Search

Metal-catalyzed annulation reactions to synthesize carbo- and heterocycles have been an attractive field of research for many years. The development of new cyclization reactions utilizing readily available less expensive metal catalyst is one of the important tasks. In this regard, this review summerizes and discusses about nickel- and cobalt-catalyzed [4+2] and [3+2] annulation reactions of ortho-halo substituted imines and alkynes. Nickel complexes under suitable reaction conditions underwent [4+2] annulation to form six-membered isoquinoline (salts) derivatives. However, cobalt complexes afforded aminoindenes via [3+2] annulation reactions. Both reactions proceed through a five membered metallacycle. The regioselective insertion of alkyne containing keto or ester groups into the metallacycle further demonstrates the difference in selectivity of these metal complexes.

Low-band gap selenophene-based polymers were synthesized. Their optoelectronic and photovoltaic properties and space-charge limited currents were compared with those of the related thiophene-based polymers. The band gaps of the Se-based derivatives were approximately 0.05–0.12 eV lower than those of their thiophene counterparts. Organic photovoltaic (OPV) devices based on the blends of these polymers and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C71 (PC71BM) were fabricated, and the maximum power conversion efficiency of the OPV device based on PSPSBT and PC71BM was 3.1%—with a short-circuit current density (Jsc) of 9.3 mA cm−2, an open-circuit voltage (Voc) of 0.79 V, and a fill factor of 0.42—under AM 1.5 G illumination (100 mW cm−2). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4550–4557

We report the spectra of UV-vis absorption, emission and excitation for fluoro-substituted triscarbene iridium complexes fac-tris(1-(4-fluorophenyl)-3-methylimidazolin-2-ylidene-C,C2′) iridium(III), fac-Ir(fpmi)3, and fac-tris(1-(2,4-fluorophenyl)-3-methyl imidazolin-2-ylidene-C,C2′ ) iridium(III), fac-Ir(dfpmi)3. The decay of emission and transient absorption curves at 266-nm excitation in the singlet metal-to-ligand charge-transfer (MLCT) band region are recorded. Using quantum chemical calculations-density functional theory (DFT) and time-dependent DFT (TD-DFT) method B3LYP, we obtained their optimized geometries, electronic structures, energies of vertical transitions and oscillator strengths. Both complexes emit in deep blue/near UV which has the highest emission energy for iridium complexes. These emission bands display vibronic structure and a small rigidochromic shift in the low-temperature. From the measured lifetime data and the emission quantum yield, we obtain a radiative rate constant kr 2.2-2.4 × 104 s−1 for the emitting state and assign the emitting state to 3π-π* for these complexes. In subpicosecond transient absorption, we observed an ultrafast rise implying that crossing rate from 1MLCT to this ligand-centered T1/T2 3π-π* state is faster than our temporal resolution (300 fs)−1. Two components appear with time constants 0.7-1.5 ps and 15-47 ps and are assigned to vibrational cooling/solvation and geometry relaxation, respectively.

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.

The reductive coupling of an aryl carbonyl group with an activated alkene to give the corresponding γ-hydroxybutyric acid (GHBA) derivative was achieved in the presence of zinc and ammonia. A board scope of GHBA derivatives could be synthesized under ambient conditions by this method. A mechanism involving a Zn-ketyl radical as the key intermediate is proposed.

The synthesis of highly substituted naphthalenes from allylarenes and alkynes is described. This reaction proceeds via π-coordination of an allylic carbon-carbon double bond to the Pd(II) center and is followed by ortho selective C-H bond activation.

With the goal of applying them in organic photovoltaics (OPVs), in this study we synthesized two organometallic alternating conjugated polymers, TPT–TPyPt and TPT–TIqPt , consisting of indacenodithiophene (thiophene/phenylene/thiophene; TPT ) and cyclometalated platinum(II) moieties and compared their optical, electrochemical, and photovoltaic properties, their space charge limited currents, and their structures (density functional theory) with those of related platinum-free organic polymers, TPT–TPy and TPT–TIq . The absorption bands of the metal-based polymers were significantly red-shifted relative to those of the metal-free polymers. We fabricated OPVs incorporating blends of these polymers and [6,6]-phenyl-C 71 -butyric acid methyl ester at various weight ratios. One of these devices exhibited a power conversion efficiency (PCE) of 2.9%, with a short-circuit current density of 7.7 mA/cm 2 , an open-circuit voltage of 0.78 V, and a fill factor of 0.48, under AM 1.5 G (100 mW/cm 2 ) illumination. To the best of our knowledge, this PCE is the highest reported for a PSC based on a cyclometalated platinum-type polymer.

