Toward Electrochromic Metallopolymers: Synthesis and Properties of Polyazomethines Based on Complexes of Transition-Metal Ions

The tridentate ligand L and its complexes with transition-metal ions have been prepared and characterized. The polycondensation reactions of transition-metal complexes with different dialdehydes led to the formation of transition-metal-complex-based polyazomethines, which have been obtained by on-substrate polymerization, and their electrochemical and electrochromic performance have been investigated. The most interesting properties are exhibited by polymers of Fe(II) and Cu(II) ions obtained by the reaction of the appropriate complexes with a triphenylamine-based dialdehyde. Fe(II) polymer P1 undergoes a reversible oxidation/reduction process and a color change from orange to gray due to the oxidation of Fe(II) to Fe(III) ions concomitant with the oxidation of the triphenylamine group. Its electrochromic properties such as long-term stability, switching times, and coloration efficiencies have been investigated, providing evidence of the utility of the on-substrate polycondensation reaction in the formation of thin films of electrochromic metallopolymers.

Strategic Synchronization of 7,7-Dimethyl-5,7-dihydroindeno[2,1-b]carbazole for Narrow-Band, Pure Violet Organic Light-Emitting Diodes with an Efficiency of > 5% and a CIE y Coordinate of < 0.03

A novel violet emitter, 1,3-bis[10,10-dimethyl-10H-indeno[2,1-b]]indolo[3,2,1-jk]indolo[1',2',3':1,7]indolo[3,2-b]carbazole (m-FLDID), was designed and synthesized by meta-oriented bis-fusion of two 7,7-dimethyl-5,7-dihydroindeno[2,1-b]carbazole (DMID) subunits for use in a pure violet organic light-emitting diode (OLED). Incorporation of the DMID subunits effectively reduced the nonradiative recombination rate, improving the photoluminescence quantum yield of the m-FLDID emitter. The meta-oriented bis-fusion of the two DMID subunits not only triggered an alternative distribution of the frontier orbitals but also effectively locked the π-conjugation chain, which ultimately resulted in a narrow-band, pure violet emission of the m-FLDID emitter. Doped m-FLDID devices possessed an external quantum efficiency (EQE) of > 5%, pure violet emission with a maximum at 407 nm, a narrow full width at half-maximum of 17 nm, and a Commission Internationale de l'éclairage y coordinate of less than 0.03. This is the first work reporting an EQE of > 5% and an extremely narrow emission spectrum for a pure violet emitter.

Synthesis of a new 1,3,4-thiadiazole-substituted phenanthroimidazole derivative, its growth on glass/ITO as a thin film and analysis of some surface and optoelectronic properties

A novel phenanthroimidazole derivative with p-type conductivity was prepared and fabricated as a heterostructure, exhibiting a negative differential resistance and photodiode properties.

Efficient donor-acceptor emitter based nonsymmetrical connection for organic emitting diodes with improving exciton utilization

A new strategy developed to construct blue emissive materials having an unsymmetrical connection with identical conjugated phenanthrimidazole groups results in the separation of the frontier orbitals and leads to donor-acceptor (D-A) architecture. The blue device with 2-(naphthalen-1-yl)-1-(4-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (p-PPI)/2-(naphthalen-1-yl)-1-(3-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (m-PPI) emissive layer (λ _EL - 434/420 nm) shows high efficiencies: current efficiency (η _c) - 5.83/3.56 cd A^-1; power efficiency (η _p) - 5.73/3.48 lm W^-1; external quantum efficiency (η _ex) - 8.98/6.48% at 3.0 V. Their cyano derivatives, p-CNPPI/m-CNPPI (λ _EL - 422/406 nm) exhibit maximum efficiencies (η _c - 6.28/4.38 cd A^-1; η _p - 6.14/4.01 lm W^-1; η _ex - 9.01/6.72%) at 2.9 V compared to the p-PPI/m-PPI devices. The weak charge transfer in the D-A emitters results in deep blue emission. The anisotropic structural characteristics of p-PPI, p-CNPPI, m-PPI and m-CNPPI induced horizontal dipole orientation in films and enhanced EL efficiency. These bipolar materials with suitable triplet energy can be used as hosts in green as well as red phosphorescent organic light emitting devices (PHOLEDs). The green/red device (λ _EL - 504/618 nm) with p-CNPPI: Ir(ppy)₃/Ir(MDQ)₂ (acac) exhibits a maximum L - 8823/38418 cd m^-2; η _ex - 24.56/17.31%; η _c - 84.30/18.09 cd A ^-1; η _p - 86.43/21.43 lm W ^-1with CIE (0.33, 0.61)/(0.65, 0.34).

