Jozef Krajčovič

Characterization and properties of the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine with 3-dodecylthiophene

Abstract The method of chemical oxidative polymerization with FeCl 3 was used to synthesize the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine (DPTA) and 3-dodecylthiophene (DDT). The copolymer was characterized by UV–VIS, Raman, 1 H and 13 C NMR and EPR spectroscopy. It has been found that the DPTA/DDT copolymer exhibits properties of the low-band-gap polymer ( E g

Optical properties of 2,3-diaza-1,3-butadiene bridged oligothiophenes A combined experimental and theoretical study

Abstract The syntheses, spectral measurements and the AM1 (Austin model 1) geometry optimisation of N , N ′-bis-thiophen-2-ylmethylene-hydrazine ( IIIa ), N , N ′-bis-(3-methyl-thiophen-2-ylmethylene)-hydrazine ( IIIb ), N -[2,2′]-bithiophen-5-ylmethylene- N ′-thiophen-2-ylmethylene-hydrazine ( IIIc ), N , N ′-bis-[2,2′]-bithiophen-5-ylmethylene-hydrazine ( IIId ), N -[2,2′; 5′,2″]-terthiophen-5-ylmethylene- N ′-thiophene-2-ylmethylene-hydrazine ( IIIe ), N -[2,2′]-bithiophen-5-ylmethylene- N ′-[2,2′; 5′,2″]-terthiophen-5-ylmethylene-hydrazine ( IIIf ) and N , N ′-bis-[2,2′; 5′,2″]-terthiophen-5-ylmethylene-hydrazine ( IIIg ) are elaborated. The electron absorption spectra for all- trans conformers are obtained by ZINDO/S method and compared with the experimental data. The influence of the chain length on the electronic polarisability and second-order hyperpolarisability is investigated using the time-dependent Hartree–Fock method in AM1 approach.

Adamantane substitutions: a path to high-performing, soluble, versatile and sustainable organic semiconducting materials

Novel ethyladamantyl solubilization side groups were found to induce π–π interactions between the conjugated cores through adamantyl–adamantyl stacking in soluble diketopyrrolopyrrole (DPP) derivatives. The closeness of the DPP cores amplifies charge transfer in the material, as far as the π–π interaction is a dominant charge-hopping pathway. As a result, tenfold enhancement of hole mobilities exceeding those obtained for insoluble derivatives was reached. Moreover, due to high crystallinity and co-planarity of the conjugated cores, electron transfer was preserved with a mobility of 0.2 cm2 V−1 s−1 for dithiophene-DPP. At the same time, the material remained soluble, which is a significant advantage for purification and processing. This approach can be universally applied for many types of semiconducting organic materials containing the imide motif, where solubilization is achieved by side-group substitution.

Synthesis of the copolymer of 2,3-di(1-tridecyl)thieno[3,4-b]pyrazine with 3-dodecylthiophene using the chemical oxidation with iron trichloride

Abstract By applying the method of chemical oxidative polymerization with FeCl 3 the copolymer of 2,3-bis-tridecylthieno[3,4- b ]-pyrazine (TTP) and 3-dodecylthiophene (DDT) was synthesized. The copolymer was characterized by the UV–VIS, FT-IR, 1 H -NMR, 13 C -NMR and EPR spectroscopy. The product is soluble in a common organic solvent (chloroform, dichloroethane, tetrahydrofurane, and toluene). The copolymer with a higher TTP content exhibits the properties of the low-band-gap polymers with an absorption edge above 900 nm (1.38 eV).

Interface inductive currents and carrier injection in hybrid perovskite single crystals

Interfaces between the absorbing perovskite and transporting layers are gaining attention as the key locus that governs solar cell operation and long term performance. The interplay of ionic and electronic processes, along with the asymmetrical architecture of any solar cell, makes the interpretation of electrical measurements always inconclusive. A strategy to progress in relating electric responses, operating mechanisms, and device architecture relies upon simplifying the probing structure. Macroscopic CH3NH3PbBr3 single crystals with symmetrical contacts are tested by means of long-time current transient and impedance spectroscopy. It is observed that interfaces govern carrier injection to (and extraction from) perovskite layers through an inductive (negative capacitance) mechanism with a response time in the range of ∼ 1 – 100 s under dark conditions and inert atmosphere. Current transient exhibits a slow recovering after the occurrence of an undershoot, signaling a complex carrier dynamics which invo...

