Organic Single Crystals Research Articles

Investigation on the optical, electronic, mechanical and thermal parameters of guanidinium p-toluenesulfonate single crystal for opto-electronic applications

Organic single crystals of guanidinium p-toluenesulfonate were synthesized and grown embracing slow evaporation solution growth technique. The grown crystal was subdued to single crystal X-ray diffraction study and powder X-ray diffraction study for the computation of cell parameters, space group and morphology for its structural confirmation. The various functional groups present in the crystalline material were determined by utilizing Fourier transform infrared (FTIR) spectral analysis. The optical transmittance study was exploited for the evaluation of absorption coefficient, refractive index and extinction coefficient. Appropriate physical parameters towards the estimation of plasma energy (19.628 eV), Penn gap (6.054), Fermi energy (15.604) and electronic polarizability from Penn analysis (5.00 × 10−23 cm3) and Clausius–Mossotti equation (5.446 × 10−23 cm3) were theoretically calculated. The values obtained from Penn analysis and Clausius–Mossotti equation are compatible with each other. The measured Vickers hardness values (at various loads) are reported to understand the mechanical properties of the crystal. We have also reported the values of indentation depth with respect to their indenter loads. The thermal results obtained from thermogravimetric-differential thermal analyses (TG-DTA) were utilized for the calculation of kinetic parameters such as effective activation energy, Arrhenius constant, enthalpy of activation, entropy of activation and Gibb's energy.

Efficient Organic Light-Emitting Transistors Based on High-Quality Ambipolar Single Crystals.

A cyano-substituted styrene derivative is synthesized and successfully prepared to lamellate single crystals through precisely controlling the crystal growth conditions. The lamellate single crystals with regular edge and smooth surface display intrinsically ordered stacking and high quality, all of which are of importance for high optoelectronic performance. The single-component light-emitting transistors based on the lamellate crystals offer striking device performance in terms of record external quantum efficiency of 2.02%, exceeding the benchmark value in this field. Such organic light-emitting single crystals provide a versatile platform for designing and engineering their structures and optoelectronic properties toward light-emitting devices.

Synthesis, crystal structure, linear properties and DFT analysis of L-Tartarate hydrogen squarate (LTS): A nonlinear optical single crystal

A novel organic non-linear single crystal of L-Tartarate hydrogen squarate (LTS) has been synthesized and successfully grown from aqueous solution by slow evaporation solution growth method. In the present investigation the title compound of L-Tartaric acid with squaric acid has been synthesized by using double distilled water as the solvent. The prepared concentrated solution was placed in an undisturbed condition and then the solution was periodically inspected. The good quality single crystals have been harvested in a time span of 40 days. Then the grown crystal was characterized by single crystal XRD, FTIR, UV–vis-NIR, and SHG. The optimized geometry, vibrational frequencies, Mulliken charge distribution, frontier molecular orbitals (FMOs), and associated energies of the ground state and the first single excited state were calculated using density functional theory (DFT) and time-dependant DFT calculations using the B3LYP/6- 311G method. Vibrational frequencies calculated in the gaseous phase compared with experimental values measured in the solid state and showed good agreement with each other. The observed results from the characterization analyses show its suitability for NLO applications when compared with some of the existing organic crystals. The relative second harmonic generation of this grown crystal was found to be 0.9 times than that of KDP crystal.

Angle-Resolved Photoemission Study on the Band Structure of Organic Single Crystals

Angle-resolved photoemission spectroscopy (ARPES) is a vital technique, collecting data from both the energy and momentum of photoemitted electrons, and is indispensable for investigating the electronic band structure of solids. This article provides a review on ARPES studies of the electronic band structure of organic single crystals, including organic charge transfer conductors; organic semiconductors; and organo-metallic perovskites. In organic conductors and semiconductors, band dispersions are observed that are highly anisotropic. The Van der Waals crystal nature, the weak electron wavefunction overlap, as well as the strong electron-phonon coupling result in many organic crystals having indiscernible dispersion. In comparison, organo-metallic perovskite halides are characterized by strong s-p orbitals from the metal and halide at the top of the valence bands, with dispersions similar to those in inorganic materials.

