Conjugated alternating copolymers containing both donor and acceptor moieties in the main chain

A straightforward synthesis toward two conjugated alternating copolymers consisting of 2,7-linked carbazole donor (2,7-Cz) and ladderized pentaphenylene with diketone bridge (LPPK) acceptor chromophores is reported: the copolymers differ by the repeat unit ratio between the 2,7-Cz and LPPK units within the backbone; energy and charge transfer properties and supramolecular organizations of donor-acceptor moieties in these copolymers have been studied via optical spectroscopy and two-dimensional wide-angle X-ray scattering (2D-WAXS); preliminary results such as the efficient energy and charge transfer and pi-stacking character in the solid state suggest that the copolymers are potentially useful for photovoltaic devices.     

New polythiophenes bearing electron-acceptor phthalocyanine chromophores

Two new donor-acceptor copolymers comprising a polythiophene backbone, and bearing phthalocyanine chromophores on the side chains have been prepared. Preliminary photophysical characterization of these materials by FTIR photoinduced absorption indicates that electron transfer from the polythiophene to the phthalocyanine units takes place.     

MOLECULAR DESIGN OF LIGHT EMITTING POLYMERS

Fluorene-based alternating and statistical copolymers were synthesized by employing reaction methods of Wittig,Heck and Suzuki. The copolymers were classified into three groups with the photoluminescence (PL) emission maxima at420, 475 and 500 nm, respectively. Statistical copolymers with two chromophores having PL emission maxima at 420 and475 nm emitted light with the emission maximum at 475 nm on photoexcitation at 365 nm and improved the quantumefficiency by the energy transfer. However, the intramolecular energy transfer was inefficient compared to the intermolecularenergy transfer when the two chromophores were apart from each other in the range of the Forster critical distance. Fluorene-pyridinedivinylene alternating copolymer was synthesized by the Wittig reaction and found to have physical, electronic andelectrochemical properties of the individual units intact. The double-layered light emitting diode (LED) with the statisticalcopolymer as an emitting layer and the pyridine-containing copolymer as an electron transporting-hole blocking layer, whichwere sandwiched between ITO and Al, displayed a quantum efficiency of 0.1%.     

新型可聚合双发色团电致发光材料的合成

自１９８７年Ｔａｎｇ［１］报道了高效、高亮度的双层有机薄膜电致发光器件以来,电致发光材料的研究受到了广泛的关注．接着在１９９０年,英国剑桥大学Ｂｕｒｏｕｇｈｅｓ等［２］首次利用聚亚苯基乙烯（Ｐｏｌｙ（ｐ ｐｈｅｎｙｌｅｎｅｖｉｎｙｌｅｎｅ）,ＰＰＶ）...     

Controlling conformations in alternating dialkylsilylene-spaced donor-acceptor copolymers by a cooperative Thorpe-Ingold effect and polymer folding

A series of dialkylsilylene-spaced copolymers 6 and 7, which contain Me(2)Si and iPr(2)Si spacer groups, respectively, and have alternating donor and acceptor chromophores, have been designed and regioselectively synthesized by hydrosilylation. The ratio of the donor and acceptor chromophores for each repeat unit is 2:1, and the two donor chromophores are linked by a trimethylene bridge. A 4-aminostyrene moiety is used as the donor and a series of acceptor chromophores with different reduction potentials are employed. Both steady-state and kinetic measurements reveal that the photoinduced electron transfer (PET) in 6 obeyed the Marcus theory in which normal and inverted regions are observed. On the other hand, the iPr(2)Si-spaced copolymers 7 exhibit absorption and emission from the charge-transfer complexes exclusively due to ground-state interactions between the donor and acceptor chromophores. The discrepancy in photophysical behavior may have arisen from the difference in distance between the adjacent donor and acceptor chromophores. The bulkiness of the substituents on the silicon atom (i.e., Me versus iPr) may exert the Thorpe-Ingold effect on the local conformation around the silicon atom. The differences in the small energetic barriers for each of the conformational states may be amplified by extending the distance of the folding structure, which results in perturbing the conformation of the polymers. These results suggest that the electronic interactions between adjacent donor-acceptor pairs in these copolymers are controlled by the synchronization of the substitution effect and corresponding polymeric structures.     