Efficient electroluminescent hybridized local and charge-transfer host materials with small singlet–triplet splitting to enhance exciton utilization efficiency: excited state transition configuration

A series of efficient electroluminescent materials with dual carrier transport properties shows enhanced singlet exciton utilization (η_s) due to small singlet–triplet splitting (ΔE_ST). The strong orbital-coupling transitions of N-(4-(1-(1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-4,5-diphenyl-1H-imidazol-2-yl)naphthalen-4-yl)phenyl)-N-phenyl benzenamine (DDPB) exhibit deep blue emission at 435 nm (CIEy, 0.07) with an external quantum efficiency of 2.01%. The electroluminescent efficiencies of 2-(1-(9H-carbazol-9-yl)naphthalen-4-yl)-1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-1H-phenanthro[9,10-d]imidazole (CDDPI) (L – 3992 cd m⁻²; η_ex – 3.01%; η_c – 2.56 cd A⁻¹; η_p – 2.12 lm W⁻¹) are higher than those of the N-(4-(1-(1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-H-phenanthro[9,10-d]imidazole-2-yl)naphthalen-4-yl)phenyl)-N-phenylbenzenamine (DBDPA) based device (L – 3015 cd m⁻²; η_ex – 2.85%; η_c – 2.01 cd A⁻¹; η_p – 1.92 lm W⁻¹). The blue emissive materials CDDPI and DBDPA are used as a host to construct green and red phosphorescent OLEDs: the green device based on CDDPI:Ir(ppy)₃ exhibits higher efficiencies (L – 8812 cd m⁻²; η_ex – 19.0%; η_c – 27.5 cd A⁻¹; η_p – 33.0 lm W⁻¹) at 2.7 V and the red device based on CDDPI:Ir(MQ)₂(acac) exhibits a maximum luminance of 39 661 cd m⁻² with excellent EL efficiencies [η_ex – 19.2%; η_c – 27.9 cd A⁻¹; η_p – 29.2 lm W⁻¹; CIE (0.64, 0.34)] compared with those of the DBDPA:Ir(MQ)₂(acac) based device [L – 37 621 cd m⁻²; η_ex – 18.5%; η_c – 25.2 cd A⁻¹; η_p – 25.8 lm W⁻¹; CIE (0.64, 0.34)].

CDDPI:Ir(ppy)₃ exhibits higher efficiencies: L = 8812 cd m⁻²; η_ex = 19.0%; η_c = 27.5 cd A⁻¹; η_p = 33.0 lm W⁻¹ at 2.7 V.

EQE Climbing Over 6% at High Brightness of 14350 cd/m2 in Deep-Blue OLEDs Based on Hybridized Local and Charge-Transfer Fluorescence

