Efficient fluorescent OLEDS based on assistant acceptor modulated HLCT emissive state for enhancing singlet exciton utilization

Phenylamine phenanthroimidazole based bipolar compounds with donor–acceptor (D–A) architecture namely, 4-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenylaniline (DDPPPA) and 4′-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (DDPBA) have been synthesized with highly fluorescent pyrene moieties at C6- and C9-positions. The C6 and C9 modification enhanced the thermal, photochemical and electroluminescent properties. Both molecules were employed as blue emitters in non doped organic light emitting devices (OLEDs) and show high performances due to hybridized local and charge-transfer properties. An OLED with DDPPPA/DDPBA emissive layer shows deep-blue emission with maximum external quantum efficiency (η_ex), current efficiency (η_c) and power efficiency (η_p) of 5.7/6.0%, 10.5/12.0 cd A⁻¹ and 8.3/9.2 lm W⁻¹, respectively. Both devices show high singlet exciton utilizing efficiency (η_s) of DDPPPA-31.33% and DDPBA-35.29%. The doped device m-MTDATA:DDPPPA/m-MTDATA:DDPBA shows maximum efficiencies of η_c −7.4/8.23 cd A⁻¹; η_p −5.8/6.13 lm W⁻¹; η_ex −4.72/5.63% (5 wt%):η_c −8.36/9.15 cd A⁻¹; η_p −6.32/6.65 lm W⁻¹; η_ex −4.86/5.45% (10 wt%):η_c −9.58/10.02 cd A⁻¹; η_p −7.8/8.25 lm W⁻¹; η_ex −5.96/6.25% (20 wt%). The doped device based on TAPC host TAPC:DDPPPA/TAPC:DDPBA exhibits maximum efficiencies of η_c −9.60/10.03 cd A⁻¹; η_p −7.81/8.26 lm W⁻¹; η_ex −5.96/6.25% (20 wt%).

OLED with C6/C9 substituted phenanthroimidazoles (DDPPPA/DDPBA) show blue emission with maximum external quantum efficiency (η_ex), current efficiency (η_c) and power efficiency (η_p) of 5.7/6.0%, 10.5/12.0 cd A⁻¹ and 8.3/9.2 lm W⁻¹, respectively.     

Strategic tuning of excited-state properties of electroluminescent materials with enhanced hot exciton mixing

Deep blue emitters with excellent stability, high quantum yield and multifunctionality are the major issues for full-color displays. In line with this, new multifunctional, thermally stable blue emitters viz., N-(4-(10-(1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)anthracen-9-yl)phenyl)-N-phenylbenzenamine (DPIAPPB) and 2-(10-(9H-carbazol-9-yl)anthracen-9-yl)-1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-1H-phenanthro[9,10-d]imidazole (CADPPI) with hybridized local charge transfer state (HLCT) and hot exciton properties have been synthesized. These molecules show high photoluminescence quantum yield (Φ_s/f): (DPIAPPB – 0.82/0.70 and CADPPI – 0.91/0.83). The CADPPI based device (EL – 467 nm) shows high efficiencies [η_c – 9.85 cd A⁻¹; η_p – 10.84 lm W⁻¹; η_ex – 4.78% at 2.8 V; CIE (0.15, 0.10)] compared to the DPIAPPB device (EL − 472 nm) [η_c – 6.56 cd A⁻¹; η_p – 6.16 lm W⁻¹; η_ex – 4.15% at 2.8 V with CIE (0.15, 0.12)]. The green device with CADPPI:Ir(ppy)₃ exhibits a maximum L – 59 012 cd m⁻²; η_ex – 16.8%; η_c – 37.3 cd A⁻¹; η_p – 39.8 lm W⁻¹ with CIE (0.30, 0.60) and the red device with CADPPI:Ir(MDQ)₂(acac) shows a maximum L – 43 456 cd m⁻²; η_ex – 21.9%; η_c – 36.0 cd A⁻¹; η_p – 39.6 lm W⁻¹ with CIE (0.64, 0.35).

The CADPPI:Ir(ppy)₃ device exhibits L – 90 12 cd m⁻²; η_ex – 18.8%; η_c − 27.3 cd A⁻¹; η_p – 29.8 lm W⁻¹; CIE (0.30, 0.60).     

