Organic Single Crystals Research Articles

Bending for Better: Flexible Organic Single Crystals with Controllable Curvature and Curvature‐Related Conductivity for Customized Electronic Devices

AbstractElectronic microdevices of self‐bending coronene crystals are developed to reveal an unexplored link between mechanical deformation and crystal function. First, a facile approach towards length/width/curvature‐controllable micro‐crystals through bottom‐up solution crystallization was proposed for high processability and stability. The bending crystal devices show a significant increase beyond seven orders of magnitude in conductivity than the straight ones, providing the first example of deformation‐induced function enhancement in crystal materials. Besides, double effects caused by bending, including the change of π electron level as well as the enhancement of carrier mobility, were determined, respectively by the X‐ray photoelectric spectroscopy and X‐ray crystallography to coexist, contributing to the conductivity improvement. Our findings will promote future creation of flexible organic crystal systems with deformation‐enhanced functional features towards customized smart devices.

Organic Single Crystal Patterning Method for Micrometric Photosensors

AbstractLight detection technologies are of interest due to their applications in energy conversion and optical communications. Single‐crystal organic semiconductors, such as rubrene, present high detectivities and charge carrier mobility, making them attractive for light‐sensing applications. Growth of high crystallinity organic crystals is achieved using vapor processes, forming crystals of arbitrary shapes and orientations and requiring posterior patterning processes. However, patterning the organic semiconductors using industry‐standard microfabrication techniques is not straightforward, as these often cause irreversible damage to the crystals. Here the fabrication of patterned micrometric rubrene photosensors is demonstrated through a combination of photolithography and Reactive Ion Etching steps. Protective layers during microfabrication minimize degradation of optoelectronic properties of the organic single crystals during fabrication. Crystals undergoing the patterning process presented a survival rate of 39%. Photoresponse values of up to 41 mA W−1 are obtained under illumination at 500 nm. This opens a route for the industrial‐scale fabrication process of high‐performance optoelectronic devices based on organic crystals semiconductors.

Growth, structural, optical, z-scan, dielectric and mechanical studies of ethyl para-hydroxybenzoate crystal for optical applications

Ethyl substituted para-hydroxybenzoate known as ethyl para-hydroxybenzoate (EHB) organic single crystal is grown by solvent controlled slow evaporation system with methanol as a solvent. The grown EHB crystal unit cell geometry is investigated using a single crystal XRD system. The Plasma, Fermi and Penn energy analyses also the molecular electronic polarizabilities are evaluated by different methods such as Clausius-Mossotti, coupled dipole method and Lorentz relations. The optical absorption and transmittance spectrum are assessed by UV–visible spectrum. The different optical constants as wavelength cut-off range, optical energy gap, extinction and absorption coefficient, refractive index, the position of conduction and valance band, optical electronegativity, nonlinear absorption coefficient, etc are calculated. The dielectric nature and molecular orbital analysis are evaluated. From the z-scan analysis, third-order nonlinear optical assets are estimated.

Linear and nonlinear optical properties of 2-Aminopyridinium fumarate fumaric acid single crystal for optoelectronic device applications

A good organic nonlinear optical single crystal of 2-Aminopyridine fumarate fumaric acid has been grown by slow evaporation technique. The analysis of single-crystal XRD demonstrates the centrosymmetric character of the grown crystal. The different functional groups and chemical composition are of 2APFF compounds were identified by using Fourier transform infrared spectral study. Spectral range of UV–vis-NIR studies shown that the transparency and band gap energy Eg = 6 eV of the grown crystal. Thermal property of 2APFF was analysed by differential scanning calorimetric technique. The mechanical properties 2APFF crystal was calculated for various load using the Vickers micro hardness tester. The dielectric behaviour of the grown crystal was studied for different temperatures at different frequencies. The third order NLO response in 2APFF was investigated using a Z-scan apparatus.

