Terminal Alkyl Chain Length Research Articles

Increasing terminal alkyl chain length for a better small molecule organic solar cell donor

Optimizing the alkyl chains within a terminal group is considered to be a highly effective approach for boosting the power conversion efficiency (PCE) of all small-molecule organic solar cells (ASM-OSCs). In this study, we focus on designing and synthesizing small molecular (SM) donor compounds with different end-group alkyl chain lengths to study their impact on OSC performance. Under optimized conditions, OSC devices based on BTR-Cl-C8:Y6 demonstrate higher PCE of 14.43 % compared to those based on BTR-Cl:Y6. Moreover, BTR-Cl-C8 exhibits reduced levels of bimolecular recombination and trap-assisted recombination, enhanced capability for exciton dissociation and charge collection, and extended carrier lifetimes. These results highlight the significance of molecular design strategies in optimizing OSC performance and offer valuable insights for the development of efficient and stable ASM-OSCs.

Carbazol-benzothiadiazole based D–A–D mesogens: Self-assembly and photophysical characteristics

Three carbazole(C)-benzothiadiazole(B) based D-A-D mesogens CBC/n (n = 12, 16) and CTBTC/16 containing terminal N-trialkoxylbenzyl carbazoles at both side of central benzothiadiazole core have been designed and synthesized. By inserting thiophene (T) unit between B and C units, the rigid core was elongated and the molecular conformation changed from twist to planar one, thereby the liquid crystal (LC) phase changed from SmA to Col/hex phase. Such molecular packings caused by inserting T unit remained in their organogels formed in organic solvents. The long-core compound CTBTC/16 containing T unit with a more planar and tighter π-π packing structure showed a significant optical red shift and a stronger intramolecular charge transfer (ICT) effect than the short-core compounds CBC/n without thiophene unit. These compounds are all strong fluorescent in solution with fluorescence quantum yields (ΦF) ranging from 38 % to 86 %. But their solid fluorescence quantum yields (ΦFs) differ greatly with values of 43 %, 11 % and 0.6 % for CBC/12, CBC/16 and CTBTC/16 respectively. Further, short core compound CBC/12 with the highest ΦFs showed different ΦFs in its three different solid aggregation states. The application of the short twist core compound CBC/12 as white light-emitting diodes (LEDs) has been realized. The influence of the thiophene unit as well as the terminal alkyl chain length on self-assembly and ΦFs of these compounds is discussed.

Nanoparticles of Push-Pull Triphenylamine-Based Molecules for Light-Controlled Stimulation of Neuronal Activity.

Organic semiconductor materials with a unique set of properties are very attractive for interfacing biological objects and can be used for noninvasive therapy or detection of biological signals. Here, we describe the synthesis and investigation of a novel series of organic push-pull conjugated molecules with the star-shaped architecture, consisting of triphenylamine as a branching electron donor core linked through the thiophene π-spacer to electron-withdrawing alkyl-dicyanovinyl groups. The molecules could form stable aqueous dispersions of nanoparticles (NPs) without the addition of any surfactants or amphiphilic polymer matrixes with the average size distribution varying from 40 to 120 nm and absorption spectra very similar to those of human eye retina pigments such as rods and green cones. Variation of the terminal alkyl chain length of the molecules forming NPs from 1 to 12 carbon atoms was found to be an efficient tool to modulate their lipophilic and biological properties. Possibilities of using the NPs as light nanoactuators in biological systems or as artificial pigments for therapy of degenerative retinal diseases were studied both on the model planar bilayer lipid membranes and on the rat cortical neurons. In the planar bilayer system, the photodynamic activity of these NPs led to photoinactivation of ion channels formed by pentadecapeptide gramicidin A. Treatment of rat cortical neurons with the NPs caused depolarization of cell membranes upon light irradiation, which could also be due to the photodynamic activity of the NPs. The results of the work gave more insight into the mechanisms of light-controlled stimulation of neuronal activity and for the first time showed that fine-tuning of the lipophilic affinity of NPs based on organic conjugated molecules is of high importance for creating a bioelectronic interface for biomedical applications.