Efficient full-colour organic light-emitting diodes based on donor–acceptor electroluminescent materials with a reduced singlet–triplet splitting energy gap

A series of efficient blue-emitting materials, namely, Cz-DPVI, Cz-DMPVI, Cz-DEPVI and TPA-DEPVI, possessing a donor–acceptor architecture with dual carrier transport properties and small singlet–triplet splitting is reported. These compounds exhibit excellent thermal properties with a very high glass-transition temperature (T_g), and thus, a stable uniform thin film was formed during device fabrication. Among the weak donor compounds, specifically, Cz-DPVI, Cz-DMPVI and Cz-DEPVI, the Cz-DEPVI-based device showed the maximum efficiencies (L: 13 955 cd m⁻², η_ex: 4.90%, η_c: 6.0 cd A⁻¹, and η_p: 5.4 lm W⁻¹) with CIE coordinates of (0.15, 0.06) at 2.8 V. The electroluminescent efficiencies of Cz-DEPVI were higher than that of the strong donor TPA-DEPVI-based device (L: 13 856 cd m⁻², η_ex: 4.70%, η_c: 5.7 cd A⁻¹, and η_p: 5.2 lm W⁻¹). Furthermore, these blue emissive materials were used as hosts to construct efficient green and red phosphorescent OLEDs. The green device based on Cz-DEPVI:Ir(ppy)₃ exhibited the maximum L of 8891 cd m⁻², η_ex of 19.3%, η_c of 27.9 cd A⁻¹ and η_p of 33.4 lm W⁻¹ with CIE coordinates of (0.31, 0.60) and the red device based on Cz-DEPVI:Ir(MQ)₂(acac) exhibited the maximum L of 40 565 cd m⁻², η_ex of 19.9%, η_c of 26.0 cd A⁻¹ and η_p of 27.0 lm W⁻¹ with CIE coordinates of (0.64, 0.37).

The Cz-DEPVI device showed high efficiencies of L: 13955 cd m⁻², η_ex: 4.90%, η_c: 6.0 cd A⁻¹, η_p: 5.4 lm W⁻¹ and CIE coordinates of (0.15, 0.06) at 2.8 V.     

Efficient donor–acceptor host materials for green organic light-emitting devices: non-doped blue-emissive materials with dual charge transport properties

Comparative optical, electroluminescence and theoretical studies were performed for (E)-4′-(1-(4-(2-(1-(4-morpholinophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (SMPI-TPA) and (E)-4-(4-(2-(4-(2-(4-(9H-carbazol-9-yl)phenyl)-1H-phenanthro[9,10-d]imidazol-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)phenyl)morpholine (SMPI-Cz). These compounds show excellent thermal properties, dual charge transport properties and form thin films under thermal evaporation. Blue OLEDs (CIE: 0.16, 0.08) based on SMPI-TPA show efficient device performance (η_ex 6.1%; η_c 5.3 cd A⁻¹; η_p 5.2 lm W⁻¹) at low turn-on voltages. Both SMPI-TPA and SMPI-Cz were utilised as hosts for green OLEDs. The devices with SMPI-Cz (30 nm):5 wt% Ir(ppy)₃ exhibit maximum luminance of 20 725 cd m⁻², and η_c and η_p values of 61.4 cd A⁻¹ and 63.8 lm W⁻¹, respectively. In comparison, devices with SMPI-TPA (30 nm):5 wt% Ir(ppy)₃ exhibit high η_c and η_p values of 65.2 cd A⁻¹ and 67.1 lm W⁻¹, respectively. Maximum η_ex values of 19.6% and 23.4% were obtained from SMPI-TPA:Ir(ppy)₃ and SMPI-Cz:Ir(ppy)₃, respectively. These device performances indicate that the phenanthroimidazole unit is a tunable building unit for efficient carrier injection and it may also be employed as a host for green OLEDs.

SMPI-Cz:Ir(ppy)₃-based devices exhibit a luminance of 20 725 cd m⁻², η_c of 61.4 cd A⁻¹ and η_p of 63.8 lm W⁻¹.     

