N-ethyl Carbazole Research Articles

A new ligand for the formation of a 3D structure by C–H···O, O–H···O hydrogen-bonds and π–π interactions

A new functional flexible ligand: 3,6-di-(1,2,4-triazole-1-yl)- N-ethyl carbazole ( L) and Co (II) coordination polymer ( 1) have been synthesized and investigated. Single crystal X-ray analysis has revealed that the 3D coordination polymer is formed by interchains OH···O and CH···O hydrogen-bonds, interlayers CH···O hydrogen-bonds and π–π interactions. NO 3 - and H 2O play an important role in constructing 3D supramolecular architectures. The blue emissions from solid fluorescence indicate that the coordination complex 1 is a promising candidate for application in optoelectronic devices.

Oxidative electropolymerizations of carbazole derivatives in the presence of bithiophene

N-Ethylcarbazole (NECZ) or carbazole (CZ) and bithiophene (BT) have been used as a mixture of monomers for the formation of electrodeposited polymer and copolymer films on platinum electrode. When beginning with a NECZ–BT mixture, the peak intensity resulting from the composite film cycling decreases with increasing initial NECZ proportion until that proportion reaches 40%. For higher NECZ proportions, no deposit could be obtained. Infrared spectra of the deposits show the presence of the characteristic bands of both monomer units in the material. In the case of CZ–BT mixtures, the electrochemical behaviours of the composite films are close to those displayed by the homopolymers, i.e. polybithiophene or dicarbazyle, containing respectively low and high proportions of CZ. Furthermore, infrared and ultraviolet-visible studies of deposits obtained for various CZ proportions yield spectra that vary according to monomer proportion.

AN ELECTROCHEMICAL STUDY OF SOLUBLE COPOLYMER OF ETHYL CARBAZOLE WITH N-METHYL PYRROLE AND 3-METHYL THIOPHENE

Copolymers of N-ethyl Carbazole (ECZ) with N-Methyl Pyrrole (N-MPy) and 3-Methyl Thiophene (3-MTh) were synthesized on platinum substrate and electrochemical investigation of polymeric films was performed. The characterization of homopolymer and copolymer films was performed by electrochemical methods (i.e. polarization curves and cyclovoltammetric measurements), solid-state conductivity measurements and spectrophotometric methods comparatively. A possible scheme for the copolymerization has been suggested. Solid state conductivity of PECz can be improved by inclusion of 3MTh and NMPy into chain. The ionization potentials, Ip, electron affinity, Ea, optical band gap, Eg, peak potentials, Ep, and doping degrees, y, of copolymer electrodes were calculated from these measurements. Copolymer electrodes have lower Ip, Eg, Ep values and better switching properties in accordance with homopolymer electrodes. Presence of alkyl group gives solubility to copolymers obtained both chemically and electrochemically.

CONTROLLED ELECTROCOPOLYMERIZATION OF THIOPHENE WITH N-ETHYL CARBAZOLE: IN-SITU AND EX-SITU SPECTROELECTROCHEMICAL INVESTIGATION AND CONDUCTIVITY RELATIONSHIP

Polymerization of thiophene (Th) was studied in the presence of N-ethyl carbazole (ECz) by in-situ and ex-situ spectroelectrochemical measurements. In-situ spectroelectrochemical measurements allow determining some soluble thiophene oligomers. Cooligomeric species of Th-ECz (which give peaks at 376, 400 nm) are in parallel line with the findings from CV measurements (current values of peaks of electrogrowth of polymer). Results also suggest that ethylcarbazole and thiophene react on the electrode surface as well as in solution, and the percentage of ECz incorporated into the polymer structure is less than in the case of the electrode surface reaction. CV's of PECz, PTh and P [Th–co–ECz] formation indicate shifts in Ep and corresponding current changes. Increase in peak currents intensities of ECz in the presence of Th, Ip1 for ECz, Th, [Th–co–ECz] is 0.05 mA, 1.6 mA, 2.0 mA, respectively, giving a ratio of 1/32/40 (Ip1) and 1/9/21 (Ip2) supporting the inclusion of ECz into copolymer structure. The conductivities of PTh and copolymer-measured by four-point-probe technique (at mole ratio of nTh/nEcz = 25) were found as 42 mS/cm and 36 mS/cm, respectively, giving a ratio of 42/36 = 1.67, which is in line with Ip values of electro growth of copolymer on the Pt [i.e., for ratios of P[Th–co–Ecz]/PTh of Ip1 40/32 = 1.3 and for Ip2 = 21/9 = 2.3].