Energy transfer in polymers—VII: Triplet energy migration and transfer in copolymers styrene-vinylbenzophenone

The efficiency of triplet energy transfer from the benzophenone group to naphthalene has been studied in a series of copolymers styrene-vinylbenzophenone, either as films or in glassy solutions at 77 K. Energy migration has been shown to be efficient in both cases. For a given copolymer, Hirayama's critical distance is larger in films than in glassy solutions. In both cases, it decreases with decreasing vinylbenzophenone content. The number of jumps between identical molecules during the life-time of the excited state has been calculated according to the hopping model and Voltz theory on energy migration. The results show that energy migration in these solid polymers is not the consequence of exchange interactions decreasing exponentially with the mean distance between the chromophores. Organized regions, characterized by a higher efficiency of transfer, have to be taken into account.     

Incorporation of pyrimidine fluorophores into poly(methylmethacrylate) polymer structures

Three polymethyl methacrylate based copolymers bearing arylvinylpyrimidine chromophores have been synthesized in four steps. Spectral properties of the copolymers have been studied in solution, powder and thin films and compared with the corresponding free chromophores. The copolymers exhibit strong emission solvatochromism and act as polarity sensors. They also exhibit halochromism: when adding acid, a bathochromic shift is observed in absorption whereas a red-shifted fluorescence is observed with increased intensity for the methoxy-substituted macromolecule.     

Synthesis and photogeneration properties of copolyacrylate having carbazole donor and trinitrofluorenone acceptor chromophores

Novel copolymers containing both donor and acceptor chromophores have been synthesized by free radical polymerization of 2-N-carbazolylethyl acrylate and 2′-acrylylethyl-4,5,7-trinitrofluorenone-2-carboxylate. The charge transfer complexation occurs in copolymers in a similar way to poly(2-N-carbazolylethyl acrylate) molecularly doped with 2,4,7-trinitrofluorenone (TNF) and a model compound, ethyl 4,5,7-trinitrofluorene-2-carboxylate (Et-TNF). Copolymer and doped systems exhibit obvious CT bands in a 440–600 nm region, where the former shows higher absorption than the latter. Glass-transition temperatures show positive deviations from the weight-average values of copolymers, indicating the partial interchain interaction of copolymers in solid state. Quantum efficiency of hole photogeneration of the copolymer with the 0.05 to 1.0 molar ratio of TNF to carbazole chromophores is higher than those of the corresponding molecularly TNF- and Et-TNF-doped poly(2-N-carbazolylethyl acrylate), especially at lower electric fields.     

Synthesis of Polymers Containing Second Order NLO-Active Thiophene and Thiazole Based Chromophores

Grounding on the evidence that thiophene or thiazole rings in donor-acceptor chromophoric systems promote enhancement of charge transfer and nonlinear optical responses, in this work NLO properties have been investigated of organic polymers containing azoic chromophores based on dinitrothiophene or nitrothiazole moieties. It has been carried out the azo coupling reaction directly between a series of copolymers and diazonium salts containing the etherocyclic group at different grafting percentages.     

Alternating oligo(p-phenylene vinylene)--perylene bisimide copolymers: synthesis,photophysics, and photovoltaic properties of a new class of donor--acceptor materials

A Suzuki polycondensation reaction has been used to synthesize two copolymers consisting of alternating oligo(p-phenylene vinylene) (OPV) donor and perylene bisimide (PERY) acceptor chromophores. The copolymers differ by the length of the saturated spacer that connects the OPV and PERY units. Photoinduced singlet energy transfer and photoinduced charge separation in these polychromophores have been studied in solution and in the solid state via photoluminescence and femtosecond pump-probe spectroscopy. In both polymers a photoinduced electron transfer occurs within a few picoseconds after excitation of the OPV or the PERY chromophore. The electron transfer from OPV excited state competes with a singlet energy transfer state to the PERY chromophore. The differences in rate constants for the electron- and energy-transfer processes are discussed on the basis of correlated quantum-chemical calculations and in terms of conformational preferences and folding of the two polymers. In solution, the lifetime of the charge-separated state is longer than in the films where geminate recombination is much faster. However, in the films some charges are able to escape from geminate recombination and diffuse away and can be collected at the electrodes when the polymers are incorporated in a photovoltaic device.     