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).     

Promotional effect of silver nanoparticle embedded Ga–Zr-codoped TiO2 as an alternative anode for efficient blue,green and red PHOLEDs

Efficient blue, green and red phosphorescent OLEDs have been harvested from silver nanoparticles embedded at a glass:Ga–Zr-codoped TiO₂ interface. The embedded silver nanoparticles at the interface removed the non productive hole current and enhanced the efficiencies. The blue emitting device (456 nm) with emissive layer Ir(fni)₃ exhibits a maximum luminance (L) of 40 512 cd m⁻² (ITO – 37 623 cd m⁻²), current efficiency (η_c) of 41.3 cd A⁻¹ (ITO – 40.5 cd A⁻¹) and power efficiency (η_p) of 43.1 lm w⁻¹ (ITO – 39.8 lm w⁻¹) and external quantum efficiency (η_ex) of 19.4% (ITO – 6.9%). A newly fabricated green device based on emissive layer Ir(tfpdni)₂(pic) shows intensified emission at 514 nm, luminance of 46 435 cd m⁻² (ITO – 40 986 cd m⁻²), current efficiency of 49.7 cd A⁻¹ (ITO – 47.3 cd A⁻¹), power efficiency of 48.6 lm w⁻¹ (ITO – 41.4 lm w⁻¹) and external quantum efficiency of 17.5% (ITO – 14.9%). The red device (618 nm) with emissive layer Ir(bbt)₂(acac) shows luminance of 8936 cd m⁻² (ITO – 8043 cd m⁻²), current efficiency of 6.9 cd A⁻¹ (ITO – 4.6 cd A⁻¹), power efficiency of 5.7 lm w⁻¹ (ITO – 4.9 lm w⁻¹) and external quantum efficiency of 9.3% (ITO – 6.9%).

Efficient blue, green and red phosphorescent OLEDs have been harvested from silver nanoparticles embedded at a glass:Ga–Zr-codoped TiO₂ interface.     

Efficient and chromaticity stable green and white organic light-emitting devices with organic–inorganic hybrid materials

Efficient inverted bottom emissive organic light emitting diodes (IBOLEDs) with tin dioxide and/or Cd-doped SnO₂ nanoparticles as an electron injection layer at the indium tin oxide cathode:electron transport layer interface have been fabricated. The SnO₂ NPs promote electron injection efficiently because their conduction band (−3.6 eV) lies between the work function (W_f) of ITO (4.8 eV) and the LUMO of the electron-transporting molecule (−3.32 eV), leading to enhanced efficiency at low voltage. The 2.0% SnO₂ NPs (25 nm) with Ir(ddsi)₂(acac) emissive material (SnO₂ NPs/ITO) have an enhanced current efficiency (η_c, cd A⁻¹) of 52.3/24.3, power efficiency (η_p, lm W⁻¹) of 10.9/3.4, external quantum efficiency (η_ex, %) of 16.4/7.5 and luminance (L, cd m⁻²) of 28 182/1982. A device with a 2.0% Cd-doped SnO₂ layer shows higher η_c (60.6 cd A⁻¹), η_p (15.4 lm W⁻¹), η_ex (18.3%) and L (26 858 cd m⁻²) than SnO₂ devices or control devices. White light emission was harvested from a mixture of Cd–SnO₂ NPs and homoleptic blue phosphor Ir(tsi)₃; the combination of blue emission (λ_EL = 428 nm) from Ir(tsi)₃ and defect emission from Cd–SnO₂ NPs (λ_EL = 568 nm) gives an intense white light with CIE of (0.31, 0.30) and CCT of 6961 K. The white light emission [CIE of (0.34, 0.35) and CCT of 5188 K] from colloid hybrid electrolyte BMIMBF₄–SnO₂ is also discussed.

Efficient inverted bottom emissive organic light emitting diodes (IBOLEDs) with tin dioxide and/or Cd-doped SnO₂ nanoparticles as an electron injection layer at the indium tin oxide cathode:electron transport layer interface have been fabricated.     

