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We report three yellow-green to yellow TADF dopants 26DAcBPy, 25DAcBPy and 26DPXZBPy containing dibenzoyl pyridine as the acceptor and dimethylacridine (Ac) and phenoxazine (PXZ) as the donors with short delayed fluorescence lifetimes of 2.3 μs, 1.9 μs, and 1.0 μs, respectively. The crystal structures show that 26DAcBPy and 26DPXZBPy have a U shape conformation and 25DAcBPy a linear chain structure. All three molecules show intramolecular hydrogen bonding between the pyridine nitrogen and the o-hydrogen of a phenyl ring. These conformations appear to be the result of hydrogen bonding, which leads to rigid structures and provides higher photoluminescence quantum yield. Lastly, these molecules show large dihedral angles between the donor group and the spacer phenyl unit leading to a well-separated HOMO and LUMO and small ΔEST values. Combined with the small ΔEST values, and good photoluminescence (PL) quantum yields, the 26DAcBPy-based devices show a maximum efficiency of 23.1% with a mild efficiency roll-off.

Simultaneous enhancement of out-coupling efficiency, internal quantum efficiency, and color purity in thermally activated delayed fluorescence (TADF) emitters is highly desired for the practical application of these materials. We designed and synthesized two isomeric TADF emitters, 2DPyM-mDTC and 3DPyM-pDTC, based on di(pyridinyl)methanone (DPyM) cores as the new electron-accepting units and di(tert-butyl)carbazole (DTC) as the electron-donating units. 3DPyM-pDTC, which is structurally nearly planar with a very small ΔEST, shows higher color purity, horizontal ratio, and quantum yield than 2DPyM-mDTC, which has a more flexible structure. An electroluminescence device based on 3DPyM-pDTC as the dopant emitter can reach an extremely high external quantum efficiency of 31.9% with a pure blue emission. This work also demonstrates a way to design materials with a high portion of horizontal molecular orientation to realize a highly efficient pure-blue device based on TADF emitters.

Thermally activated delayed fluorescence (TADF) emitters are attractive for display and lighting applications. Here, a series of highly efficient blue TADF emitters including 3,5-bis((3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(pyridin-4-yl)methanone (4BPy-mDTC), (3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(pyridin-3-yl)methanone (3BPy-mDTC), (3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(pyridin-2-yl)methanone (2BPy-mDTC) and (3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(phenyl)methanone (BP-mDTC) were designed and synthesized. The molecular structures feature two meta carbazole substituents attached to a benzoylpyridine (BPy) group or to a benzophenone (BP) group. These compounds show high thermal stability (Td = 371–439 °C), blue emissions (458–488 nm), high photoluminescence quantum yields (PLQY) (75–96%) in thin films and very small energy gaps between S1 and T1 (ΔEST) of 0.01–0.05 eV. In addition, they all reveal TADF properties including small ΔEST, two components in the transient PL decays, prompt emission and temperature-dependent delayed emission. The BPy series appears to give much higher photoluminescence quantum yields (PLQY > 92%) than BP-mDTC (75%) plausibly due to the more rigid structure caused by the interaction between pyridine nitrogen and the aromatic C–H bond. Furthermore, 4BPy-mDTC shows a more delayed component compared to 3BPy-mDTC and 2BPy-mDTC. The electroluminescent devices based on 4BPy-mDTC and 2BPy-mDTC as the dopant emitters exhibit sky blue emission with maximum external quantum efficiencies (EQEs) over 28%, and current and power efficiency and maximum luminance up to 67.0 cd A−1, 60.1 lm W−1 and 20 000 cd m−2, respectively. The presence of the pyridine ring and the position of the nitrogen atom in the molecules are critical for the high quantum yield and device efficiency. The PLQY EQE and luminance are dramatically improved by changing the phenyl into a pyridine group in the dopant in these devices.