In this report, several benzoylpyridine-carbazole based fluorescence materials bearing carbazolyl or 4-(t-butyl)carbazolyl groups at the ortho, meta and para carbons of the benzoyl ring, were synthesized and studied for their TADF properties. Some of these molecules show very small ΔEST < 0.05 eV and transient PL characteristics indicate that they are thermally activated delayed fluorescence (TADF) materials. In general, they show low fluorescence efficiencies in solutions, but the efficiencies increase drastically in the thin films with some reaching more than 90%. For examples, o- and m-dicarbazolyl substituted DCBPy (2,5-di(9H-carbazol-9-yl)phenyl)(pyridin-4-yl)methanone) and DTCBPy ((3,5-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)(pyridin-4-yl)methanone) in cyclohexane show fluorescence efficiencies of 14 and 36%, but in the thin films, the values increase to 88.0 and 91.4%, respectively. Based on the TDDFT calculation, the HOMOs of DCBPy and DTCBPy are mainly distributed over the two carbazolyl groups and slightly extended to the phenyl ring. The LUMOs are mostly localized on the BPy core and slightly extended to the phenyl ring. There is a small degree of spatial overlap between the HOMO and LUMO in these two molecules. 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. The interaction between donor and acceptor substituents likely plays a key role to achieve very small ΔEST with high photoluminescence. In addition to the above two compounds, we also prepared a series of different benzoylpyridine-carbazole derivatives, the results will also be reported.

An efficient C–H activation method for the ortho alkynylation of aromatic N-methoxyamides with hypervalent iodine–alkyne reagent using a ruthenium catalyst is described. The reaction proceeds under mild reaction conditions with broad substrate scope. A possible catalytic cycle involving a ruthenium carboxylate assisted C–H bond cleavage is proposed from the preliminary mechanistic evidence.

The reaction probably proceeds through a Lewis acidic CuII-assisted rearrangement of benzylic azide to N-methylaniline, followed by a [4+2] cycloaddition with alkene.

The process is found to form the desired carboxylic acids with complete (E) selectivity except for substrate (XV), where an E/Z mixture is identified.

A concise approach to the synthesis of oxindoles and phenanthridones from anilides is described. In the presence of catalytic amount of Pd(OAc) 2 , 2-iodoacetates and 2-iodobenzoates can be used to functionalize ortho C–H bond of anilides, which subsequently undergo intramolecular cyclization to give the products. A possible reaction mechanism that involves a Pd II /Pd IV catalytic cycle is proposed with the support of detailed mechanistic studies.

A highly diastereoselective method for the synthesis of dihydroepoxybenzofluorenone derivatives from aromatic/vinylic amides and bicyclic alkenes is described. This new transformation proceeds through cobalt-catalyzed C-H activation and intramolecular nucleophilic addition to the amide functional group. Transition-metal-catalyzed C-H activation reactions of secondary amides with alkenes usually lead to [4+2] or [4+1] annulation; to the best of our knowledge, this is the first time that a [3+2] cycloaddition is described in this context. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. Mechanistic studies imply that the C-H bond cleavage may be the rate-limiting step.

We describe a highly step and atom economical cobalt-catalyzed cyclization of 1,6-enynes with aldehydes to synthesize functionalized pyrrolidines and dihydrofurans with high chemo- and stereoselectivity. The catalytic reaction plausibly proceeds via the cobaltacycle intermediate generated from the reaction of enyne substrate with cobalt catalyst, followed by switchable C—H functionalization of weakly coordinating aldehydes depending on the electronic nature of the ligand.