Influence of the molecular structure of calamitic compounds with trifluoromethoxy terminal group on the induction of the smectic a phase. Part I

ABSTRACT For the liquid crystalline mixtures of compounds with positive and negative dielectric anisotropies, the induction of the liquid crystal smectic A phase can be observed. This effect can be very favourable for definite specific purposes. The main aim of this work is to determine the influence of the molecular structure of compounds with a polar trifluoromethoxy (-OCF3) group on the induction strength of the orthogonal smectic A (SmA) phase. In order to reach this target, the phase diagrams of the mixtures were established using the polarised optical microscope observations. The presence of a triple bond, phenyl and cyclohexyl rings as well as fluorine atoms in the core and the length of terminal alkyl chains of the tested compounds were considered. The length of the rigid core has the greatest effect on the induction strength of the SmA phase, while the length of the alkyl chain (3–5 carbon atoms) has relatively minor influence. Explaining the correlation between the molecular structure and the induction strength, the dipole moments and the polarisability of the molecules should be taken into account. For shorter molecules, changes in the molecular structure have more significant influence on the temperature and concentration range of the orthogonal SmA phase.

Molecular design directs self-assembly of DPP polycatenars into 2D and 3D complex nanostructures

Novel diketopyrrolopyrrole (DPP) based polycatenars characterized with a long π-conjugated rigid calamitic core, different side groups (t-Boc, H or PEO) at the lactam N atoms of the central DPP core and terminal hydrophobic paraffinic chains were prepared via Sonogashira coupling reaction as key steps. The influence of different side groups, different links and the length of terminal alkyl chains on the properties of these DPP derivatives was discussed. Such DPP polycaterners can self-assemble into bicontinuous cubic phase (Cubv/Ia3¯d) and hexagonal columnar phase (Colhex) in their pure states, as well as organogels in solution. UV and PL spectra investigation reveals that these compounds can display broad and strong absorption in the region of 275–650 nm and can emit in the NIR region (650–850 nm) with low energy gap (1.94 ev), meanwhile ICT effects have been detected between such DPP polycaternars and C70, indicating the potential application of these compounds in solar cell.

Quantification of per‐ and polyfluoroalkyl substances with a modified total organic carbon analyzer and ion chromatography

AbstractQuantification of per‐ and polyfluoroalkyl substances (PFAS) via mass spectrometry is highly sensitive but targets a limited number of compounds and the instrumentation is not available in many laboratories. We developed a methodology to determine total organofluorine by modifying a total organic carbon analyzer, which is common in laboratories across disciplines. Evolved hydrogen fluoride was captured in an impinger and analyzed by ion chromatography. Recovery of fluorine from 20 PFAS was dependent on terminal functional group and alkyl chain length. The method detection limit based on perfluorooctanoic acid (PFOA) spiked samples was 36 μg‐F/L (52 μg PFOA/L). Fluorine recoveries of spiked PFAS in river water and wastewater were similar to those spiked in deionized water. The recovery of inorganic fluorine present in sodium fluoride was 91%. Therefore, researchers should be cautious when applying methods that pre‐combust samples to differentiate organo‐ and inorganic fluorine, because the combustion process may cause inadvertent losses of inorganic fluorine, resulting in an overestimation of organofluorine.Article Impact StatementResults enable the quantification of per‐ and polyfluoroalkyl substances using equipment present in a greater number of laboratories than mass spectrometry‐based methods.

Modulation of terminal alkyl chain length enables over 15% efficiency in small-molecule organic solar cells

Modulation of terminal alkyl chain length enables over 15% efficiency in small-molecule organic solar cells

How mobile phase composition and column temperature affect enantiomer elution order of liquid crystals on amylose tris(3-chloro-5-methylphenylcarbamate) as chiral selector.

A comprehensive study into the effects of mobile phase composition and column temperature on enantiomer elution order was conducted with a set of chiral rod-like liquid crystalline materials. The analytes were structurally similar and comprised variances such as length of terminal alkyl chain, presence of chlorine, number of phenyl rings, and type of chiral center. Experiments were carried out in polar organic and reversed-phase modes using amylose tris(3-chloro-5-methylphenylcarbamate) immobilized on silica gel as the chiral stationary phase. For all liquid crystals, reversal of elution order of enantiomers was observed based on type of used cosolvent and/or its content in the mobile phase; for some of the liquid crystals a temperature-induced reversal was also observed. Both linear and nonlinear dependencies of natural logarithm of enantioselectivity on temperature were found. Tested mobile phases comprised pure organic solvents and binary and tertiary mixtures of acetonitrile with organic solvents and/or water. Effect of acidic/basic mobile phase additives was also tested. Effect of structure of chiral selector is briefly discussed.

