Igor P. Koskin

Bio: Igor P. Koskin is an academic researcher from Novosibirsk State University. The author has contributed to research in topics: Phenylene & Luminescence. The author has an hindex of 5, co-authored 9 publications receiving 66 citations. Previous affiliations of Igor P. Koskin include Russian Academy of Sciences.

Way to Highly Emissive Materials: Increase of Rigidity by Introduction of a Furan Moiety in Co-Oligomers

Abstract: Rigid linear organic co-oligomers are prospective materials for organic optoelectronics In this work, we explored intramolecular factors affecting the torsional rigidity and its influence on optoelectronic properties of the alternating furan/phenylene and thiophene/phenylene co-oligomers in both ground and first singlet excited states Furan/phenylene co-oligomer exhibits almost twice higher torsional rigidity than its thiophene analog Effect of intramolecular O…H and S…H interactions on torsional barriers was found to be negligible as compared with the conjugation efficiency The higher torsional rigidity of furan and thiophene co-oligomers has been proven to be reflected in the fine-structure of the UV-Vis absorption spectrum of the former The increase of furan co-oligomer rigidity as compared with its thiophene analog lowers reorganization energy for hole, electron and exciton transfer Remarkably the substitution of thiophene by furan almost 20 times lowers reorganization energy for exciton transfe

Stimuli responsive aggregation-induced emission of bis(4-((9H-fluoren-9-ylidene)methyl)phenyl)thiophene single crystals

Abstract: Aggregation induced emission (AIE) materials are in the spotlight of current materials development due to their unique properties and potential applications in light-emitting devices, bio-imaging and sensors. In this work we synthesised and thoroughly studied a novel luminogen based on bis(4-((9H-fluoren-9-ylidene)methyl)phenyl)thiophene (BFMPT) showing polymorph-dependent AIE. BFMPT crystallises in two polymorphs of different crystal shapes and colours, however both of them are highly-luminescent with the same photoluminescence (PL) quantum yield of 40%. Polymorph I can undergo irreversible phase transition to polymorph II. Deep quantum chemical study of BFMPT revealed that inter- and intramolecular interactions in both polymorphs are very similar and the main contributor to the optical difference between the polymorphs is a variation of BFMPT conformation. The thermal stress was demonstrated to negligibly affect the PL efficiency of BFMPT crystals. Due to high intrinsic torsional freedom and high solid-state PL efficiency, BFMPT could serve as a basis for the molecular design of high performance AIE materials.

Long-range exciton transport in brightly fluorescent furan/phenylene co-oligomer crystals

Abstract: The design of light-emitting crystalline organic semiconductors for optoelectronic applications requires a thorough understanding of the singlet exciton transport process. In this study, we show that the singlet exciton diffusion length in a promising semiconductor crystal based on furan/phenylene co-oligomers is 24 nm. To achieve this, we employed the photoluminescence quenching technique using a specially synthesized quencher, which is a long furan/phenylene co-oligomer that was facilely implanted into the host crystal lattice. Extensive Monte-Carlo simulations, exciton–exciton annihilation experiments and numerical modelling fully supported our findings. We further demonstrated the high potential of the furan/phenylene co-oligomer crystals for light-emitting applications by fabricating solution-processed organic light emitting transistors.

Crystal packing control of a trifluoromethyl‐substituted furan/phenylene co‐oligomer

Abstract: Furan/phenylene co-oligomer single crystals are considered as future materials for organic optoelectronics. Here, the effects of trifluoromethyl substituents on the crystallization, structure and optical properties of furan/phenylene co-oligomer 1,4-bis{5-[4-(trifluoromethyl)phenyl]furan-2-yl}benzene are studied systematically. The solution growth methods and physical vapor transport result in the formation of three polymorphs depending on the growth method and the solvent. Single-crystal X-ray analysis reveals the crystal structures to correspond to H-, J- or mixed aggregates. All obtained crystals exhibit high photoluminescence efficiency and have optical properties which strongly depend on the crystal packing. Variable-temperature X-ray powder diffraction analysis shows the thermal transition of two forms (H- and J-aggregates) into a third one (mixed aggregate). Terminal trifluoro­methyl groups induce weak intermolecular interactions which control the crystal packing and optical properties of co-oligomer single crystals.