Donor-acceptor polymers: a conjugated oligo(p-phenylene vinylene) main chain with dangling perylene bisimides

Two new donor-acceptor copolymers that consist of an enantiomerically pure oligo(p-phenylene vinylene) main chain with dangling perylene bisimides have been synthesized by using a Suzuki cross-coupling polymerization. Absorption and circular dichroism spectroscopy revealed that the transition dipole moments of the donor in the main chain and the dangling acceptor moieties of the copolymers are coupled and in a helical orientation in solution, even at elevated temperatures. A strong fluorescence quenching of both chromophores indicates an efficient photoinduced charge transfer after photoexcitation of either donor or acceptor. The formation and recombination kinetics of the charge-separated state were investigated in detail with femtosecond and near-steady-state photoinduced absorption spectroscopy. The charge-separated state forms within 1 ps after excitation, and recombination occurs with a time constant of 45-60 ps, both in solution and in the solid state. These optical characteristics indicate a short distance and appreciable interaction between the electron-rich donor chain and the dangling electron-poor acceptor chromophores.     

含荧光生色基团烯类单体及其聚合物的光化学行为

近年来关于电荷转移现象的研究因理论及应用方面的重要性而备受瞩目。缺电子性丙烯酰类单体可以和给电子性化合物形成激态电葆转移复合物进而引发光聚合。我们合成了一系列同一分子中既含有给电子性荧光生色团又含缺电子性双键的烯类单体,发现这类单体在相同生色团浓度下的荧光强度均无穷氏人相应的聚合物的荧光强度。我们将这咎现象称为荧光结构自猝灭效应（ＳＳＱＥ）,以区别于众所周知的浓度自猝灭现象。对于电子状态与之相反的     

Light harvesting and energy transfer within coumarin‐labeled polymers

Linear copolymers that have pendant coumarin‐2 and coumarin‐343 chromophores were prepared as analogues to previously synthesized light‐harvesting dendrimers. The chromophore ratios within these polymers were maintained similar to those of the various generation dendrimers to investigate the effect of polymer architecture on the energy‐transfer efficiency between the coumarin‐2 donors and coumarin‐343 acceptors. Both physical and photophysical properties of these polymers were analyzed and compared to those of the analogous dendrimers. Energy‐transfer efficiencies were relatively high in the polymers; however, deleterious excimer formation between the coumarin‐343 chromophores diminished the quantum yield of fluorescence of the polymers when compared to the analogous dendrimers. Overall, it was found that the ultimate performance of the dendritic light‐harvesting antennae was superior to that of the polymeric analogues, but the polymers were more practical in terms of synthetic accessibility. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1366–1373, 2001     

DNA molecular photonics

Synthetic DNA conjugates in which one or both ends of a short duplex is capped by a stilbene chromophore have been prepared and characterized crystallographically. Selective excitation of the chromophore can be used to initiate electron transfer processes in which a nucleobase serves as either an electron donor or an electron acceptor. These processes include hole- and electron injection and hole migration. The dynamics of these processes and its dependence on distance, driving force, and base sequence have been investigated by means of femtosecond time-resolved spectroscopy. Duplexes with identical chromophores at both ends have been used to study both the dynamics of electron transfer processes and exciton coupling between the two chromophores by means of circular dichroism spectroscopy. Duplexes with different chromophores can also be used to study distance dependence of both electron transfer and exciton coupling.     

