key: cord-0065969-tewpcwof authors: Alamro, Fowzia S.; Gomha, Sobhi M.; Shaban, Mohamed; Altowyan, Abeer S.; Abolibda, Tariq Z.; Ahmed, Hoda A. title: Optical investigations and photoactive solar energy applications of new synthesized Schiff base liquid crystal derivatives date: 2021-07-22 journal: Sci Rep DOI: 10.1038/s41598-021-94533-6 sha: 838fedb5cef0a7b8bf599378a5edacbdea5bc026 doc_id: 65969 cord_uid: tewpcwof New homologues series of liquid crystalline materials namely, (E)-3-methoxy-4-[(p-tolylimino)methyl]phenyl 4-alkloxybenzoates (I-n), were designed and evaluated for their mesomorphic and optical behavior. The prepared series constitutes three members that differ from each other by the terminally attached alkoxy chain group, these vary between 6 and 12 carbons. A laterally OCH(3) group is incorporated into the central benzene ring in meta position with respect to the ester moiety. Mesomorphic characterizations of the prepared derivatives are conducted using differential scanning-calorimetry (DSC), polarized optical-microscopy (POM). Molecular structures were elucidated by elemental analyses and NMR spectroscopy. DSC and POM investigations revealed that all the synthesized derivatives are purely nematogenic exhibiting only nematic (N) mesophase, except for the longest chain derivative (I-12) that is dimorphic possesses smectic A and N phases. Moreover, all members of the group have a wide mesomorphic range with high thermal nematic stability. A comparative study was established between the present derivative (I-6) and their previously prepared isomer. The results indicated that the location exchange of the polar compact group (CH(3)) influences the N mesophase stability and range. The electrical measurements revealed that all synthesized series I-n show Ohmic behaviors with effective electric resistances in the GΩ range. Under white light illumination, the effective electric conductivity for the compound I-8 is five times that obtained in dark conditions. This derivative also showed two direct optical band gaps in the UV and visible light range. In addition, I-6 has band energy gaps of values 1.07 and 2.79 eV, which are suitable for solar energy applications. The physical analyses data of products I-n are given in Supplementary Materials. A very thin layer of the sample was prepared by sandwiching them between a glass slide and a coverslip.The dimensions of the cell was 22 mm × 22 mm × 0.03 mm. " i.e., the film thickness was ~ 30 μm. The temperature of cell was controlled using temperature controller with an accuracy ± 0.1 °C. Mesomorphic and optical investigations of present derivatives, I-n. The mesomorphic and optical characteristics of the investigated synthesized derivatives have been analyzed by DSC and POM. Figure 2 displayed typical heating/cooling DSC thermograms of prepared compound I-6 as a representative example. Figure 2 was observed that, the mesophase transitions from Cr → N, and N → I for short-chain length I-6 derivative. Transition peaks observations vary according to the structural shape of synthesized materials, I-n. Significant endothermic and exothermic peaks were observed depending on the attached terminal alkoxy chain length group that is ascribed to mesomorphic transition and the cooling cycle confirmed those observed upon decrement the temperature. Optical images of the I-6 derivative under POM are illustrated in Fig. 3 . Schlieren/threads textures of the N mesophase were identified upon heating and cooling scans. The phase transition temperatures, as measured from DSC analysis, and their associated enthalpies for all the investigated compounds, I-n, are col- www.nature.com/scientificreports/ lected in Table 1 . The effect of terminal alkoxy chain length on their mesomorphic behavior has been depicted in Fig. 4 . Table 1 and Fig. 4 show that all prepared members of the series I-n are mesomorphic in nature with high mesomorphic thermal stability and a wide mesophase range dependent on their terminal chain length. Moreover, Compounds I-6 and I-8 are monomorphic possessing purely N phase while the longer chain compound I-12 possesses two mesomorphic transitions (dimorphic) enantiotropically defined as SmA and N mesophases. It can also be seen from Table 1 and Fig. 4 that the melting point of compounds varies regularly with the chain length (n). Compound I-6 exhibits an enantiotropic nematic phase with the highest nematic thermal stability and temperature range 203.1 and 96.8 °C, respectively. For I-8 