Bulk crystal growth, crystalline perfection and optical homogeneities of 2AP4N single crystals for second and third order frequency conversion and terahertz (THz) device applications

Bulk size organic 2AP4N single crystals were grown by a point seed rotation technique using methanol solvent. The lattice dimensions of the grown crystal and their various crystalline planes have been analyzed by XRD measurement and also the lattice strain was calculated. The lattice perfection was examined by HRXRD and found to be extremely good. The optical transparency and cut-off value of the grown crystal were analyzed by the UV–Vis NIR measurement. The crystalline homogeneity has been confirmed by the birefringence and Mach-Zehnder interferometry techniques. The SHG measurement has been carried out with different particles. The refractive indices of grown crystal have been measured in different wavelengths by prism coupling technique and the Sellmeier's co-efficient has been calculated. The Type-I and Type-II phase-matching angles were determined and the crystal was cut along the phase-matching angles. The third order nonlinear optical parameters were analyzed by Z-scan technique. In addition, the crystal shows potential to generate pulsed Terahertz (THz) radiation by optical rectification using 800 nm wavelength at 140 fs, obtained from Ti: Sapphire Laser. The generated THz spectrum is extended up to 3.0 THz. The maximum conversion efficiency of the generated signal is of the order of 0.64 × 10 −5 %. •Optically high quality with bulk size single crystal was grown by seed rotation technique •The grown crystal has high optical homogeneities and crystalline perfection •SHG efficiency is 4.5 times that of KDP material •Type-I and Type-II phase matching elements have been made •Third-order nonlinear susceptibility ‘ χ (3) ’ is 8.68 × 10 −8 esu. •The maximum conversion efficiency of the generated THz signal is 0.64 × 10 −5 %.

Influence of sodium bromide on the growth of succinic acid crystal

Sodium succinate a semi organic single crystal was grown by solution growth slow evaporation method taking water as solvent. Identification of functional groups was done through the spectral FTIT studies. The transparency of the sodium succinate was confirmed by UV–Vis-NIR spectral analysis. To check the thermal stability and to confirm the melting point of the grown crystal, TGA-DSC studies were taken. Using Nd-YAG Q-switched laser with wavelength (1064 nm) the laser damage threshold was measured.

Synthesis, spectroscopic analysis and DFT studies of N-(2-methyl-5-nitro-phenyl)benzamide organic single crystal

N-(2-methyl-5-nitro-phenyl)benzamide (N2M5NPBA) compound was synthesized by benzoylation of 2-methyl-5-nitroaniline. N2M5NPBA single crystal was grown by slow evaporation technique using DMSO as solvent. Single crystal X-ray diffraction study of N2M5NPBA crystal have monoclinic system under space group P21/C with the lattice parameters a = 4.9490 Å, b = 10.1916 Å, c = 24.969 Å, α = γ = 90°, β = 91° and V = 1259.1 Å3. Nitro and amide functional groups presence in N2M5NPBA crystal was identified in FT-IR spectral characterization. The molecular geometry of title molecule was optimized and theoretical analysis was performed by density functional theory (DFT) using B3LYP/6-311++G (d, p) basis set. UV-Visible spectrum analysis of N2M5NPBA predict the cut-off wavelength was 278 nm (bandgap energy ~4.19 eV). 1H & 13C NMR spectrum were recorded the grown N2M5NPBA crystal to confirm the chemical structure. The thermal intransigence of the grown N2M5NPBA crystal was determined by the TGA (thermal stability up to 528 K) and accurate melting point was confirmed from DSC. The absence of phase transformation was confirmed by TG-DTA analysis. The second harmonic generation (SHG) efficiency of N2M5NPBA single crystal was evaluated by Kurtz-Perry powder test and the outcome of N2M5NPBA crystal is 2.2 times higher than that of KDP crystal.

