Rate of complex formation for poly-n-vinyl carbazole and n-ethyl carbazole with various electron acceptors

The rates of complex formation for poly-N-vinyl carbazole and its saturated monomer analogue, N-ethyl carbazole, with various electron acceptors (chloranil, trinitrobenzene and picric acid) have been investigated. In mole ratios 1:1, the complex forming reactions in chloroform proceed rapidly, as measured by a “stopped flow” method; the rate constants are of the order of 10³ 1. mole^?1 sec^?1. The rate constants are smaller than those of the complexes with tetracyanoethylene as acceptor and decrease with decreasing electron affinity of the acceptor. The rate constants also depend on the molecular weight of the donor.     

痂囊腔菌素A与咔唑化合物间的光致电子转移

研究了咔唑、咔唑-9-乙酸、3-溴-咔唑-9-乙酸在缺氧条件下对天然苝醌化合物痂囊腔菌素A(简记为EA)的荧光猝灭行为;由竹红菌甲素(HA)和乙素(HB)的荧光寿命估算了EA在乙腈中的荧光寿命,并进而计算了三个咔唑化合物的双分子猝灭速度常数.结果表明,三个咔唑化合物在EA的可见光吸收区无光吸收,据此推测其对EA的荧光猝灭作用归因于咔唑化合物作为电子给体而EA作为电子受体的光致电子转移作用.三个咔唑化合物的Stern-Volmer猝灭常数分别为698、704和1 063L·mol-1;乙酸基对咔唑环的光致电子转移速率几乎没有影响,而溴原子取代能够增加咔唑化合物对EA的荧光猝灭程度和光致电子转移速率.此外,EA在乙腈中的荧光寿命为1.98ns,而三个咔唑化合物的双分子猝灭速率常数分别为3.52×1011,3.56×1011和5.37×1011 L·mol-1·s-1.     

Excited-state proton transfer kinetics of carbazole

Rate constants for the excited-state proton transfer reaction of carbazole in aqueous alkaline solution have been determined using picosecond single photon counting. Fluorescence decay measurements show that the back reaction is slow compared to the fluorescence decay time and therefore equilibrium is not attained in the excited state. The validity of a pK value for the lowest excited state determined from steady-state fluorescence measurements assuming equilibrium is discussed. It is concluded that the thermodynamic pK^* value for carbazole is 10.98.     

Random multiacceptor poly(2,7‐carbazole) derivatives containing the pentacyclic lactam acceptor unit TPTI for bulk heterojunction solar cells

Here, a family of donor/acceptor (D/A) alternating copolymers and random two‐acceptor and three‐acceptor copolymers were synthesized via Suzuki polymerization based on heptadecan‐9‐yl substituted carbazole as a donor and 4,7‐Bis(5‐bromothiophene‐2‐yl)benzo[c][1,2,5]thiadiazole (DTBT), 2,5‐diethylhexyl‐3,6‐bis(5‐bromothiophene‐2‐yl)pyrrolo[3,4‐c]‐pyrrole‐1,4‐dione (DPP) and 2,8‐dibromo‐4,10‐bis(2‐ethylhexyl)thieno[2′,3′:5,6] pyrido[3,4‐g]thieno[3,2‐c]isoquinoline‐5,11(4H,10H)‐dione (TPTI) as acceptors. For the first time, a relatively new electron‐deficient TPTI unit was used as an acceptor in carbazole‐based conjugated polymers. Introduction of the electron‐deficient TPTI unit into the polymer backbone increased the open‐circuit voltage (V_oc) of the resulting polymer solar cells up to 0.96 V. PCTPTI and PCDTBT‐TPTI exhibited external quantum efficiencies (EQE) up to 75%. All random two‐acceptor copolymers showed broadened absorption profiles compared to the D/A alternating analogues. In order to further improve the light absorption, a random three‐acceptor copolymer was synthesized for the first time, resulting in the broadest absorption in the range of 350–750 nm. Highest occupied molecular orbital (HOMO) energies and V_oc values of the resulting polymers could be successfully tuned by introducing different monomer units into the polymer backbone in different ratios. These results indicate that TPTI is a promising acceptor unit for conjugated polymers and that the random copolymer approach is a successful tool for fine tuning of polymer properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2781–2786     

Spectrophotometric studies of the formation of charge transfer complex of iron(III) with N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane di-Schiff base ligand in methanol

The complex formation reaction between N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) di-Schiff base ligand as an electron donor and iron(III) chloride as an electron acceptor have been studied spectrophometrically in methanol at 28°C. The values of equilibrium constants, K and molar absorptivities, ε were obtained from the Benesi–Hildebrand, Scott and Foster–Hammick–Wardley equations. The results indicate the formation of 1?:?1 charge transfer complex. The absorption band energy of the complex, E _CT, the ionization potential of the BPIE Schiff base ligand, I ^D, and the Gibbs energy changes of the above reaction, ΔG ⁰, were calculated. Finally, the kinetics of the complex formation reaction were studied and was found to be second-order in each reactant. The values of the rate constants of the forward and reverse reactions k ₁ and k _?1 were determined.     

