The relationship between the structure, optical and thermodynamic properties of an emerging family of linear organic luminophores, consisting of 2,1,3-benzothiadiazole, and conjugated electron-donating biphenyl (2Ph-) and phenyl-xylene (Ph-Xy-) groups with trimethylsilyl (TMS) and n-hexyl (Hex) terminal substituents has been investigated. The new luminophores were synthesized via the Pd-catalysed Suzuki reaction with the purified products yields of 27-42%. It has been shown that an increase in the size of terminal substituents leads to an increase in the dipole moment of novel compounds. It was found that the fluorescence quantum yield (QY) has the values of 56% (R=-H), 67% (R=TMS) and 85% (R=Hex) for the crystals of the compounds with R-2Ph- donor groups, while the QY is close to 90% and practically independent of the terminal substituents for the crystals based on the compounds with donor R-Ph-Xy groups, which can be explained by the stabilizing effect of methyl groups of the xylene fragment (-Xy-) on the conformation of the molecule. Photostability of the molecules increases with the size of their terminal substituents. Replacement of 2 phenyls with 2 xylene fragments gives an order of magnitude increase in the solubility. The introduction of Hex end groups into the molecule decreases its melting point, while TMS groups increase it.

Annulated organic molecular structures with planar, fused backbones exhibit superior properties compared to non-fused systems, including high crystallinity, strong π–π stacking, and excellent charge transport characteristics. The rational design of annulated compounds with targeted characteristics presents a significant challenge that requires a comprehensive understanding of structure–property relationships. This work addresses this by synthesizing a series of novel push–pull systems featuring benzothieno[3,2-b]benzothiophene (BT) or its nitrogen-rich analogue, indolo[3,2-b]indole (ID), as electron-donating units, connected via a phenylene π-spacer to two distinct electron-accepting groups (carbonyl or dicyanovinyl). The thermal, structural, optical and electrochemical properties of these compounds were thoroughly investigated. Computational studies of the optical and electrochemical properties, including those of unsubstituted ID and BT model cores, showed excellent agreement with experimental data, validating the theoretical models. Notably, ID-based derivatives exhibited remarkably high photoluminescence quantum yield and enhanced solubility compared to their BT counterparts, along with thermal properties that are more favorable for device fabrication. This work provides the first systematic comparison of these annulated cores, offering novel structure–property insights that may support the rational design of organic functional materials and contribute to the further development of organic electronics.

Novel donor-acceptor arylsilane molecules, Si(PP-DCV)4 and Si(PT-DCV)4, featuring three-dimensional starshaped geometries, were synthesized and investigated in comparison to model compounds. These compounds, comprising a tetraphenylsilane core linked to terminal phenyldicyanovinyl groups through phenylene or thienyl It-spacers, exhibit a range of promising physicochemical properties, including high thermal stability (up to 490 degrees C), deep-lying HOMO energy levels (up to -6.4 eV), ambipolar charge carrier mobility, efficient light absorption, and high crystallinity. A comprehensive experimental and theoretical investigation, in comparison to model compounds, revealed the nonordinal optical properties of these compounds, elucidating the nature of electronic transitions and fluorescence efficiency. Substitution of the phenylene spacer with a thiophene spacer led to significant changes, including a red shift in the absorption spectrum, an increased extinction coefficient, lower HOMO energy levels, enhanced crystallinity, and improved ambipolar charge carrier mobility in films. Additionally, the polar and amphiphilic nature of these donor-acceptor molecules enabled the formation of stable nanoparticles (50-110 nm) in aqueous solutions without surfactants. These findings highlight the potential of these materials for applications in optoelectronic and biological applications.

