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The BOLEDs/green- Ir(ppy)3)/red-Ir(MDQ)2(acac) device with TPA-2SPPITPA show maximum EQE of 6.13/27.23/19.01%, CE of 5.92/81.87/28.76 cd/A, PE of 5.15/75.23/24.73 lm/W and CIE of (0.15, 0.07)/ (0.33, 0.60)/(0.65,0.33).

The non-doped blue device with TPATPA-CNPPI shows luminance of 15 892 cd m−2, CE of 19.58 cd A−1, PE of 17.84 lm W−1, EQE of 8.96%, EUE of 73.40% and small roll-off efficiency (RO) of 1.11%.

We have reported pyridine styrylphenanthroimidazole derivatives, SPPI-C2Py, SPPI-N1Py and SPPI-C2N1Py, as efficient electron transport materials (ETMs) for blue fluorescent OLEDs (FOLEDs) and host materials for phosphorescent organic light emitting diodes (PHOLEDs). The optical and carrier transport abilities of pyridine styrylphenanthroimidazoles have been analyzed in terms of the linkage position as well as number of pyridine fragments. Devices with SPPI-C2Py, SPPI-N1Py and SPPI-C2N1Py as ETMs exhibit a maximum current efficiency (CE) of 14.28, 9.63 and 16.93 cd A−1, power efficiency (PE) of 9.32, 4.74 and 11.23 lm W−1 and external quantum efficiency (EQE) of 7.93, 5.50 and 8.68% relative to the widely used ETM BPhen (CE – 11.69 cd A−1; PE – 5.01 lm W−1; EQE – 5.89%). The blue PHOLEDs using SPPI-C2Py, SPPI-N1Py and SPPI-C2N1Py as hosts exhibit a CE of 34.32, 30.65 and 43.23 cd A−1, PE of 32.09, 28.32 and 40.54 lm W−1 and EQE of 18.56, 16.32 and 22.43%. The red PHOLEDs using SPPI-C2N1Py as a host exhibit a maximum CE of 25.78 cd A−1, PE of 22.68 lm W−1 and EQE of 18.56%. The yellow PHOLEDs using SPPI-C2N1Py as a host exhibit a maximum CE of 70.53 cd A−1, PE of 40.86 lm W−1 and EQE of 25.89%, respectively. These findings demonstrated that the new born pyridine styrylphenanthroimidazoles can be employed as potential ETMs for blue FOLEDs and hosts for blue, red and yellow PHOLEDs.

A novel molecular design strategy has been exploited for blue luminogens, NSPI-DVP and CNSPI-DVP consisting of triphenylethene (TPE) at the C5 and C10 positions of phenanthroimidazole with high-lying charge-transfer (CT) state to harvest dark triplet excitons. These materials show hybridised local and charge transfer (HLCT) states and aggregation-induced emission (AIE) properties. Non-doped OLEDs with NSPI-DVP and CNSPI-DVP show high exciton utilization efficiency (EUE) of 36.00 and 64.00%, power efficiency (PE) of 4.99 and 4.72 lm W−1, external quantum efficiency (EQE) of 3.2 and 5.3% and current efficiency (CE) of 5.61 and 5.03 cd A−1, respectively. The non-doped device with CNSPI-DVP shows excellent performance with negligible efficiency roll-off and high exciton utilization efficiency (EUE) than NSPI-DVP. The doped OLEDs with CBP:x wt% NSPI-DVP (EQE-7.60/8.98%) and CBP:CNSPI-DVP (EQE-8.12/9.81%) show higher efficiencies than that of non-doped devices. The improvement of C5/C10 modified phenanthrimidazole mechanofluorochromic (MFC) materials with AIE behaviour could open a new way to enhance OLEDs performances.

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 CCAPIb shows the blue emission (450 nm) with maximum current efficiency (ηc), power efficiency (ηp), and external quantum efficiency (ηex) 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.

The coupling effect of surface plasmons of noble-metal nanoparticles with excitons in organic materials enhanced the efficiency of devices (organic light-emitting diodes (OLEDs)). PEGylated graphen...