Blue organic light-emitting diodes with hybridized local and charge-transfer excited state realizing high external quantum efficiency

Donor–spacer–acceptor (D–π–A) materials CAPI and CCAPI, with hybridized local and charge transfer (HLCT) emissive states, have been synthesized. The twisting D–π–A architecture promotes the partial separation of HOMO and LUMO, leading to an enhanced % CT component, and the anthracene moiety in CAPI and CCAPI increases the conjugation length, leading to an enhanced % LE component. The non-doped device with CCAPI^b shows the blue emission (450 nm) with maximum current efficiency (η_c), power efficiency (η_p), and external quantum efficiency (η_ex) of 16.83 cd A⁻¹, 15.32 lm W⁻¹, and 12.0%, respectively, as well as exciton utilization efficiency (EUE) of 95% with a luminance of 32 546 cd m⁻² and a roll-off efficiency of 0.53%. The new design strategy has great potential for developing high-performance blue electroluminescent materials.

Donor–spacer–acceptor (D–π–A) materials CAPI and CCAPI, with hybridized local and charge transfer (HLCT) emissive states, have been synthesized.     

A hybrid inorganic–organic light-emitting diode using Ti-doped ZrO2 as an electron-injection layer

We have fabricated stable efficient iridium(iii)-bis-5-(1-(naphthalene-1-yl)-1H-phenanthro[9,10-d]imidazole-2-yl) benzene-1,2,3-triol (acetylacetonate) [Ir(NPIBT)₂ (acac)] doped inverted bottom-emissive green organic light-emitting diodes using Ti-doped ZrO₂ nanomaterials as the electron injection layer. The current density (J) and luminance (L) of the fabricated devices with Ti-doped ZrO₂ deposited between an indium tin oxide cathode and an Ir(NPIBT)₂ (acac) emissive layer increased significantly at a low driving voltage (V) compared with control devices without Ti-doped ZrO₂. The Ti-doped ZrO₂ layer can facilitate the electron injection effectively and enhances the current efficiency (η_c) of 2.84 cd A⁻¹ and power efficiency (η_p) of 1.32 lm W⁻¹

Ti-doped ZrO₂ facilitates electron injection effectively, leading to enhanced current efficiency of 2.84 cd A⁻¹ and power efficiency of 1.32 lm W⁻¹     

Efficient blue electroluminescence with an external quantum efficiency of 9.20% and CIEy < 0.08 without excimer emission

Aromatically substituted phenanthroimidazoles at the C6 and C9 positions enhanced the thermal, photochemical and electroluminescence properties due to extension of conjugation. These new materials exhibit good photophysical properties with high thermal stability, good film-forming property and high luminous efficiency. The electroluminescence performances of C6 and C9 modified phenanthroimidazoles as host emitters were evaluated as well as the dopant in the fabricated devices. Among the non-doped devices, pyrene substituted PPI-Py or PPICN-Py based devices show maximum efficiency: PPI-Py/PPICN-Py: η_c (cd A⁻¹) – 9.20/9.98; η_p (lm W⁻¹) – 8.50/9.16; η_ex (%) – 5.56/5.80. The doped OLEDs, m-MTDATA/TAPC:PPI-Cz (4.81/4.85%), m-MTDATA/TAPC:PPICN-Cz (5.23/5.26%), m-MTDATA/TAPC:PPI-An (5.01/5.04%), m-MTDATA/TAPC:PPICN-An (5.25/5.28%), m-MTDATA/TAPC:PPI-Py (5.61/5.65%) and m-MTDATA/TAPC:PPICN-Py (5.76/5.78%) show improved device efficiencies compared to non-doped devices. Designing C6/C9 modified phenanthrimidazole fluorophores is an efficient strategy for constructing highly efficient OLEDs.

Aromatically substituted phenanthroimidazoles at the C6 and C9 positions enhanced the thermal, photochemical and electroluminescence properties due to extension of conjugation.     