Structure and Dielectric Properties of Anisotropic n-Alkyl Anilino Squaraine Thin Films

Solution-processed and thermally annealed thin films from a series of n-alkyl terminated anilino squaraines are systematically investigated regarding their structural and optical properties by means of X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). Their characteristic intense double-hump-shaped absorbance spectra consisting of coupled H-aggregate and intermolecular charge transfer (ICT) resonance bands make them appealing for fundamental light–matter interaction studies, and their environmental sustainability invites for consumer optoelectronic applications. Now, the single-crystal structure of the n-pentyl anilino squaraine (nPSQ) provides a missing link to identify potential odd–even effects with respect to the terminal alkyl chain for bulk crystals. While all single crystals adopt a triclinic unit cell with biaxial dielectric properties, the thin films condense into effectively uniaxial anisotropic thin films. Here, the inherently low sensitivity to the out-of-plane complex refractive index of SE in reflection is reasonably compensated by adding transmission SE and transmission intensity data. With that, a general picture of the structural and dielectric properties of n-alkyl anilino squaraine thin films is launched, revealing that the terminal alkyl chain length affects the structural and optical properties in a twofold way: we observe a steady change which is superimposed by an anisotropic odd–even effect.

Synthesis and mesomorphic behaviour of highly ordered liquid crystalline D-A-D-type Carbazole-TPD-Carbazole

ABSTRACT Novel symmetrical carbazole-thieno[3,4-c]pyrrole-4,6-dione-carbazoles (Carbazole-TPD-Carbazole) were designed and synthesised as donor–acceptor-donor (D-A-D) materials. The correlations between their molecular structures, differing only in the length of the symmetrical terminal linear alkyl chains attached to a carbazole-TPD-carbazole moiety in the molecular core, and their mesomorphic behaviour, transition temperatures, energy levels and band gaps were studied for a potential use of these D-A-D materials as hybrid organic semiconductors for plastic electronics applications.

Mesomorphic properties of lactic acid derivatives and their racemic mixtures in comparison with analogous non-chiral compounds

ABSTRACT We have synthesised a series of lactic acid derivatives and studied their mesomorphic properties. Studied compounds consist of a molecular core laterally substituted by a chlorine atom, and we modified both terminal chains. We concentrated on the effect of the terminal alkyl chain length in the chiral part. For selected homologues, both enantiomers were prepared and mixed in racemic mixtures. We studied the mesomorphic behaviour and for one homologue a reentrancy of the SmA phase below the tilted SmC phase was detected, for both chiral enantiomers and for the racemic mixture. For chiral compounds with the SmC* phase, ferroelectric properties were studied by dielectric spectroscopy and switching properties were described. Reentrancy of the SmA phase was experimentally proved by several experimental techniques including x-ray measurements. For racemic mixtures and non-chiral analogues, we reached a good alignment, which allowed us to measure the birefringence and analyse the behaviour at the phase transitions.

Synthesis and self-assembly of benzothiadiazole-cored α-cyanostilbene hexacatenar mesogens

ABSTRACT A novel series of biscyanovinyl diphenylbenzothiadiazole-based polycatenars with 3,4,5-trialkoxyl benzene units at both ends were synthesized in high yield. The terminal alkyl chain length had great effect on the self-assembly properties. Upon terminal alkyl chain elongation, these compounds showed a mesophase transition from Colrec/p2 mm phase to Colhex/p6 mm phase in their bulk states and could aggregate into organogels with complex morphologies varying from 2D nanosheets via partial spheres to absolute 3D spherical flower-like morphologies. The results indicated that changing the alkyl chain length could tune supramolecular assembly nanostructures of the polycatenars effectively.

