A Silanol-Functionalized Polyoxometalate with Excellent Electron Transfer Mediating Behavior to ZnO and TiO 2 Cathode Interlayers for Highly Efficient and Extremely Stable Polymer Solar Cells

Combining high efficiency and long lifetime under ambient conditions still poses a major challenge towards commercialization of polymer solar cells. Here we report a facile strategy that can simultaneously enhance the efficiency and temporal stability of inverted photovoltaic architectures. Inclusion of a silanol-functionalized organic–inorganic hybrid polyoxometalate derived from a PW9O34 lacunary phosphotungstate anion, namely (nBu4N)3[PW9O34(tBuSiOH)3], significantly increases the effectiveness of the electron collecting interface, which consists of a metal oxide such as titanium dioxide or zinc oxide, and leads to a high efficiency of 6.51% for single-junction structures based on poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:IC60BA) blends. The above favourable outcome stems from a large decrease in the work function, an effective surface passivation and a decrease in the surface energy of metal oxides which synergistically result in the outstanding electron transfer mediating capability of the functionalized polyoxometalate. In addition, the insertion of a silanol-functionalized polyoxometalate layer significantly enhances the ambient stability of unencapsulated devices which retain nearly 90% of their original efficiencies (T90) after 1000 hours

Efekt protonace na dynamiku excitovaného stavu pyrimidinových chromoforů

The effect of protonation on the photophysics and especially on the excited state dynamics of two pyrimidine chromophores, bearing the A-(pi-D)(2) and A-(pi-D)(3) structure, is studied by means of fs-ps and ns time resolved fluorescence spectroscopy. Three different acids, namely camphorsulphonic (CSA), acetic (AcOH) and trifluoroacetic acid (TFA) were used. The chromophores bear the pyrimidine electron deficient heterocycle as electron-withdrawing group, used as protonation site, as well as diphenylamino electron donors. Protonation is revealed through the emergence of red-shifted absorption and fluorescence bands accompanied by a quenching of the fluorescence of the neutral molecules. Time-resolved dynamics reveal that protonation with CSA and TFA do not influence the excited state lifetime of the chromophores, pointing to a static quenching process. On the other hand, the lifetime is decreased upon protonation with AcOH. Further investigation based on the Stern-Vollmer plots showed that addition of AcOH leads to both dynamic and static quenching.Byl studován efekt protonace na fotofyziku dvou pyrimidinových chromoforů prostřednictvím fluorescenční spektroskopie. Byly využity tři kyseliny, kafrsulfonová, octová a trifluoroctová

Exploring Solvent and Substituent Effects on the Excited State Dynamics and Symmetry Breaking of Quadrupolar Triarylamine End-Capped Benzothiazole Chromophores by Femtosecond Spectroscopy

: We investigate herein the excited state dynamics and symmetry breaking processes in three benzothiazole-derived two-photon absorbing chromophores by femtosecond fluorescence and transient absorption (fs-TA) spectroscopies in solvents of various polarity. The chromophores feature a quasi-quadrupolar D-π-A-π-D architecture comprised of an electron-withdrawing benzothiazole core and lateral triphenylamine donors (Qbtz-H), while the acceptor strength of the central unit is enforced by attached cyano groups (Qbtz-CN) and the electron-donating strength of the arylamine moieties by introduction of peripheral methoxy groups (Qbtz'-CN). Steady state spectroscopy reveals positive solvatochromism, which is mostly pronounced for Qbtz'-CN. Femtosecond spectroscopy of Qbtz-H reveals the coexistence of the Franck-Condon (FC) state and states populated after symmetry breaking (SB) in low-polarity solvents such as toluene and tetrahydrofuran, while the SB state becomes favorable in polar acetonitrile. For the other two molecules possessing a stronger electron-accepting unit and thus more polar excited state, SB takes place even in low-polarity solvents, as shown by fs-TA spectroscopy. Global fitting of the fs-TA spectra together with investigation of the evolution associated spectra (EAS) reveals the existence of an initial FC state in Qbtz-H, in all studied solvents, which relaxes toward Intermediate Charge Transfer (I-CT) and SB states. On the other hand, for Qbtz-CN and Qbtz'-CN in more polar solvents, the FC state undergoes ultrafast relaxation toward symmetry-broken charge transfer (SB-CT) states which in turn show very fast recombination to the ground state. Our measurements confirm that the extent of symmetry breaking is larger for D-π-A-π-D systems with the stronger acceptor core and increases further by increasing electron-donating strength of triarylamine moieties, giving rise to symmetry breaking in these nonionic quadrupolar molecules with ethynylene (triple bond) π-spacers also in less polar solvents

Trifenylaminové fluorofory nesoucí koncové diaziny. Syntéza, charakterizace, fotofyzikální vlastnosti a dvoufotonová absorpce

A series of six tripodal push-pull fluorophores with D-(pi-A3) arrangement has been designed and synthesized. The structure of these fluorophores consists of a central electron-donating triphenylamine core and peripheral electron-withdrawing diazine units (pyridazine, pyrimidine, and pyrazine moieties), which are linked by an ethynylene pi-spacer. The preparation of the fluorophores involves threefold Sonogashira cross-coupling reaction starting from the key tris(4-ethynylphenyl)amine intermediate. The structure and spatial arrangement of two fluorophores were completely confirmed by X-ray analysis. Thermal and electrochemical behavior of prepared fluorophores were investigated by differential scanning calorimetry and cyclic voltammetry. Their linear optical properties were examined by UV-Vis absorption, steady-state and time resolved fluorescent spectroscopy while 2 PA analysis was used for a study of the nonlinear optical response. Experimental data were supported by DFT calculations. Based on the experimental as well as theoretical data, structure-property relationships have been thoroughly revealed.Byla připravena série šesti tripodálních fluoroforů s D-(pi-A3) uspořádáním. Struktura derivátů obsahuje centrální elektronově donorní trifenylaminový skelet a postranní elektronakceptorní diaziny (pyridazin, pyrimidin, pyrazin) vázané přes ethynylenové můstky. Příprava je založena na trojnásobném Sonogashirově cross-couplingu z výchozího tris(4-ethynylfenyl)aminu. Struktura látek byla potvrzena rentgenostrukturní analýzou. Termální a elektrochemické vlastnosti byly zkoumány s pomocí DSC a cyklické voltametrie. Dále byla použita UV-Vis absorpční spektroskopie a 2 PA analýza. Experimentální výśledky byly konfrontovány s výsledky DFT kalkulací