A one-pot reaction of substituted benzaldehydes with alkyne-amines by a Rh-catalyzed C-H activation and annulation to afford various natural and unnatural protoberberine alkaloids is reported. This reaction provides a convenient route for the generation of a compound library of protoberberine salts, which recently have attracted great attention because of their diverse biological activities. In addition, pyridinium salt derivatives can also be formed in good yields from α,β-unsaturated aldehydes and amino-alkynes. This reaction proceeds with excellent regioselectivity and good functional group compatibility under mild reaction conditions by using O2 as the oxidant.

Four cobalt-catalyzed oxidative annulation reactions of nitrogen-containing arenes with alkynes proceeds by C-H activation, thus leading to biologically useful quaternary ammonium salts, including pyridoisoquinolinium, cinnolinium, isoquinolinium, and quinolizinium salts, in high yields. The results are comparable to those reactions catalyzed by rhodium and ruthenium complexes. The transformation of the salts into various N-heterocycles has also been demonstrated.

A novel copper promoted synthesis of substituted quinolines from various benzylic azides and internal alkynes has been demonstrated. The reaction features a broad substrate scope, high product yields and excellent regioselectivity. In contrast to the known two-step process of acid promoted [4 + 2] cycloaddition reaction and oxidation, the present methodology allows the synthesis of quinolines in a single step under neutral reaction conditions and can be applied to the synthesis of biologically active 6-chloro-2,3-dimethyl-4-phenylquinoline (antiparasitic agent) and 3,4-diphenylquinolin-2(1H)-one (p38αMAP kinase inhibitor). A plausible reaction mechanism involves rearrangement of benzylic azide to N-arylimine (Schmidt reaction) followed by intermolecular [4 + 2] cycloaddition with internal alkynes.

Cationic N-heterocycles are an important class of organic compounds largely present in natural and bioactive molecules. They are widely used as fluorescent dyes for biological studies, as well as in spectroscopic and microscopic methods. These compounds are key intermediates in many natural and pharmaceutical syntheses. They are also a potential candidate for organic light-emitting diodes (OLEDs). Because of these useful applications, the development of new methods for the synthesis of cationic N-heterocycles has received a lot of attention. In particular, many C-H activation methodologies that realize high step- and atom-economies toward these compounds have been developed. In this review, recent advancements in the synthesis and applications of cationic N-heterocycles through C-H activation reactions are summarized. The new C-H activation reactions described in this review are preferred over their classical analogs.

A novel method for the synthesis of functionalized vinyl arenes by reaction of N-methoxybenzamides or N-phenoxyacetamide (XIV) with vinylstannanes via C—H activation is described.

In recent years, transition-metal-catalyzed directing-groupassisted C H activation has emerged as a sustainable and intriguing protocol for the construction of C C, C N, C O, and C X bonds. In particular, one-pot C C/C N bondforming reactions have been used as key steps for the synthesis of nitrogen-containing natural products and heterocycles in drug discovery. In this context, rhodium catalysts have proven valuable for applications in the step-economical synthesis of complex molecular scaffolds. Although a vast number of rhodium(III)-catalyzed directing-group-assisted C H activation reactions of alkenes and alkynes and nucleophilic addition reactions have been reported, rhodium(III)-catalyzed oxidative C H coupling reactions between arenes or between an arene and an organometallic reagent remain relatively unexplored. Organoboron reagents are stable and powerful reagents for versatile transformations, including the well-known Suzuki–Miyaura coupling. However, very few examples of the use of organoboron reagents as the coupling reagents in palladiumand rhodium(I)-catalyzed C H activation reactions are known. In 2009, Miura and co-workers reported a rhodium(III)-catalyzed oxidative coupling of aryl boronic acids with alkynes to give naphthalenes and anthracenes. We have become interested in the use of N-methoxybenzamides as an important motif for rapid access to phenanthridinone derivatives, which are well-represented in natural products and drugs. Recently, Wang et al. and our research group reported the palladium-catalyzed synthesis of phenanthridinone derivatives from N-methoxybenzamides with iodoarenes and simple arenes, respectively. Although a variety of methods have been documented, a more straightforward alternative method with wide scope under mild conditions is desired for the synthesis of phenanthridinones. Our continuing efforts in metal-catalyzed C H bond activation and cyclization reactions prompted us to explore the reaction of N-methoxybenzamides with aryl boronic acids. Herein we report the Rh-catalyzed regioselective synthesis of phenanthridinones from N-methoxybenzamides and aryl boronic acids through one-pot C C/C N bond formation under mild conditions. To the best of our knowledge, this is the first rhodium-catalyzed dual oxidative C H bond coupling of two aromatic compounds to give a formal [4+2] cyclization product (Scheme 1).