Lateral substituted phenyl biphenylcarboxylates ‒ non-chiral analogues of ferroelectric liquid crystals

ABSTRACTWe report mesomorphic properties of non-chiral liquid crystalline molecules and study the effect of lateral halogen (fluoro, chloro) substitution in the molecular core and the length of terminal chains. We have prepared nine homologue series with the molecular core substituted at different positions with respect to the ester linkage group. Additionally, we have modified the length of both terminal alkyl chains (hexyl, octyl, decyl and dodecyl) symmetrically for both terminal chains. The effects of the lateral substitution and the chain length are analysed with respect of the possibility to reduce the transition temperatures and tune the properties of presented liquid crystalline molecules.

Application of thermodynamic model to study the ferroelectric properties of biphenyl alkyloxy benzoate homologous series of SSFLC

ABSTRACTBased on a thermodynamic model, as developed by us [Singh A, Singh S. Thermodynamic model for the description of smectic C* and smectic A–smectic C* phase transition properties. Phase Transit. 2010;83:205–222; Singh S, Singh S. Thermodynamic model for the investigation of phase transition properties of homologous series of nAL and nHL ferroicmesogens. Phase Transit. 2014;87:427–437], we have studied relative temperature dependences of spontaneous polarization and tilt angle for three members C10, C11 and C12 of a homologous series, biphenyl alkyloxy benzoate, of surface stabilized ferroelectric liquid crystal (SSFLC) material. We found that the order parameter coupling terms make crucial contributions to the transition parameters and have to be included in free-energy density expansion. The values of these parameters depend on the length of terminal alkyl chain. A close agreement between theory and experiment has been found.

Effect of lateral substitution by chlorine and fluorine atoms of 4-alkyl-p-terphenyls on mesomorphic behaviour

The effect of halogen substitution on thermotropic liquid crystalline materials has a significant impact on many physical and chemical properties. Replacement of hydrogen atom by one of halogen can change and tune many important parameters such as dielectric anisotropy, viscosity, clearing and melting points, type and range of liquid crystalline phase and many others. Steric effect of halogen atoms and their polarity are two of the most important parameters, which have significant input to liquid crystalline properties. This work shows the correlation between the position of small size polar substituents (chlorine and fluorine atoms), their number and length of terminal alkyl chains (where alkyl chains are from ethyl to pentyl) on mesomorphic properties of twelve homologous series of terphenyl derivatives. Correlations for investigated compounds are supported by computational analysis of molecular polarizabilities, torsion angles between benzene rings and dipole moments. This work may be helpful for planning new structures of liquid crystalline compounds with predicted mesomorphism. Synthesized compounds show a strong tendency to form highly ordered smectic phases, while nematic phase is observed only for eleven compounds.

Polar Order, Mirror Symmetry Breaking, and Photoswitching of Chirality and Polarity in Functional Bent-Core Mesogens.

In recent years, liquid crystals (LCs) responding to light or electrical fields have gained significant importance as multifunctional materials. Herein, two new series of photoswitchable bent-core liquid crystals (BCLCs) derived from 4-cyanoresorcinol as the central core connected to an azobenzene based wing and a phenyl benzoate wing are reported. The self-assembly of these molecules was characterized by differential scanning calorimetry (DSC), polarizing light microscopy (POM), electro-optical, dielectric, second harmonic generation (SHG) studies, and XRD. Depending on the direction of the COO group in the phenyl benzoate wing, core-fluorination, temperature, and the terminal alkyl chain length, cybotactic nematic and lamellar (smectic) LC phases were observed. The coherence length of the ferroelectric fluctuations increases continuously with decreasing temperature and adopts antipolar correlation upon the condensation into superparaelectric states of the paraelectric smectic phases. Finally, long-range polar order develops at distinct phase transitions; first leading to polarization modulated and then to nonmodulated antiferroelectric smectic phases. Conglomerates of chiral domains were observed in the high permittivity ranges of the synclinic tilted paraelectric smectic phases of these achiral molecules, indicating mirror symmetry breaking. Fine-tuning of the molecular structure leads to photoresponsive bent-core (BC)LCs exhibiting a fast and reversible photoinduced change of the mode of the switching between ferroelectric- and antiferroelectric-like as well as a light-induced switching between an achiral and a spontaneous mirror-symmetry-broken LC phase.