Evaluation of the parameters of 1:1 charge transfer complexes from spectrophotometric data by non-linear numerical method

The non-linear numerical method for evaluation of equilibrium constants and molar extinction coefficients of molecular complexes from a spectrophotometric experiment is described, which in contrast to linear models has no limitations with respect to concentrations of the components. The proposed procedure is applied to donor–acceptor interaction in solution between N-ethyl carbazole (EtCz) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) or n-hexyl 2,5,7-trinitro-9-dicyanomethylenefluorene-4-carboxylate (HexDTFC) to evaluate the method and to obtain the parameters of charge transfer complexes (CTCs) formation. Association constants ( K) and molar extinction coefficients ( ε) of CTCs derived from non-linear approach (EtCz–TCNQ: K=2.49±0.19 M −1; ε=2950±160 M −1 cm −1. EtCz–HexDTFC: K=12.1±0.3 M −1; ε=1335±24 M −1 cm −1) are close to that from linear models but show lower standard errors in parameter estimations.

Spectroelectrochemical study of N‐ethyl‐carbazole in the presence of acrylamide

AbstractPolymerization of N‐ethylcarbazole (NECz) in the presence of acrylamide (AAm) has been investigated by in situ and ex situ UV–visible spectrophotometric measurements to obtain information about the reaction pathway, because NECz gives soluble oligomeric species allowing such measurements. A tentative mechanism is proposed in the light of these results. The redox properties of the new polymers have been studied for possible sensor application.© 2001 Society of Chemical Industry

Resonance Raman spectroscopic studies on the conducting state of polyvinylcarbazole and its model compounds

The conductivity in polyvinylcarbazole (PCVz), a well known photoconducting polymer, has been attributed to the migration of the cation radicals along the chain. In this paper, chemically generated monomer and dimer radical cations of the carbazolyl group and the conducting form of PVCz have been investigated by resonance Raman (RR) spectroscopy. Vibrational assignments are presented for the observed frequencies by comparison with similar compounds and also by density functional theoretical calculations. The structure of the monomer and dimer radical cations have been inferred from the RR spectra. It has been observed that Raman bands of the radical cation of PVCz in which the charge is localized on the dimer, undergo a downshift compared to that of N-ethylcarbazole (NEC) dimer radical cation. This shift has been tentatively attributed to the interaction of the PVCz dimer radical cation with the neutral carbazole which may be facilitated by the conformational rearrangement required for the exchange of charge with neutral carbazole.

Enhancement of intersystem crossing by substitution: assignment of a long-lived triplet state by magnetic field effects in a non-viscous medium

The photoinduced electron transfer reactions in four similar donor–acceptor systems, N-ethyl carbazole (ECZ)-1,4-dicyanobenzene (DCB), 1,4,5,8,9-pentamethyl carbazole (PMC)-DCB, ECZ-1,2,4,5-tetracyanobenzene (TCNB) and PMC-TCNB have been studied to establish the effect of substitutions on the mechanistic pathways of electron transfer (ET) reactions. The initial spin states of the transients have been characterized by laser flash photolysis and magnetic field effect studies. The presence of more –CN groups in TCNB compared to DCB alters the ET pathways, by enhancing intersystem crossing. The temperature and free energy dependencies of these systems have been utilized to evaluate the process from the theoretical viewpoint.

Electronic structures of carbazole and its derivatives: A semi-empirical study on the substitution effects of carbazole

The electronic structures of carbazole, N-phenylcarbazole (NPC), cyanophenylcarbazole (CPC) and N-ethylcarbazole (NEC) have been calculated using the quantum chemical semi-empirical MINDO/3 method. In this paper, electronic ground states and first singlet excited states of the systems mentioned were investigated. It is observed that the excitation energy of carbazole based on the calculated difference in heats of formation agrees quite well with experimental data obtained from supersonic expansion studies. Calculated energy levels of molecular orbitals and their graphical forms are used qualitatively in elucidating the S 0 → S 1 excitation electronic origin red shifts observed in carbazole derivatives with respect to the electronic origin of the parent carbazole. It is noted that the red shifts are not just a result of the destabilization of the HOMO of carbazole but are also determined by the nature of the substituting moieties. It is also observed that the LUMO of CPC is not derived from the parent carbazole which partially explains the difference in electronic behaviour as compared with the other derivatives.

Spectroscopy and dynamics of jet-cooled aromatic amines, self and solvated complexes

Spectroscopic studies in nozzle expansions were carried out on dimethylamino-benzonitrile (DMABN), dimethyl amino methyl benzoate, dimethylamino ethyl benzoate, carbazole, N-ethyl carbazole, (4-cyano N-phenyl) carbazole; the complexes between DMABN and a variety of solvents; the complexes between 4ABN and polar and non-polar solvents; and the complex between carbazole and benzonitrile. All compounds were chosen because in polar solution, they exhibit anomalos fluorescence, characterised by being broad, and red-shifted, attributed to a Twisted Intramolecular Charge-Transfer (TICT) state. In the supersonic jet, red-shifted emission was frequently observed, but in no case could it be attributed unequivocally to TICT state emission. Alternatives are dimers, excimers, or self-complexes which could cluster solvents.

