Pendant Carbazolyl Groups Research Articles

Wide bandgap poly(meta-styrene) derivatives containing pendant carbazolyl groups as hosts for efficient solution-processed organic light emitting diodes

Two novel wide bandgap poly(meta-styrene) derivatives as hosts for solution-processed organic light emitting diodes were synthesized via free-radical polymerization.

Synthesis and study of a new polyorganophosphazene

AbstractIn this study, a new polyorganophosphazene with pendant carbazolyl groups was synthesized, and its structure was characterized by IR, 1H‐NMR, and 31P‐NMR spectroscopy. To understand its carrier photogeneration and transport property, we also studied fluorescence spectra and photovoltage spectra. Fluorescence spectra show that the polymer possesses properties dissimilar to those of PVK. There are only two emission peaks at ≈ 360 nm in its spectra, which coincides with that of the monomer model compound, 9‐ethylcarbazole. This may be because of the influence of the spacer. The results of SPS shows that band–band transition mainly comes from electron π–π* transition, and the polymer is a p‐type semiconductor. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1446–1451, 2001

Synthesis and characterization of bi-functional photorefractive polymers

A novel bi-functional photorefractive acrylate polymer with pendant carbazolyl groups and azo derivatives as side chains was synthesized, in which azo derivatives as electro-optic chromophores and carbazolyl as photoconductive moiety were covalently linked on the acrylate backbone. Photorefractive experiments showed that a high two-beam coupling gain coefficient of 93cm−1, diffraction efficiency of 12% and electro-optic coefficient of 26pm/V were obtained. With increasing writing beam's intensity, the two-beam coupling enhanced gradually, and then reached saturation. Using the method of four-wave mixing, the photoisomerization grating was observed.

Photoconductivity in polymers. Chemical structures and physical mechanisms

AbstractSynthesis and photoconductivity measurements are presented for two different types of photoconductors: i) polymers with pendant carbazolyl groups and ii) conjugated polymers. The temperature‐ and field dependence of the effective carrier mobility has been measured in a series of polymethacrylates with pendant carbazolyl groups and is discussed in relation to theoretical models. Time‐of‐flight measurements show that conjugated polymers like poly(methylphenylsilane) and poly(1,4‐phenylenevinylene) exhibit extremely high carrier mobilities.

Polymers with pendant carbazolyl groups, 5. Photoconductive properties of some carbazole derivatives with electron donor and acceptor groups

AbstractIn this paper photocurrents of N‐isopropylcarbazole (NIPC) derivatives in polycarbonate hosts are reported and compared to data for a benzotriazole derivative (BTA). The carbazole moiety was substituted with both electron donor and acceptor substituents and the photoconductivity was measured as a function of concentration, electrical field, and temperature using the time‐of‐flight (TOF) technique. The observed increase of the effective mobility of charge carriers at low dopant concentrations upon substitution with a moderate electron acceptor is in contrast to literature data for some other materials. We interpret this increase as being due to an increase in the delocalisation radius of the transport state of the substituted carbazole molecule. The field dependence of the effective mobility shows Poole‐Frenkel behaviour, which is attributed to polaron formation. Comparison of the effective mobility of the NIPC derivatives with BTA shows that the size of the molecule plays a decisive role for the absolute value of the effective mobility.

Polymers with pendant carbazolyl groups, 4. Photoconductive properties of some polysiloxanes with pendant carbazolyl groups

AbstractThe photoconductive properties of a series of polysiloxanes with pendant carbazolyl groups (1a—c) are described. In these polymers the carbazole moieties are separated from the siloxane backbone by alkylene spacers of different length. The properties of the novel compounds are compared with the well known photoconductor poly(N‐vinylcarbazole) and the model compound N‐isopropylcarbazole. Effective charge carrier mobilities were measured by means of the time‐of‐flight technique. Polymer 1a exhibits the largest carrier mobility of the three polysiloxanes. The mobilities for polymers 1b and 1c are somewhat smaller and comparable to poly(N‐vinylcarbazole). The transport of charge carriers in an amorphous material can be described as a hopping process. The activation energy for that process was calculated from the temperature dependence of the carrier mobility. The polysiloxanes 1a—c show the same activation energy of about 0,6 eV. The activation energies in poly(N‐vinylcarbazole) and N‐isopropylcarbazole are of the same magnitude as in the polysiloxanes. Two different models were used for evaluating the mobility data. The field dependence of the carrier mobility is best described by a modified version of Gill's model whereas no distinction between the two models could be made from the temperature dependence of the mobility.