Investigation on experimental and theoretical studies of NLO active organic single crystal: 3-methyl-1-[(2,3,5,6-tetramethylphenyl)methyl]piperidin-1-ium bromide

A single crystal of nonlinear optically active 3-methyl-1-[(2,3,5,6-tetramethylphenyl)methyl]piperidin-1-ium bromide (D13MP) was created by the conventional evaporation technique. The crystal’s high NLO activity made it a useful compound in optoelectronics. The structure and other constraints were resolved using SCXRD, which confirmed the triclinic crystal framework with the P-1 space group. The relative contributions of various inter molecular connections of D13MP crystal are discussed using Hirshfeld surface analysis and fingerprint plot illustration. The UV–visible spectral studies result in the linear optical transparency excellence of the developed crystal. Index of refraction and NLO competence of the D13MP were found utilizing Brewster's angle method. TGA/DTA and DFT analysis techniques were applied to examine D13MP's thermal steadiness and HOMO-LUMO energy band gap.

Crystal structure, physico-chemical and third order nonlinear traits of the novel (2E)-1-(3,4-dimethoxyphenyl)-3-(4-propoxyphenyl) prop-2-en-1-one (DMPP) chalcone single crystal

Optically highly versatile novel third-order organic nonlinear single crystals of (2E)-1-(3,4-dimethoxyphenyl)-3-(4propoxyphenyl)prop-2-en-1-one (DMPP) which adapts to orthorhombic Pbca space group is crystallized by slow evaporation growth technique. Fourier transform infrared analysis affirms the presence of various functional groups in DMPP. Transparency and lower cut-off wavelength of the crystal were obtained using linear optical properties. The thermal stability without any weight loss is up to 220°C. The molecular structure of DMPP was confirmed by 1H NMR and 13C NMR analysis. From the electrical conductivity studies, the suitability of DMPP chalcone for device fabrication with a very low activation energy value of 0.04 ​at 1 ​MHz and conductivity value of 10−4 ​S/m was observed for the first time. Further B3LYP/6-31G++ level has been used to obtain static first-order and second order hyperpolarizability parameters. The calculated value of first-order hyperpolarizability was calculated to be 96 times better than that of standard urea and several orders better compared to other 3,4 dimethoxy derivatives. The experimental third order nonlinear measurements were done by continuous-wave (cw) 632.8 ​nm laser. From the Z-scan measurements, the calculated imaginary and real third-order nonlinear optical susceptibility are of the order of 10−5 e.s.u. The experimental and computational results disclose that DMPP is a novel third-order optically active single crystal and a noteworthy material for nonlinear optical applications.

Highly sensitive detecting system to precisely evaluate the emission spectra and quantum efficiency of organic crystal light-emitting transistors.

The lack of a reliable and sensitive measure system has strongly hindered the progress of organic single-crystal light-emitting transistors, since their emission spectra and absolute intensity were rather difficult to be measured as a consequence of small area and weak emission, as well as their edge emission feature. Hence, a tailor-made detecting system was set up by combining a semiconductor analyzer and a rotatable microscope coupling with a highly sensitive grating spectrometer. The detecting system solved the important issue of quantitatively characterizing the optoelectronic properties of organic transistors, especially those based on single crystals. With organic lamellar single crystals, we confirmed that the measurement system was reliable and had enough sensitivity to precisely evaluate the performance of light-emitting transistors corresponding to the emission spectra.

Optical, electrical, HOMO-LUMO and first-order hyperpolarizability studies on 2-amino-5-bromopyridinium 4-hydroxybenzoate-an organic single crystal for opto-electronic applications

Organic single crystals of 2-Amino-5-bromopyridinium 4-hydroxybenzoate were grown by slow evaporation technique at room temperature. Single crystal XRD confirms that the crystal belongs to orthorhombic system with noncentrosymmetric space group Pna21. Functional groups presents in the synthesized compound were confirmed by FTIR analysis. UV-Vis studies shows that crystal has a lower cutoff wave length at 388 nm with an optical band gap of 2.9 eV. Dielectric studies were carried out to study the charge transport mechanism in the crystal. Photoconductivity measurements were performed. Powder SHG efficiency of the compound was found to be three times the value of KDP.