New aromatic-aliphatic polyesters based on N-alkyl carbazole groups in the main chain. Synthesis-structure-properties relationships

Polyesters based on N-butyl or N-octylcarbazole units in the main chain were synthesized either by direct polycondensation between the carbazole dicarboxylic acids and ethylene glycol or from alcoholysis of the 2-hydroxyethyl diesters in the presence of different catalytic systems. Depending on the reaction conditions together with the nature and the concentration of the catalyst, diethylene glycol (DEG) is formed as a side-reaction product. DEG is incorporated in the polyester chain concurrently with EG and leads to the formation of ether links in the spacers. The DEG content as well as the length of the alkyl pendant group of the carbazole unit were found to have a drastical effect on the thermal properties. Furthermore, these materials form charge transfer complexes through carbazole nuclei with electron acceptor and electron donor molecules as well.     

苯二甲酸二甲酯对咔唑荧光的淬灭

用邻苯二甲酸二甲酯(DMTP)可猝灭咔唑的荧光,由此相反,在DMTP-乙基咔唑体系中,末观察到激基复合物荧光.本文对此解释为激基复合物的形成能力不仅依赖于电子给予体的电离势和电子接受体的电子亲和力,而且还取决于附着于电子给予体和电子接受体的生色团上侧基间的相互作用.     

Novel liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties for fluorescent OLEDs

A novel class of nematic liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties has been synthesised using simple and highly efficient reaction pathways. The electroluminescent colour of these novel oligomers can be varied in a controlled manner by molecular design. The values of the ionisation potential and the electron affinity of these electroluminescent oligomers can also be matched by structural design to the Highest Occupied Molecular Orbital (HOMO) energy level of the electron-blocking layer and the Lowest Unoccupied Molecular Orbital (LUMO) energy level of electron-transporting layer in the Organic light emitting diodes to create low charge-injection barriers for electrons and holes, respectively leading to electroluminescence with an efficacy up to 4.1 cd A^?1.     

Electron donor-acceptor interaction of 3,4-dimethylaniline with 2,3-dicyano-1,4-naphthoquinone

The electron donor–acceptor (EDA) interaction between 2,3-dicyano-1,4-naphthoquinone (DCNQ) and 3,4-dimethylaniline (3,4-DMA) is studied in chloroform, dichloromethane and 1:1 (v/v) mixture of chloroform and dichloromethane. The rate of formation of the product was measured as a function of time using UV–vis spectrophotometer. The formation constant (K) and molar extinction coefficient (?) values for the formation of EDA complex were evaluated in the temperature range of 20–35 °C. The pseudo-first-order rate constant (k₁) and the second-order rate constant (k₂) for the disappearance of EDA complex and for the formation of product were evaluated. The activation parameters (ΔH^#, ΔS^# and ΔG^#) of the reaction were determined by temperature dependence of rate constants using the Arrhenius plots. The effect of relative permittivity of the medium on the reaction is discussed. The observed results indicate that formation of final product proceeds through initial formation of EDA complex as an intermediate. The product of the reaction was purified by column chromatography method and identified as 3-(N-3,4-dimethyl-phenylamino)-2-cyano-1,4-naphthoquinone by elemental analysis, IR and NMR spectroscopy. On the basis of kinetic, analytical and spectroscopic results, a plausible mechanism for the formation of EDA complex and its transformation into product is proposed.     

A novel total synthesis of the bioactive poly-substituted carbazole alkaloid carbazomadurin A

A new total synthesis of the neuronal cell-protecting carbazole alkaloid carbazomadurin A is described. The key step was an allene-mediated electrocyclic reaction involving an indole [b]-bond for the construction of a highly substituted carbazole ring. The E-alkenyl side chain at the C1 position of carbazole was introduced between O-triflate and alkenyl pinacol borate using the Suzuki-Miyaura reaction. SEM groups were cleaved with TBAF and the formyl group was reduced to provide carbazomadurin A.     