Kinetic and spectroscopic study of triplet state and ionic pathways in the laser-induced photoexcitation of N-ethylcarbazole in fluid solutions

When fluid solutions of N-ethylcarbazole (NEC) are irradiated by 308-nm pulses from an excimer laser, transient triplets and ions may be observed in the microsecond time regime. The formation of ions is favored in more polar solvents such as acetonitrile (AcN) and that of triplets in nonpolar solvents such as paraffin oil. The quantum yield of triplet formation from initial excitation is 0.23. Triplet states decay through concurrent first- and second-order channels: the second-order process, triplet-triplet annihilation, leads to formation of excited singlet states with an efficiency of 0.12. Transient carbazolyl cations and anions display double-exponential decays. To account for this behavior, a mechanism involving initial electron donation by the multiply excited chromophore to a nearby NEC molecule or solvent molecule is proposed; subsequent decay occurs primarily by germinate recombination of the resulting ion pair. The quantum yield for cation production is 0.037. Delayed fluorescence is AcN also decays by a double-exponential decay curve with rate constants, suggesting that the emission arises mainly from ion recombination.

Photoconductivity of sensitized poly( N-ethyl carbazole)methane with 2,4,7-trinitrofluorenone

Photoconductivity of poly( N-ethyl carbazolyle)methane was greatly enhanced in the visible region by the addition of a small amount of 2,4,7-trinitrofluorenone having a molar ratio of monomer:dopant from 1:0.06 to 1:0.3. The current-voltage characteristics were studied in the visible wavelength range, and the current increased superlinearly with the increase of doping level. The activation energies for dark and photoconductivity are 0.244–0.202 eV and 0.238–0.194 eV, respectively, at different doping levels. The photoresponse shows two charge transfer bands corresponding to two transitions of the complex.

Photophysics of photoconducting polymers with pendant bichromophores I: Intramolecular photoprocesses in 9-[γ-( N-carbazolyl)propyl]-9-methyl-2,7-dinitrofluorene

Electronic absorption and luminescence spectroscopies were used to study the intramolecular photoprocesses in the bichromophoric D—A compound 9-[γ-( N-carbazolyl)propyl]-9-methyl-2,7-dinitrofluorene ( II) together with the monochromophoric model molecules N-ethylcarbazole (NEC) and 9-γ-hydroxypropyl-9-methyl-2,7-dinitrofluorene ( I). It was shown that no intramolecular charge transfer interaction exists between the carbazolyl and the 2,7-dinitrofluorene chromophores in the electronic ground state of the bichromophoric compound II in EPA at room temperature and at 77 K. In contrast, the strong quenching effect of the fluorescence and phosphorescence emission of the carbazolyl chromophore in the bichromophoric molecule II was explained in terms of intramolecular energy transfer and the possible electron transfer interactions between the carbazolyl and the 2,7-dinitrofluorene groups. These two intramolecular photoprocesses in II were characterized well by the Förster critical transfer distance ( R 0 = 2.6 Å at 296 K and R 0 = 30.4 Å at 77 K) and by the Rehm-Weller free energy change of the electron transfer step (Δ G ET < 0) respectively. Electron transfer processes are usually facilitated by good orbital overlap, but this is not favored by the spatial conformation of the chromophores in II. This is in agreement with the fact that the phosphorescence lifetime (τ P = 0.12 ± 0.01) and the phosphorescence quantum yield (φ P = 0.060 ± 0.006) of the monochromophoric molecule I remain the same in II and in the polymer ( III) (polysebacate containing II as a pendant group). We concluded that long-range energy transfer (Förster type) seems to be the dominant path in these systems.

Synthesis and charge-transfer spectra of dinitrofluorenone-containing polyesters

π-Electron acceptor polyesters are synthesized by polycondensation of the cesium salt of 4,5-dinitrofluorenone-2,7-dicarboxylic acid with α,ω-dibromoalkanes and p-xylylene dibromide. The properties of the polyesters depend on the length of the hydrocarbon residue between the acceptor fragments. The charge-transfer complexes of the synthesized polyesters with N-ethyl carbazole, poly-N-vinyl carbazole, and poly-N-epoxypropyl carbazole are studied and it is established that in all cases their 1 : 1 complexes are formed. The stability constants are only weakly dependent on the length of the methylene chain of the polyesters.