White-light emission from the colloidal hybrid electrolyte 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF4)–TiO2(A) is discussed herein. The HMIMBF4–TiO2(A) hybrid electrolyte showed an increase in the lifetime as compared to bare anatase TiO2 (TiO2(A)). The blue emission at 420 nm from HMIMBF4 is attributed to the π–π* transition of the imidazolium moiety, and strong green and yellow emissions at 517 and 568 nm, respectively, are due to defect emissions of TiO2 NPs. In the HMIMBF4–TiO2(A) colloidal hybrid electrolyte, the combination of blue emission from the ionic liquid and defect emission from TiO2 NPs produced intense white light. Fabricated HyLEDs showed enhanced device efficiency by the surface modification of rutile TiO2 (TiO2(R)) using HMIMBF4 ionic liquid. HMIMBF4, with a thickness of 250/850 nm, exhibited maximum current efficiency (ηc – cd A−1) of 322.22/361.53, power efficiency (ηp – lm W−1) of 6.2/7.1, external quantum efficiency (ηex – %) of 322.22/361.53 and luminance (ηL – cd m−2) of 70.14/1490.95. Spontaneously aligned dipole polarization within the ionic liquid HMIMBF4 layer reduced the electron injection barrier and led to enhanced device efficiencies.

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 (ηex), current efficiency (ηc) and power efficiency (ηp) 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 (ηs) of DDPPPA-31.33% and DDPBA-35.29%. The doped device m-MTDATA:DDPPPA/m-MTDATA:DDPBA shows maximum efficiencies of ηc −7.4/8.23 cd A−1; ηp −5.8/6.13 lm W−1; ηex −4.72/5.63% (5 wt%):ηc −8.36/9.15 cd A−1; ηp −6.32/6.65 lm W−1; ηex −4.86/5.45% (10 wt%):ηc −9.58/10.02 cd A−1; ηp −7.8/8.25 lm W−1; ηex −5.96/6.25% (20 wt%). The doped device based on TAPC host TAPC:DDPPPA/TAPC:DDPBA exhibits maximum efficiencies of ηc −9.60/10.03 cd A−1; ηp −7.81/8.26 lm W−1; ηex −5.96/6.25% (20 wt%).

The development of high-performance catalysts for oxygen-evolution reaction (OER) is paramount for cost-effective conversion of renewable electricity to fuels and chemicals. Here we report, highly efficient, ultra-durable and earth-abundant Ni@Fe-NP electrocatalysts developed by solvothermal method for oxygen evolution reaction (OER). The newly developed oxygen electrode show prolonged stability and high catalytic-activity in line with water oxidation keeping alkaline condition which requires overpotential of only 211 mV at current density of 10 mA cm−2. Collectively, the as-prepared amorphous Ni@Fe-NP rippled nanostructured electrode is the most effective oxygen evolution electrode in alkaline solution. Therefore, this study will offer exciting new avenues for designing self-supported electrode materials towards water splitting and other applications.

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: ηc (cd A−1) – 9.20/9.98; ηp (lm W−1) – 8.50/9.16; ηex (%) – 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.

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 (λEL – 434/420 nm) shows high efficiencies: current efficiency (ηc) – 5.83/3.56 cd A−1; power efficiency (ηp) – 5.73/3.48 lm W−1; external quantum efficiency (ηex) – 8.98/6.48% at 3.0 V. Their cyano derivatives, p-CNPPI/m-CNPPI (λEL – 422/406 nm) exhibit maximum efficiencies (ηc – 6.28/4.38 cd A−1; ηp – 6.14/4.01 lm W−1; ηex – 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 (λEL – 504/618 nm) with p-CNPPI: Ir(ppy)3/Ir(MDQ)2 (acac) exhibits a maximum L – 8823/38418 cd m−2; ηex – 24.56/17.31%; ηc – 84.30/18.09 cd A −1; ηp – 86.43/21.43 lm W −1with CIE (0.33, 0.61)/(0.65, 0.34).