derivative, it has possesses also an enantiotropic N mesophase with nematogenic stability and range nearly 162.1 and 64.3 °C, respectively. While the derivative bearing the longest chain length (I-12) possesses less thermal nematic stability (151.9 °C) and the lowest melting temperature 61.3 °C. So that, compound I-12 has induced smectic A mesophase and its mesomorphic range has been broader (90.6 °C). In general, the molecular architecture, polarizability, and dipole moment of the synthesized materials are highly impacted by the electronic nature of the terminals. In addition, the mesomorphic character is influenced by an increment in the polarity and/or polarizability of the molecular mesogenic moieties. The mesomorphic range of present investigated homologue increased in the order: I-6 > I-12 > I-8. The mesophase behavior of rod-like molecules is directly impacted by molecular-molecular interactions that depend essentially on their geometrical structure of the polar terminal and lateral groups and their special orientation. Mesomorphic properties observations results of the contribution of these factors to different extents. On the other hand, the DSC examination indicated to, the investigated imine derivatives exhibit high thermal stabilities more than 300 °C, which covers the transition window of mesophase temperature that detected thermally and extends over this transition too. On the other hand, the normalized transition entropy changes, ΔS N-I /R, of the present series (I-n) are collected in Table 1 . Data showed that small entropy changes values are observed that mainly depend on the kind of terminal substituents. The small values observed for the entropy change can be attributed to the decrease of the length-to-breadth ratio resulting from their lower anisotropy in terms of their molecular geometry [61] [62] [63] [64] . The induction, conjugation forces, the specific dipolar interactions as well as the π-π stacking interactions 61-64 play important roles in the molecular orientation and thus in the arrangement of molecules and formation of the mesophase. In addition, the thermal cis/trans isomerization of the azomethine linkage was an essential factor in the lower entropy changes observed, as documented in previous studies 65, 66 . Moreover, due to their nematic nature, this of the mesophase, this was exhibits of the lowest order mesophase. While the higher entropy changes of SmA-N transition for compound I-12 are attributed to the increment in its molecular biaxiality 67,68 . Table 1 . Mesophase transition temperatures, o C (enthalpy of transition), mesomorphic range (ΔT, o C), and the normalized entropy of transition, ΔS/R, for present series In. Cr-N = solid to the nematic mesophase transition. Cr-SmA = solid to the smectic A mesophase transition. SmA-N = smectic A to the nematic mesophase transition. N-I = nematic to the isotropic liquid mesophase transition. ΔH= enthalpy of transition, kJ/mole; ΔS/R= normalized entropy of transition, unitless (due to the entropy change ΔS is divided by R= gas constant). T Cr-SmA T Cr-N T SmA-N T N-I ΔT ΔS N-I /R Figure 4 . Impact of terminal chain-length on the mesomorphic transitions of the present homologue, I-n. www.nature.com/scientificreports/ In order to investigate the effect of exchange the mesogenic part between the aromatic rings on the mesophase and thermal behaviors of the compounds, thus a comparison is conducted between the presently prepared member I-6 and their previously corresponding isomer, II-6 69 for their mesophase behaviors. Compound II-6 possesses enantiotropic N mesophase with stability and temperature range nearly 141.3 and 51.1 °C, respectively. While the present investigated derivative I-6 has a wide nematic range with high thermal stability. In addition, the conjugated Schiff 's bases I-6 and II-6 ( Fig. 5) suggests that the insertion of one more double bond stabilities of the mesophases and increment the phase transition temperatures. It seems that the increase in length of molecule contributes to these effects. The comparison revealed that the thermal stability of the formed mesophase varies according to the enhanced molecular dipole moment and polarizability of the mesogenic part, which is dependent upon the location of polar groups. Moreover, the mesophase range and stability depend on the location of the terminal and linking groups in the mesogenic skeleton of the molecule. Optical spectra and energy gap calculation. Because liquid crystals are anisotropic