Laser-induced fluorescence of jet-cooled complexes of carbazole and N-ethyl carbazole with alkyl cyanides

Fluorescence excitation spectra of complexes of carbazole and N-ethyl carbazole with a series of six alkyi cyanides, in a supersonic jet, are presented. The former chromophore undergoes hydrogen bonding with these ligands; N-ethylation of the chromophore prevents hydrogen bonding, but formation of complexes apparently similar in terms of both intermolecular interaction strength and geometry is observed.

One-electron photooxidation of N-ethylcarbazole in the presence of carbon tetrachloride. Products and mechanism of the photochemical reaction

The mechanism of the photodecomposition of N-ethylcarbazole (NEC) in the presence of carbon tetrachloride has been discussed on the basis of the photoproducts identified. The photodissociation of the N-ethyl bond and the electron transfer in the transiently formed ex-CT complex, [Formula: see text], have been proposed as the primary photochemical processes involved irr the singlet excited NEC molecule. The latter, treated as the main process, leads to the radical cation of NEC, chloride ion, and trichloromethyl radical in the solvent cage, [NEC+•Cl−ĊCl3]. The other reactions in the system studied are analysed following the decomposition of NEC+• in the presence of Cl− and ĊCl3, which can occur by the N-ethyl group and (or) by the aromatic ring. The formation of intermediate products such as[Formula: see text]in the solvent cage gives rise to secondary photochemical reactions in the system studied. The polarity and chemical activity of the reaction media used strongly influence the nature of the secondary photochemical transformations both in and outside the solvent cage. The formation mechanism of the photochemical reaction products in CCl4 when ammonia was used, after and during irradiation, has been explained mainly by the transformations of the radical αr and cation αk as well as by the carbazyl radical β, which is also formed in the reaction medium. On the other hand, reaction of the cation [Formula: see text] explains the formation of the photoproducts in the irradiated solution of NEC with CCl4 in ethanol. These photochemical results have been compared to the photochemical reactions involved in the carbazole–CCl4 system.

HOW HYDROGEN BONDING OF CARBAZOLE TO ETHANOL AFFECTS ITS FLUORESCENCE QUENCHING RATE BY ELECTRON ACCEPTOR QUENCHER MOLECULES

— Absorption spectra and fluorescence quenching of carbazole (C) and N-ethyl carbazole (EC) by some aliphatic halocarbons have been studied in 3-methylpentane (3MP) and ethanol (EtOH). Both steady-state and transient kinetic measurements were used to determine the quenching rate constants (kq). These rate constants were found to be sensitive to the polarity and also to the hydrogen bonding ability of the solvents used. Endothermic electron transfer reactions were shown to take place in these systems. When the electron donor C is involved in hydrogen bonding with EtOH, the net effect is a decrease in kq. This is explained by taking into account the red-shifted (0,0) transition energy (Es) of the 1Lb absorption band when the reaction is nearly diffusion controlled. For reaction far from diffusion controlled, the Es value correction to kq is not enough to explain the low kqvalue observed.

Molecular relaxation processes in poly( N-acryloyl-10,11-dihydrodibenz [ b, f]azepine)

The preparation and homopolymerization of N-acryloyl-10,11-dihydrodibenz[ b, f]azepine is described. The relaxation behaviour is characterized using dielectric relaxation, pulsed n.m.r. and thermally stimulated depolarization (t.s.d.) techniques. In order to assist the assignment of relaxation data to molecular behaviour 5-chloroacetyl and 5-propionyl derivatives of iminobibenzyl were prepared and studied by dielectric relaxation in the matrix-isolated state. Comparison with N-ethyl carbazole under similar conditions revealed the existence of a relaxation in the polymer associated with nitrogen inversion in addition to a relaxation due to the glass transition. The data may be useful in studies relating to the pharmacological activity of the dibenz[ b, f]azepine ring system.

Kinetics of complex formation of poly-n-vinyl carbazole and n-ethyl carbazole with electron acceptors at different molar ratios

The rates of complex formation for poly-N-vinyl carbazole and its saturated low molecular analogue, N-ethyl carbazole, with tetracyanoethylene, chloranil, trinitrobenzene and picric acid in chloroform solution have been investigated at molar ratios of donor to acceptor, D/ A = 1, 2, 4, 8 and 10. The reaction rate was studied by the “stopped flow” method. At mole ratio D/ A > 1 the complex forming reactions follow kinetics of first order. The apparent rate constants were calculated by the least squares method. The complex formation rate constants for the monomer analogue are higher than those for the polymer. They also depend on the electron affinity of the acceptor. The reaction rate rises with increase of the electron affinity of the acceptor.

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 10 3 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.