Two benzoylpyridine-carbazole based fluorescence materials DCBPy and DTCBPy, bearing two carbazolyl and 4-(t-butyl)carbazolyl groups, respectively, at the meta and ortho carbons of the benzoyl ring, were synthesized. These molecules show very small ΔEST of 0.03 and 0.04 eV and transient PL characteristics indicating that they are thermally activated delayed fluorescence (TADF) materials. In addition, they show extremely different photoluminescent quantum yields in solution and in the solid state: in cyclohexane the value are 14 and 36%, but in the thin films, the value increase to 88.0 and 91.4%, respectively. The OLEDs using DCBPy and DTCBPy as dopants emit blue and green light with EQEs of 24.0 and 27.2%, respectively, and with low efficiency roll-off at practical brightness level. The crystal structure of DTCBPy reveals a substantial interaction between the ortho donor (carbazolyl) and acceptor (4-pyridylcarbonyl) unit. This interaction between donor and acceptor substituents likely play a key role to achieve very small ΔEST with high photoluminescence quantum yield.

An efficient method for the one-pot synthesis of substituted phenanthridinone derivatives from N-methoxybenzamides and aryltriethoxysilanes through rhodium-catalyzed dual C-H bond activation and annulation reactions is described. A double-cycle mechanism is proposed to account for this catalytic reaction. In addition, isotope-labeling studies were performed to understand the intimate mechanism of the reaction.

A series of tetradentate Schiff base metallomesogenic diols and their model compounds were synthesized from two simple dihydroxy benzenes. The metallomesogenic diol was constructed from three ring containing mesogen linked through ester and azomethine with terminal hydroxy group. This upon complexation with copper(II) formed metallomesogenic diol with varing terminal chain length. The related model metallomesogenic compounds were also synthesized with varying chain length with terminal methyl group and compared the properties with metallomesogenic diols. Extensive characterization of all metallomesogenic compounds and intermediates were carried out by FT-IR, 1 H & 13 C NMR, EPR, VSM, Mass (EI and FAB) and UV–Vis spectroscopy. Hot stage polarizing microscope, Differential scanning calorimetry was used to ensure the phase characteristics such as nature of phase, melting and clearing temperatures and phase range. The appearance of enantiotropic smectic A phases indicated high molecular polarizability of the core due to the metal ion. The role of copper(II) ion on mesogens were discussed.

A series of tetradentate Schiff base metallomesogenic diols were synthesized from two simple dihydroxy benzenes. The metallomesogenic diol was constructed from three ring containing mesogen linked through ester and azomethine with terminal hydroxy group. This upon complexation with copper(II) formed metallomesogenic diol with varying terminal chain length. A series of metallomesogenic polyurethanes were synthesized using these metallomesogenic diols as chain extenders for the prepolymers based on polytetramethylene glycol (PTMG) of varying molecular weight ( M n = 650, 2000) and 2,4-toluene diisocyanate (TDI), or 4,4′-methylene bis(phenyl isocyanate) (MDI). The molar ratio of metallomesogenic diol and PTMG were varied in the polyurethane to find their role in liquid crystalline and mechanical properties. Extensive characterization of all metallomesogenic compounds and intermediates were carried out by FT-IR, 1 H and 13 C NMR, EPR, VSM, Mass (EI and FAB) and UV–visible spectroscopy. Hot stage polarizing microscope and differential scanning calorimetry were used to ensure the phase characteristics such as nature of phase, melting and clearing temperatures and phase range. The appearance of enantiotropic smectic A phases indicated high molecular polarizability of the core due to the metal ion.

An efficient method for the synthesis of substituted isoquinolinium salts from benzaldehydes, amines, and alkynes via ruthenium-catalyzed C-H bond activation and annulation in one pot is described.

The combination of the concept of metallopolymers with urethane chemistry offers a versatile approach for the synthesis of new polyurethane materials. Polyurethanes are a distinct class of materials with tremendous industrial importance, and it is of interest to develop these materials with modified thermal and liquid crystalline behavior for advanced applications. Generally, polyurethanes suffer a major disadvantage of poor thermal stability. This can be improved upon by chemical modification of their structures by the incorporation of thermally stable heterocyclic ring structures along with transition metals. Metal-containing polyurethanes prepared from a polymeric diol, diisocyanate and a metal containing diol (metallodiol and metallomesogenic diol) as a chain extender are attracting contemporary research interest. The addition of a polymeric diol (polyol) induces flexibility to the polyurethane by reducing the glass transition temperature, increases its solubility and imparts elastomeric properties. Multifunctional polymers are materials poised for applications in different avenues with preference for plastic electronics. An introduction-cum-overview of synthesis and applications of metal-containing polyurethanes is presented in this chapter.