Polymers with pendant carbazolyl groups, 2. Synthesis and characterization of some novel liquid crystalline polysiloxanes

AbstractThe synthesis of the liquid crystalline polysiloxanes 8a‐c is reported. In these polymers carbazolyl groups are incorporated in the mesogenic units. 8a‐c were prepared from the Schiff's bases 7a‐c and poly(hydrogenmethylsiloxane) in a polymer analogous reaction. The liquid crystalline polymers were characterized by DSC and polarizing microscopy. The Schiff's bases 7a‐c are nematic, whereas the polysiloxanes 8a‐c exhibit smectic mesophases within a broad temperature range. Unfortunately, the polymers show no remarkable increase of conductivity upon illumination.

Donor acceptor interactions in polymeric systems, 6. Effects of the molecular weight of carbazolyl containing polyesters and the length of spacer between donor groups on the complex formation with 2,4,7‐trinitrofluorenone

AbstractEDA complex formation between 2,4,7‐trinitrofluorenone (TNF) and polyesters bearing pendant 9‐carbazolyl groups was studied in ethylene dichloride. The formation constant (K) decreases with increasing length of the main chain repeating units separating pendant donor groups and with decreasing degree of polycondensation. In all cases, the values of K in polymeric systems are larger than those for the monomer model system by factors less than three. Thermodynamic parameters for complex formation were also determined. The general trend of the polymer effect is to increase − ΔH, while the entropy term is not much different from the monomer model system. The origin of polymer effects is interpreted as due not only to neighbouring group effects but also to remote group effects, and simultaneous participation of more than one carbazolyl group in complexing an acceptor molecule is considered. The results are compared with the EDA complex formation by ethylenic polymers and polyurethanes with pendant carbazolyl groups.

Donor acceptor interactions in polymeric systems, 5. A polyurethane with pendant carbazolyl groups

AbstractA polyurethane having pendant carbazolyl groups separated by four methylene groups was prepared and the EDA complex formation with 2,4,7‐trinitrofluorenone (TNF) was studied in chloroform. EDA complexes of the polymer and the monomer model compound are spectroscopically indistinguishable. The formation constant (K) of the polymer complex is about equal to that of the monomer model compound in the oligomeric range whereas K increases with increasing molecular weight of the polymer. This trend of polymer effect is the same for the complex formation with other acceptors such as tetracyanoethylene (TCNE) and 1,3,5‐trinitrobenzene (TNB). The formation of the polymer complex is entropically favoured although the negative enthalpy change is larger for the monomer model compound. The reasons are discussed.

Donor acceptor interactions in polymeric systems, 7. Structure matching effect in interpolymer EDA complex formation

AbstractInterpolymer EDA complex formation between polyesters bearing pendant carbazolyl groups and polyurethanes bearing pendant trinitrofluorenonyl groups was investigated in dioxane at 25°C. Complex formation depends on the degree of polycondensation (DP) as well as on structure matching of polymeric D and polymeric A. With increasing DP, the solubility of the D polymer‐A polymer mixture trends to decrease. Even when the polymer complexes do not precipitate, the Ketelaar's plots do not always fall on a straight line. These phenomena were interpreted as due to higher order complex formation and/or dependence of the formation constant on the fraction of saturation. It was found that polymeric donor acceptor pairs in which the number of atoms in a repeating main chain unit are identical for D and A polymers form a stronger complex than other combinations. It was concluded that structure matching of an interacting pair is a favourable condition to form tight complexes as in the case of antigenantibody interactions.