Derivatives of 4,7-diphenyl-2,1,3-benzothiadiazole are highly stable compounds that fluoresce efficiently both in solutions and in the crystalline state. Thanks to their wide range of remarkable optoelectronic characteristics, they can rightly be called smart materials. This paper presents the results of an investigation into the polymorphism of 4,7-bis(4-(trimethylsilyl)phenyl)-2,1,3-benzothiadiazole (TMS-P-BTD) crystals under weakly and strongly non-equilibrium crystallization conditions from the vapor phase (PVD), solutions, and melt. Using single-crystal X-ray diffraction analysis at room temperature, two new polymorphic crystal modifications have been identified: orthorhombic II (sp. gr. Pnaa, Z/Z′ = 12/1.5) and triclinic III (sp. gr. P-1, Z/Z′ = 8/4). It was determined that the densest polymorph III melts at 154 °C. The least dense orthorhombic polymorph II dominates under kinetic growth conditions, melts independently at 151 °C, but transforms into polymorph III upon prolonged annealing. It has been established that the previously identified monoclinic polymorph I (P21/c, Z/Z′ = 32/8) transforms into polymorph III upon heating in the range of 75–110 °C. In the series of polymorphs I→II→III, a blue shift in the fluorescence spectrum maximum is observed: approximately 375 cm−1 for polymorph II and ~635 cm−1 for polymorph III relative to the position of the maximum λmax,I = 497 nm for polymorph I. The observed spectral-fluorescence features of the TMS-P-BTD crystal polymorphic phases are consistent with the structure of the flattest molecular conformers within the crystal unit cells.

The work presents the results of investigation of the phase behavior, crystal growth from solutions, structure, and absorption-fluorescent properties of the crystals of 4,7-bis(5-(4-(trimethylsilyl)phenyl)thien-2-yl)benzothiadiazole (TMS-P-T-BTD) and its isomer 4,7-bis(4-(5-(trimethylsilyl)thien-2-yl)phenyl)benzothiadiazole (TMS-T-P- BTD). The structure of the toluene-grown single crystals of both TMS-P-T-BTD and TMS-T-P-BTD was investigated using single-crystal X-ray diffraction at temperatures of 295 and 90 K. In the crystal unit cell of TMS-P-TBTD, which is triclinic (space group P1, Z = 1), statistical disorder in the arrangement of molecules was established, resulting in the emergence of a so-called "average" molecule with dual (50 %) orientation of the central 2,1,3-benzothiadiazole fragment., The molecules of TMS-P-T-BTD in the crystal exhibit an almost planar conformation. It was found that crystals of the isomer TMS-T-P-BTD of triclinic modification (space group P-1, Z = 2) are solvated: in the unit cell there is one solvent molecule- toluene- per two molecules of the basic compound. In the asymmetric block of the unit cell of the solvated crystals of TMS-T-P-BTD, there are two molecules with different conformations. Studies of the absorption-fluorescent properties of TMS-P-T-BTD and TMS-T-P-BTD molecules in the crystals showed that swapping the thiophene and phenyl fragments significantly alters the energy and probability of electronic transitions, as well as the relative position of n pi* and pi pi* levels. Both the probability of singlet- singlet transitions and the probability of singlet- triplet conversion change. The splitting of n pi* levels, caused by the arrangement of thiophene fragments in the TMS-P-T-BTD molecule, leads to a strong dependence of the fluorescent (kr) and phosphorescent (knr) characteristics of the isomer on the immediate environment. In the TMS-P-T-BTD crystal, this results in the complete suppression of fluorescence.

The crystallization and absorption/fluorescent properties of linear conjugated molecules derived from 2,1,3-benzothiadiazole, specifically, 4,7-bis(2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Ph-Xy-BTD) and 4,7-bis(4'-hexyl-2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Hex-Ph-Xy-BTD), have been studied. The synthesis of a new derivative of Hex-Ph-Xy-BTD is described. It was found that the presence of terminal n-hexyl substituents in Hex-Ph-Xy-BTD reduces the melting temperature, increases solubility, and has a positive effect on crystallization as compared to Ph-Xy-BTD. Hex-Ph-Xy-BTD single crystals were grown from a hexane solution, and their structure was elucidated using single-crystal X-ray diffraction, confirming a monoclinic system (sp. gr. P21/c, Z = 4). Absorption and fluorescence spectra were obtained and analyzed for solutions in tetrahydrofuran, as well as for the Ph-Xy-BTD and Hex-Ph-Xy-BTD crystals, along with the study of the quantum yield and fluorescence lifetime.