Two efficient fluorescent molecules, viz., (E)-2-(2-4-(1-2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-4,5-diphenyl-H-imidazole-2-yl)-[1,1-biphenyl]-4-yl)vinyl-1-yl(naphthalene-1-yl)-1H-phenanthro[9,10-d]imidazole (DDIBNPPI) and (E)-4-(2-(2-(-4′-1(2,3-dihyderobenzo[b][1,4]dioxin-5-yl)-4,5-diphenyl-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)vinyl)-1H-phenanthr[9,10-d]imidazole-1-yl)-1-napthronitrile (DDIBPPIN), were designed and synthesized. DDIBNPPI and DDIBPPIN were obtained by rupturing the covalent bond of phenanthrimidazole core to prevent aggregation-induced quenching. In DDIBPPIN, naphthonitrile group was incorporated into azomethine nitrogen of phenanthrimidazole to enhance charge-transfer ability. The DDIBPPIN/CBP:DDIBPPIN-based device shows blue emission with ηc (current efficiency) of 4.91/4.10 cd/A, ηp (power efficiency) of 4.56/3.84 lm/W, and ηex (external quantum efficiency) of 5.11/5.96%. The ηs (exciton utilization efficiency) values of DDIPNPPI and DDIBPPIN are of 27.0 and 30.3%, respectively. The DDIPNPPI and DDIBPPIN materials employed as a host to fabricate green and red phosphorescent organic light-emitting diodes. The red/white devices (with 0.4% dopant concentration) with DDIBPPIN:Ir(MDQ)2(acac) exhibit maximum L of 69889/26319 cd/m2, ηex of 19.6/16.6%, ηc of 34.6/35.6 cd/A, and ηp of 35.8/36.6 lm/W. The device with DDIBPPIN:Ir(ppy)3/DDIPNPPI:Ir(ppy)3 exhibits green emission [Commission Internationale de l’Eclairage (0.30,0.60)/(0.30,0.60)] with maximum L of 69906/69482 cd/m2, ηex of 17.9/17.0%, ηc of 59.8/58.6 cd/A, and ηp of 63.6/61.3 lm/W. The white device using DDIBPPI:Ir(ppy)3 (with 0.4% dopant concentration) exhibits maximum L of 22152 cd/m2, ηex of 15.8%, ηc of 31.4 cd/A, and ηp of 36.1 lm/W.

New multifunctional blue-emissive materials with superior thermal properties, viz., 4,4′-bis(1-(4-naphthyl)-1H-phenanthro[9,10-d]imidazol-2-yl)binaphthyl (NPIBN), 4,4′-bis(1-(4-cyanonaphthyl)-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl (CNPIBP), and 4,4′-bis(1-(4-cyanonaphthyl)-1H-phenanthro[9,10-d]imidazol-2-yl)binaphthyl (CNPIBN) have been synthesized. The said molecules show high photoluminescence quantum yield (Φs/f: NPIBN-0.75/0.68, CNPIBP-0.85/0.76, and CNPIBN-0.90/0.88). The fabricated nondoped/doped device with CNPIBN/4,4′-bis(carbazol-9-yl)biphenyl: CNPIBN display maximum efficiencies (ηex 4.96/5.4%; ηc 7.46/7.56 cd A–1; ηp 6.85/6.91 lm W–1) at low turn-on voltage (3.5/3.8 V). Nondoped devices based on D−π–A architecture, 4-(2-(5-(9H-carbazol-9-yl)thiophen-2-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile exhibit maximum efficiencies (ηex 2.32%; ηc 4.00 cd A–1; ηp 3.42 lm W–1) compared to 4-(2-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (ηex 2.01%; ηc 3.89 cd A–1; ηp 3.15 lm W–1).

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 (ηc) of 41.3 cd A−1 (ITO – 40.5 cd A−1) and power efficiency (ηp) of 43.1 lm w−1 (ITO – 39.8 lm w−1) and external quantum efficiency (ηex) 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%).

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 (Tg), 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, ηex: 4.90%, ηc: 6.0 cd A−1, and ηp: 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, ηex: 4.70%, ηc: 5.7 cd A−1, and ηp: 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, ηex of 19.3%, ηc of 27.9 cd A−1 and ηp 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, ηex of 19.9%, ηc of 26.0 cd A−1 and ηp of 27.0 lm W−1 with CIE coordinates of (0.64, 0.37).

A series of efficient electroluminescent materials with dual carrier transport properties shows enhanced singlet exciton utilization (ηs) due to small singlet–triplet splitting (ΔEST). 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; ηex – 3.01%; ηc – 2.56 cd A−1; ηp – 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; ηex – 2.85%; ηc – 2.01 cd A−1; ηp – 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; ηex – 19.0%; ηc – 27.5 cd A−1; ηp – 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 [ηex – 19.2%; ηc – 27.9 cd A−1; ηp – 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; ηex – 18.5%; ηc – 25.2 cd A−1; ηp – 25.8 lm W−1; CIE (0.64, 0.34)].

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 (Wf) 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 (ηc, cd A−1) of 52.3/24.3, power efficiency (ηp, lm W−1) of 10.9/3.4, external quantum efficiency (ηex, %) 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 ηc (60.6 cd A−1), ηp (15.4 lm W−1), ηex (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 (λEL = 428 nm) from Ir(tsi)3 and defect emission from Cd–SnO2 NPs (λEL = 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.