Ionic photodissociation of some polymers quenched with electron donor or acceptor in solution

Ionic photodissociation processes of vinyl polymers with pendant carbazolyl groups in solution have been studied by nonsecond laser photolysis. The ionic dissociation yield decreases in the order of monomer, oligomers, and polymers.

Singlet Excitation Energy Transfer in the Vinyl Polymers with Pendant Carbazolyl Groups

Abstract The migration of electronic excitation energy in films of poly(N-vinylcarbazole) (PVCz) prepared by the radical and cationic polymerizations(PVCz(r) and PVCz(c) respectively), poly[2-(9-carbazolyl)ethyl vinyl ether] (PCz-EVE), brominated PVCz(BPVCz), and poly(9-acryloylcarbazole) (PACz) has been studied by means of fluorescence-quenching experiments, using dimethyl terephthalate or perylene as a guest molecule. No clear difference in the concentration of the effective intrinsic trap sites was observed between PVCz(r) and PVCz(c) films. The concentration of the sandwich-like excimer site(cE) in a PVCz(r) film was nearly equal to that in a PVCz(c) film, while the concentration of the second excimer site (cS) in a PVCz(r) film was higher than that in a PVCz(c) film by a factor of about 1.6. The value of cE was much larger than that of cS for both films. The second excimer site seems to be a shallow trap. The number of carbazolyl chromophores covered by a singlet exciton during the lifetime was in the following order: PCzEVE>PVCz(r)≈PVCz(c)>PACz≈BPVCz. This order was explained by the concentration of the intrinsic trap sites depending on the distance between neighboring Cz chromophores, the lifetime of the singlet exciton, and the concentration of extrinsic trap sites.

Carbon‐13 and proton magnetic resonance studies of poly(N‐vinylcarbazole) in solution

AbstractSpin‐lattice relaxation times T1 of individual carbons and protons were measured by the partially relaxed Fourier transform (PRFT) method for poly(N‐vinylcarbazole) in solution. The 13C‐T1 value of the methylene carbon is about one‐half of that of the methine carbon, and the carbazolyl CH carbons have T1 values close to that of the skeletal CH carbons. The effective correlation time for the skeletal carbon is estimated as ca. 0,95 ns on the basis of the measured T1 and 13C‐1H nuclear Overhauser effect (NOE) factor. Moreover, the 13C normal Fourier transformation (NFT) spectrum and proton T1 indicate strong steric interactions between the pendant carbazolyl groups in the polymer. The results demonstrate that the polymer in solution has a rigid local structure with hindered internal rotation of the bulky side‐chain groups.

Emission Spectra of the Vinyl Polymers with Pendant Carbazolyl Groups

Abstract The emission properties of poly(N-vinylcarbazole) (PVCz) prepared by radical and cationic polymerization (PVCz(r) and PVCz(c) respectively), the oligomers of N-vinylcarbazole, and poly[2-(N-carbazolyl)ethyl vinyl ether] (PCzEVE) were investigated in solutions. The fluorescence spectrum of PVCz(r) was different from that of PVCz(c). This seems to be attributable to the difference in the tacticity between them. On the basis of this result, the structure of the second excimer site is discussed. PCzEVE, in which the carbazolyl chromophores are widely spaced on the skeletal chains by –O–CH2–CH2– bonds, showed an interesting, new, structureless emission band with a peak at 27000 cm−1. This was different from both the monomeric structured fluorescence and the sandwich-like excimer one which were observed for the model compounds and the polymers. The emission properties of PCzEVE were unique among the vinyl polymers with aromatic chromophores widely spaced on the skeletal chain.