materials and mesogenic materials cannot be aligned using existing techniques, the measured physical properties are referred to as effective optical absorbance and effective electrical conductivity. A Perkin Elmer spectrophotometer (Lambda 950 UV-VIS-NIR) was used to measure the effective optical absorbance and transmission spectra of the present investigated series, I-n, over a wavelength range of 250 to 2500 nm utilizing a blank glass substrate in the reference beam. The samples were sandwiched between two glass substrates. Figure 6A ,B shows how the effective absorbance and transmittance spectra of the films are affected by wavelength. In comparison to I8 and I12, the effective absorbance spectra in Fig. 6A show that I-6 has a high absorption behavior. For present homologue I-n, all films display high absorbance up to 402, 416, and 450 nm for I-6, I-8, and I-12, respectively. The absorbance then drops to a plateau at about 850 nm, before dropping again to a minimum absorbance around 1268 nm. www.nature.com/scientificreports/ exciton positions 70 . This red-shift and high absorption in UV and visible regions is a desirable feature for design energy-efficient solar cells 71 . The optical spectra refer to the homogeneity of the prepared films by decreasing the terminal length of the prepared series because the optical properties depend mainly on morphology and chemical composition. All films showed transmission less than 5% in the wavelength range from 300 to 800 nm, Fig. 6B . Then, the transmission increased exponentially in the near IR region to reach maxima of ~ 14%, 9%, and 8%@1266 nm for I-12, I-8, and I-6, respectively. After that, the transmission decreased as the wavelength increased. The concept of the crystalline solids band gap (E g ) can be expanded to include disordered and highly deficient phases, such as amorphous bodies (glass) and liquids. In this scenario, Eg can be called quasigap (Eg*), which refers to the existance of both localized and widespread electronic states near the edges, as well as in its depth 72 where hν is the photon energy and α a is the absorption coefficient. The values of E g for I-6, I-8, and I-12 are obtained by extending the linear segments of the plot of (α a hυ) 2 vs. hυ to zero as shown in Fig. 7A -C. Interestingly as reported in Table 2 , there are two values of the band gaps for the I-6, I-8, and I-12. For the shortest terminal chain compound (I-6), its values of the band gaps are 1.07 and 2.79 eV, which are suitable for solar energy applications [10] [11] [12] [13] [14] . By increasing the terminal length of the flexible chain, the values of the band gaps are shifted to 1.13 and 3.14 eV for the I-12 derivative. The observed increase in the main bandgap from 2.79 eV for I6 to 3.14 eV for I12 is ascribed to the influence of the density of localized states. This behavior is consistent with the previously reported studies 75 . The reduction of the bandgap is very important for solar energy applications, specially photoelectrochemical hydrogen generation, and solar cells [76] [77] [78] . Urbach energy (E U ) refers to the disorder in the material and represents the width of the exponential absorption edge (Urbach tail of the valence and conduction bands 79 . I.e., Urbach energy is the energy that refers to the creation of localized energy states at the boundaries of the energy gap due to structural disorder of the material and gives the spectral dependence of the absorption coefficients at photon energies less than the bandgap of the material. The exponential dependency of the E U can be determined according to the following equation 79 : www.nature.com/scientificreports/ where α ao is the band tail parameter that can be given by 80 : where c is the speed of light, σ o is electrical conductivity at absolute zero, ΔE represents the width of the tail of the localized state in the forbidden gap. Figure 8A and B shows the plot of ln(α) vs. hν for the two band gaps of I-6, I-8, and I-12. The values of E U1 and E U2 were obtained from the slopes of the linear fitting of these curves and reported in Table 2 . The statistical parameters, standard deviation (SD) and correlation coefficient (R 2 ), are also reported in this table. The values are 0.857 ± 0.009 and 0.990 ± 0.009 eV for I-6 and 0.956 ± 0.010 and 0.629 ± 0.040 eV for I-12, which refers to the extension of the bandgap edges to cover a wide range of the spectral range. Electrical properties. The effective electrical properties of the