The size effect of copper, gold and silver nanoparticles on green OLEDs with MNP-PEDOT:PSS as hole injection layer (HIL) and 4,4′-bis(9-carbazolyl)-biphenyl(CBP): Ir(MMPIPA)2 (acac) as emissive material were analysed. The OLEDs performance was enhanced by copper, gold and silver NPs with 21, 20 and 55 nm, respectively. The external quantum efficiency (ηex) of green OLEDs with Au (20 nm: III) and Ag (55 nm: IV) has been enhanced by 60% and 64%: power efficiency (ηp) enhanced by 46.9% and 38.7% and current efficiency (ηp) enhanced by 50.0% and 72.2%, when compared with control device (I) respectively. In addition higher efficiencies was harvested from OLEDs with codoped NPs [Au (20 nm) -Ag (55 nm), L - 51,262 cd/m2; ηex - 9.8%; ηc - 35.3 cd A−1 and ηp - 8.2 lm W−1 and Cu (21 nm) - Ag (55 nm), L - 49,856 cd/m2; ηex - 8.3%; ηc - 32.1 cd A−1 and ηp - 7.5 lm W−1]. The ηex, ηp and ηc of codoped green OLEDs with Au-Ag NPs was improved by 96.0, 67.3 and 96.1%, respectively, compared to control device. The size controlled NPs can synergistically enhanced OLEDs performances by improving the internal quantum efficiency.

The electroluminescent properties of asymmetrically twisted phenanthrimidazole derivatives comprised of fluorescent anthracene or pyrene unit namely, 1-(1-(anthracen-10-yl)naphthalen-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (ANSPI), 1-(1-(pyren-1-yl) naphthalene-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (PNSPI), 4-(2-(4-(anthracen-9-yl) styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (ASPINC) and 4-(2-(4-(pyren-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PSPINC) for blue OLEDs have been analyzed. The asymmetrically twisted conformation interrupt π-conjugation effectively results in deep-blue emission. The pyrene containing PSPINC based non-doped blue device (476 nm) shows maximium efficiencies (current efficiency (ηc)-4.23 cd/A; power efficiency (ηp)-2.86 lm/W; external quantum efficiency (ηex)-3.48%: CIE (0.16, 0.17) at 3.10 V. Among the doped blue devices, An(PPI)2:ASPINC shows high efficiencies (ηc-12.13 cd/A; ηp-5.98 lm/W; ηex-6.79%; L-23986 cd m−2; EL-458 nm) at 3.15 V with CIE (0.15, 0.17) than An(PPI)2:PSPINC based device which is inconsistent with non-doped device performances. The green and red PhOLEDs show higher efficiencies with Ir(ppy)3: ASPINC (ηc-50.6 cd/A; ηp-53.4 lm/W; ηex-17.0%; L-61581 cd m−2; EL-501 nm, CIE (0.31, 0.60) at 3.32 V and (bt)2Ir(dipba): ASPINC (ηc-15.2 cd/A; ηp-16.5 lm/W; ηex-14.5%; L-13456 cd m−2; EL-610 nm), CIE (0.63, 0.36) at 3.20 V, respectively. The complete energy transfer between the host and dopant molecules improved the efficiency of PHOLEDs.

Blue-emitting 1-(2, 3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-phenyl-1H-phenanthro[9,10-d]imidazole (1), 1-(2, 3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-p-tolyl-1H-phenanthro[9,10-d]imidazole (2), 1-(2, 3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(4-methoxyphenyl)-1H-phenanthro[9,10-d]imidazole (3), 1-(2, 3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(3,4-dimethoxyphenyl)-1H phenanthro[9,10-d]imidazole (4) and 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(3,4,5-trimethoxyphenyl)-1H −phenanthro[9,10-d]imidazole (5) were synthesized for OLEDs. These dihydrobenzodioxin phenanthroimidazoles exhibit excellent thermal stability with high glass-transition temperature favourable to form thin films under thermal evaporation. Efficient devices have been fabricated with dihydrobenzodioxin phenanthroimidazoles as a emissive layer between NPB (4, 4-bis(N-(1-naphthyl)-N-phenylamino)biphenyl) and Alq3 (tris(8-hydroxyquinoline) aluminium) layers. Device employing 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(3,4,5-trimethoxyphenyl)-1H-phenanthro[9,10-d]imidazole as buffer layer exhibit emission at 424 nm with current and power efficiencies of 6.15 cd A−1 and 5.12 lmw−1, respectively, external quantum efficiency (ηex) of 4.11% and luminance of 40132 cd m−2. This outstanding performances reveal that the great potential of dihydrobenzodioxin phenanthroimidazoles as alternative emissive materials for OLEDs.