Triplet Excitation Energy Transfer in the Vinyl Polymers with Pendant Carbazolyl Groups

Abstract The triplet energy transfer in poly(N-vinylcarbazole)(PVCz) prepared by radical and cationic polymerization (PVCz(r) and PVCz(c) respectively), poly[2-(N-carbazolyl)ethyl vinyl ether](PCzEVE), and brominated PVCz (BPVCz) has been investigated by measuring the delayed emission spectra in solid films and rigid solutions at 77 K. The prompt and delayed fluorescence spectra both in the solid film and in the rigid solution at 77 K were different for PVCz(r) and PVCz(c). This seems to be due to the difference in tacticity between them. PCzEVE, in which the Cz groups are connected from afar to the skeletal chains by means of –O–CH2–CH2–bonds, showed the delayed fluorescence and the phosphorescence both in the rigid solutions and in the solid films at 77 K. The BPVCz film showed only the excimer phosphorescence. In the solid films of PVCz(r), PVCz(c), and PCzEVE, the Cz chromophore-delayed fluorescence increased with an increase in the concentration of triplet quenchers, such as naphthalene and fluorene. This phenomenon suggests the presence of a heterogeneous triplet-triplet annihilation in these aromatic vinyl polymer films. The quenching of the Cz chromophore phosphorescence both by the doping of the naphthalene in the solid films and by the doping of the 1,3-pentadiene in the rigid solutions obeyed the Stern-Volmer equation, and the migration coefficient, λ, and the mean exciton migration length, L, were obtained. The values of λ and L were in the following order; PVCz(r)>PVCz(c)>PCzEVE (>BPVCz) in the solid film and PVCz(r)>PVCz(c) in the rigid solutions. The order was explained by both the concentration of the intrinsic trap sites for triplet excitons and the distance between neighboring Cz chromophores in one polymer chain.

Photoconductivity of poly(N‐acryloylcarbazole)

AbstractThe photoconductivity of poly(N‐acryloylcarbazole) (PACz), with the pendant carbazolyl group only a short distance from the skeletal chain of the polymer but separated from it by a carbonyl group, is investigated and compared with that of poly(N‐vinylcarbazole) (PVCz). There is no significant difference between PACz and PVCz in the temperature, light intensity, and spectral dependences of the photocurrent. The photoconductivity of PACz, however, is much inferior to that of PVCz and even to that of poly(N‐carbazolylethylvinylether), a representative vinyl polymer with pendant carbazolyl groups far from the skeletal chain. The poor photoconductivity of PACz is discussed in relation to the intensity of the electronic interaction between neighboring carbazolyl groups in the polymer chain and to singlet exciton migration. It is attributed mainly to an extremely low efficiency of extrinsic carrier generation via a singlet exciton, which is due to the poor electron‐donating character and the extremely short lifetime of a singlet exciton in the presence of the carbonyl group.

Photoconductivity of Poly(N-vinylcarbazole). VI. Photocoductivity of PoIy(β-N-carbazoIylethyl vinyl ether)

β-N-carbazolylethyl vinyl ether, a representative vinyl monomer with widely-spaced pendant carbazolyl groups connected to the skeletal chain, was synthesized and polymerized in 50—80% yields with a cationic initiator. The photoconductivity of the polymer (PCzEVE) was investigated together with that of an oligomer of N-vinylcarbazole (VCzOlig) and of poly(N-vinylcarbazole) (PVCz). The VCzOlig has almost the same photoconductive properties as observed for PVCz. In the case of PCzEVE, the photocurrent with positive or negative electrode illumination (iph+ or iph−) is ohmic and shows only a peak at 380 nm corresponding to the absorption edge. The magnitude of iph+ is nearly equal to that of iph− in every wavelength region even in a high applied fields. This behavior is quite different from that for PVCz. Moreover, the magnitude of the photocurrent of PCzEVE is much smaller than that of PVCz and of VCzOlig. The poor photoconductivity of PCzEVE was discussed in relation with the singlet exciton migration, and was attributed to the difficulty of carrier migration because of the weakness of the electronic interaction between neighboring carbazolyl groups. The indispensable conditions essential for more highly photoconductive polymers were given.