In this study, tetrafluoro-tetracyano-quinodimethane (F4-TCNQ)-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was spin-coated on a pre-patterned ITO glass and used as hole conducting layer materials in organic photovoltaic cells. The multi-layered ITO/F4-TCNQ-PEDOT:PSS/CuPc/CuPc:C60/C60/BCP/Al organic photovoltaic cells were fabricated to evaluate the J − V characteristics such as short circuit current (Jsc), open circuit voltage (Voc), fill factor (FF) and energy conversion efficiency (ηe) of the device. A higher power conversion efficiency obtained from the device with a concentration of 0.1 wt% F4-TCNQ in the PEDOT:PSS layer was achieved compared to those adopted from device without F4-TCNQ doping in the PEDOT:PSS layer, and current density-voltage characteristics was also improved well with incorporation of F4-TCNQ in PEDOT:PSS films.

In this study, polymeric nanocomposites of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and functionalized multi-walled carbon nanotubes (MWCNTs) were spin coated on a pre-patterned ITO glass and used as a hole conducting layer in organic photovoltaic cells. The multi-layered ITO/MWCNT-PEDOT:PSS/CuPc/C60/Al devices were fabricated to investigate the current density-voltage characteristics and power conversion efficiency. The power conversion efficiency obtained from the device with a concentration of 1.0 wt% MWCNT in the PEDOT:PSS layer was increased twice as those adopted from device without MWCNT doping in the PEDOT:PSS layer and current density-voltage characteristics was also improved well with incorporation of MWCNTs.

An efficient synthesis of highly substituted isoquinolinium salts from ketimines and alkynes via a Rh(iii)-catalyzed C–H bond activation and annulation reaction is described.

A series of divalent metal (Co 2+ , Ni 2+ , Cu 2+ )-incorporated tetradentate Schiff base complexes of the generic name 1,2-bis[(4-(2-hydroxy)ethoxy-2-hydroxyphenyl}methyl ketimino]ethane-metal(II) (BHEHPMKE-M)-metal-containing dihydroxy monomers-were synthesized and characterized by UV-visible, FT-IR, MS, and atomic absorption spectroscopies and elemental analysis. Structure of one of the monomers was also confirmed by single-crystal X-ray diffraction technique. Several metal-containing polyurethanes were prepared using these dihydroxy compounds and 1,4-butanediol as chain extenders for prepolymers based on poly(oxytetramethylene) glycol-2000 (PTMG-2000) and 4,4'-methylene bis(phenyl isocyanate) (MDI). The amount of metal-containing monomer was varied from 0 to 1 equivalent to find the influence of the metal-incorporated tetradentate Schiff base segment on thermal and mechanical properties of polyurethanes. The properties of metal-containing polyurethanes were compared with those prepared using 1,4-butanediol and 1,2-bis[{4-(2-hydroxy)ethoxy phenyl}-methyl ketimino]ethane-a diol without metal-as chain extenders. The polymers were characterized by FT-IR, GPC, DSC, TGA, viscosity, and solubility measurements. The glass transition temperature (T g ) of the polyurethane prepared from the Schiff base diol (without metal) was found to increase when used alone as chain extender. Thermal and mechanical properties of polyurethanes were also found to improve markedly by the introduction of metal-incorporated tetradentate Schiff base moiety into the polymer chain. The viscosity of the metal-containing polyurethane decreased abruptly upon increasing the metal content.

The one-pot synthesis of substituted phenanthridinones involves a rhodium-catalyzed dual C—H bond activation and annulation reactions.

An efficient method for the synthesis of substituted isoquinolinium salts from benzaldehydes, amines, and alkynes via ruthenium-catalyzed C–H bond activation and annulation in one pot is described.

A series of Schiff base hydroxy-mesogens and their model compounds have been synthesized. The mesogen is constructed from three-ring-containing mesogens linked through ester and azomethine groups with a terminal hydroxy group. The related model compounds were also synthesized with varying chain length with a terminal methyl group and their properties were compared with that of hydroxy mesogens. Extensive characterization of all mesogenic compounds was carried out by Fourier-transform IR, 1H and 13C NMR and mass spectroscopy. The phase characteristics such as nature of phase, melting and clearing temperatures and phase range were evaluated using a hot-stage optical polarizing microscope and differential scanning calorimetry. The appearance of enantiotropic smectic phases is due to the high molecular polarizability of the triaromatic core with azomethine and ester linkages.