could lead to a high horizontal emitting dipole ratio (Θ // ), thus improving the optical out-coupling efficiency (Φ out ). [19] Yang et al designed a rigid and linear TADF molecule (PhNAI-PMSBA) with an excellent Θ // of 95 % and Φ out of 43.2 % in the mCPCN host.…”