A Study of the Nonlinear Optical Properties of Stilbazolium Derivative Crystal

In this report we start from ab initio calculations to get the structural properties of an isolated molecule of an organic crystal. Since the knowledge of the effects of neighboring molecules their study became necessary for an appropriated description of nonlinear optical properties in the solid state and more efficient design of such materials requires theoretical models that describes in detail the structural and electronic properties of the crystalline environment. The derivative of an organic stilbazolium single crystal, (E)-1-ethyl-2-(4-nitrostyryl) pyridin-1-ium iodide (NSPI); the NSPI crystallizes in the centric triclinic system with the P1space group. Here the dipole moment, the linear polarizability, and second hyper polarizability of the asymmetric unit of the compound were investigated through a super molecule approach in combination with an iterative scheme. In this approach the electrostatic interactions of the atoms of molecules embedded are represented by point charges. In addition to these calculations, other interesting results are obtained when we compare the results for isolated molecule and the molecule under the influence of its crystalline environment (embedded molecule); under such an influence we find a very interesting result for the average 2nd hyperpolarizability: 290,000% higher in the isolated molecule when compared to the embedded one.

Synthesis, crystal growth, spectroscopic characterization and DFT studies of 4-(E)-1-(4-chlorophenyl)-3-(4-nitrophenyl)prop-2-en-1-one (CPNP) single crystal as a nonlinear optical (NLO) material

Abstract An organic nonlinear optical single crystal of 4-(E)-1-(4-chlorophenyl)-3-(4-nitrophenyl) prop-2-en-1-one [CPNP] was synthesized and its single crystal grown by solution growth technique. XRD analysis of the CPNP single crystal confirms that the crystal belongs to orthorhombic system with non centrosymmetric space group Pna21. The characteristic functional groups in the crystal were identified by FT-IR analysis. The CPNP crystal exhibits an optical transparency of 76% with optical band gap energy of 2.88eV. The HOMO-LUMO energy gap calculated from DFT for a single-molecule in the gas phase was found to be 3.88 eV. The thermal stability of the CPNP crystal was analyzed by TGA/DSC analysis. The CPNP crystal exhibits photoluminescence property with strong emission at 615nm in the orange red region. The LDT value of the CPNP crystal was found to be 1.72 GW/cm2. The SHG efficiency of CPNP crystal is 0.75 times greater than that of standard urea.

Studies on structural, optical, homo-lumo and mechanical properties of piperazinium p-hydroxybenzoate monohydrate single crystal for nonlinear optical applications

An organic single crystal of piperazinium p-hydroxybenzoate monohydrate (PPH) was grown by solution growth technique. It belongs to monoclinic system with space group P21/c. Density functional theory (DFT) computations were used by B3LYP/6–311++G (d,P) basis set to optimize molecular geometry and HOMO-LUMO energies. The infrared spectrum confirms the functional groups present in the grown crystal. The UV–Visible, PL and Thermal studies were also analyzed. Hardness property was measured by Vicker's microhardness tester. The chemical etching studies confirms that PPH crystal possesses a layer growth pattern. Second harmonic generation efficiency of PPH crystal has 1.5 times larger than KDP crystal.

Organoferroelasticity Mediated by Water of Crystallization

Despite the general conception of brittleness, organic single crystals composed of various kinds of molecules can show ferroelasticity by mechanical twinning. This is attributed to flexibilities in molecular structures, e.g., conformation, and noncovalent bonds, e.g., length and angle. Herein, we find ferroelasticity by mechanical twinning mediated by water of crystallization in a single crystal of a zwitterion: sulfanilic acid monohydrate. Shaping of an organic single crystal is demonstrated ferroelastically from linear to bent shape and from contracted to elongated shape. Rotation of sulfonate anions along with recombination and changes in lengths and angles in flexible hydrogen bonds of small water molecules helps ferroelastic mechanical twinning. Our findings demonstrate designability of mechanically twinnable organic crystals from the viewpoints of organic chemistry and crystal engineering based on hydrogen bonds.