Fotofyzikální a protonační time-resolved studie donor-akceptorového rozvětveného systému s pyridinovými akceptory

A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues, by means of ambient and low temperature steady state spectroscopy and femtosecond to nanosecond time-resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors, and acetylene pi-bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed intramolecular charge transfer state on the picosecond time scale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Forster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral toward the protonated species on the 1 ps time scale is revealed.Porovnávací studie fotofyzikálních vlastností oktupolárních pyridin-trifenylaminů s jejich kvadrupolárními a dipodálními analogy pomocí steady-state spektroskopie a femtosekundové až nanosekundové time-resolved fluorescenční spektroskopie při běžné a nízké teplotě. Látky byly studovány v rozpouštědlech s různou polaritou, byl studován také vliv přídavků kyseliny octové vedoucí k protonaci pyridinových skupin. Díky kontrolované protonaci vzorky vykazovaly širokopásovou emisi pokrývající téměř celé viditelné spektrum

Excited State and Injection Dynamics of Triphenylamine Sensitizers Containing a Benzothiazole Electron-Accepting Group on TiO₂ and Al₂O₃ Thin Films

The excited state and electron injection dynamics of three new organic sensitizers, comprising a triphenylamine moiety connected by an ethenylene (C−C double-bond) or ethynylene (C−C triple-bond) π-spacer to an electron-withdrawing benzothiazole bearing a cyanoacrylic acid anchoring group, have been studied using a combination of steady-state and femtosecond-resolved spectroscopies. The measurements were carried out for the three dyes in predominantly neutral and completely deprotonated forms in liquid solutions and bound on nanocrystalline TiO2 and Al2O3 thin films. In addition, quantum-chemical calculations were performed to predict absorption spectra of the sensitizers and their corresponding cation radicals. Time-resolved fluorescence (TRF) measurements on TiO2 indicate that electron injection takes place on a <0.2 ps time scale. Transient electronic absorption (TA) measurements provide evidence for the formation of radical cations not only in dye-sensitized TiO2 films but also in Al2O3 ones. The cation lifetime in Al2O3 is significantly shorter compared to TiO2, indicating a faster recombination of injected electrons with the dye cations. In addition, the ground-state bleach band in dye-sensitized TiO2 films experiences a gradual red-shift, which is indicative of a transient Stark effect. Finally, femtosecond transient absorption measurements in the IR region point to an ultrafast generation of injected electrons for all dyes. A faster recombination of the injected electrons with the dye cations is observed for the sensitizer decorated with auxiliary electron-donating methoxy groups on the triphenylamine moiety

Aggregation-Induced Enhanced Emission of a Dimethylacridan Substituted Pyrimidine Derivative

International audienceA pyrimidine chromophore bearing an acridan fragment was synthesized and its photophysical properties were studied. In solution, this compound is characterized by an important positive emission solvatochromism with a shift of 5800 cm(-1) between nonpolar heptane and dichloromethane (DCM) associated with large Stokes shifts (up to 9100 cm(-1) in DCM). Mono-exponential fluorescence decays are observed in heptane whereas more complicated bi- or three-exponential decays are observed in more polar solvents due to an interplay between locally excited and charge transfer excited state. Additionally, an aggregation-induced enhanced emission process was demonstrated in THF/water mixtures. At low temperature (77 K), in a polymethylmethacrylate (PMMA) thin film, the presence of an accessible triplet state (T1) was demonstrated, which was not observed in solution. Finally, we show that it is possible to protonate the chromophore in thin film leading to panchromatic dual emissio

Effect of protonation on the photophysical properties of 4-substituted and 4,7-disubstituted quinazoline push-pull chromophores

International audienceWhite-light emission from single molecular systems has attracted a great deal of attention due to their advantages over multicomponent emitters. Azaheterocyclic push-pull derivatives have been demonstrated to be white emitters by combining neutral and protonated forms in the appropriate ratio, although limited cases of white-light emission have been reported from quinazoline derivatives. Herein, we describe a series of push-pull 4-substituted and 4,7-disubstituted quinazolines that show white photoluminescence both in solution and in the solid state. All of the materials were prepared by straightforward Suzuki-Miyaura crosscoupling reactions and the compounds exhibited remarkable emission solvatochromism. In some cases the presence of acid prompted the appearance of emission bands of complementary colors. Thus, multicolor photoluminescence, including white light, could be finely tuned by the controlled protonation of the electron-deficient quinazoline ring

Modulation of (non)linear optical properties in tripodal molecules by variation of the peripheral cyano acceptor moieties and the π-spacer

A series of twelve tripodal push-pull molecules with a central triphenylamine donor and peripheral cyano substituted acceptors has been prepared. These molecules possess systematically altered π-linkers as well as cyano acceptors. Based on the experimental properties measured by differential scanning calorimetry, electrochemistry, one and two photon absorption/emission spectroscopy, supported by the DFT calculations, thorough structure–property relationships were elucidated