Photoinduced intramolecular electron transfer between fluorescein and carbazole

Several dyads consisting of a fluoreseein covalently linked with a carhazole at site 2 or site 6 have been synthesized and characterized.Studies of absorption spectra,emission spectra and fluorescence lifetime quern hing Indicate that the ground-state interaction between fluorescein and carhazole in dyads is negligible and the intramolecular electron transfer (ET) reactions are mainly of dynamic process.Moreover,the efficiency and raie conslam of lectron transfer reactions in ZFO4 (carbazole linked at site 2'of fluorescein) are larg er than those in 4FOZ (carbazole linked at site 6 of fluorescein) 0 74; KET 11×108S-1),because the mutual orientation of donor and acceptor in ZFO4 is nearly face-to-face,which is more favorable to the process than the shoulder-to-shoulder mutual orientation in 4FOZ.Estimations are also formed of the free energy change of the photomduced electron transfer and the back reactions in the dyads.     

Novel carbazole dendrimers having a metal coordination site as a unique hole-transport material

We have synthesized novel carbazole dendrimers via the cyclotrimerization of aminophenylketones in the presence of titanium tetrachloride. These dendrimers have the ability to assemble metal ions such as Sn²⁺ and Eu³⁺ with no significant difference in their generation, suggesting the dendrimer with an interior with a small density up to the third generation. We show the dendrimers with higher generations have the higher HOMO values. The most electron rich molecule, the G3 dendrimer, has the highest HOMO value of −5.2 eV. However, for the HOMO energy levels of the carbazole dendrimer complex with Eu(OTf)₃, the energy levels of the carbazoles did not change based on almost the same redox potentials as those of the dendrimers, themselves. Using the carbazole dendrimers and their europium complex, a homogeneous film was produced, which enhanced the performance of the electroluminescence device in comparison with only the dendrimer as the hole-transporting layer. This approach was managed by a solution process, i.e., the spin-coating method, without using the coevaporation technique based on the large equilibrium constants of the coordination of metal ions on the imine sites (K = 10⁵ M⁻¹).     

Intra- and intermolecular quenching of carbazole photoluminescence by imidazolidine radicals

Mechanisms of carbazole photoluminescence quenching by the free and chemically bound nitroxyl radicals in the model bound system “carbazole (CBZ)—imidazolidine nitroxyl radical R^•” were investigated and the photophysical properties of the system were studied and compared with those of free CBZ and R^• in solution. The quantum yield and lifetime of fluorescence from the local singlet excited state of the carbazole moiety in the bound CBZ—R^• system is three orders of magnitude lower than in free CBZ. The lifetime of the local triplet excited state of the carbazole moiety in the bound system is shorter than 50 ns. The rate constants for intermolecular quenching of the singlet and triplet excited states of free CBZ by R^• in acetonitrile were found to be (1.4±0.1)·10¹⁰ and (1.5±0.2)·10⁹ L mol⁻¹ s⁻¹, respectively. The most plausible mechanisms of both free and covalently bound carbazole luminescence quenching by nitroxyl radicals are exchange energy transfer and acceleration of internal conversion due to electron exchange.     

Photophysics of intramolecular electron donor—acceptor systems; N-carbazolyl(CH2)ntetrachlorophthalimide

In systems N-carbazolyl—(CH₂)_n—tetrachlorophthalimide (n = 2, 3, 4, 7) virtually complete quenching of the carbazole fluorescence via an intramolecular electron-transfer mechanism occurs, with concomitant formation of an emissive polar excited state. The rate of formation of this polar excited state is found to exceed considerably those reported for formation of intramolecular exciplex states in other non-conjugated bichromophoric systems with a less pronounced electron donor—acceptor character.     

Charge transfer complexes of N-substituted 2-pyrrolidinones

The complex formation of 1-ethyl-2-pyrrolidinone, 1-benzyl-2-pyrrolidinone and 1-phenyl-2-pyrrolidinone with iodine, iodine monobromide and iodine monochloride has been studied by u.v. and visible spectroscopic methods in carbon tetrachloride, dichloromethane, 1,2-dichloroethane, n-heptane and cyclohexane. The results show the equilibrium constants (K), complexation enthalpies (ΔH) and the wavelengths of maximum absorption bands (λ_max) of the complexes to vary markedly with the solvent. The decrease in the K values with increasing acceptor number (AN) of the solvent may be due to the competition of the solvent and the halogen molecule for the amide; for halogenated hydrocarbon solvents can act as weak electron acceptors. The complex formation ability of the electron donors decreases in the order 1-ethyl-2-pyrrolidinone ⪢ 1-benzyl-2-pyrrolidinone ⪢ 1-phenyl-2-pyrrolidinone, and the electron acceptor properties decrease in the order iodine monochloride ⪢ iodine monobromide ⪢ iodine.     