Novel Riboflavin-Inspired Conjugated Bio-Organic Semiconductors

Flavins are known to be extremely versatile, thus enabling routes to innumerable modifications in order to obtain desired properties. Thus, in the present paper, the group of bio-inspired conjugated materials based on the alloxazine core is synthetized using two efficient novel synthetic approaches providing relatively high reaction yields. The comprehensive characterization of the materials, in order to evaluate the properties and application potential, has shown that the modification of the initial alloxazine core with aromatic substituents allows fine tuning of the optical bandgap, position of electronic orbitals, absorption and emission properties. Interestingly, the compounds possess multichromophoric behavior, which is assumed to be the results of an intramolecular proton transfer.

Design rules for the large two-photon absorption diketopyrrolopyrrole-based quadrupolar symmetrical chromophores

Two-photon absorption of a series of symmetrical diketopyrrolopyrrole (DPP) derivatives is studied by means of density functional theory applied to second-order response function. Several important issues in modeling are highlighted which must be addressed for a reliable reproduction of the experimental results. A comparison of the theoretical results with the experimental ones indicates that the computed two-photon absorption (TPA) cross sections show a good agreement for the three-state model in case of symmetrical quadrupolar DPP derivatives with donor ending groups. Although the results of TPA cross section observed for the systems with strong electron accepting ending groups seem to be overestimated for the three-state model. At the same time using an algorithm for the direct calculation of the third-order processes by the solving dynamic coupled-perturbed Hartree–Fock equation shows relatively good qualitative results for both donor and acceptor ending groups; however, it was found to be less accurate quantitatively for the already published experimental results. Thus, to obtain a valid overview, supposedly, both methods have to be considered. In general, in the present paper, a strategy toward molecular tailoring of large TPA cross-sectional materials is described, which can be extremely useful tool to predict materials’ properties prior to synthesis and measurements.

The Influence of Diketopyrrolopyrrole Chemical Structure on Organic Field-Effect Transistors Performance

Organic semiconductors are suitable for application in biosensors and sensors based on transistors. The influence of soluble group modifications on the performance of diketopyrrolopyrrole-based organic field-effect transistors (OFETs) is studied. The lowest mobility 1·10-9 cm2/Vs was observed for non-symmetric substitution O,N. Measurable charge carrier mobility was observed due to reduction of the density charge trapping states after application of organosilane self-assembled monolayers (SAMs) on thinner gate-dielectrics (90 nm). We report similar drift mobility 1·10-7 cm2/Vs for smallest soluble group “butyl” as for biggest group “EthylAdamantyl” in N,N and O,O substitution prepared by spin-coating.

Optical and Optoelectronic Characterization of Novel Diketopyrrolopyrroles for Organic Electronics and Photonics

Organic molecules are potential materials for cheap organic electronics and photonics. Small molecules have some major benefits when compared to polymeric materials (a perfectly defined chemical structure, purification of a single molecule is easier, the analysis of the relationship between structure and properties is more straightforward, etc.) and this has led to greater interest in these materials. The aim of this study was to synthesize and characterize novel DPP with N,N-substitution for use in organic electronics and photonics. The easy solubility of some prepared materials facilitates the preparation of thin film structures, e.g. by printing technology which is appropriate for their possible future commercial production. The materials were characterized with respect to their molecular structure. Optical and electrical properties of the devices were investigated. These small molecule thin films were prepared by spin-coating and vacuum evaporation. Their optical properties were studied by absorption and fluorescence spectroscopy, the electrical conductivity was studied by steady state current-voltage characterization. Photoluminescence quantum yield (PLQY) and photoluminescence lifetime was measured as well. Subsequently, the different structures of organic solar cells were prepared and their photovoltaic properties were studied.