Epitaxial etching of organic single crystals

Organic single crystals (OSCs) have received increasing interest in the last decades for their potential applications in flexible electronics. Although there are various subtractive manufacturing methods of organic electronics, the subtractive manufacturing of OSCs is still a challenge, since OSCs are assembled via weak van-der-Waals interactions which are vulnerable and cannot afford damages and suffer the degradation of performances after the process. Here, we develop an epitaxial etching strategy which clips the OSCs and keeps high-quality crystalline nature of the resulting materials. As a result, high-quality organic micro-ribbon arrays are fabricated which maintains 89% charge mobility in average compared with original OSCs, showing great potential of this subtractive manufacturing method in future organic electronics.

Squaraine organic crystals with strong dipole effect toward stable lithium-organic batteries

Although organic redox molecules as electrode materials can achieve a high specific capacity through molecular design engineering, effective strategies to overcome their low cycling stability have not yet been developed. Herein, we establish a novel strategy that utilizes a strong dipole effect to suppress the high solubility of organic molecules and, thus, improve cycling stability. Two organic single crystals of squaraine derivative molecules with different substituents, 2,4-di(piperidin-1-yl)cyclobutane-1,3-dione (SAPD) and 2,4-di(pyrrolidin-1-yl)cyclobutane-1,3-dione (SAPL), were synthesized by facile routes. In particular, the SAPL cathode exhibited a discharge capacity of 371 mA h g–1 at 48 mA g–1 (0.1 C) and a nearly 78% capacity retention after 1000 cycles at 0.24 A g–1 (0.5 C). It also exhibited a capacity of 135 mA h g–1 even at 4.8 A g–1 (10 C) without hybridizing with graphene or carbon nanotubes. We studied the molecular interactions of SAPD and SAPL via detailed density functional theory calculations and revealed their lithium-ion storage mechanisms by using ex-situ technologies. Through comparing their intermolecular interactions, we found the stronger dipole effect can elevate cycling performance better. Hence, our design strategy can serve as a promising path for constructing high-performance lithium-organic batteries with long-term cycling stability.

Room temperature exciton\u2013polariton Bose\u2013Einstein condensation in organic single-crystal microribbon cavities

Exciton–polariton Bose–Einstein condensation (EP BEC) is of crucial importance for the development of coherent light sources and optical logic elements, as it creates a new state of matter with coherent nature and nonlinear behaviors. The demand for room temperature EP BEC has driven the development of organic polaritons because of the large binding energies of Frenkel excitons in organic materials. However, the reliance on external high-finesse microcavities for organic EP BEC results in poor compactness and integrability of devices, which restricts their practical applications in on-chip integration. Here, we demonstrate room temperature EP BEC in organic single-crystal microribbon natural cavities. The regularly shaped microribbons serve as waveguide Fabry–Pérot microcavities, in which efficient strong coupling between Frenkel excitons and photons leads to the generation of EPs at room temperature. The large exciton–photon coupling strength due to high exciton densities facilitates the achievement of EP BEC. Taking advantages of interactions in EP condensates and dimension confinement effects, we demonstrate the realization of controllable output of coherent light from the microribbons. We hope that the results will provide a useful enlightenment for using organic single crystals to construct miniaturized polaritonic devices.

One-pot synthesis of metal-free, yellow-emitting phosphor with organic single crystal as a matrix

In recent years, there is a rapid growth on the research of metal-free phosphor. A typical example is blend of photoluminescent carbon nanomaterials with a matrix. Normally, the C dots were prepared first, which were then mixed with the matrix. A drawback of this strategy is that multiple steps have to be involved, which is time consuming. In this work, we show that by simply heating a readily-available small organic molecule (phthalic acid) in a high-boiling solvent with reactive group (formamide), ready-to-use and metal-free phosphor can be produced in high yields (over 70%). The phosphor contains single crystals of phthalic anhydride with photoluminescent species adsorbed on the surfaces, which shows yellow emission in solid state with a fluorescence quantum yield (Φ) of 28.53%. The phosphor can be directly used to prepare light-emitting diodes (LEDs), which results in a yellow LED on the UV chip and a white LED on the blue-emitting chip.

