High‐Performance All‐Aryl Phenazasilines via Metal‐Free Radical‐Mediated CH Silylation for Organic Light‐Emitting Diodes

Abstract

complicated synthetic routes to prepare heteroatom-containing materials with specifically introduced heteroatoms on the desired positions of an aromatic molecule, and it becomes even more challenging, when multiple and/or multitype heteroatoms are designed to be introduced. [5][6][7] Phenazasilines, which contain both Si and N heteroatoms in a fused six-membered ring, are typical examples. [8,9] Structurally similar to the popular donor moiety of 9,10-dihydroacridine by replacing its 9-C with Si, [10] phenazasilines can benefit from both 9,10-dihydroacridine-alike architecture and Si incorporation, exhibiting intrinsically promising properties as hole-transporting materials for organic field effect transistors [11] with a hole mobility of 10 −4 cm 2 V −1 s −1 and an ON-OFF ratio close to 10 5 , thermally activated delayed fluorescence (TADF) emitters [12] for organic light emitting diodes (OLEDs) with external quantum efficiency (EQE) up to 22.3%, and host materials [13] for phosphorescent OLEDs (PhOLEDs) with EQE of 12%. Nevertheless, the synthesis of phenazasilines, either traditionally through extended heating of diphenylsilane with phenothiazines [14] and cyclization reaction between 2,2′-dilithiodiarylamine intermediates and dichlorosilanes, [15] or recently by rhodium-catalyzed double activation of SiH and CH bonds for dehydrogenation and SiC coupling, [13] suffers from the low yields, complicated precursors, long synthetic routes, or high chemical costs. These synthetic difficulties significantly hinder the investigations and applications of phenazasilines, although they have already shown promising optical and electronic properties for high-performance device applications due to the combined effects of Si and N heteroatom incorporation.With planar π-conjugated molecular structure, phenazasilines are especially attractive for OLEDs to function as emitters, charge transporters, and host materials. However, due to the planar molecular geometry of phenazasilines with a phenyl-fused azasiline ring, strong π-π stacking and heavy intermolecular interaction are generally observed, especially in the solid state, leading to broad and redshifted excimer emission and coarse film morphology. [16,17] To alleviate the intermolecular interactions, bulky phenyl substituents on the Heteroatom-containing organic molecules show a unique combination of properties for high-performance optoelectronic applications. With both Si and N heteroatoms in an aromatic architecture, phenazasilines are promising for optoelectronic devices, except for their synthetic difficulties. Through a newly developed two-step SiH/CH coupling silylation in a metal-free intramolecular radical-mediated catalysis mechanism, all-aryl phenazasilines that can be hardly synthesized by previous methods are facilely prepared and found to have excellent optoelectronic properties with both high thermal stability and high solubility due to the effects of bulky diphenyl substituents on Si, which cannot only strengthen the intramolecular interactions but also ...

Breaking the Efficiency Limit of Fluorescent OLEDs by Hybridized Local and Charge-Transfer Host Materials

“…A control device using a traditional host material of N , N -dicarbazolyl-3,5-benzene (mCP) in an identical device configuration was performed to verify that the triplet excitons in TPMCN -hosted devices are effectively harvested for light emission (Figure S4). The maximum EQE reaches 3.0% when 0.5 wt % C545T is doped in mCP, showing a typical device behavior of FOLEDs (Table S1). The effective harvesting of triplet excitons in HLCT-SF OLEDs should be the main reason for the doubled EQEs up to 6.3%.…”

“…In light of the efficient FRET from TPMCN to C545T , matched frontier orbital energy levels of the host and guest, and bipolar charge transport properties of the host, HLCT-SF OLEDs were fabricated in a conventional device architecture of ITO/MoO 3 (10 nm)/TAPC (25 nm)/ TPMCN : x wt % C545T (20 nm)/TmPyPB (35 nm)/LiF (1 nm)/Al (100 nm), where x is 0.3, 0.5, 1.0, and 1.5 (Figure S2). ITO (indium tin oxide) and Al serve as the anode and cathode; MoO 3 and LiF are used in the hole- and electron-injection layers; TAPC (1,1-bis­[4-[ N , N ′-di­( p -tolyl)­amino]­phenyl]­cyclohexane) and TmPyPB (1,3,5-tri­[(3-pyridyl)-phen-3-yl]­benzene) are the hole- and electron-transporting materials, respectively.…”

A triphenylacrylonitrile phenanthroimidazole cored butterfly shaped AIE chromophore for blue and HLCT sensitized fluorescent OLEDs

“…54,55 A control device was fabricated with the conventional host of CBP with a similar device structure of ITO/NPB (40 nm)/CBP:x wt% TPATPA-CNPPI (20 nm)/TPBi (25 nm)/LiF (1 nm)/Al (100 nm) to confirm the triplet exciton (T*) harvesting process of devices with the TPATPA-CNPPI host. 56 The doped devices [TPATPA-CNPPI doped in CBP (0.5 wt%, 1.0%, 1.5% and 2.0 wt%)] show current efficiencies of 12.63, 14.02, 16.86 and 10.01 cd A À1 and power efficiencies of 10.05, 11.89, 12.23 and 8.56 lm W À1 . The EQEs of 4.98, 5.03, 5.10 and 3.85% reflect the behavior of conventional FOLEDs and the effective triplet exciton harvesting in HLCT-SF OLEDs should be the reason for the maximum EQE.…”

Constructing Donor-Resonance-Donor Molecules for Acceptor-Free Bipolar Organic Semiconductors

“…Electrochemical properties of the D-r-D molecules were studied by cyclic voltammetry (CV) experiments (Figure S17). From the onset of the oxidative wave, the highest occupied molecular orbital (HOMO) energy levels were identified to be very close (−6:15 ± 0:01 eV), and with the aid of the optical E g s, the lowest unoccupied molecular orbital (LUMO) of these molecules was deduced to be also very similar (−2:31 ± 0:01 eV) [35]. DFT calculations are well in line with the experimental results, revealing that the carbazole unit dominates both the HOMOs and LUMOs of the D-r-D 4 Research molecules; this should be the exact reason for their very close frontier orbital energy levels (Figure 3(a)).…”

“…To experimentally evaluate the effects of the multidimensional dynamic channels for carrier transport by tuning the whole molecule capable of both hole and electron transport through resonance linkage, normal single-carrier transporting devices of the Dr-D molecules were investigated (Figure 4) [35]. All these molecules exhibit hole-dominant characteristics with larger hole-only current densities (J) than the electron-only J.…”