Carbazolyl Side Groups Research Articles

Synthesis and photophysical properties of a poly(methyl methacrylate) polymer with carbazolyl side groups

The photophysical properties of solutions and films of poly(methyl methacrylate) (PMMA) containing 1.6 mol % of randomly distributed pendant ethyl carbazolyl groups have been studied under steady-state and time-resolved conditions. The polymer was prepared by esterification of poly(methyl methacrylate-co-methacrylic acid) by 9H-carbazole-9-ethanol. At room temperature, the steady-state fluorescence spectrum is attributed to isolated lumophores in solution, but is much more complex in films where emission is detected from isolated groups, ground-state dimers and excimers. At 77 K, emission from both solutions and films contains a component of phosphorescence whose wavelengths overlap fluorescence from excited ground-state dimers and excimers. From the temperature dependence of the steady-state emission spectra of the films, recorded from 30 to 410 K, several types of relaxation processes are identified at temperatures similar to those of unmodified PMMA. Data by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and fluorescence spectroscopy are compared. They include the γ-relaxations from motions of small segments of the chains at 120-130 K (by fluorescence spectroscopy), the β-relaxation from motions of lateral ester groups (by DMTA and fluorescence spectroscopy) at 310 K and α-relaxations (glass transition onset) at 380 K (by DSC and DMTA).

Fluorescence Emissions and Torsional Conformations in π-Conjugated Chains of PolyDCHD-HS

The fluorescence emission of polyDCHD-HS in solution at room and low temperature and as an amorphous film has been investigated. Extended segments along the polymer backbone are responsible for the observed fluorescence spectrum of polyDCHD-HS in benzene solution. Spectra of the polymer in cyclohexane solution and as an amorphous film give evidence of an additional red-shifted fluorescence, assigned to local substructures behaving as emission centers. Model calculations with the TD-DFT theoretical framework on planar and distorted enyne oligomers have allowed correlation of the S0 → S1 transition energies to chain segments with different torsional angles around the C−C⋮C−C axis. In the ensuing structural model, benzene molecules interact attractively with carbazolyl side groups of polyDCHD-HS, thus enhancing the chain rigidity. The interaction energy of carbazolyl groups with cyclohexane is smaller than that with benzene. This leads to more folded chains and, plausibly, also to clusters of few chain segments.

Second-order nonlinear optical property of polyphosphazenes containing charge-transporting agents and indole-based chromophore

A new post functional strategy was developed to prepare polyphosphazenes with a high density of the indole based chromophore (nitro-indole or sulfonyl-indole chromophores) and carbazolyl side groups. Thus polyphosphazene ( P1) with carbazolyl and indole groups was first prepared by direct nucleophilic substitution reaction with poly(dichlorophosphazene). Then, polyphosphazenes ( P2– P4) containing charge-transporting agent (carbazolyl groups) and indole azo chromophores were synthesized via a post azo coupling reaction between P1 and p-nitrobezenediazonium fluoroborate or p-ethylsulfurylbenzenediazonium fluoroborate in N-methylpyrrolindone (NMP). The structures of P1– P4 were characterized, and the poled film of P2– 4 revealed a resonant d 33 values in the range of 7–26 pm/V by second harmonic generation (SHG) measurements.

Synthesis and characterization of polysiloxanes containing carbazolyl and sulfonyl-indole based chromophore as side chains

A new post-functional strategy was developed to prepare polysiloxanes with the sulfonyl-indole based chromophore and carbazolyl side groups. Thus a polysiloxane ( P1) with indole and carbazolyl groups as side chains was first synthesized through hydrosilylation reaction, and then the post-azo coupling of p-ethylsulfonylbenzenediazonium fluoroborate toward the indole rings afforded the multifunctional sulfonyl-indole based chromophore-functionalized polysiloxane ( P2 and P3). The polymers were easily soluble in common organic solvents, and their maximum absorption appeared at 394 nm, which is about 30 nm blue-shifted compared to the corresponding chromophore with nitro acceptors, and could result in a wider transparency window. The poled films of P2 and P3 reveals a resonant d 33 value of 12 and 18 pm/V, respectively, by second harmonic generation (SHG) measurements.

Influence of carbazol‐9‐yl substitution in polysilanes on charge carrier trapping and recombination

AbstractA series of poly{[3‐(carbazol‐9‐yl)propyl]silane‐co‐methylphenylsilane}s were investigated by optical absorption, photoluminescence and thermoluminescence measurements. It was found that the optical absorption bands of the carbazolyl side groups superimpose on those of the Si backbones in the ultraviolet range. This feature reduces photodegradability of Si‐Si bonds during UV irradiation. The TL spectra recorded in the 15 ‐ 325 K temperature range after photoexcitation at 15 K show that the carbazolyl side groups act as trapping sites in polysilanes. Increasing density of carbazolyl groups results in increasing population of deeper (ca. 150 meV) traps. Spectral analyses of the thermoluminescence at different temperatures are discussed and compared with analogous results for poly(9‐vinylcarbazole) (PVK). It is concluded that the monomeric mechanism of luminescence dominates at low temperatures while the excimeric mechanism prevails at higher temperatures, similarly to PVK.