The two-photon excitation spectrum of a carbazole single crystal at 4.2 K

The low-energy system in the polarized two-photon excitation spectrum of carbazole at 4.2 K has been measured by detecting fluorescence pulses from deliberately added anthracene. Herzberg—Teller activity was detected for Some A₁ vibrations. The two-photon operators contribute to the two-photon cross section in the order yy ≈ zz ? xx.     

Solvent effects on kinetics of an heteroatomic nucleophilic substitution reaction in ionic liquid and molecular solvents mixtures

Rate constants, k _A, for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 2-propanol mixed with hexane, benzene, and 2-methylpropan-2-ol and 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO₄]) with dimethyl sulfoxide at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: 2-methylpropan-2-ol > dimethyl sulfoxide > 2-propanol > hexane > benzene > [Emim][EtSO₄]. Molecularmicroscopic solvent parameters corresponding to the selected binary mixtures were utilized to study the kinetics of a nucleophilic substitution reaction in order to investigate and compare the effects of the solvents on a chemical process. The influence of solvent parameters including normalized polarity (E _T ^N ), dipolarity/polarizability (π*), hydrogen bond donor acidity (α), and hydrogen bond acceptor basicity (β) on the second-order rate constants were investigated and multiple linear regressions gave much better results with regard to single parameter regressions. The dipolarity/polarizability of media has a positive effect in all mixtures regarding zwitterionic character of the reaction intermediate and the hydrogen bond acceptor basicity of the solvent by stabilizing of activated complex increases the reaction rate.     

Photoinduced intramolecular electron transfer of fluorescein and violgen, carbazole

A series of polyads consisting of covalently-(CH2)4-linked fluorescein with carbazole and violger.Live been synthesized and characterized The studies of absorption,emission spectra and fluorescence lifetime quenching indicated that the intramolecular fluorescence quenching of fluorescein by violgen is mainly a static process through the formation of non emission complex (fluorescence quenching efficiency φQ=0.97,lifetime quenching efficiency φH 0,quenching efficiency of formation of non-emission complex φC=0.97); while the quenching by carbazole is mainly a dynamic electron transfer process (φQ=0.63,φET=0.63,φC=0).In the violgen-fluorescein-carbazole triads,φQ=0.97,Q ET=0.65,φC=0.32,which suggests that the photoinduced interaction of fluorescein-carbazole pair and that of violgen-fluorescein pair are in a competitive process,the dynamic electron transfer from carbazole to fluorecein is dominant in the process The free energy change of the photoinduced electron transfer and the back reac-tiorns i     

N-Arylation of carbazole by microwave-assisted ligand-free catalytic CuI reaction

N-Arylation of carbazole has been achieved in high yields within 1 h using a microwave-assisted catalytic CuI reaction with no organic ligand. The N-arylation can be performed by various arylhalides, such as phenyl, pyridine, thiophene, and thiazole moieties. Specifically, N-arylated bromocarbazoles were converted into useful synthetic intermediates for functionalized carbazole materials.     

Stilbene like carbazole dimer-based electroluminescent materials

Two carbazole dimers (1 and 10) were synthesized from 9-ethyl-9H-carbazole-3-carbaldehyde and 6-bromo-9-ethyl-9H-carbazole-3-carbaldehyde by McMurry C-C coupling reaction. Palladium(0)-catalyzed C-N coupling reactions of 10 and various diarylamines result in the formation of stable carbazole derivatives in good yields. These compounds are fluorescent in blue to yellow region with moderate to good quantum yields. Also, they are thermally stable and capable of hole-transporting due to the presence of the carbazole moieties. The electroluminescent devices fabricated using 1, 2, and 3 as hole-transporters/emitters with a bilayer structure ITO/Cpd/TPBI or Alq₃/LiF/Al (Cpd=1, 2, and 3) exhibit good performance (e.g., η_ext=1.0-2.1%; η_p=0.9-1.9 lm/W; η_c=2.4-4.8 cd/A at a current density of 100 mA/cm²).