investigated films are tested using a Keithley measurement source unit (Model 4200 SMU). The samples were provided with Ohmic contacts using silver paste (Resistivity < 0.04 Ω.cm). Variation of the applied voltage (V) from − 10 to 10 V with different scan steps, 1V to 0.005V, is used to record the current-voltage (I-V) characteristics of the I-6, I-8, and I-12 films, as shown in Fig. 9A -C. The behaviors are almost linear (Ohmic behaviors). As a result, the materials' resistances are nearly constant and independent of the current flowing through them. Recent research has discovered that at low voltage, polymeric and organic systems behave like Schottky diodes. The Schottky diode is a semiconductor diode made up of a semiconductor and a metal junction that has a low forward voltage drop and a fast switching operation. But in the present investigation, the relation between log (I) and V 1/2 is non-linear as illustrated in Fig. 10A , which implies that our films do not follow the Schottky diode behavior. Under white light illumination, Fig. 9A , the values of the current increased, and the I-V behavior is shifted from the ohmic relation. As the scan step increased, the current intensity is also increased, insets of Figs. 9B and 10A. Figure 10B shows Table 1 )of prepared sample where the liquid crystalline phase range increasing in order I-6 > I-12 > I-8. The mesomorphic range of liquid crystalline materials is affected by many parameters as the polarity and polarizability of whole molecular shape this would be reflected in the resulting resistance data. The observation of more ordered smectic phase for the longer chain length derivative (I-12) could be explained in the term of the enhancement of the (2) α a = α ao exp E ph /E u → E u = δE ph /δ(ln(α a )) www.nature.com/scientificreports/ polarity and the polarizability with lengthening of the alkoxy terminal chain 32, 33 . The effective electric resistance of I-8 film is increased from 20.8 GΩ to 22.8 GΩ by decreasing the scan step from 1 V to 0.01 V as shown in Fig.10C which has the lowest entropy change value (see Table 1 ). The values of the effective electric conductance (σ) are obtained and shown in Fig. S1 (Supplementary Data). The value of the effective electrical conductance is increased from 0.91 nS in dark to 4.60 nS under white light illumination since the electrical conductance depends mainly on the number and mobility of charge carriers 81, 82 . This indicates the coherent photocurrent generation, which is the basis of the photovoltaic cell 83 . New mesomorphic laterally methoxy-substituent homologues series named, (E)-3-methoxy-4-[(p-tolylimino) methyl]phenyl 4-alkoxybenzoate (I-n), were synthesized and characterized by different thermal, optical, and electrical tools. The prepared series included three materials that differ from each other by the terminal length of the flexible chain. A lateral OCH 3 group is inserted into the central benzene ring. Elucidations of structures were carried out by elemental analyses, FT-IR, and NMR spectroscopy. Characterizations of present compounds are investigated using DSC, POM, UV spectrophotometer, Keithley measurement-source unit, and UV/Vis/ IR Perkin Elmer spectrophotometer. DSC and POM investigations indicate that all synthesized compounds are enantiotropic monomorphic exhibiting only N mesophase, except for the longest chain derivative (I-12) that is dimorphic possesses smectic A and N phases. Additionally, all compounds have a broad mesomorphic range with high thermal nematic stability. A comparative study was made between the present derivative (I-6) and their corresponding isomer and results indicated that the exchange of the location of the polar CH 3 group influences the N mesophase range and stability. The effective electrical measurements revealed that, with electric resistances in the GIGA range, all investigated derivatives (I-n) exhibited Ohmic behaviors. The effective electric conductivity of the compound I-8 is five times higher under white light illumination than in dark conditions. Moreover, In the UV and visible light ranges, this member (I-8) has revealed two direct optical band energy gaps. Further, it was found that the band energy gaps for I-6 are 1.07 eV and 2.79 eV, which confirming that it is appropriate for solar energy applications. www.nature.com/scientificreports/ Perovskite solar cells: The new epoch in photovoltaics High-performance large-area organic solar cells enabled by sequential bilayer processing