Round and round: An unusual cobalt-catalyzed regio- and enantioselective reductive [3+2] cycloaddition of cyclic enones with alkynes affording bicyclic tertiary alcohols is described. A possible mechanism involving the formation of a cobaltacyclopentene intermediate is proposed.

An efficient Ru(II)-catalyzed amidation of 2-arylpyridines with isocyanates via C-H bond activation is described.

A cobalt-catalyzed reductive coupling of terminal alkynes, RC≡CH, with activated alkenes, R'CH=CH(2), in the presence of zinc and water to give functionalized trans-disubstituted alkenes, RCH=CHCH(2)CH(2)R', is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl(2)/P(OMe)(3)/Zn catalyst system to afford 1,2-trans-disubstituted alkenes with high regio- and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl(2)/P(OPh)(3)/Zn system providing a mixture of 1,2-trans- and 1,1-disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3-enynes and acetylene gas with alkenes. Furthermore, a phosphine-free cobalt-catalyzed reductive coupling of terminal alkynes with enones, affording 1,2-trans-disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air-stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.

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.

Pd-catalyzed selective ortho-olefination of arenes assisted by an allylic C-C double bond at room temperature using O(2) as a terminal oxidant is described. A possible mechanism involving the initial coordination of allylic C═C bond to Pd followed by selective o-C-H bond metalation is proposed.

A simple efficient method for the iron(III)-catalyzed synthesis of substituted β-chlorovinyl ketones and α,β-alkynyl ketones from terminal and silyl-substituted alkynes with acid chlorides, respectively, is described. This method features easily available starting materials, a cheap and non-toxic catalyst, simple manipulation and mild reaction conditions. Evidence shows that the catalytic addition of the acid chloride to a terminal alkyne to give (Z)-β-chlorovinyl ketones favours a concerted pathway via a four-membered ring transition state between the two alkyne carbons and the carbon-chloride bond of the acid chloride.

Many steps make light work: substituted phenanthridinones can be obtained with high regioselectivity and in very good yields by palladium-catalyzed cyclization reactions of N-methoxybenzamides with arenes. The reaction proceeds through multiple oxidative C-H activation and C-C/C-N formation steps in one pot at room temperature, and thus provides a simple method for generating bioactive phenanthridinones.

A new catalytic system for β-alkylation of lactic acid with primary alcohols has been developed. In the presence of nickel(II) acetate tetrahydrate [Ni(OAc)2(H2O)4] and base, lactic acid reacts with primary alcohols to afford the corresponding coupled α-hydroxy carboxylic acids in good to excellent yields via a hydrogen transfer process without any hydrogen acceptor or hydrogen donor.

Three new FPt1 [(2-(4′,6′-difluorophenyl)pyridinato-N,C2′)(2,4-pentanedionato- O,O)Pt(II)] analogues, Ph-FPt, CzP-FPt, and mCzP-FPt, chelated with a 3-aryl-substituted acac ligand were synthesized. As shown by the results of X-ray diffraction, the nearest neighboring molecules in the FPt1, Ph-FPt, and CzP-FPt crystals have a Pt–Pt distance of ~4.5, 4.5, and 7.0 A, respectively. In contrast, in the mCzP-FPt crystals, the nearest neighboring molecules exhibit a Pt–Pt distance of only 3.49 A. All four Pt complexes show the same monomeric emission spectrum in dilute solution. However, in the crystalline state, mCzP-FPt with a clear Pt–Pt bimetallic interaction shows only the low-energy orange broadband emission; complexes FPt1, Ph-FPt, and CzP-FPt without significant Pt–Pt interaction (Pt–Pt distance > 4 A) give higher-energy emission closely resembling that of the monomeric species. The results provide clear evidence that the Pt–Pt bimetallic interaction is responsible for the low-energy broadband emission of these Pt complexes. Unlike in the crystalline state, all of the four platinum complexes in the thin film give only the low-energy broadband emissions with some difference in wavelength. In a similar manner, these platinum complexes-based, non-doped electroluminescence (EL) devices also emit only low-energy orange broadband light. The non-doped EL device using CzP-FPt as the emitter showed a very promising external quantum efficiency of 10%, nearly five times higher than that of the FPt1 control device. The higher EL efficiency of the CzP-FPt non-doped device is mainly ascribed to the lower concentration of Pt–Pt dimers that effectively suppresses the self-quenching between the orange emissive dimers.