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 (ηex 6.1%; ηc 5.3 cd A−1; ηp 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 ηc and ηp 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 ηc and ηp values of 65.2 cd A−1 and 67.1 lm W−1, respectively. Maximum ηex 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.

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 (ηPL) (LE) and high exciton utilization (ηs) (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 (ηc) of 2.32 cd A−1, power efficiency (ηp) of 2.01 lm W−1 and external quantum efficiency (ηex) 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), ηex of 3.15%, ηc of 2.56 cd A−1 and ηp of 2.45 lm W−1.

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 (ηc) of 2.84 cd A−1 and power efficiency (ηp) of 1.32 lm W−1

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 2ET1 > ES1. 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.

Organic molecules having propeller shaped architecture integrated with aggregation induced emission (AIE) fluorophores namely, (E)-4-(10-(2-(4′-(1,2,2-triphenylvinyl)-[1,1′-biphenyl]-4-yl)vinyl)-9H-pyreno[4,5-d]imidazol-9-yl)-1-naphthonitrile (TPE-SPNC) and (E)-4-(10-(2-(4′-(1-cyano-2,2-diphenylvinyl)-[1,1′-biphenyl]-4-yl)vinyl)-9H-pyreno[4,5-d]imidazol-9-yl)-1-naphthonitrile (TPA-SPNC) have been synthesized and explored their mechanofluorochromic (MFC) properties. The thermal, electrochemical and photophysical properties of TPE-SPNC and TPA-SPNC have been analyzed. The pyrenoimidazoles, TPE-SPNC and TPA-SPNC show strong aggregation induced emission (AIE) and reversible mechanochromic behavior. In the aggregated state, the restricted intramolecular rotation (RIR) of phenyl rings of TPE (TPE-SPNC) and TPA (TPA-SPNC) are suppressed which reduced the non-radiative excited state energy loss leading increase of fluorescence intensity. The quantum yield of TPE-SPNC/TPA-SPNC in distinct forms are of 21.89%/49.14% (pristine), 56.90%/66.89% (grinding) and 63.01 %/71.24% (annealing). The powder X-Ray diffraction (PXRD) reveal that the morphological change of these pyrenoimidazoles from crystalline to an amorphous could be attributed for mechanochromism.

Organic light-emitting devices (OLEDs) were fabricated with Au-doped ZnO and or ZnO nanoparticles (NPs) as hole injection layer (HIL) and CBP: Ir (TSDPI)2 (pic) as emissive layer to enhance device performances. The photoluminescence intensity of 4,4′-N,N’-dicarbazole-biphenyl(CBP): Ir (TSDPI)2 (pic)/Au −ZnO film at 514 nm is increased by 2.01 times than device with CBP: Ir (TSDPI)2 (pic)/ZnO film. The current efficiency(ηc) and luminance efficiency (L)of green OLEDs with CBP: Ir (TSDPI)2(pic)/10% wt Au −doped ZnO film was 58.6% and 57.0%, respectively higher than CBP: Ir (TSDPI)2 (pic)/ZnO film and 71.6% and 66.0%, respectively higher than device without HIL. This enhanced efficiencies with Au-doped ZnO was correlated with the out-coupling efficiency due to localized surface plasmon resonance (LSPR) generated by Au NPs incorporated in Au-doped ZnO.

A series of phenanthroimidazole derivatives have been synthesized and used as non-doped blue emitters in organic light-emitting devices. Hybrid local and charge transfer (HLCT) state molecules (D-π-A) have been designed by the incorporation of effective hot exciton RISC and high PL efficiency to maximize the external quantum efficiency of fluorescent OLEDs. These compounds show high fluorescent quantum yield as well as good thermal and film-forming abilities. The emissive properties of the materials have been found to be related to the dihedral angles in these compounds. Among the pyrene substituted phenanthrimidazoles, Py-SPICN based device shows excellent performances with maximum current efficiency of 3.41 cd A −1 , power efficiency of 2.80 Lm W −1 and EQE of 1.48%. The non doped device using Cz-TPICN dopant exhibits a maximum current efficiency of 3.65 cd A −1 , power efficiency of 3.10 Lm W −1 and external quantum efficiency of 1.64% with Commission Internationale de’Eclairage (CIE) coordinates of (0.15, 0.10).