A thermally activated delayed fluorescence exciplex to achieve highly efficient and stable blue and green phosphorescent organic light-emitting diodes

The development of a thermally activated delayed fluorescence (TADF) exciplex with high energy is of great significance in achieving highly efficient blue, green, and red organic light-emitting diodes (OLEDs) for use in full-color displays and white lighting. Highly efficient and stable blue and green phosphorescent OLEDs were demonstrated by employing a TADF exciplex (energy: 2.9 eV) based on 4-substituted aza-9,9′-spirobifluorenes (aza-SBFs). Blue PhOLEDs demonstrated a maximum current efficiency (CE) of 47.9 cd A⁻¹ and an external quantum efficiency (EQE) of 22.5% at 1300 cd m⁻² (2.5 times the values of aza-SBF-based systems), with the best blue PhOLED demonstrating a CE, power efficiency (PE) and EQE of 60.3 cd A⁻¹, 52.7 lm W⁻¹, and 26.2%, respectively. Green PhOLEDs exhibited a CE of 78.1 cd A⁻¹ and EQE of 22.5% at 9360 cd m⁻², with the best green PhOLED exhibiting a maximum CE, PE, and EQE of 87.4 cd A⁻¹, 101.6 lm W⁻¹, and 24.5%, respectively. The device operational lifetime was improved over 17-fold compared to reference devices because of the high thermal stability of the materials and full utilization of the TADF exciplex energy, indicating their potential for application in commercial OLEDs.

A high energy TADF exciplex (415 nm) based on aza-spirobifluorene derivatives was demonstrated to achieve efficient and stable PhOLEDs.     

Tailoring the molecular design of twisted dihydrobenzodioxin phenanthroimidazole derivatives for non-doped blue organic light-emitting devices

Three fused polycyclic aryl fragments, namely, naphthyl, methoxynaphthyl, and pyrenyl have been used to construct blue-emissive phenanthroimidazole-functionalized target molecules, i.e., 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (1), 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(1-methoxynaphthalen-4-yl)-1H-phenanthro[9,10-d]imidazole (2), and 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(pyren-10-yl)-1H-phenanthro[9,10-d]imidazole (3). The up-conversion of triplets to singlets via a triplet–triplet annihilation (TTA) process is dominant in these compounds due to 2E_T1 > E_S1. The pyrenyl dihydrobenzodioxin phenanthroimidazole (3)-based nondoped OLED exhibits blue emission (450 nm) with CIE (0.15, 0.14), a luminance of 53 890 cd m⁻², power efficiency of 5.86 lm W⁻¹, external quantum efficiency of 5.30%, and current efficiency of 6.90 cd A⁻¹. The efficient device performance of pyrenyl dihydrobenzodioxin phenanthroimidazole is due to the TTA contribution to the electroluminescent process.

Efficient blue emitters, 1-(2,3-dihydrobenzodioxinyl)-2-naphthylphenanthroimidazole, 1-(2,3-dihydrobenzodioxinyl)-2-methoxynaphthylphenanthroimidazole and 1-(2,3-dihydrobenzodioxinyl)-2-pyrenylphenanthroimidazole have been reported.     

Optimization of the electron transport in quantum dot light-emitting diodes by codoping ZnO with gallium (Ga) and magnesium (Mg)

In our study, to optimize the electron–hole balance through controlling the electron transport layer (ETL) in the QD-LEDs, four materials (ZnO, ZnGaO, ZnMgO, and ZnGaMgO NPs) were synthesized and applied to the QD-LEDs as ETLs. By doping ZnO NPs with Ga, the electrons easily inject due to the increased Fermi level of ZnO NPs, and as Mg is further doped, the valence band maximum (VBM) of ZnO NPs deepens and blocks the holes more efficiently. Also, at the interface of QD/ETLs, Mg reduces non-radiative recombination by reducing oxygen vacancy defects on the surface of ZnO NPs. As a result, the maximum luminance (L_max) and maximum luminance efficiency (LE_max) of QD-LEDs based on ZnGaMgO NPs reached 43 440 cd m⁻² and 15.4 cd A⁻¹. These results increased by 34%, 10% and 27% for the L_max and 450%, 88%, and 208% for the LE_max when compared with ZnO, ZnGaO, and ZnMgO NPs as ETLs.

Optimized QD-LEDs are fabricated using Ga–Mg-codoped ZnO NPs as ETL, which reached the LE_max and PE_max at 15.4 cd A⁻¹ and 10.3 lm W⁻¹.     

