E. L. Aleksandrova

Photophysical and electrical properties of polyphenylquinolines containing carbazole or indolo[3,2-b]carbazole fragments as new optoelectronic materials

Photophysical and electrical properties of new synthesized 2,6-polyphenylquinolines (PPQs) containing an oxygen or phenylamine bridging group between quinoline cycles and, as an arylene radical, alkylated derivatives of carbazole or indolo[3,2-b]carbazole are studied. It is shown that the photosensitivity for new PPQs is 104–105 cm2/J and the photogeneration quantum yield of free carriers is as high as 0.15. Photophysical parameters increase with the phenylamine bridging group in place of the oxygen one and when using indolocarbazole instead of carbazole. It is found that a film of polyphenylquinoline containing an oxygen bridging group and an alkylcarbazole fragment in the polymer repeat unit exhibits “white” luminescence. Both electron and hole transport with a mobility of ∼10−6 cm2/(V s) are detected in films of all studied polymers. The conductivity value and type can be controlled by varying the chemical structure of the (oxygen or phenylamine) bridging group between PPQ cycles and by choosing carbazole or indolo[3,2-b]carbazole derivatives as an arylene radical.

Synthesis and photophysical properties of soluble polyimides and polyquinazolones containing side-chain chalcones or azo chromophores

Soluble aromatic and carboxyl- and hydroxyl-containing polyimides, mixed polyimides, and polyquinazolones of various chemical structures, as well as a series of new dicyanoazobenzene chromophores, are synthesized. From 20 to 80 mol % of chromophore groups are incorporated into side chains of the polymers. The thermal, photosensitive, and nonlinear optical properties (second-harmonic generation) of the chromophore-containing polymers are investigated. The polymers with covalently attached groups of the dye DR-13 or azo-derivatives of 4-phthalonitrile demonstrate the highest nonlinearity. The T g values of the polyimides vary from 165 to 215°C; their temperatures corresponding to 5% weight loss lie in the range 290–350°C; and the measured coefficients of second-harmonic generation, d 33, for a number of polarized films based on chromophore-containing polymers attain several tens of picometers per volt. The incorporation of chromophore groups into the side chains of the polymers causes an increase in the photosensitivity of polyimides by an order of magnitude relative to that of the parent polymers (S 0.1 = (3−4) × 105 cm2/J in the range of dye absorption).

Carbazole-containing polyphenylquinolines as a basis for optoelectronic materials with white luminescence

The photophysical properties of poly-2,2′-(1-dodecyl carbazole-4,7-yl)-6,6′-(oxy)-bis-(4-phenylquinoline) in a solution, as a film, and in a poly(methyl methacrylate) or poly-N-vinylcarbazole host matrix have been studied. Considerable positive solvatochromism in the photoluminescence spectra, compared with solvatochromism in the absorption spectra, indicates that the dipole moment of the donor-acceptor complex increases in the excited state. Calculations show that the dipole moments of the complex in the ground and excited states differ by more than an order of magnitude. Upon transition to films, photoluminescence is observed in the entire visible spectral range (white luminescence). The intensity of the white luminescence grows by an order of magnitude when the polymer is dispersed in a poly(methyl methacrylate) matrix. The integrated photosensitivity and parameters of the photogeneration process (quantum yield of carrier photogeneration, quantum yield of free carrier formation, and thermalization radii) have been determined.

Structural control over conductivity and conduction type in thin films of polyphenylquinones

Carrier transport in newly synthesized 2,6-polyphenylquinolines containing an oxygen or phenylamine bridge group between phenylquinoline moieties and alkylated derivatives of carbazole or indolo[3,2-b]carbazole as an arylene radical has been studied. Both electron and hole transport is observed in films of all the polymers studied, with mobility on the order of 10−16 cm2 V−1 s−1, which increases on passing from an oxygen-to a phenylamine-type bridging group and from carbazole-to indolocarbazole-based derivatives. It is demonstrated that the conductivity and conduction type can be controlled by varying the type (oxygen or phenylamine) of bridging group between the phenylquinoline moieties or by the selection of an arylene radical.

Copolymers of carbazole- and indolocarbazole-containing phenylquinolines as new materials for electroluminescent devices

The photophysical and electrical properties of copolymers based on 2,6-polyphenylquinolines containing a bridging oxygen or phenylamine group between quinoline rings and octyl- or dodecylcarbazole or dioctylindolo[3,2-b]carbazole fragments in the aromatic radical are studied. It is shown that the introduction of carbazole and indolo[3,2-b]carbazole fragments emitting in the visible spectral range into the aromatic radical of a copolymer makes it possible to obtain white luminescence. The intensity of this luminescence exceeds, for copolymers in a photoinert matrix, that of the initial homopolymers. This circumstance, combined with rather high carrier mobilities on the order of 5 × 10−6 cm2 V−1 s−1, makes the copolymers promising for the development of electroluminescent devices on their basis.

