Reductive Doping Inhibits the Formation of Isomerization-Derived Structural Defects in N-doped Poly(benzodifurandione) (n-PBDF).

Recently, solution-processable n-doped poly(benzodifurandione) (n-PBDF) has been made through in-situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n-PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n-PBDF was proposed, based on the observation of structural isomerization from (E)-2H,2'H-[3,3'-bibenzofuranylidene]-2,2'-dione (isoxindigo) to chromeno[4,3-c]chromene-5,11-dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization-derived structural defects are absent in n-PBDF backbone. It lays a solid foundation for the future development of n-PBDF as a benchmark polymer for organic electronics and beyond.

Highly Conductive and Solution-Processable n-Doped Transparent Organic Conductor.

Transparent conductors (TCs) play a vital role in displays, solar cells, and emerging printed electronics. Here, we report a solution-processable n-doped organic conductor from copper-catalyzed cascade reactions in the air, which involves oxidative polymerization and reductive doping in one pot. The formed polymer ink is shelf-stable over 20 days and can endure storage temperatures from -20 to 65 °C. The optimized n-doped thin-film TC exhibits a low sheet resistance of 45 Ω/sq and a high transmittance (T550 > 80%), which can rival indium tin oxide. The transparent organic conductor exhibits excellent durability under accelerated weathering tests (85 °C/85% RH). Furthermore, the n-doped polymer film can also function as an electrode material with a high volumetric capacity. When it is paired with p-doped PEDOT:PSS, a record-high coloration efficiency is obtained in a dual-polymer electrochromic device.

Aryl-Annulated [3,2-a] Carbazole-Based Deep-Blue Soluble Emitters for High-Efficiency Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes with CIEy <0.1.

In this study, we demonstrated two deep-blue TADF emitters, BO-tCzPhICz and BO-tCzDICz, for solution-processable thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). They were synthesized by employing an organoboron acceptor and 9-(3,6-di-tert-butyl-9H-carbazol-9-yl)-5-phenyl-5,12-dihydroindolo[3,2-a]carbazole (tCzPhICz) and 12-(3,6-di-tert-butyl-9H-carbazol-9-yl)-15H-diindolo[2,3-b:1',2',3'-lm]carbazole (tCzDICz) as bulky aryl-annulated [3,2-a] carbazole donors, respectively. Both emitters showed sufficient solubility in organic solvents, narrow deep-blue emission, and small energy difference (ΔEST) between singlet and triplet states, which can be applied to solution-processable deep-blue TADF-OLEDs. Solution-processed OLEDs exploiting these TADF emitters displayed deep-blue electroluminescence with CIEy <0.1, and high external quantum efficiencies of 17.8 and 14.8% were observed for BO-tCzPhICz and BO-tCzDICz, respectively. The emitter bearing bulky ICz-based donating units shows highly promising potential for high-efficiency solution-processable deep-blue TADF-OLEDs.

Novel V-Shaped Bipolar Host Materials for Solution-Processed Thermally Activated Delayed Fluorescence OLEDs.

Three V-shaped host molecules with a cyclohexane linker were successfully synthesized for thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The unipolar host molecules, BBCzC and BTDC, contained two 9-phenyl-9H-3,9'-bicarbazole (PBCz) moieties and two 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (PDBNA) moieties, respectively. BCzTC, a bipolar host molecule, consisted of a donor unit, PBCz, and an acceptor unit, PDBNA, connected by a cyclohexane linker. Three host molecules showed good solubility in various organic solvents, making them suitable for solution processing. Among the solution-processed green TADF-OLEDs using three host molecules and a green TADF emitter, the one with BCzTC showed the highest external quantum efficiency of up to 30% with a high power efficiency of 71 lm W-1 and a current efficiency of 102 cd A-1. Compared with BBCzC and BTDC, BCzTC exhibited a relatively high photoluminescence quantum yield (PLQY), an excellent balance in hole and electron transport properties in the emitting layer, and more efficient energy transfer to the emitter, giving such an excellent device performance.

Deep Learning Optical Spectroscopy Based on Experimental Database: Potential Applications to Molecular Design.