Revealing mechanism of obtaining the valence band maximum via photoelectron spectroscopy in organic halide perovskite single crystals

In recent years, organic halide perovskites have attracted increasing attention from scientists. To understand the device's operational mechanism, obtaining their valence band maxima (VBMs) using ultraviolet photoelectron spectroscopy plays a critical role in determining their electronic structures and related energy level alignments. Two methods are commonly used to extract their valence band (VB) edge from either linear or logarithmic intensity scales to reach the agreement with theoretical calculations. However, the consistency behind these two methods is not revealed. In this report, we have quantitatively studied VB edges for CH3NH3PbI3 and CH3NH3PbBr3 single crystals using different photon energies. After considering both their origins of orbital hybridizations and density of state (intensity) distributions at various momentum spaces, it is revealed that precise VBMs from linear scales can be realized. The VBMs obtained from M symmetry points are 1.13 eV away from the Fermi level for CH3NH3PbI3 and 1.29 eV for CH3NH3PbBr3, suggesting that the VBMs (at the R point) are 0.86 eV for CH3NH3PbI3 and 0.89 eV for CH3NH3PbBr3. Our findings explain the mechanism of precisely obtaining VBMs from these halide perovskite single crystals.

Structural, optical, FT-IR and SHG studies of L-Isoleucine D-Valine: A spectroscopic and DFT approach

Organic nonlinear optical single crystal of L-Isoleucine D-Valine (LIDV) with dimensions 3 X 3 X 4 mm3 was successfully grown by the slow evaporation solution growth technique (SEST). The structural analysis of the grown crystals has been analyzed by Powder X-ray diffraction which revealed that grown (LIDV) crystal belongs to monoclinic crystal system with P21 space group. The structure of LIDV is optimized using Density Functional Theory (DFT) method. The vibrational band assignments were performed at B3LYP/6-31G + (d, p) theory level. The theoretical IR frequencies are found to be in good agreement with the experimental IR frequencies. Nonlinear optical (NLO) behavior of LIDV is examined by the theoretically predicted values of first hyper polarizability. The cut-off wavelength and the optical band gap value of the grown crystal is found using Optical studies. The SHG efficiency of the grown material is found to be 2.5 times the reference material.

Microspacing In-Air Sublimation Growth of Ultrathin Organic Single Crystals

Organic single crystals play indispensable roles in high-performance electronic devices because of their completely eliminated or minimized impurities and disorder, wherein ultrathin thickness is a...

Naturally and Elastically Bent Organic Polymorphs for Multifunctional Optical Applications

AbstractRecently, mechanically bendable organic single crystals have been widely studied as emerging flexible materials. However, only a very small percentage of organic crystals have been found to be elastic or plastic. In this study, crystal engineering is employed as a powerful strategy to improve the probability of constructing flexible organic crystals. Based on an organic compound, two polymorphs Cry‐R and Cry‐O with bright red and orange emissions, respectively, are obtained. Cry‐R, being brittle inherently, can form a naturally bent crystal with an optical waveguide as efficient as the straight crystal. The other polymorph Cry‐O can be elastically bent, almost into a loop, and displays an optical waveguide and amplified spontaneous emission in both the straight and bent state, demonstrating its multifunctional applications in flexible optical devices. In addition, the Y‐shaped crystals of Cry‐O obtained by natural growth are found to transduce single emitted light through the two branches and thus generate dual output signals simultaneously, which further highlights the utility of “crystal flexibility”. The results not only suggest a guideline to modify the mechanical compliance by crystal engineering but also provide a model of flexible organic crystals for multifunctional optical applications.

Crystal growth, structural, nonlinear optical and theoretical investigations of Benzilic acid crystals

Organic single crystals of Benzilic Acid (BA) were grown by slow solvent evaporating method by using acetone as solvent. The unit cell parameter values and the crystal system are recognized by using single crystal XRD technique. The optical assessment of BA molecules is observed by with UV-Vis spectral analysis as the ultraviolet range between 200 and 400 nm and the visible region between 400 and 800 nm. The nonlinear optical (NLO) properties such as second harmonic efficiency nature of BA crystal were analyzed using Nd:YAG laser. The laser-induced damage threshold assessment of BA crystal is measured as 2.76 GW/cm2. From the Density Functional Theory (DFT), the molecular structural feature and vibrational frequencies were defined by using the Gaussian system along with comparisons of experimental frequencies. Using the DFT method, the derived vibrational frequency values showed an admirable accord with experimental frequencies. The charge interactions within the BA molecules are confirmed by HOMO and LUMO energy value. The first-order molecular hyperpolarizabilities, dipole moment, polarizability and Mulliken charge analysis of the BA molecule are also evaluated.