A novel triphenylacrylonitrile based AIEgen for high contrast mechanchromism and bicolor electroluminescence

A novel thermally stable and aggregation-induced emission (AIE) active compound, 2,2''-(([1,1′-biphenyl]-4,4′-diylbis(phenylazanediyl))bis(4,1-phenylene))bis(3,3-diphenylacrylonitrile) (BP2TPAN) was synthesized through a C–N coupling reaction between 2-(4-bromophenyl)-3,3-diphenylacrylonitrile (Br-TPAN) and N,N′-diphenyl-1,4-phenylenediamine, under mild conditions using Pd(OAc)₂ and P(t-Bu)₃ as a catalyst. The BP2TPAN was characterized by nuclear magnetic resonance spectroscopy, high resolution mass spectrometry and elemental analysis. The thermal analysis showed that the glass transition and decomposition temperatures (5% weight loss) are 96 and 414 °C, respectively. The fluorescent emission peaks changes at 540 and 580 nm upon grinding were attributed to a transformation from crystal to amorphous occurring by altering the condensed state. The photoluminescence quantum yield and fluorescence lifetime of the as prepared and ground samples were 74.3 and 8.4%, 3.4 and 5.1 ns, respectively. The difference of the luminous efficiency of before and after grinding samples indicates BP2TPAN has a high contrast more importantly, both doped and nondoped OLED devices emit different color, the doped one is highly efficient and its L_max, CE_max, PE_max and EQE are up to 15 070 cd m⁻², 11.0 cd A⁻¹, 7.5 lm W⁻¹, and 3.1%, respectively.

An AIE luminogen with high contrast mechanochromic and bicolor electroluminescence.     

Surfactant-dependant thermally induced nonlinear optical properties of l-ascorbic acid-stabilized colloidal GNPs and GNP–PVP thin films

Gold nanoparticle (GNP) colloids stabilized with various concentrations of l-ascorbic acid were synthesized by the chemical reduction method and characterized by UV-Vis spectroscopy, XRD, FT-IR spectroscopy and TEM. XRD and TEM studies confirmed the reduction in particle size with the stabilizer concentration. UV-Vis spectra showed a blue shift in the LSPR peak. FT-IR peaks ascertained the strong encapsulation of GNPs with l-ascorbic acid functional groups. The nonlinear optical (NLO) properties of colloidal GNPs and GNP–PVP composite thin film were investigated using the Z-scan technique with CW laser excitation at 632.8 nm. The effects of stabilizer concentrations on nonlinear refractive index (n₂), nonlinear absorption coefficient (β) and third-order susceptibility (χ⁽³⁾) of colloidal GNPs and GNP–PVP composite thin films were investigated. The values of the NLO parameters for the thin films were as large as n₂ = 10⁻⁵ cm² W⁻¹, β = 10⁻⁵ cm W⁻¹ and χ⁽³⁾_eff = 10⁻⁵ esu. For colloidal GNPs, these parameters were n₂ = 10⁻⁶ cm² W⁻¹, β = 10⁻⁶ cm W⁻¹ and χ⁽³⁾_eff = 10⁻⁷ esu. In both these cases, the NLO parameter values were found to decrease as the stabilizer concentration increased from 1 to 5 mM. The considerable enhancement in the NLO parameters may be attributed to the thermal lensing effect originating from the thermo-optic phenomenon. From the results, the influence of the concentration of the stabilizer on the NLO properties is obvious.

Gold nanoparticle (GNP) colloids stabilized with various concentrations of l-ascorbic acid were synthesized by the chemical reduction method and characterized by UV-Vis spectroscopy, XRD, FT-IR spectroscopy and TEM.     