Three deep-blue emitters PPi-Pid, PPi-Xid, and PPi-Mid based on a novel conjugated system phenantroimidazole-π-indolizine have been designed and synthesized. Here, indolizine with appropriate π-conjugation length was used as the acceptor profited from its high-photoluminescence quantum yield and good electron-withdrawing ability. Fluorescent organic light-emitting diodes (OLEDs) based on PPi-Pid, PPi-Xid, and PPi-Mid achieved deep-blue emissions with the Commission Internationale de L'Eclairage coordinates of (0.151, 0.076), (0.155, 0.052), and (0.153, 0.052); high brightness of 14350, 4377, and 4002 cd/m²; and high external quantum efficiencies (EQEs) of 6.01, 3.90, and 4.28%, respectively. Moreover, it is noticeable that all of the devices exhibited efficiencies increasing with brightness. In particular, the PPi-Pid-based device exhibited high EQE over 6% at a high brightness of 14350 cd/m². Such high brightness along with high EQE is very rare whether in deep-blue fluorescent or thermally activated delayed fluorescent OLEDs.

Hot exciton transition for organic light-emitting diodes: tailoring excited-state properties and electroluminescence performances of donor–spacer–acceptor molecules

The photophysical, electrochemical and electroluminescent properties of newly synthesized blue emitters with donor–π–acceptor geometry, namely, 4′-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-(2-[1,1′-biphenyl]vinyl)-4-amine (NSPI-TPA), 4′-(1-(2-methylnaphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-(2-[1,1′-biphenyl]vinyl)-4-amine (MNSPI-TPA), 4-(2-(4′-(diphenylamino)-(2-[1,1′-biphenyl]vinyl)-4-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)-1-naphthalene-1-carbonitrile (SPNCN-TPA) and 4-(2-(4-(9H-carbazol-9-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (SPNCN-Cz) were analyzed. The conjugation length in the emitters is not conducive to pure emission and hence, a molecular twisting strategy was adopted in NSPI-TPA, MNSPI-TPA, SPNCN-TPA and SPNCN-Cz to enhance pure emission. The emissive state (HLCT) of twisted D–π–A molecules containing both LE and CT (HLCT) states was tuned for high PL (η_PL) (LE) and high exciton utilization (η_s) (CT) efficiencies by replacing triphenylamine (strong donor) with carbazole (weak donor). Among strong donor compounds, namely, NSPI-TPA, MNSPI-TPA and SPNCN-TPA, the SPNCN-TPA-based device exhibited blue emission (451 nm) with CIE coordinates (0.15, 0.08), maximum current efficiency (η_c) of 2.32 cd A⁻¹, power efficiency (η_p) of 2.01 lm W⁻¹ and external quantum efficiency (η_ex) of 3.02%. The device with SPNCN-Cz emitter exhibited higher electroluminescence efficiencies than the SPNCN-TPA-based device, with pure blue emission (443 nm, CIE: 0.15,0.07), η_ex of 3.15%, η_c of 2.56 cd A⁻¹ and η_p of 2.45 lm W⁻¹.

SPNCN-Cz device exhibits η_ex (3.15%), η_c (2.56 cd A⁻¹), η_p (2.45 lm W⁻¹) with CIE (0.15, 0.07).

Achieving efficient violet-blue electroluminescence with CIE y <0.06 and EQE >6% from naphthyl-linked phenanthroimidazole-carbazole hybrid fluorophores

Naphthyl-linked donor–π–acceptor fluorophores were utilized to achieve high performance and good color purity violet-blue emission in organic light-emitting devices (OLEDs).

In this work, we revealed a new approach for the development of efficient violet-blue emitting materials featuring a hybrid local and charge transfer (HLCT) excited state through the incorporation of naphthyl group(s) as a weak n-type π spacer in a donor–π–acceptor (D–π–A) system. The resulting materials (TPINCz and TPIBNCz) show improved intramolecular charge transfer properties and highly efficient violet-blue fluorescence. It is demonstrated that the pattern of the π spacers has significant influence on the photophysical properties. The incorporation of a naphthyl/binaphthyl spacer between the donor and acceptor moieties can alleviate the common dilemma that enhancing device performance by increasing the charge transfer excited properties often leads to red-shifted emissions. A device using TPINCz as an emissive dopant shows a violet-blue emission with CIE coordinates of (0.153, 0.059) and a record high EQE of 6.56 ± 0.11% at a brightness of 1000 cd m^–2. To the best of our knowledge, this performance is the highest among the reported devices with CIE_y ≤0.08. Our study provides a new pathway for the design of high-performance violet-blue emitters with a D–π–A architecture in organic electroluminescence applications.

