Epimers with distinct mechanical behaviours

This study highlights the impact of relative stereochemistry in epimer compounds on their mechanical properties; the crystals of one series of esters are ductile and deform plastically upon bending, whereas the other series are all brittle. Nanoindentation studies show that the hardness, H, and elastic moduli, E, of the brittle crystals are substantially larger than those of the ductile ones. For the brittle crystals, the H values range from 153(10) to 293(37) MPa and E from 2.85(0.33) to 9.10(0.51) GPa, whereas for the ductile crystals, the H values range from 76(2) to 125(11) MPa and E from 1.40(0.36) and 2.75(0.06) GPa. These are rationalized by recourse to the distinct crystal structural features, especially in terms of interdigitation in the molecular planes in the brittle crystals and slip planes in the ductile crystals. The indentation fracture toughness, Kc, values of the (2′S) crystals are higher than those typically reported for molecular crystals, due to the corrugated nature of their crystal packing which enhances the crack tortuosity. The Kc values are in the range 0.215 (0.08) to 0.278 (0.06) MPa m½ and the brittleness index values are in the range 711(19) to 1053(50) m−½

Indentation Plasticity and Fracture Studies of Organic Crystals

This review article summarizes the recent advances in measuring and understanding the indentation-induced plastic deformation and fracture behavior of single crystals of a wide variety of organic molecules and pharmaceutical compounds. The importance of hardness measurement for molecular crystals at the nanoscale, methods and models used so far to analyze and estimate the hardness of the crystals, factors affecting the indentation hardness of organic crystals, correlation of the mechanical properties to their underlying crystal packing, and fracture toughness studies of molecular crystals are reviewed

Molecular basis for the mechanical response of sulfa drug crystals

Comprehension of the nanomechanical response of crystalline materials requires the understanding of the elastic and plastic deformation mechanisms in terms of the underlying crystal structures. Nanoindentation data were combined with structural and computational inputs to derive a molecular-level understanding of the nanomechanical response in eight prototypical sulfa drug molecular crystals. The magnitude of the modulus, E, was strongly connected to the non-covalent bond features, that is, the bond strength, the relative orientation with the measured crystal facet and their disposition in the crystal lattice. Additional features derived from the current study are the following. Firstly, robust synthons well isolated by weak and dispersive interactions reduce the material stiffness; in contrast, the interweaving of interactions with diverse energetics fortifies the crystal packing. Secondly, mere observation of layered structures with orthogonal distribution of strong and weak interactions is a prerequisite, but inadequate, to attain higher plasticity. Thirdly, interlocked molecular arrangements prevent long-range sliding of molecular planes and, hence, lead to enhanced E values. In a broader perspective, the observations are remarkable in deriving a molecular basis of the mechanical properties of crystalline solids, which can be exploited through crystal engineering for the purposeful design of materials with specific properties

Crystal Structure-Mechanical Property Correlations in <i>N</i>‑(3-Ethynylphenyl)-3-fluorobenzamide Polymorphs

During the solution-mediated crystallization of <i>N</i>-(3-ethynylphenyl)-3-fluorobenzamide, small variation in the process conditions can lead to two new polymorphic forms in addition to the three previously reported forms. Structural features of the two new forms and mechanical properties of the three stable polymorphs, among the five forms, have been investigated using instrumented nanoindentation. The results show that among the three stable forms (Form <b>I</b>, Form <b>II</b>, and Form <b>III</b>) of the compound, the Form <b>II</b> crystal exhibits the lowest hardness (<i>H</i>) and elastic modulus (<i>E</i>), while these values are nearly similar for Form <b>I</b> and Form <b>III</b> crystals. Interestingly, the direct correlation of mechanical properties with the density of crystals was found for three polymorphs, but their melting points do not follow similar trends. The quantitative analysis of structural features with the inputs from energy frameworks suggests that the anisotropy in mechanical properties of the three polymorphs originate from the different orientations of strong to moderate N–H···O hydrogen bonds and weak to strong π···π stacking interactions, which mainly stabilize the crystal packing of the three polymorphs

Guest solvent-dependence of the nanomechanical response in substituted dihydropyrimidinone crystals

The nanomechanical responses of two crystalline phases of a dihydropyrimidine analogue (1) were similar irrespective of the presence (or absence) of the guest solvent. In contrast, the mechanical responses of two differently solvated forms of the second related (2) crystals were significantly different. These contrasting behaviors are rationalized in terms of intermolecular interactions and energy distributions.We acknowledge IISER Bhopal for research facilities andinfra-structure.Wethank Miss. Annie Cleetus for helping us in re-crystallization of solvatomorphs. MSRNKacknowledges SERB,DST (India) for an Early Career Researcher Award (File No:ECR/2016/000827)