Organic semiconductor materials are interesting due to their application in various organic electronics devices. [1]benzothieno[3,2-b][1]benzothiophene (BTBT) is a widely used building block for the creation of such materials. In this work, three novel solution-processable regioisomeric derivatives of BTBT—2,7-bis(3-octylthiophene-2-yl)BTBT (1), 2,7-bis(4-octylthiophene-2-yl)BTBT (2), and 2,7-bis(5-octylthiophene-2-yl)BTBT (3)—were synthesized and investigated. Their optoelectronic properties were characterized experimentally by ultraviolet–visible and fluorescence spectroscopy, time-resolved fluorimetry, and cyclic voltammetry and studied theoretically by Time-Dependent Density Functional Theory calculations. Their thermal properties were investigated by a thermogravimetric analysis, differential scanning calorimetry, polarizing optical microscopy, and in situ small-/wide-angle X-ray scattering measurements. It was shown that the introduction of alkyl substituents at different positions (3, 4, or 5) of thiophene moieties attached to a BTBT fragment significantly influences the optoelectronic properties, thermal stability, and phase behavior of the materials. Thin films of each compound were obtained by drop-casting, spin-coating and doctor blade techniques and used as active layers for organic field-effect transistors. All the OFETs exhibited p-channel characteristics under ambient conditions, while compound 3 showed the best electrical performance with a charge carrier mobility up to 1.1 cm2·V−1s−1 and current on/off ratio above 107.

Luminescent organic semiconductors with high charge carrier mobility are in high demand for organic optoelectronic devices. The properties of organic semiconductors crucially depend on the length of substituents that are not directly involved in their pi-conjugated system, such as alkyl chains. In this study, a series of novel symmetric 4-alkylphenyl derivatives of [1]benzothieno[3,2-b]benzothiophene (Cn-PBTBT) with C6, C8, C10 and C12 alkyl chains were synthesized and investigated through TGA, DSC, POM, SAXS/WAXS, UV-vis absorption and photoluminescence spectroscopies, and their semiconductor properties were studied in OFETs. It was found that increasing the alkyl chain length mainly influenced the thermal stability, absorption spectra in thin films, phase behavior, solubility and charge-carrier mobility. All these molecules easily formed 2D crystals, showing charge-carrier mobilities in OFETs in the range of 1-5 cm2 V-1 s-1, with the highest values for C10-PBTBT and C12-PBTBT, while C6-PBTBT showed the highest solubility and no significant phase changes until ca. 150 degrees C. The alkyl chain engineering demonstrated can serve as an efficient tool for the smart molecular design of high-mobility luminescent organic semiconductors.

Synthesis and examination of two highly luminescent oligophenylene derivatives of 2,1,3-benzothiadiazole with branching centers based on benzene-1,3,5-triyl units are described. These studies in combination with DFT calculations have shown that the presence of the branching centers causes differences in the absorption characteristics and similarity of the emission properties. High molar extinction coefficients (up to 15 x 10 4 dm 3 mol -1 cm -1 ) in the medium UV-range and blue-green emission with quantum yields of 79-93% make them promising components of wavelength-shifting materials for optical devices.