(Invited) Novel Technique to Measure Thermal Diffusivity of Soft Crystal in Micro Scale

To control thermal properties in nano- and micro scale is one of the important topics with regards to the phonon engineering. Recently, the mechanical molecular crystals have been developed, which have the potential applications of actuators and soft robots. Most of the crystal motions are induced by photoisomerization or mechanical stress.Thermal phase transition and the photothermal effect are considered as the underlying mechanism for the motions, such as bending, twisting, jumping, and rotating, etc., of the mechanical molecular crystals, called soft crystals. However, due to the lack of the measured data of heat transport properties such as thermal diffusivity or thermal conductivity of single crystals in micro volume size, the quantitative analysis of thermal phenomena in the molecular crystals has not yet been quantitatively analyzed. For example, the photo-thermally induced temperature rise produces the localized temperature distribution near the surface, and thermal diffusivity should be utilized to calculate the temperature distribution in the specimen.To overcome such situation, we propose a micro scale temperature wave analysis (micro-TWA) method to measure the thermal diffusivity of soft crystals in micro scale. (Figure 1) This method enables to measure the axial orientation in single crystals. Furthermore, coupled with the photo-thermal stimulation, the kinetic measurement of thermal diffusivity under the stress induced and photo induced field has been realized. Demonstration of the super elastic phase transition of soft crystal, 3,5- difluorobenzoic acid (3,5−F2bza) and terephthalamide(TPA) will be presented. This is a proposal of the new measurement method, because the experimental determination of the thermal diffusivity in micro scale of organic single crystals, under operating the deformation control, is still a challenge. The experimental validity is discussed with the theoretical analysis using the reference sample. Figure 1

Spin injection and transport in single-crystalline organic spin valves based on TIPS-pentacene

Single crystals of organic semiconductors with perfect crystal structure and minimal density of defects can exhibit high mobility and low spin scattering compared with their amorphous or polycrystalline counterparts. Therefore, these materials are promising candidates as the spin transport media to obtain long spin relaxation times and spin diffusion lengths in spintronic devices. However, the investigation of spin injection and transport properties in organic single crystals is hindered by the inability to construct devices such as single-crystalline organic spin valves (OSVs). Herein, thin and large organic single crystals of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) were grown on a liquid substrate and transferred to a target substrate carrying ferromagnetic electrodes to construct single-crystalline OSVs. The magnetoresistance (MR) responses of the single crystals were investigated to study their spin injection and transport properties. MR value as high as 17% was probed with an intermediate layer thickness of 269 nm. More importantly, spin transport was still observed in a single crystal of a thickness up to 457 nm, which was much larger than that of polycrystalline thin film. Our research provides a general methodology for constructing single-crystalline OSVs and paves the way to probe the intrinsic spin transport properties of organic semiconductors based on single crystals.

Experimental and computational investigation of novel dihydrated organic single crystal of 2,4,6-triaminopyrimidine and 3,5-dintrobenzoic acid: Linear and nonlinear optical response with limiting performance

Newly synthesized dihydrated organic crystal (TAP+DNB−.2H2O) of 2,4,6-triaminopyrimidine (TAP) with 3,5-dinitrobenzoic acid (DNB) was grown by slow evaporation technique and this crystal belongs to monoclinic P-1 space group. Infrared spectroscopy combined with DFT calculation has been used to confirm the presence of the expected functional group of the titular crystal. Further, the UV–Vis absorption spectroscopy has been utilized to determine various optical parameters such as excitation wavelength, optical band gap, and extinction coefficient from the point of view of optical application. In addition to this, TD-DFT/B3LYP computational theory was also applied to simulate the UV–Vis absorption spectrum for supporting the experimental result. The effect of complex formation from its constituents has been explored using frontier molecular orbitals analysis. Furthermore, the mapping of the 3D Hirshfeld surface and its related fingerprint plots were used for qualitative and quantitative analysis of the intermolecular interactions which involve among different molecular moiety in the synthesized crystal. The third-order nonlinear optical response of this molecular complex (TAP+DNB−.2H2O) have been investigated in detail using the z-scan technique with CW diode laser (520 ​nm). Also, theoretical nonlinear optical parameters have been investigated by the DFT method. The thermal characteristic of the growth dihydrate crystal has been studied by thermal gravimetric-differential thermal analysis (TG-DTA).