via nonhalogenated solvents Large-area organic solar cells: Material requirements, modular designs, and printing methods Organic solar cells based on non-fullerene acceptors Next-generation organic photovoltaics based on non-fullerene acceptors Nonfullerene acceptor molecules for bulk heterojunction organic solar cells Toward over 15% power conversion efficiency for organic solar cells: current status and perspectives Simple and low-cost synthesis of Ba-doped CuO thin films for highly efficient solar generation of hydrogen Influence of the spin deposition parameters and La/Sn double doping on the structural, optical, and photoelectrocatalytic properties of CoCo2O4 photoelectrodes Preparation and characterization of MCM-48/nickel oxide composite as an efficient and reusable catalyst for the assessment of photocatalytic activity Graphite/rolled graphene oxide/carbon nanotube photoelectrode for water splitting of exhaust car solution Synthesis and characterization of biogenic iron oxides of different nanomorphologies from pomegranate peels for efficient solar hydrogen production Highly efficient and thermally stable fullerene-free organic solar cells based on a small molecule donor and acceptor 97.3% efficiency nonfullerene all organic small molecule solar cells with absorption-complementary donor and acceptor All-small-molecule nonfullerene organic solar cells with high fill factor and high efficiency over 10% Improve the performance of the all-small-molecule nonfullerene organic solar cells through enhancing the crystallinity of acceptors High-efficiency all-small-molecule organic solar cells based on an organic molecule donor with alkylsilyl-thienyl conjugated side chains Organic and solution-processed tandem solar cells with 17.3% efficiency Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature Applications of liquid crystals in biosensing and organic light-emitting devices: Future aspects Thin films of discotic liquid crystals and their applications Photovoltaic effects in ferroelectric liquid crystals based on phenylterthiophene derivatives Studying discotic liquid crystalline physical gel formation and their applications in solar cells Bulk heterojunction solar cells based on self-assembling disc-shaped liquid crystalline material Charge transfer reactions in nematic liquid crystals Self-assembled liquid-crystalline ion conductors in dye-sensitized solar cells: Effects of molecular sensitizers on their performance Experimental and computational simulations of nematogenic liquid crystals based on cinnamic acid in pure and mixed state Synthesis, thermal and optical characterizations of new lateral organic systems Mesomorphic, optical and DFT aspects of near to room-temperature calamitic liquid crystal Synthesis, mesomorphic and computational characterizations of nematogenic schiff base derivatives in pure and mixed state Optical and thermal investigations of new schiff base/ester systems in pure and mixed states Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures II. 4-Hexadecyloxyphenyl arylates and aryl 4-hexadecyloxy benzoates Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures VI [1] The effect of molecular length Lateral protrusion and mesophase behaviour in pure and mixed states of model compounds of the type 4-(4′-substituted phenylazo)-2-(or 3-) methyl phenyl-4'-alkoxy benzoates The molecular physics of liquid crystals edited by GR Luckhurst and GW Gray Morphological, optical and dielectric behavior of chiral nematic liquid crystal mixture: study on effect of different amount of chirality Dielectric properties of a strongly polar nematic liquid crystal compound doped with gold nanoparticles Synthesis, optical and DFT characterizations of laterally fluorinated phenyl cinnamate liquid crystal non-symmetric system New nitro-laterally substituted azomethine derivatives; Synthesis, mesomorphic and computational characterizations Perylene-based liquid crystals as materials for organic electronics applications Discotic liquid crystals Polycyclic aromatic hydrocarbons obtained by lateral core extension of mesogenic perylenes: Absorption and optoelectronic properties Liquid-crystalline small molecules for nonfullerene solar cells with high fill factors and power conversion efficiencies L-proline catalyzed green synthesis and anticancer evaluation of novel bioactive benzil bis-hydrazones under grinding technique Multicomponent synthesis, DFT calculations and molecular docking studies of novel thiazolyl-pyridazinones