Investigation of the optical, photoluminescence, and dielectric properties of P-Toludinium picrate single crystals

The present work deals with the synthesis and characterization of p-Toluidinium picrate (PTP), an organic non-linear optical single crystal, produced by the solvent evaporation growth technique at room temperature condition. For the physical characterization, different instrumental techniques like powder XRD analysis for the crystallinity, FTIR, and laser Raman spectral analyses for the nature of chemical bonding and functionality, the ultraviolet spectrum for the optical absorption properties, etc. were employed. Following the instrumental analysis, on testing of the photoluminescence properties, we observed the first emission peak at 359 nm in the UV region, and two other emission peaks around 443 nm and 460 nm corresponding to the blue emission region. Also, we investigated PTP's dielectric behavior at different frequencies and room temperature, where the solid-state parameters such as plasma energy, Penn gap, Fermi energy, and polarizability were measured. Based on the overall analysis of optical, photoluminescence, and dielectric properties, it can be mentioned that the synthesized PTP crystals might have potential applications in the development of semiconducting, supercapacitor, and non-linear optical devices.

High-resolution patterning of organic semiconductor single crystal arrays for high-integration organic field-effect transistors

The pursuit of low-cost, high-performance electronic applications with solution-processible organic semiconductors drives the development of efficient methods to pattern organic semiconductor single crystals (OSSCs). However, fluid instabilities and a complex evaporation process have limited patterning of OSSCs with high resolution. Here, we present a solvent-free patterning approach, capillary force-driven molecule flow (CFDMF), to achieve highly aligned 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) single crystal patterns with sub-micron resolution and high fidelity. The position as well as pattern shape and resolution of the C8-BTBT single crystal arrays can be predetermined through photolithography. Using this method, we have demonstrated a high-integration circuit comprising over 169 organic field-effect transistors (OFETs) with a high resolution of 310 dpi. The resultant OFETs show good field-effect properties with an average mobility of 4.44 cm2 V−1 s−1. This patterning technique constitutes a major step toward the use of the high-mobility OSSCs for integrated device applications.

Growth and investigations of 3rd order NLO properties of novel semi organic tartaric acid lithium sulfate single crystal for photonics application

Single crystals of tartaric acid lithium sulfate (TALS), a semi-organic nonlinear optical crystal has been successfully grown by slow evaporation solution growth technique. Single crystals were grown in a life span of 3 weeks. The grown crystals were characterized by single crystal X-ray diffraction to identify the lattice parameters. Fourier Transform Infra Red studies confirm the presence of various functional groups present in the crystal. Optical, mechanical, microscopic image and thermal stabilities of the title crystal was carried out to know the properties of the titled compound. Third order non-liner studies have also been studied by Z-scan techniques. Nonlinear absorption and nonlinear refractive index were found out and the third order bulk susceptibility of compound was also estimated. The negative sign in the refractive index indicates the self-defocusing nature of the crystal.

Growth and THz generation in organic nonlinear optical crystal: N,N′ bis(4-nitrophenyl)-(1R,2R)-diaminocyclohexane (BNDC)

We report on the growth of large size organic single crystal of a C2-symmetric bis amide molecule, N,N′ bis(4-nitrophenyl)-(1R,2R)-diaminocyclohexane (BNDC) for the first time. Optical quality BNDC single crystals of sizes 1.7 × 1.9 × 0.5 cm3 and 1.5 × 0.5 × 0.2 cm3 are successfully grown from mixed solvents by varying the molar ratios. The physical properties of the as-grown BNDC crystals are studied and discussed in detail. From the powder X-ray diffraction study, the lattice parameters of the as-grown BNDC crystal are determined to be a = 10.237 A, b = 12.827 A and c = 13.622 A (α = β = γ = 90°) which matches with the reported CCDC file (155122). BNDC crystal melts at 212 °C and no phase change behavior is observed. BNDC crystal shows good optical transmittance between 519 and 2000 nm. The slim P–E hysteresis loop reveals soft magnetism in BNDC crystal. The presence of ferroelectric domains is visualized using AFM. We demonstrate the THz generation in BNDC crystal for the first time using Ti:Sapphire Laser with a wavelength of 800 nm of 140 femtosecond pulses with 80 MHz repetition rate. We employed optical rectification technique for THz generation, and efficiency of generated power of the electric field for BNDC crystal was of the order of 10–4 V at 700 mW incident laser power.