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.

Two phosphorescent iridium complexes (psbi)2Ir(acac) and (ppbi)2Ir(acac) (psbi = 1-phenyl-2-styryl-1H-benzo[d]imidazole, ppbi = 1-phenyl-2-(1-phenylprop-1-en-2-yl)-1H-benzo[d]imidazole, acac = acetylacetonate) were synthesized, and their photophysical, electrochemical and electroluminescent properties were also studied. Organic light-emitting devices with these two complexes as dopant emitters having the structure ITO/NPB (10 nm)/TCTA (20 nm)/x%Ir:CBP (y nm)/BCP (10 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The device based on (psbi)2Ir(acac) exhibited a maximum brightness of 56,162 cd m−2, while the device based on (ppbi)2Ir(acac) gave a maximum brightness of 31,232 cd m−2. At high brightness of 1000 cd m−2 and 10,000 cd m−2, high current efficiencies of 25.7 cd A−1 and 20.7 cd A−1 were achieved, respectively, for the (psbi)2Ir(acac)-based EL device. For the EL device based on (ppbi)2Ir(acac), current efficiencies of 20.1 cd A−1 at 1000 cd m−2 and 14.2 cd A−1 at 10,000 cd m−2 were observed.

A highly regio- and stereoselective nickel-catalyzed three-component coupling of alkynes with enones and alkenyl boronic acids to afford highly substituted 1,3-dienes is described. The reaction can also be extended to cyclization of enynes with coupling to alkenyl boronic acids. A possible reaction mechanism involving a five-membered nickelacycle as a key intermediate is proposed.

By utilizing the relatively broad orange–red excimer emission of an iridium complex (DMBA) 2 Ir(acac) (DMBA = 5,6-dihydro-9,10-methylenedioxy-benzo[c]acridine, acac = acetylacetonate) together with an efficient blue phosphorescent iridium complex FIrpic, two types of efficient white organic light-emitting diodes were fabricated. Through the optimization of the thickness, location, and doping concentration of each emitting layer, both of the two types of devices exhibited pure white emission with CIE coordinates close to the ideal white emission (0.33, 0.33). Compared with the double-emitting-layer structure, a triple-emitting-layer device structure with a blue-emitting layer sandwiched between two orange–red-emitting layers led to more stable white emission at different biases/brightnesses with maximum efficiencies of up to 12.2%, and 27.0 cd A −1 for the forward viewing direction, corresponding to the total efficiencies of 19.7%, 45.9 cd A −1 and 32.1 lm W −1 . At a high brightness of 1000 cd m −2 , the EL efficiencies remained high at 8.8% and 19.2 cd A −1 .

A red-emitting iridium complex (DMBA)2Ir(acac) (DMBA = 5,6-dihydro-9,10-methylenedioxy benzo[c]acridine, acac = acetylacetone) containing rigid cyclometalated ligand DMBA was synthesized and its photophysical, electrochemical and electroluminescent properties were characterized. Organic light emitting devices utilizing the complex as dopant emitter were fabricated. When double hole-transporting layers were adopted, the brightness and efficiencies of electroluminescent devices were improved greatly. Based on the excimer emission, a maximum brightness of 66,312 cd m−2 at 15 V, together with a maximum external quantum efficiency of 17.7% at 5.0 V was achieved at a doping concentration of 5%. The result suggests that the introduction of a methylenedioxy group into the N-heterocycle of the cyclometalated ligand leads to higher-energy MLCT transitions and a blue shift of the photoluminescence spectrum.