Reversible structural phase transition and dielectric behaviour associated with the ordering-disordering of molecular rotation in an organic supramolecular solid

• A pure organic single crystal, [H 2 dabco][Ma] 2 (1) undergoes a reversible structural phase transition at ~250 K and possesses a unique three-dimensional network structure. • The origin of the phase transition and the dielectric anomaly is ascribed to the order-disorder transformation of [H 2 dabco] 2+ cations and the resulting relative molecular rotation from the equilibrium position. A pure organic single crystal, [H 2 dabco][Ma] 2 ( 1 ) ([H 2 dabco] 2+ = diprotonated 1,4-diazabicyclo[2,2,2]octane, [Ma] = malic acid), was prepared and characterised. Differential scanning calorimetry, potential energy calculations, and dielectric property measurements indicated the occurrence of a reversible structural phase transition at ~250 K, while single-crystal X-ray diffraction revealed that 1 possesses a unique three-dimensional network structure with the [H 2 dabco] 2+ cation bridged by two [Ma] − anions through N–H•••O hydrogen bonds. At 296 K, the [H 2 dabco] 2+ cation exists in a rotationally disordered state and is fixed into the two-dimensional layered structure of [Ma] − anions through N–H•••O hydrogen bonds. Upon cooling to 100 K, the above cation is frozen into an ordered state and shifts towards the top anion and the bottom anion at one end along the hydrogen bond. The origin of the phase transition and the dielectric anomaly is ascribed to the order-disorder transformation of [H 2 dabco] 2+ cations and the resulting relative molecular rotation from the equilibrium position. One pure organic single crystal, [H 2 dabco][Ma] 2 ( 1 ) ([H 2 dabco] 2+ = diprotonated 1,4-diazabicyclo[2,2,2]octane, [Ma] ‐ = malic acid), was synthesized and underwent the structural phase transitions from space group P 2 1 /c to C 2/c. The conformations of dabco rings in the RTP (296 K) and the LTP (100 K) are markedly different owing to the order-disorder rotation of [H 2 dabco] 2+ cations. This results in the phase transition and dielectric anomaly of compound and provides useful strategies of finding new organic dielectric materials.

CHCl3-Dependent Emission Color and Jumping Behavior of Cyclic Chalcone Single Crystals: The Halogen Bond Network Effect

As a conventional strategy to modulate the structure and properties of inorganic single crystals, hydration/solvation is rarely found to function in pure organic single crystal. Herein, we report chalcone single crystals with CHCl3-dependent emission color and jumping behavior. Two crystals: a pure crystal phase (1) with green-yellow emission and a CHCl3-containing co-crystal phase (1•2CHCl3) with orange-red emission were constructed by fine-controlling the crystallization conditions. The special halogen bond network in the crystal packing structure effectively narrows the bandgap and thereby redshift the emission of 1•2CHCl3. 1•2CHCl3 would revert to 1 together with emission color change when losing CHCl3. These findings are similar to the effect of H2O in hydrated inorganic crystals. Notably, owing to a special pre-organized “molecular pair” structure for [2 + 2] cycloaddition, the pure crystal phase 1 exhibits violently photo-induced jumping phenomenon, indicating large potentials in intelligent devices. This work would overturn the previous perception that the structurally simple solvent molecules without conjugation cannot greatly affect the structure and properties of pure organic single crystals and provide a new strategy to construct multi-colored organic fluorescent crystals.