Flickering Polarons Extending over Ten Nanometres Mediate Charge Transport in High‐Mobility Organic Crystals

AbstractProgress in the design of high‐mobility organic semiconductors has been hampered by an incomplete fundamental understanding of the elusive charge carrier dynamics mediating electrical current in these materials. To address this problem, a novel fully atomistic non‐adiabatic molecular dynamics approach termed fragment orbital‐based surface hopping (FOB‐SH) that propagates the electron‐nuclear motion has been further improved and, for the first time, used to calculate the full 2D charge mobility tensor for the conductive planes of six structurally well characterized organic single crystals, in good agreement with available experimental data. The nature of the charge carrier in these materials is best described as a flickering polaron constantly changing shape and extensions under the influence of thermal disorder. Thermal intra‐band excitations from modestly delocalized band edge states (up to 5 nm or 10–20 molecules) to highly delocalized tail states (up to 10 nm or 40–60 molecules in the most conductive materials) give rise to short, ≈ 10 fs‐long bursts of the charge carrier wavefunction that drives the spatial displacement of the polaron, resulting in carrier diffusion and mobility. This study implies that key to the design of high‐mobility materials is a high density of strongly delocalized and thermally accessible tail states.

Trap-state suppression and band-like transport in bilayer-type organic semiconductor ultrathin single crystals

Fundamental study of the carrier transport in both the channel layer and the electrode-channel contact of organic semiconductor crystals is indispensable for achieving high-performance organic field-effect transistors. In this paper, we report the temperature-dependent carrier transport of high-mobility organic semiconductors called $2\text{--}\text{decyl}\text{--}7\text{-phenyl-}[1]\text{benzothieno}[3,2\text{--}b][1]\mathrm{benzothiophene}$ (Ph-BTBT-C10) and $3\text{-decyl-}9\text{-phenyl-}[1]\text{benzothieno}[3,2\text{--}b]\text{naphtho}[2,3\text{--}b]\text{thiophene}$ (Ph-BTNT-C10). The use of single-crystal films with controlled bilayer-number thickness enabled the simultaneous study of intralayer and interlayer transport at cryogenic temperatures. Four-probe measurement of two-bilayer- and three-bilayer-thick films of Ph-BTBT-C10 suggests that the access resistance is dominated by tunneling transport across the insulating alkyl-chain layers. Single-crystal thin-film transistors of these materials showed band-like carrier transport down to 80 K and the carrier mobility of Ph-BTBT-C10 reached $34\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}/\mathrm{V}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$. Detailed analysis of the low-temperature characteristics revealed small activation energy of approximately 5 meV and a sharp distribution of band tail states. These findings suggest that high crystallinity owing to the bilayer-type crystal structure effectively suppresses the localization of gate-induced carriers.

Controlled 2D growth of organic semiconductor crystals by suppressing “coffee-ring” effect

Owing to enhanced charge transport efficiency arising from the ultrathin nature, two-dimensional (2D) organic semiconductor single crystals (OSSCs) are emerging as a fascinating platform for high-performance organic field-effect transistors (OFETs). However, “coffee-ring” effect induced by an evaporation-induced convective flow near the contact line hinders the large-area growth of 2D OSSCs through a solution process. Here, we develop a new strategy of suppressing the “coffee-ring” effect by using an organic semiconductor: polymer blend solution. With the high-viscosity polymer in the organic solution, the evaporation-induced flow is remarkably weakened, ensuring the uniform molecule spreading for the 2D growth of the OSSCs. As an example, wafer-scale growth of crystalline film consisting of few-layered 2,7-didecylbenzothienobenzothiophene (C10-BTBT) crystals was successfully accomplished via blade coating. OFETs based on the crystalline film exhibited a maximum hole mobility up to 12.6 cm2·V−1·s−1, along with an average hole mobility as high as 8.2 cm2·V−1·s−1. Our work provides a promising strategy for the large-area growth of 2D OSSCs toward high-performance organic electronics.