Synthesis and structural characterization of a new polysiloxane with second-order nonlinear optical effect

A new polysiloxane (P2), with a high density of the indole-based chromophore and carbazolyl side groups, was prepared. Thus a polysiloxane (P1), with indole and carbazolyl groups as side chains, was first synthesized through a hydrosilylation reaction, and then the post-azo coupling of p-nitrobenzenediazonium fluoroborate toward the indole ring gave the mulifunctional indole-based chromophore-functionalized polysiloxane (P2). Molecular structural characterization for the polymers was determined by 1H-NMR, IR, and UV–visible spectra, gel permeation chromatography, and differential scanning calorimetry. The polymers were easily soluble in common organic solvents. The poled film of P2 revealed a resonant d33 value of 27 pm/V by second-harmonic generation measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 769–774, 2004

Soluble polydiacetylenes: molecular properties and solid state organization

The solution properties of a novel soluble polydiacetylene, poly[1,6-bis(3,6-dihexadecyl- N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS), have been investigated by use of spectroscopic (UV–VIS absorption, fluorescence and FT-Raman) and light scattering techniques in benzene and toluene. The unique spectroscopic and molecular properties of these solutions are reported and discussed in relation to the particular interactions of the polymer substituents with aromatic solvents. The introduction of the long alkyl-substituents on the carbazolyl side groups not only improves the processability relative to the parent unsubstituted polymer but also suppresses the chromic effects observed in other soluble polydiacetylenes. The side groups are also responsible for the peculiar supramolecular organization observed in the powder phase of the red form.

Photoelectric properties of organic polysilane containing carbazolyl side groups

The photoelectric properties of a series of N-carbazolyl-substituted silane copolymers have been studied by optical absorption, photoluminescence, and time-of-flight transient photocurrent measurements. It is found in N-carbazolyl-substituted silane copolymers that the optical absorption and the photoluminescence bands of the carbazolyl side groups, superimposed on those of the Si backbones, are observed in the blue to ultraviolet spectrum region. The hole drift mobilities of the copolymers are essentially the same as those of polymethylphenylsilane (PMePhSi) and are higher than those of poly(N-vinylcarbazole), and the photocarrier generation efficiencies of the copolymers are higher than those of PMePhSi. These results indicate that the photogenerated charge carriers on the carbazolyl side groups transfer to the Si backbones and then proceed through the Si backbones.

Hole transport in substituted polydiphenylacetylene light-emitting devices: mobility improvement through carbazole moiety

Carrier-transport control is a critical factor in achieving high performance of organic light-emitting devices (LEDs). We have compared hole conduction between polydiphenylacetylene (PDPA) derivatives without and with a carrier-transport moiety, such as poly[1-( p- n-butylphenyl)-2-phenylacetylene] (PDPA- nBu) and poly[1-( p- n-carbazolyphenyl)-2-phenylacetylene] (PDPA-Cz), respectively. Hole transport is studied by current–voltage measurements and fitted using the space-charge limited current model. It is shown that the hole mobility can be improved several orders of magnitude by attaching carbazolyl side groups to the PDPA back bone (PDPA-Cz), as compared to that of PDPA- nBu. The electroluminescence is studied and compared in heterostructured LEDs using PDPA- nBu and PDPA-Cz as hole-transport layers. It is found that carrier transport and balance have significant roles in the performance of the substituted PDPA-based electroluminescent devices.

Vibration Mode Interaction in the Raman Spectra of Poly(1,6-bis[N-carbazolyl]-2,4-hexadiyne)

The Raman spectrum of the polydiacetylene, poly(1,6-bis[N-carbazolyl]-2,4-hexadiyne), has been reexamined and analyzed in terms of the resonant interaction of backbone and side-group vibration modes. Fourier transform infrared Raman spectra have been recorded for partially and fully polymerized samples. These data complement earlier studies of the resonance-Raman spectra of partially polymerized crystals conducted at low temperatures. The multipeaked spectrum, which is observed in the vicinity of the stretching vibration of the backbone carbon double bond, is analyzed utilizing these results. A model that incorporates the resonant interaction of the carbon double-bond mode with three vibrational modes of the carbazolyl side groups is shown to provide a good fit to the available experimental data.