Spectroscopic study of polyphenylquinolines - materials with efficient intramolecular charge transfer

The energy structure and nature of intramolecular charge transfer have been determined for a series of synthesized 2,6-polyphenylquinolines (PPQs) containing resorcinol, oxygen, and phenylamine bridging groups between phenylquinoline cycles and possessing an arylene radical in the form of alkylated derivatives of carbazole or indolo[3,2-b]carbazole, as well as arylated derivatives of carbazole with nitro- and fluorine substituents. The analysis was based on data on their absorption spectra, photosensitivity, carrier photogeneration quantum efficiency, and luminescence. It is shown that the PPQ monomeric unit is a composite intramolecular charge-transfer complex (ICTC) between the donor arylene fragment and the acceptor quinoline cycle; the latter, in turn, is an ICTC between the donor bridging group and quinoline ring (when acceptor fluorine or nitro substituents are introduced into the carbazole structure, the complex becomes ternary), and the narrowest band gap (2.3 eV) corresponds to the PPQ having a phenylamine bridging group and a fragment of indolo[3,2-b]carbazole.

Synthesis and electrooptical properties of triphenylamine- and oxadiazole-containing polymers

Soluble aromatic polyimides and copolyimides are synthesized on the basis of 4,4′-diaminotriphenylamine and oxadiazole-containing diamines. Poly(ester oxadiazoles) are prepared from acid dichlorides or oxadiazole-containing acid dihydrazides. The optical, electrochemical, and thermal properties of the polymers are investigated. It is shown that oxadiazole-containing polyimides and poly(ester oxadiazoles) are able to transfer electrons, while triphenylamine-containing polyimides and copolyimides can transfer holes and electrons.

Sensitization of the photoelectric effect in carbazole- and indolocarbazole-containing poly(phenylquinoline)s by benzothiadiazole acceptor molecules

The efficient sensitization of the photoelectric effect in mixed compositions of poly(phenylquinoline)s (PPQ) with 2,1,3-benzothiadiazole (BTDZ) molecules is established. The introduction of 10 wt % BTDZ results in extension of the spectral sensitivity range of PPQ and an increase in the photosensitivity and photocurrent by factors of 4.5 and more than 6, respectively. It is shown that the effect is caused by complex formation between PPQ donor fragments and BTDZ acceptor molecules; the strongest, in comparison with the increase in photosensitivity, is probably caused by the transport of free photogenerated carriers (electrons) over sensitizer molecules introduced into the polymer.

Synthesis of new photosensitive silicon-containing poly(salicylideneazomethynes)

Photosensitive silicon-containing poly(salicylideneazomethynes) have been synthesized. It has been shown that these polymers are characterized by the presence of intramolecular donor-acceptor interactions between valence shells of silicon and nitrogen atoms; as a result, polyconjugation appears according to the nonclassical mechanism. The photo-and electrophysical properties of the polymers have been examined. The introduction of an oxygen spacer into a polymer facilitates an increase in the photosensitivity and quantum yield of free charge carrier photogeneration, and it has almost no effect on the conductive behavior of the polymers.

Structural features of the photogeneration mechanism of free charge carriers in element-containing polydisalicylidene azomethine series

Photophysical properties of new polytetra- and polydisalicylidene azomethines (PSAMs) with chains containing Si, Ge, Sn, or transition metal atoms and atoms of a number of other divalent metals are studied. Based on data on ultraviolet and infrared spectra, it was found that the noncovalent transannular donor-acceptor interaction N M (M is semimetal or metal) occurs in polymers, which leads to the formation of a polymer chain of six-membered cycles. As a result, polyconjugations arise in PSAMs by a “non-classical” mechanism. Due to multiple donor-acceptor interactions of unshared electron pairs of azomethine groups with vacant d-orbitals in metals, polymers feature conductive, photosensitive, and photoconductive properties. The photosensitivity and quantum yield of photogeneration of free charge carriers for PSAMs are close to the values characteristic of classical conducting polymers. It was shown that the PSAM properties are controlled by the azomethine fragment structure and acceptor properties of metal. A mechanism of free carrier photogeneration was suggested.