Newly synthesised oxime and lactone derivatives from Dipterocarpus alatus dipterocarpol as anti-diabetic inhibitors: experimental bioassay-based evidence and theoretical computation-based prediction

Dipterocarpus alatus-derived products are expected to exhibit anti-diabetes properties. Natural dipterocarpol (1) was isolated from Dipterocarpus alatus collected in Quang Nam province, Vietnam; afterwards, 20 derivatives including 13 oxime esters (2 and 3a–3m) and 7 lactones (4, 5, 6a–6e) were semi-synthesised. Their inhibitory effects towards diabetes-related proteins were investigated experimentally (α-glucosidase) and computationally (3W37, 3AJ7, and PTP1B). Except for compound 2, the other 19 compounds (3a–3m, 4, 5, and 6a–6d) are reported for the first time, which were modified at positions C-3, C-24 and C-25 of the dipterocarpol via imidation, esterification, oxidative cleavage and lactonisation reactions. A framework based on docking-QSARIS combination was proposed to predict the inhibitory behaviour of the ligand-protein complexes. Enzyme assays revealed the most effective α-glucosidase inhibitors, which follow the order 5 (IC₅₀ of 2.73 ± 0.05 μM) > 6c (IC₅₀ of 4.62 ± 0.12 μM) > 6e (IC₅₀ of 7.31 ± 0.11 μM), and the computation-based analysis confirmed this, i.e., 5 (mass: 416.2 amu; polarisability: 52.4 ų; DS: −14.9 kcal mol⁻¹) > 6c (mass: 490.1 amu; polarisability: 48.8 ų; DS: −13.7 kcal mol⁻¹) > 6e (mass: 549.2 amu; polarisability: 51.6 ų; DS: −15.2 kcal mol⁻¹). Further theoretical justifications predicted 5 and 6c as versatile anti-diabetic inhibitors. The experimental results encourage next stages for the development of anti-diabetic drugs and the computational strategy invites more relevant work for validation.

Dipterocarpus alatus-derived products are expected to exhibit anti-diabetes properties.     

Nopinone-based aggregation-induced emission (AIE)-active difluoroboron β-diketonate complex: photophysical,electrochemical and electroluminescence properties

Four difluoroboron (BF₂) β-diketonate nopinone complexes 3a–3d that exhibited typical aggregation-induced emission (AIE) properties were synthesized using the natural renewable β-pinene derivative nopinone as the starting material. The thermal, photophysical, electrochemical and electroluminescent properties as well as the AIE properties of complexes 3a–3d were analyzed systematically. The data of photophysical and electrochemical demonstrated that compound 3b with a methoxy group exhibited the largest bathochromic shift, the highest absolute photoluminescence quantum yields and narrowest optical bandgap among 3a–3d. Using 3b as the emitter, electroluminescent (EL) device I exhibits blue-green light with CIE coordinates of (0.2774, 0.4531) and showed a better performance with a luminous efficacy (η_p) of 7.09 lm W⁻¹ and correlated color temperature (T_C) of 7028 K. The results demonstrate that new AIE compounds are promising solid-state luminescent materials with practical utility in electroluminescent materials.

Four difluoroboron (BF₂) β-diketonate nopinone complexes 3a–3d which exhibited typical AIE property were synthesized. Owing to high absolute fluorescence quantum yields of 3b, EL device based on 3b was fabricated, which exhibits a blue-green light.     

Impact of tunable 2-(1H-indol-3-yl)acetonitrile based fluorophores towards optical,thermal and electroluminescence properties

Herein, we have synthesized 4,5-diphenyl-1H-imidazole and 2-(1H-indol-3-yl)acetonitrile based donor–π–acceptor fluorophores and studied their optical, thermal, electroluminescence properties. Both the fluorophores exhibit high fluorescence quantum yield (Φ_f = <0.6) and good thermal stability (T_d10 = <300 °C), and could be excellent candidates for OLED applications. Moreover, the ground and excited state properties of the compounds were analysed in various solvents with different polarities. The geometric and electronic structures of the fluorophores in the ground and excited states have been studied using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The absorption of BIPIAN and BITIAN in various solvents corresponds to S₀ → S₁ transitions and the most intense bands with respect to the higher oscillator strengths are mainly contributed by HOMO → LUMO transition. Significantly, the vacuum deposited non-doped OLED device was fabricated using BITIAN as an emitter, and the device shows electroluminescence (EL) at 564 nm, maximum current efficiency (CE) 0.687 cd A⁻¹ and a maximum external quantum efficiency (EQE) of 0.24%.