Long-lived photoexcited states in polydiacetylenes with different molecular and supramolecular organization

With the aim of determining the importance of the molecular and supramolecular organization on the excited states of polydiacetylenes, we have studied the photoinduced absorption spectra of the red form of poly[1,6-bis(3,6-didodecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-S) and the results compared with those of the blue form of the same polymer. An interpretation of the data is given in terms of both the conjugation length and the interbackbone separation also in relation to the photoinduced absorption spectra of both blue and red forms of poly[1,6-bis(N-carbazolyl)-2,4-hexadiyne] (polyDCHD), which does not carry the alkyl substituents on the carbazolyl side groups. Information on the above properties is derived from the analysis of the absorption and Raman spectra of this class of polydiacetylenes.

Effect of interchain separation on the photoinduced absorption spectra of polycarbazolyldiacetylenes.

The photoinduced absorption spectra of a novel polycarbazolyldiacetylene with long aliphatic chains on the carbazolyl side groups are measured and compared with those of the unsubstituted polyDCHD. The two polymers in the blue form exhibit very similar electronic absorption spectra and Raman frequencies. This fact indicates that the conjugation length of the polydiacetylene backbone is not too affected by the long substituents. In contrast, the near steady-state photoinduced absorption spectra show that different photogeneration mechanisms are involved in the two polymers. This result can be ascribed to the role played by the interchain distance in the dynamics of the relaxation processes in polydiacetylenes.

Synthesis and optical properties of a novel soluble polycarbazolyldiacetylene

AbstractA novel soluble polydiacetylene with 3,6‐dialkyl‐substituted carbazolyl side groups (polyDCHD‐S) has been prepared. Its electronic and vibrational properties have been studied in the crystalline state. The results are compared with those of polyDCHD taken as reference. PolyDCHD‐S shows a very high conjugation length like polyDCHD but an increased interchain separation. High non‐linear optical response is then expected; that — together with the processability of the polymer — suggests attractive applications in photonic devices based on thin film technology.

Visible and uv spectra of a polydiacetylene with a side group conjugated to the main chain

The polarized reflection spectra of single crystals of PDA-CPDO [poly-1-(N-carbazolyl)penta-1, 3-diyn-5-ol], which are π conjugated between the side groups and the main chain, have been measured in the photon energy region from 1.38 to 32 eV for the first time with a polarized synchrotron radiation source. Absorption spectra have been calculated using the Kramers–Kronig relation. Transitions in the visible absorption spectrum, which have been previously attributed to an interband transition in a similar polydiacetylene, have been found to be highly dichroic with respect to the direction along the polymer backbone. The absorption spectrum in this region reveals two broad (ΔE≳0.4 eV) peaks at 1.9 and 2.7 eV with an almost equal absorption coefficient of 7.5×104 cm−1. The spectral features in the range from 3 to 8 eV result from electronic transitions of the carbazolyl side groups. A single broad (ΔE∼10 eV) absorption band observed at 18 eV is due to either transitions of σ electrons to higher σ* or π* states of the carbazolyl group, or to ionization processes.

Fluorescence decay curves and time-resolved spectra of poly(N-epoxypropylcarbazole), PEPCA, at room temperature and at 11 K

Time-resolved fluorescence spectra of solid films of low-molecular-weight poly(N-epoxypropylcarbazole), PEPCA, measured at room temperature and at 11 K are reported. The spectra reveal the presence of two types of emitting centra in the polymer. Below 400 nm, noninteracting carbazolyl side groups emit fluorescence typical of the monomer unit. Above 400 nm, structured emission with peaks at 410, 430, and 460 nm has been observed. Comparison of the detected spectra with that of crystalline N-isopropylcarbazole together with other evidence supports strongly the suggestion that the latter emission is due to intermolecular arrays of the side groups arranged in such a way that their molecular planes are parallel or nearly parallel to each other with antiparallel orientation of the short in-plane molecular axes of the nearest neighbours. The time-resolved spectra and the decay curves show that excitation energy is transfered from monomer side groups to those built in the crystallike arrays and that this transfer becomes less effective at low temperatures.

ODMR and triplet state kinetics of a carbazolyl substituted diacetylene crystal

Carbazolyl substituted diacetylene (DCH) monomer crystals showing phosphorescence from four traps have been investigated by optically detected magnetic resonance (ODMR) at 1.2 K. These localized triplet states are attributed to the carbazolyl side groups. Their population and depopulation rate constants and zero field splitting parameters (0.097 <|D|< 0.1002 cm−1; 0.0068 <|E|<0.0105 cm−1) have been determined. The results suggest that the traps are disturbed substituents. The proposed interaction of the trap states with an exciton band at 23926 cm−1 is supported by temperature dependent lifetime measurements.