Synthesis and mesomorphic properties of 4,4”-dialkynyl-2’,3’-difluoro-p-terphenyls – the influence of C≡C acetylene linking bridge

ABSTRACTDielectrically negative liquid crystals (LC) based on the terphenyl molecular core are widely used class of rod-like mesogenes. One of the most important parameters from applications point of view is optical anisotropy at nematic phase. Hence some applications require high values of birefringence (optical anisotropy in the case of nematic medium), which can be ensured by mesomorphic molecules having high anisotropy of electronic polarisabilities Δα. The molecular design of presented terphenyls is based on the idea of elongation of conjugated π electronic system by terminal acetylene bridge (C ≡ C), as a linking element to terminal alkyl chains. In this work, we developed synthesis of 4,4’’-dialkynyl-2’,3’-difluoroterphenyls with different length of terminal alkyl chains. All synthesised compounds have wide nematic phase ranges. Synthetic problems of this work will be presented. The purity and structures of the final products and intermediates were confirmed by spectral methods: gas chromatography GC-MS, GC-FID, IR spectroscopy and nuclear magnetic resonance NMR. The phase transition temperatures, phase situation and enthalpy data were determined by polarising optical microscopy (POM) and differential scanning calorimetry.

Thermomechanical and Conductive Properties of Thiol–Ene Poly(ionic liquid) Networks Containing Backbone and Pendant Imidazolium Groups

A series of covalently cross-linked poly(ionic liquid) networks were prepared using thiol–ene “click” photopolymerization. In these networks, imidazolium groups are placed in the backbone and pendant to the main chain, creating a “hybrid”-type network architecture. The pendant imidazolium groups were incorporated into the networks from monofunctional “ene” monomers that contained either a terminal alkyl group at the imidazolium N-3 position of variable length (R = C1, C4, C8, C12, C16, or C20) or a variable alkyl tether spacer (n = 6 or 10) between the newly formed sulfide and the imidazolium ring. Thermal characterization of these networks indicated a general decrease in Tg as the length of the terminal alkyl chain length increased from C1 to C8, followed by an abrupt increase in Tg up to C20 due to increased van der Waals interactions between longer chains. X-ray scattering data confirmed the presence of chain-extended crystallites within the network cavities for the C16 and C20 systems, leading to the observed increase in Tg and the appearance of a melting transition for both systems. Ionic conductivities of the PIL networks were determined from dielectric relaxation spectroscopy (10–6 to 10–7 S/cm at 30 °C, 30% RH), and a direct correlation with polymer Tg was found.

Bent-core liquid crystals based on 6-substituted 3-hydroxybenzoic acid: the role of substitution and linkage group orientation on mesomorphic properties

ABSTRACTWe have prepared and studied new series of bent-core liquid crystals based on laterally substituted 3-hydroxybenzoic acid. The physical properties of the materials were tuned by the type of lateral substitution in the vicinity of the carboxylic unit. Further modification was achieved by reorientation of connecting ester linkages in the elongating side arms and by changing the length of terminal alkyl chains. The physical properties of the materials were determined by differential scanning calorimetry (DSC), polarising optical microscopy and for selected compounds by x-ray diffraction analysis. The introduction of fluorine as lateral substituent leads to the appearance of a lamellar or columnar mesophase. On contrary, methyl- or chlorine-substituted compounds are mostly crystalline. We have found a strong correlation between the size of the lateral substituent and the mesogenicity of the studied materials.

Bent-shaped liquid crystals based on 4-substituted 3-hydroxybenzoic acid central core – Part II

ABSTRACTThe synthesis and mesomorphic properties of new series of bent-shaped liquid crystals are presented. The properties of the materials were tuned by the character of the lateral substituent in position 4 of the central aromatic ring and length of terminal alkyl chains. Further modification of physical properties was achieved by the introduction of an additional ester unit in the terminal alkyl chain. The physical properties of the studied materials were determined by differential scanning calorimetry, polarising optical microscopy and for selected compounds by x-ray diffraction. The influence of structural changes as well as the orientation of ester linkages (in comparison with previously described materials) is discussed. The addition of the fifth ester unit into the structure of the studied compounds leads to significant changes in their mesomorphic behaviour.