Linear conjugated molecules consisting of benzothiadiazole (BTD) and phenyl rings are highly efficient organic luminophores. Crystals based on these compounds have great potential for use as light-emitting elements, in particular, scintillation detectors. This paper compares the peculiarities of growth, structure, and fluorescent properties of crystals based on 4,7-diphenyl-2,1,3-benzothiadiazole (P-2-BTD) and its organosilicon derivative 4,7-bis(4-(trimethylsilyl)phenyl) BTD ((TMS-P)(2)-BTD). The conditions for the formation of centimeter-scale single crystals were found for the former, while it was possible to prepare also bulky faceted individual crystals for the latter. The structures of P-2-BTD and (TMS-P)(2)-BTD crystals at 85 and 293 K were investigated by single-crystal X-ray diffraction. The crystal structure of P-2-BTD has been refined (sp. gr. P1, Z = 4), and for (TMS-P)(2)-BTD crystals, the structure has been solved for the first time (sp. gr. P2(1)/c, Z = 32). Experimental and theoretical investigations of the absorption-fluorescent properties of solutions and crystals of the molecules have been carried out. The luminophores are characterized by a large Stokes shift for both solutions and crystals with a high fluorescence quantum yield of 75-98% for solutions and 50-85% for the crystals. A solvatochromic effect was observed for solutions of both luminophores: an increase in the values of the fluorescence quantum yield and the excited state lifetime were established with increasing the solvent polarity. Fluorescence properties of solutions and crystals have been analyzed using the data on crystal structure and conformation structure of the molecules as well as density functional theory calculations of their electronic structure. The results have shown that the crystal packing of P-2-BTD molecules exhibits uniformity in conformational states, while (TMS-P)(2)-BTD molecules display a variety of conformational structures in the crystals. This unique combination of features makes them a remarkable example among the other molecular systems for identifying the relationship between the structure and absorption-fluorescence properties through comparative analysis.

The results of studying the growth of para-quaterphenyl (4P) and its derivative—4,4”'-bis(trimethylsilyl)-para-quaterphenyl (TMS-4P-TMS)—crystals from solutions are presented. It has been established that TMS-4P-TMS crystals exhibit better growth characteristics as compared to 4Р. Parameters of the phase transitions of 4P and TMS-4P-TMS in closed crucibles were refined using differential scanning calorimetry. The crystal structure of TMS-4P-TMS in the triclinic space group P 1̅ (Z = 2) has been decrypted for the first time using single-crystal X-ray diffraction and was studied in a wide temperature range. A crystallographic analysis of the studied compounds in crystals was performed using the Hirshfeld surface method, and modeling of intermolecular interactions was performed.

Liquid organic luminophores (LOLs) have been actively investigated as a new generation of functional materials in various fields of organic optoelectronics and photonics. However, many issues, including the structure-properties relationships and the development of LOLs emitting light in the red spectral range, remain poorly investigated. Here we report on the synthesis and investigation of a series of novel conjugated luminescent molecules consisting of a central 2,1,3-benzothiadiazole electron-withdrawing unit and lateral thiophene or phenylene electron-donating fragments with terminal trialkylsilyl units as solubilizing groups (SGs). Thermal and thermo-oxidative stability, phase behavior, structural properties, rheology, and optical and electrochemical properties of the obtained luminophores were studied and compared to their counterparts without SGs or with ineffective SGs for liquefaction. The target compounds are luminescent liquids with low glass transition temperatures (up to -65 degrees C) and viscosities (up to 1.7 Pa s) or liquid crystal materials emitting light in almost the entire visible spectral range with high photoluminescence quantum yield (PLQY) both in solutions (up to 97 %) and films (up to 87 %). For the first time, the application of LOLs as a new generation of organic liquid scintillators was demonstrated, achieving a light yield up to 1.7 times higher than that of a standard liquid scintillator.

The authors discuss results from studying the photophysical properties of linear molecules based on 2,1,3-benzothiadiazole, specifically 4,7-di([para-biphenyl]-4-yl)benzothiadiazole (Ph-Ph-BTD) and 4,7-bis(2,5-dimethyl-[1,1'-biphenyl]-4-yl)benzothiadiazole (Ph-Xy-BTD). The synthesis of a new phenylxylene derivative of benzothiadiazole—Ph-Xy-BTD—is described. The thermal stability of the Ph-Ph-BTD and Ph-Xy-BTD compounds is studied. Their parameters of melting and solubility are determined, and the absorption spectra of solutions in n-hexane and THF are recorded. It is shown that having pendant methyl substituents in Ph-Xy-BTD lowers its melting point, increases its solubility, reduces the probability of a transition between the ground and excited state orbitals, and raises the energy of transition. The effect solvation has on the spectra, fluorescence quantum yield, and lifetime of the fluorescence of compounds in THF and n-hexane is studied. Static dipole moments in the ground (HOMO) and excited states (LUMO) of Ph-Ph-BTD and Ph-Xy-BTD molecules are determined. It is shown that the conformation of the excited state (LUMO) changes during the relaxation of the solvate and becomes more planar than that of the ground state (HOMO). A relationship is revealed between the conformation of the excited state of the studied compounds and the polarity of the solvent.