A synergy between the push–pull electronic effect and twisted conformation for high-contrast mechanochromic AIEgens

Abstract: Mechanochromic (MC) luminogens in response to external stimulus have shown promising applications as pressure sensors and memory devices. Meanwhile, research on their underlying mechanism is still in the initial stage. Here, three pyridinium-functionalized tetraphenylethylenes bearing n-pentyloxy, hydrogen and nitro groups, namely TPE-OP, TPE-H and TPE-NO, are designed to systematically investigate the influence of the push–pull electronic effect and molecular conformation on MC luminescence. Upon anisotropic grinding and isotropic hydrostatic compression, TPE-OP with strong intramolecular charge transfer (ICT) affords the best MC behavior among them. Analysis of three polymorphs of TPE-H clearly indicates that planarization of the molecular conformation plays an important role in their bathochromic shifts under mechanical stimuli. Theoretical calculations also verify that high twisting stress of AIEgens can be released under high pressure. This study presents a mechanistic insight into MC behaviour and an effective strategy to achieve high-contrast MC luminescence.

Fluorinated Thiophene-Phenylene Co-Oligomers for Optoelectronic Devices.

Abstract: Organic optoelectronics requires materials combining bright luminescence and efficient ambipolar charge transport. Thiophene-phenylene co-oligomers (TPCOs) are promising highly emissive materials with decent charge-carrier mobility; however, they typically show poor electron injection in devices, which is usually assigned to high energies of their lowest unoccupied molecular orbitals (LUMOs). A widely used approach to lower the frontier orbitals energy levels of a conjugated molecule is its fluorination. In this study, we synthesized three new fluorinated derivatives of one of the most popular TPCOs, 2,2'-(1,4-phenylene)bis[5-phenylthiophene] (PTPTP) and studied them by cyclic voltammetry, absorption, photoluminescence, and Raman spectroscopies. The obtained data reveal a positive effect of fluorination on the optoelectronic properties of PTPTP: LUMO levels are finely tuned, and photoluminescence quantum yield and absorbance are increased. We then grew crystals from fluorinated PTPTPs, resolved their structures, and showed that fluorination dramatically affects the packing motif and facilitates π-stacking. Finally, we fabricated thin-film organic field-effect transistors (OFETs) and demonstrated a strong impact of fluorination on charge injection/transport for both types of charge carriers, namely, electrons and holes. Specifically, balanced ambipolar charge transport and electroluminescence were observed only in the OFET active channel based on the partially fluorinated PTPTP. The obtained results can be extended to other families of conjugated oligomers and highlight the efficiency of fluorination for rational design of organic semiconductors for optoelectronic devices.

Charge transport in isoindigo-dithiophenepyrrole based D-A type oligomers: A DFT/TD-DFT study for the fabrication of fullerene-free organic solar cells.

Abstract: In this paper, we have designed a series of isoindigo-dithiophenepyrrole based oligomers with donor-acceptor architecture. The donor and acceptor units are joined by a thiophene linkage. We have substituted the 5,5′-positions of the isoindigo acceptor unit with different +I groups, viz., —CH3, —NH2, —SH, —OH, —OCH3, and —CH=CH2, and —I groups, viz., —F, —NO2, —CN, —COCH3, —COOH, and —CF3. We have studied the structural, charge injection, and transport properties employing the density functional theory (DFT) formalism. Our study explores that the presence of bulky substituents adversely affects these properties. Values of frontier orbital energies, ionization potentials, and electron affinities are calculated for each compound to predict the ease of charge injection from metal electrodes to these compounds. Most of our compounds show the ease of hole injection ability and show a large electron injection barrier. Computation of reorganization energies followed by the charge transfer integral and charge transfer rate have also been performed. Our findings reveal that compounds substituted with +I groups possess larger hole mobilities than the compounds with —I groups. Substitution of a dimer of compound 9 with —NO2 leads to the highest hole and electron mobility. Dipole moment values have also been calculated to study the charge transport properties. We have also computed the absorption properties of the compounds using the time-dependent DFT method. Our study indicates that absorption properties are changed by the attachment of substituents and can be tuned according to the requirements. Among the studied compounds, the —OCH3 substituted dimer (dimer 6) exhibits the largest bathochromic shift with a λmax of 554 nm. From this study, we can infer that our designed compounds are promising candidates for fabrication of optoelectronic devices.