Non-doped deep blue emitters based on twisted phenanthroimidazole derivatives for organic light-emitting devices (CIE y ≈ 0.04)

Three blue emitters via twisted donor–acceptor molecular design strategy show extremely good color purity without impairing the excellent photophysical and electrical properties. The color purity of nondoped devices can meet the blue OLED requirements of NTSC.

Sultam-Based Hetero[5]helicene: Synthesis, Structure, and Crystallization-Induced Emission Enhancement

A deep-blue-emitting sultam-based hetero[5]helicene was synthesized in four steps, and its crystal structure and physical properties were characterized. The helicene displays more than two-fold crystallization-induced emission enhancement as well as atypical blue-shifting of its solid-state emission relative to the solution phase. This rapid synthesis of an unusual sulfonamide-based helicene fluorophore is expected to generate new molecular design options that will help address the ongoing challenges associated with designing pure-blue emitters for organic optoelectronic and sensing applications.

High-Performance Blue OLEDs Based on Phenanthroimidazole Emitters via Substitutions at the C6- and C9-Positions for Improving Exciton Utilization

Donor-acceptor (D-A) molecular architecture has been shown to be an effective strategy for obtaining high-performance electroluminescent materials. In this work, two D-A molecules, Ph-BPA-BPI and Py-BPA-BPI, have been synthesized by attaching highly fluorescent phenanthrene or pyrene groups to the C6- and C9-positions of a locally excited-state emitting phenylamine-phenanthroimidazole moiety. Equipped with good physical and hybridized local and charge-transfer properties, both molecules show high performances as blue emitters in nondoped organic light-emitting devices (OLEDs). An OLED using Ph-BPA-BPI as the emitting layer exhibits deep-blue emission with CIE coordinates of (0.15, 0.08), and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.56 %, 3.60 cd A(-1) , and 3.66 lm W(-1) , respectively. On the other hand, a Py-BPA-BPI-based, sky-blue OLED delivers the best results among nondoped OLEDs with CIEy values of < 0.3 reported so far, for which a very low turn-on voltage of 2.15 V, CIE coordinates of (0.17, 0.29), and maximum CE, PE, and EQE values of 10.9 cd A(-1) , 10.5 lm W(-1) , and 5.64 %, were achieved, respectively. More importantly, both devices show little or even no efficiency roll-off and high singlet exciton-utilizing efficiencies of 36.2 % for Ph-BPA-BPI and 39.2 % for Py-BPA-BPI.

Efficient deep-blue non-doped organic light-emitting diode with improved roll-off of efficiency based on hybrid local and charge-transfer excited state

Acceptor–donor–acceptor triphenylamine–phenanthroimidazole derivate (TPA–2PPI) servers as an emitter, whose device exhibits deep-blue emission, high efficiency and slow roll-off of efficiency.

Phenanthroimidazole derivatives as emitters for non-doped deep-blue organic light emitting devices

We synthesized eight phenanthroimidazole derivatives as blue emitters for OLED application and investigated the relationship between the molecule structure and optoelectronic properties.

The effect of meta coupling on colour purity, quantum yield, and exciton utilizing efficiency in deep-blue emitters from phenanthroimidazole isomers

Three isomers were employed to investigate the essential reason for the meta-tuning effect on their PL and EL properties.

Deep blue organic light-emitting devices enabled by bipolar phenanthro[9,10-d]imidazole derivatives

Novel phenanthroimidazole derivatives with D–π–A structures have been successfully designed and prepared. Non-doped organic light emitting diodes (OLEDs) were fabricated by employing the compounds, which display deep blue emission.