N-Methyl indole reacts with but-2-yn-1-ol in the presence of PtCl(2) in MeOH giving indole derivatives having a substituted 3-oxobutyl group at the 3-position in good yield. Under the reaction conditions, various substituted indoles and substituted propargyl alcohols are successfully involved in the reaction giving the corresponding addition products in good to moderate yields. The catalytic reaction can be further extended to N-phenyl pyrrole. In the present multi-step reaction, PtCl(2) likely plays dual roles: as the catalyst for the rearrangement of propargyl alcohols to the corresponding alkenyl ketones and as the catalyst for the addition of indoles to the alkenyl ketones. Experimental evidence is provided to support the proposed mechanism.

The reaction of benzynes with N-heteroaromatics including quinolines, isoquinolines, and pyridines and various terminal alkynes or ketones with an alpha-hydrogen in the presence of KF and 18-crown-6 in THF at room temperature for 8 h gave various N-arylated 1,2-dihydroheteroaromatics in good to moderate yields. Some of these product structures are found in various naturally occurring and biologically active heterocyclic compounds. The reaction involves an unusual multiple construction of new C--C, C--N, and C--H bonds and the cleavage of a C--H bond in one pot. It is likely that the three-component coupling proceeds through the nucleophilic addition of quinoline to benzyne, which generates a zwitterionic species. The latter then attracts a proton from terminal alkyne (or ketone) to generate an N-arylated quinolinium cation and an acetylide anion. Further reaction of these two ions provides the final substituted 1,2-dihydroquinolines. In the reaction, the terminal alkyne acts first as a proton donor and then as a nucleophile. The application of a three-component coupling reaction product, 1,2-dihydro-2-pyridinyl alkyne in a stereospecific [4+2] Diels-Alder cycloaddition reaction with N-phenyl maleimide to give an isoquinuclidine derivative, an important core present in various natural products, is demonstrated.

An efficient short total synthesis of benzo[c]phenanthridine alkaloids including oxyavicine, oxynitidine, and oxysanguinarine is described. Thus, N-methyl-o-bromobenzaldimines 1 b-d undergo regioselective cyclization with 4-(benzo[d][1,3]dioxol-5-yl)but-3-yn-1-ol (2 b) in the presence of [Ni(cod)(2)] (cod=1,5-cyclooctadiene). In situ oxidation of the resultant isoquinolinium salts gives isoquinolinone derivatives 5 b-d with benzo[d][1,3]dioxol-5-yl substitution at the C(3) atom and a (CH(2))(2)OH group at the C(4) atom. Later, oxidation of the alcohol group in 5 b-d to the aldehyde moiety followed by acid-catalyzed cyclization and dehydration completes the total syntheses to give oxyavicine, oxynitidine, and oxysanguinarine in 67, 65, and 60 % yields, respectively. The synthesis requires four steps from o-bromobenzaldehyde derivatives. Transformations of these alkaloids to the other alkaloids in this family are also discussed herein.

We have synthesized three triptycene derivatives, TCTP (2,6,14-triscarbazolyltriptycene), TATP (2,6,14-tris-(diphenylamino)triptycene) and TPOTP (2,6,14-tris(diphenylphosphoryl)triptycene) which show very high triplet energy gaps (2.94–3.15 eV) and glass transition temperatures (Tgs) ≧ 170 °C. The HOMO and LUMO levels of these three materials indicate that TCTP and TATP possess hole transport characteristics, while TPOTP has electron transport characteristics. These carrier-transporting properties are further supported by the current density–voltage characteristics of the hole-only and electron-only devices of the materials. TATP could be employed as a general host for blue, green and red electrophosphorescence devices providing high brightness, and good current and power efficiencies. The devices using TCTP and TPOTP as the host for the phosphorescence emitter FIrpic showed maximum external quantum efficiencies as high as 10.1% and 16.9%, respectively. By using a blend of TCTP and TPOTP as blue co-host for FIrpic (iridium(III) bis(4,6-difluorophenylpyridinato)picolinate), the device shows an external quantum efficiency of 15.5% at 4.5 V, current efficiency (ηc) of 31.9 cd A−1 at 4.5 V, power efficiency (ηp) of 25.1 lm/W at 4.0 V, respectively. The co-host system greatly improves the performance of the device at normal operation brightness due to the decrease of driving voltage and the balance of hole and electron transport in the device.