Accurate and reliable prediction of the optical and photophysical properties of organic compounds is important in various research fields. Here, we developed deep learning (DL) optical spectroscopy using a DL model and experimental database to predict seven optical and photophysical properties of organic compounds, namely, the absorption peak position and bandwidth, extinction coefficient, emission peak position and bandwidth, photoluminescence quantum yield (PLQY), and emission lifetime. Our DL model included the chromophore-solvent interaction to account for the effect of local environments on the optical and photophysical properties of organic compounds and was trained using an experimental database of 30 094 chromophore/solvent combinations. Our DL optical spectroscopy made it possible to reliably and quickly predict the aforementioned properties of organic compounds in solution, gas phase, film, and powder with the root mean squared errors of 26.6 and 28.0 nm for absorption and emission peak positions, 603 and 532 cm-1 for absorption and emission bandwidths, and 0.209, 0.371, and 0.262 for the logarithm of the extinction coefficient, PLQY, and emission lifetime, respectively. Finally, we demonstrated how a blue emitter with desired optical and photophysical properties could be efficiently virtually screened and developed by DL optical spectroscopy. DL optical spectroscopy can be efficiently used for developing chromophores and fluorophores in various research areas.

High-Performance, Solution-Processable Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes Realized via the Adjustment of the Composition of the Organoboron Acceptor Monomer in Copolymer Host Materials.

Organic polymers that exhibit features pertinent to functioning as host materials for thermally activated delayed fluorescence (TADF) emitters have considerable potential in solution-processable organic light-emitting diodes (OLEDs), allowing simple, low-cost, and large-area applications. In particular, polymer hosts have superior characteristics, including facile functionality to introduce various electron donor and acceptor entities, the ability to uniformly disperse and contain small molecular dopants, and the ability to produce more smooth and homogeneous films, compared to those of their small-molecule counterparts. This manuscript describes the design and development of three new styrene-based copolymers (ABP91, ABP73, and ABP55) bearing diphenylacridine as the electron donor and 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene as the electron acceptor. In particular, ABP91, ABP73, and ABP55 were synthesized via variations in the ratio of donor to acceptor monomers to substantiate their influence in OLED applications. With the ability of the styrene backbone of interrupting the direct electronic coupling between the adjacent electron donor and acceptor entities through non-conjugated linkages, high triplet energy can be inherited by the resulting polymers (>2.70 eV). Furthermore, these materials manifest thermal robustness through high decomposition temperatures (between 348 and 366 °C) and high glass transition temperatures (between 234 and 277 °C). Consequently, solution-processable OLEDs fabricated using the newly synthesized copolymers as host materials and the familiar t4CzIPN as a green-emissive TADF dopant deliver state-of-the-art performance with maximum external quantum efficiencies of 21.8, 22.2, and 19.7% for ABP91, ABP73, and ABP55, respectively. To our knowledge, this is, to date, the best performance reported when organic polymers are used as host materials in solution-processable TADF OLEDs. The pragmatic outcomes obtained in this study can provide useful insights into the structure-property relationship to the OLED community for the further development of efficient polymer hosts for use in solution-processable TADF OLEDs.

Rational Design of Carbazole- and Carboline-Based Polymeric Host Materials for Realizing High-Efficiency Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diode.

Recently, various host materials have been developed for solution-processed thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Compared with small-molecule hosts, polymeric hosts are advantageous for inducing a uniform distribution and segregation of dopant molecules in the emissive layer without undesired large-scale phase separation. In this study, new polymer hosts were demonstrated, in which a bipolar conjugative moiety consisting of a carbazole (Cz) donor and an α-carboline (α-Cb) acceptor was bound to the polystyrene backbone through a non-conjugated linker. They exhibited high triplet energies of >2.8 eV, and their emission spectra overlapped with the absorption spectrum of a green TADF emitter, which allowed facile energy transfer from the polymeric host to the small-molecule dopants. High device performance was observed, with external quantum efficiencies (EQEs) of 13.65, 17.09, and 17.48% for solution-processed green TADF-OLEDs using PSCzCz, PSCzCb, and PSCbCz, respectively, as hosts for the EML. The EQEs of bipolar host (PSCzCb and PSCbCz)-based devices were higher than those of unipolar host (poly(N-vinylcarbazole) and PSCzCz)-based devices owing to the well-balanced charge-carrier transport. According to these results, the polymeric host bearing a bipolar Cz and α-Cb coupled moiety is a promising material for solution-processable TADF-OLEDs.