CuFe2O4-encapsulated ZnO nanoplates have been synthesized by hydrothermal procedure and characterized by scanning (SEM) and transmission (TEM) electron microscopies, selected area electron (SAED) and X-ray (XRD) diffractometries, vibrating sample magnetometry (VSM) and energy dispersive X-ray (EDS), Raman, solid state electrochemical impedance (EIS), UV-visible diffuse reflectance (DRS), photoluminescence (PL) and time-correlated single photon counting (TCSPC) lifetime spectroscopies. The lifetime of charge carriers produced in CuFe2O4/ZnO is not less than that in ZnO nanoplates. So is the photocatalytic activity. The magnetically recoverable CuFe2O4/ZnO nanoplates show sustainable photocatalytic activity on recycling. The composite nanoplates are bactericide as well. They inactivate E. coli effectively, even in the absence of direct light. The synthesized photostable CuFe2O4-encapsulated ZnO nanoplates are three-in-one material.

Far-field surface plasmon enhanced green electroluminescence in organic light-emitting devices (OLEDs) is harvested by tuning the gold nanoparticles (Au NPs) density at the interface of the anode:hole transport layer (HTL) in OLEDs using Ir(DMSPI)2(acac) as emissive layer. Au NPs increases the hole injection with 35/μm2 density at the indium tin oxide (ITO):N,N′-di-1-naphthyl-N,N′-diphenylbenzidine (NPB) interface and leads to enhanced emission intensity as a result of increased radiative rate (kr). The Au NPs modified anode in OLEDs injects holes effectively into the NPB layer and stabilizes its energy level which results in an increase of current density. The reduced hole injection barrier (HIB) was analyzed by using the Richardson–Schottky equation. The far-field plasmonic coupling with hole injection ability of Au NPs at the ITO:HTL interface enhanced the device efficiencies at low turn-on voltage in this work. However, the anode with 6.0/μm2 density of Au NPs shows poor hole injection ability into th...

The interfacial electron-hole recombination at the interface of zinc copper ferrite/zinc oxide composite nanosemiconductor: 1-(1-benzylpiperidin-4-yl)-2-(3, 4-dimethoxyphenyl)-1H-phenanthro[9,10-d]imidazole (BDPI) in the fabricated Cu-ZnO-BDPI-Ag heterostructure have been studied. In which Ag-BDPI HIB is higher than ZnO-BDPI HIB and ZnO-BDPI EIB is lower than Cu-ZnO-BDPI EIB. Therefore electrons flow from Ag into the ZnO CB is possible until reaching the lowest energy state since ZnO has high electron mobility and hence Ag-to-BDPI-to-ZnO charge transfer direction is the dominant one. X-ray photo electron spectroscopy (XPS) shows doped iron and copper existed as Fe2+ and Fe3+ and Cu2+, respectively, in zinc copper ferrite/zinc oxide composite. Scanning electron microscope (SEM) image of zinc copper ferrite/zinc oxide composite show that they appear to be cocoon-like shape and the selected area electron diffraction (SAED) pattern supports the nano crystalline character of the synthesized material. The faster interfacial charge transfer of zinc copper ferrite/zinc oxide composite was analyzed by Nyquist plot. The near zero remanence magnetic indicates the superparamagnetic behavior of zinc copper ferrite/zinc oxide composite. The binding energy and energy gap of the benzylpiperidine phenanthrimidazole–iron oxide composites dependent on nature of iron oxide cluster and the charge transfer in BDPI–Fe3O4 composite is faster than the same in other composites. Molecular docking technique has also been carried out to understand the BDPI–DNA interactions.

The electroluminescence intensity of a dodecanethiol-functionalized silver (DT-Ag) NP/CPB:Ir(mpidmb)2(acac) film was increased by about 2.23 times in comparison with that of a control device, CPB:Ir(mpidmb)2(acac), due to coupling between excitons of emissive layer and the localized surface plasmon resonance (LSPR) of DT-Ag NPs. The current efficiency of a device with a DT-Ag NPs layer at 100 cd cm−2 (42.3 cd A−1) was 17.0 cd A−1 higher than that of the control device (25.3 cd A−1). The increase in current efficiency in the case of DT-Ag NP-coated devices was strongly related to the energy transfer between radiated light generated from the CBP:Ir(mpidmb)2(acac) emissive layer and the LSPR excited by the DT-Ag NPs layer.