A synthetic scheme allowing the preparation of nanostructured organosilicon luminophores of branched or dendritic structure with up to 18 bithiophenesilane donor fragments and one central acceptor fragment has been elaborated. This universal scheme has been successfully upscaled to 20 g of the product, and its efficiency has been verified by the synthesis of two earlier unknown bithiophenesilane dendrimers with dense molecular shell and the central acceptor fragment, 1,4-bis(5-phenylthienyl-2-yl)benzene. The synthesis of more branched dendrimers under the Suzuki reaction conditions has led to the formation of the side products with the rupture of the Si–C(thiophene) bond, not typical of the synthesis of analogous compounds with lower branching degree under the same conditions.

Thiophene-phenylene co-oligomers (TPCOs) have shown their high potential for organic light-emitting devices because of their high luminescence and efficient charge transport. However, unsubstituted TPCOs have relatively wide optical bandgaps and the high-lying lowest unoccupied molecular orbital (LUMO) energies so that efficient electron transport is a challenge. Electron-withdrawing groups (EWGs) and fluorinated fragments embedded into the TPCO molecule structure could result in the lower LUMO energy and narrower optical bandgap. Here, we report the synthesis of two novel TPCOs series with either phenylene or perfluorinated phenylene central core and end-capped with various EWGs (aldehyde, 2-ethylhexyl cyanoacetate, hexyl rhodanine and dicyano-rhodanine) and with long alkyl terminal and side chains increasing the solubility. All the oligomers synthesized were found to be thermally stable and crystalline materials with relatively low LUMO energies (down to-3.50 eV), narrow bandgaps (down to 1.9 eV), and efficient photoluminescence in the green - deep red spectral regions both in solution and solid-state. The TPCOs with 2-ethylhexyl cyanoacetate EWG were crystallized in large-area single-crystal monolayers, which showed strongly polarized photoluminescence and demonstrated their high potential as active layers in solution-processed single-layer organic light-emitting transistors.

A seriesof new tetrachromophoric systems based on stereoregulartetracyclosiloxanes and dibenzoylmethanatoboron difluoride derivativeshave been synthesized and characterized by a complex of physicochemicalmethods. The photophysical properties of the synthesized compoundsare studied by electronic absorption, steady-state, and time-resolvedfluorescence spectroscopy. In the synthesized compounds, four dibenzoylmethanatoborondifluoride (DBMBF2)-based fluorophores are in an all-cisarrangement with respect to a cyclotetrasiloxane scaffold. DFT calculationspredict that they can form H-type dimers, trimers, or tetramers withan antiparallel orientation of their ground-state dipole moments.Under UV excitation, solutions of these compounds in polar and nonpolarsolvents exhibit complex fluorescence consisting of monomer- and excimer-likeemissions with different lifetimes. Global fitting analysis revealsthe presence of at least four kinetically distinguishable speciesin the excited state. The studied compounds in solutions have CIEchromaticity coordinates very close to the white color point and arepromising objects for the development of next-generation single-emissionmaterials for white illumination.