as potential antimicrobial agents against antibiotic-resistant bacteria ] thiadiazoles and other diazoles bearing indole moieties and their antimicrobial evaluation Clean grinding technique: A facile synthesis and in silico antiviral activity of hydrazones, pyrazoles, and pyrazines bearing thiazole moiety against SARS-CoV-2 main protease (Mpro) One-pot synthesis of novel thiazoles as potential anti-cancer agents. Drug Des An old dog with new tricks: Schiff bases for Isoxazoline-and isoxazole-liquid crystalline schiff bases: A puzzling game dictated by entropy and enthalpy effects Photochemical behaviour of Schiff base liquid crystals based on isoxazole and isoxazoline ring. A kinetic approach Optical second harmonic generation in polyazomethine ether Processible polyazomethines and polyketanils: From aerospace to light-emitting diodes and other advanced applications Mesomorphic, morphologic and thermotropic properties of 4-hexyl-N-(4-hexadecyloxysalicylidene) aniline A new liquid crystal of considerable value for the separation of closely related solvents by gas chromatography Chiral (S)-5-octyloxy-2-[{4-(2-methylbuthoxy)-phenylimino}-methyl]-phenol liquid crystalline compound as additive into polymer solar cells Side-chain liquid-crystalline polysiloxanes containing ionic mesogens and cholesterol ester groups Synthesis, characterization and mesomorphic properties of side chain liquid crystalline oligomer having schiff base type mesogenic group Synthesis, thermal and optical behaviour of non-symmetric liquid crystal dimers α-(4-benzylidene-substitutedaniline-4′-oxy)-ω-[pentyl-4-(4′-phenyl) benzoateoxy] hexane Methylene-and ether-linked liquid crystal dimers II. Effects of mesogenic linking unit and terminal chain length Non-symmetric dimers: Effects of varying the mesogenic linking unit and terminal substituent Non-symmetric dimeric liquid crystals the preparation and properties of the α-(4-cyanobiphenyl-4′-yloxy)-ω-(4-n-alkylanilinebenzylidene-4′-oxy) alkanes Comparison of the mesogenic properties of monomeric, dimeric, and side-chain polymeric liquid crystals Symmetric and non-symmetric chiral liquid crystal dimers The preparation and properties of low molar mass liquid crystals possessing lateral alkyl chains Laterally substituted dimeric liquid crystals Synthesis, optical characterizations and solar energy applications of new Schiff base materials Effects of lanthanum and sodium on the structural, optical and hydrophilic properties of sol-gel derived ZnO films: A comparative study Thieno [3, 4-c] pyrrole-4, 6-dione-3, 4-difluorothiophene polymer acceptors for efficient all-polymer bulk heterojunction solar cells Analysis of photoluminescence, UV absorbance, optical band gap and threshold voltage of TiO2 nanoparticles dispersed in high birefringence nematic liquid crystal towards its application in display and photovoltaic devices Influences of lead and magnesium co-doping on the nanostructural, optical properties and wettability of spin coated zinc oxide films Low bandgap donor-acceptor π-conjugated polymers from diarylcyclopentadienone-fused naphthalimides Efficient photoselectrochemical hydrogen production utilizing of APbI3 (A= Na, Cs, and Li) perovskites nanorods Phase-junction Ag/TiO2 nanocomposite as photocathode for H2 generation Outstanding stability and photoelectrochemical catalytic performance of (Fe, Ni) co-doped Co3O4 photoelectrodes for solar hydrogen production Structural, optical and photocatalytic properties of Fe and (Co, Fe) co-doped copper oxide spin coated films Structural and optical characterization of ZnO thin films for optoelectronic device applications by RF sputtering technique Analysis of blockade in charge transport across polymeric heterojunctions as a function of thermal annealing: A different perspective Study of charge transport in composite blend of P3HT and PCBM Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes The authors acknowledge the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University for financial support through the Fast-track Research Funding Program. The authors declare no competing interests. The online version contains supplementary material available at https:// doi. org/ 10. 1038/ s41598-021-94533-6.Correspondence and requests for materials should be addressed to H.A.A.Reprints and permissions information is available at www.nature.com/reprints.Publisher's note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. 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