Herein, we have synthesized 4,5-diphenyl-1H-imidazole and 2-(1H-indol-3-yl)acetonitrile based donor–π–acceptor fluorophores and studied their optical, thermal, electroluminescence properties.     

Ethylenediamine mediated luminescence enhancement of pollutant derivatized carbon quantum dots for intracellular trinitrotoluene detection: soot to shine

Vehicle-generated toxic pollutants are composed of gaseous smoke and particulate byproducts accumulated as a black substance at its exhaust. This particulate matter (soot) is utilized for the green synthesis of highly stable, non-toxic, environment friendly, carbon quantum dots (CQD). The CQDs are synthesized via the simple hydrothermal route in the absence (C1) and presence (C2) of oxidants. The as-synthesized CQDs are amine functionalized using ethylenediamine. The amine functionalized CQDs (C1N and C2N) are explored for trinitrotoluene detection. From transmission electron microscopy, the average size of C1 and C2 was found to be about 4.2 nm and 5.6 nm respectively. The incorporation of amine groups lead to an increase in quantum yields from 5.63% to 12.7% for C1 and from 3.25% to 8.48% for C2 QDs. A limit of detection (LOD) of 13 ppb was displayed by C1N while the LODs of 11 ppb and 4.97 ppb were delivered by C2N at λ_ex 370 nm and λ_ex 420 nm respectively. The Stern–Volmer constant for C1N is 2.02 × 10⁶ M⁻¹ while for C2N at λ_ex 370 nm and λ_ex 420 nm is 0.38 × 10⁶ M⁻¹ and 0.48 × 10⁶ M⁻¹ respectively. Furthermore, C1N presents high selectivity for TNT compared to C2N. Owing to their higher luminescence, C1N particles are successfully demonstrated for their applicability in intracellular TNT detection.

Vehicle-generated toxic pollutants are composed of gaseous smoke and particulate byproducts accumulated as a black substance at its exhaust.     

Structural transformation of methasterone with Cunninghamella blakesleeana and Macrophomina phaseolina

An anabolic-androgenic synthetic steroidal drug, methasterone (1) was transformed by two fungi, Cunninghamella blakesleeana and Macrophimina phaseclina. A total of six transformed products, 6β,7β,17β-trihydroxy-2α,17α-dimethyl-5α-androstane-3-one (2), 6β,7α,17β-trihydroxy-2α,17α-dimethyl-5α-androstane-3-one (3), 6α,17β-dihydroxy-2α,17α-dimethyl-5α-androstane-3,7-dione (4), 3β,6β,17β-trihydroxy-2α,17α-dimethyl-5α-androstane-7-one (5), 7α,17β-dihydroxy-2α,17α-dimethyl-5α-androstane-3-one (6), and 6β,9α,17β-trihydroxy-2α,17α-dimethyl-5α-androstane-3-one (7) were synthesized. Among those, compounds 2–5, and 7 were identified as new transformed products. MS, NMR, and other spectroscopic techniques were performed for the characterization of all compounds. Substrate 1 (IC₅₀ = 23.9 ± 0.2 μg mL⁻¹) showed a remarkable anti-inflammatory activity against nitric oxide (NO) production, in comparison to standard LNMMA (IC₅₀ = 24.2 ± 0.8 μg mL⁻¹). Whereas, its metabolites 2, and 7 showed moderate inhibition with IC₅₀ values of 38.1 ± 0.5 μg mL⁻¹, and 40.2 ± 3.3 μg mL⁻¹, respectively. Moreover, substrate 1 was found to be cytotoxic for the human normal cell line (BJ) with an IC₅₀ of 8.01 ± 0.52 μg mL⁻¹, while metabolites 2–7 were identified as non-cytotoxic. Compounds 1–7 showed no cytotoxicity against MCF-7 (breast cancer), NCI-H460 (lung cancer), and HeLa (cervical cancer) cell lines.

Fungal transformation of methasterone resulted in six products (2–7). 2–5, and 7 were identified as new. Substrate 1 showed remarkable anti-inflammatory activity but was cytotoxic. Products 2 and 7 showed moderate activity but were non-cytotoxic.