Among short donor–acceptor molecules with a central benzothiadiazole fragment, 4,7-di-2-thienyl-2,1,3-benzothiadiazole (T-BTD) is one of the most well-known compounds, valued for its photophysical and semiconductor properties. We have synthesized a derivative of 4,7-di-2-thienyl-2,1,3-benzothiadiazole with trimethylsilyl end-substituents, 4,7-bis(5-(trimethylsilyl)thiophen-2-yl)benzothiadiazole (TMS-T-BTD). The phase transition parameters and thermal stability of T-BTD and TMS-T-BTD were investigated using DSC and TGA methods. The presence of the trimethylsilyl end-groups in TMS-T-BTD significantly enhances solubility, increases the melting temperature, and improves the resistance of TMS-T-BTD to evaporation in the liquid state. Single crystals of T-BTD and TMS-T-BTD were grown from solutions, with the largest sizes being 7 × 2 × 0.5 mm3 and 8 × 1 × 0.45 mm3, respectively. Using single-crystal X-ray diffraction at 293 K, the crystal structure of T-BTD was refined in the rhombic system (sp.gr. Pcab, Z = 8), while for TMS-T-BTD, it was determined for the first time in the monoclinic system (sp.gr. P21/c, Z = 4). The relationship between observed growth anisotropy and molecular packing in the crystals was analyzed. The results of investigations into the spectral-fluorescent properties of solutions in hexane and THF are presented. The solvatochromic effect was studied in a series of solvents, including hexane, THF, dichloromethane, and acetonitrile. The photostability of the compounds in hexane solutions was examined. It was found that the quantum yield of photodestruction for T-BTD is 13 times higher than that of TMS-T-BTD. The fluorescent properties of T-BTD and TMS-T-BTD crystals were investigated.

Silk fibroin (SF) holds promise for the preparation of matrices for tissue engineering and regenerative medicine or for the development of drug delivery systems. Regenerated fibroin from Bombyx mori cocoons is water-soluble and can be processed into scaffolds of various forms, such as fibrous matrices, using the electrospinning method. In the current study, we studied the correlation between concentrations of fibroin aqueous solutions and their properties, in order to obtain electrospun mats for tissue engineering. Two methods were used to prevent solubility in fibroin-based matrices: The conversion of fibroin to the β-conformation via treatment with an ethanol solution and chemical cross-linking with genipin (Gp). The interaction of Gp with SF led to the appearance of a characteristic blue color but did not lead to the gelation of solutions. To speed up the cross-linking reaction with Gp, we propose using chitosan-containing systems and modifying fibrous materials via treatment with a solution of Gp in 80% ethanol. It was shown that the composition of fibroin with chitosan contributes to an improved water resistance, reduces defective material, and leads to a decrease in the diameter of the fibers. The electrospun fiber matrices based on regenerated fibroin modified by cross-linking with genipin in water–alcohol solutions were shown to promote cell adhesion, spreading, and growth and, therefore, could hold promise for tissue engineering.

Organic luminescent materials are widely used in various electronic and optoelectronic devices upon growing demands of science and technology. Enhancement of spectral-luminescence characteristics for such materials and in depth understanding of "structure-property" relationships remain challenging tasks. Herein, we report on synthesis and comprehensive investigation of the series of novel luminescent push-pull molecules with triphe-nylamine unit as an electron donor block and thiophene as a it-spacer, which end-capped with various types of electron-withdrawing groups (EWGs), which are commonly used for the molecular design of various functional materials in organic electronics. The results allowed us to evaluate the impact of EWG type used on the target materials characteristics. Phenyl-substituted EWGs were found to be more suitable for the design of highly thermally and electrochemically stable materials with relatively high melting temperatures and melting en-thalpies. Depending on the EWG nature luminescence maxima of the luminophores demonstrated significant variability, e.g. from 509 nm to 750 nm, while the photoluminescence quantum yield (PLQY) values laid in the range of 1-89%. All luminophores showed good compatibility with a polystyrene (PS) matrix, in which PLQYs were generally higher (up to 25-fold enhancement) compared to the corresponding solutions or polycrystalline films. The changes of spectral characteristics observed for these luminophores were well described using basic relations of the semi-empirical theory of solvatochromism. Based on lifetime of excited states measurements, it was shown that the excited state non-radiative deactivation constants values the major contributors to PLQY values in THF solutions, while increase of the PLQY values in PS films can be associated with decrease of the probability of non-radiative deactivation of the excited states.