Intrachain energy transfer in silylene-spaced alternating donor-acceptor divinylarene copolymers

Silylene-spaced donor-acceptor divinylarene copolymers are synthesized by hydrosilylation of bisalkynes 7 with bisvinylsilanes 3; efficient intrachain energy transfer between donor-acceptor chromophores is observed.     

Intramolecular triplet energy transfer in multi-chromophoric dyes and its influence on the photostability

The photostability of organic dyes plays a very important role in practically all aspects of the development and applications of these dyes. In recent years, intramolecular transfer of triplet excitation energy between isolated chromophores on the same molecule has been a subject of intensive studies. Many multi-chromophoric organic dyes with covalent linkage between the chromophores, one of which can act as a triplet acceptor of the excess energy, have been synthesized and studied. The significant increases in photostability of such assembled dyes have been reported, suggesting that some chromophores can act as internal photostabilizers. These modified dyes have enhanced photostability and hence potential applications in a wide range of areas such as laser dyes, electroluminescent (EL) devices and solar cells.     

Synthesis and optical properties of green‐light‐emitting copolymers containing side‐chain oxadiazole units

Atom transfer radical polymerization was used to prepare well‐defined vinyl polyoxadiazole homomacromonomers with a properly modified α‐dicarboxylic acid methyl ester as the initiator. Macromonomers of various molecular weights with narrow polydispersities in some cases were obtained, as proved by gel permeation chromatography (GPC). The structures of the obtained macromonomers were then identified with ¹H NMR spectroscopy. These macromonomers were subsequently copolymerized with a dihydroxy anthracene based monomer by a polycondensation technique, and this resulted in polymacromonomers. Coil–rod–coil copolymers containing side‐chain anthracene and oxadiazole units were also synthesized by atom transfer radical polymerization. The resulting copolymers combined an anthracene derivative as the rigid block with a random copolymer of the desired anthracene‐ and/or oxadiazole‐based monomers as the flexible block. These copolymers were primarily characterized with GPC and ¹H NMR techniques. Additionally, the optical properties of all these copolymers were investigated in detail, and they suggested energy transfer from the oxadiazole to the anthracene chromophores, which became much more efficient in the solid state. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1049–1061, 2005     

Dye-containing S*c side-on/end-on copolymers

Mesomorphic copolysiloxanes, which combine 'normal' end-on linked chiral mesogenic units inducing S*_c phases and side-on fixed chromophores were prepared. The interplay of the different orientational tendencies of these moieties, which are perpendicular (end-on linked mesogenic groups) or parallel (side-on fixed chromophores) to the polymer chain, lead to a strong destabilization of the S*_c phase. However, copolymers with up to about 10 mol % of chromophores still show a smectic C* phase. FTIR measurements show that both moieties orient parallel to each other and perpendicular to the polymer chains. These copolymers are interesting to consider as coloured guest-host S*_c materials for coloured displays or as pyro-electric detectors.     

新型双发色团染料荧光光谱及其寿命的研究

有效的染料激光操作需要较高的荧光量子效率,若丹明是在500~700 nm光谱区中一类最重要的激光染料.然而,染料的基态分子和三线态对辐射能量的吸收将会大大降低激光输出效率,再者,由于若丹明类染料在紫外区的吸收系数较小,为了有效吸收泵浦能量(如用XeCI准分子激光,308 nm),就必须使用高浓度染料溶液,在这种情况下,若丹明类染料较小的Stokes位移就势必造成基态分子更大的重复吸收,即造成更大的谐振腔损耗^[1].     

Solvent effects on competitive intramolecular electron transfer and energy transfer in a covalently linked porphyrin-phthalocyanine heterodimer

Photophysical properties of a porphyrin-phthalocyanine heterodimer covalently linked with a dipentoxy chain have been studied.Absorption spectra show that there is weak exciton coupling between the two chromophores in the ground state.Fluorescence spectra show that intramolecular energy transfer from porphyrin to phthalocyanine moiety occurs in competition with electron transfer.The efficiency of these two processes depends upon the mutual orientation of the two chromophores.The effect of solvent polarity on the intramolecular processes is also discussed.