A self-powered photoactive room temperature gas sensor based on a porphyrin-functionalized ZnO nanorod/p-Si heterostructure

The integration of self-powered photodetectors and highly selective gas sensors into a unified system has revolutionized the development of next-generation optoelectronic gas sensors towards overcoming the limitations of high power consumption and poor selectivity in traditional systems. In this scenario, this work describes a superior optoelectronic gas sensor based on 5-(4-carboxyphenyl)-10,15,20-triphenyl porphyrin (H2TPPCOOH)-functionalized vertically aligned 1D ZnO nanorods grown on p-Si. The dual impact of porphyrin functionalization on the powering and chemical sensing properties of the ZnO NR/p-Si heterostructure was investigated. The resulting porphyrin-functionalized device demonstrated a maximum VOC of 0.1 V and Isc of 12.16 mu A with good sensitivity and fast response towards triethylamine (TEA) vapors at room temperature. The level of defects in the device and the gas sensing mechanism were studied using the Scanning Kelvin Probe system, and the photoelectric mechanism is explained through energy band diagrams. The ambipolar charge transport in the device plays a significant role in chemical sensing at room temperature at zero power consumption. Hence, this work offers valuable insights for designing self-sustained, stable, cost-effective, miniaturized smart chemical sensors, which are highly selective to specific VOC biomarkers in complex gas mixtures, with a potential for on-chip integration and point-of-care health monitoring.The integration of self-powered detectors and selective gas sensors into a single system introduces a next-generation of optoelectronic gas sensors that overcome the limitations of power consumption and poor selectivity

The mechanism of bending in a plastically flexible crystal

Mechanically adaptable molecular crystals have potential applications in flexible smart materials and devices. Here, we report the mechanism of plastic deformation in single crystals of a small organic molecule (N-(4-ethynylphenyl)-3-fluoro-4-(trifluoromethyl)benzamide) that can be repeatedly irreversibly bent and returned to its original shape without concomitant delamination or loss of integrity. Along with the quantification of the crystals' local and bulk mechanical properties (hardness, indentation modulus and Young's modulus), micro-focus synchrotron X-ray diffraction mapping show that upon deformation, molecular layers lined with trifluoromethyl groups cooperatively slip past one another resulting in their impressive plastic malleability

Dimorphs of a Benzothiophene-quinoline Derivative with Distinct Mechanical, Optical, Photophysical and Conducting Properties

Because of distinct molecular conformations, packing modes, interaction types, and consequently their physicochemical properties, polymorphic forms of organic conjugated small molecules are intrinsically ideal for elucidating the relationship between their microstructures and the transcribed properties. Ethyl-2‐(1‐benzothiophene‐2‐yl)quinoline‐4‐carboxylate (BZQ) exists as dimorphs with distinct crystal habits―blocks (BZB) and needles (BZN). The crystal forms differ in their molecular arrangements―BZB has a slip-stacked column-like structure in contrast to a zig-zag crystal packing with limited π–overlap in BZN―and their photophysical and conducting properties. The BZB crystals characterized by extended π-stacking along [100] demonstrated semiconductor behavior, whereas the BZN, with its zig-zag crystal packing and limited stacking characteristics, was reckoned as an insulator. Monotropically related crystal forms also differ in their nanomechanical properties, with BZB crystals being considerably softer than BZN crystals. This discrepancy in mechanical behavior can be attributed to the distinct molecular arrangements adopted by each crystal form, resulting in unique mechanisms to relieve the strain generated during nanoindentation experiments. Waveguiding experiments on the acicular crystals of BZN revealed the passive waveguiding properties of the crystals. Excitation of these crystals using a 532 nm laser confirmed the propagation of elastically scattered photons (green) and the subsequent generation of inelastically scattered (orange) photons by the crystals. Further, the dimorphs display dissimilar photoluminescence properties; they are both blue-emissive, but BZN displays twice the quantum yield of BZB. This study underscores the integral role of polymorphism in modulating the mechanical, photophysical, and conducting properties of functional molecular materials. Importantly, our findings reveal the existence of light-emitting crystal polymorphs with varying electric conductivity, a relatively scarce phenomenon in the literature

Self-Powered Photodetectors with Nickel-Doped ZnO Nanorods for Operation in Low-Light Environments

The development of next-generation optoelectronic devices relies on the necessity for self-powered, fast, and high-sensitivity photodetectors with a wide-spectral response. This Article investigates the impact of nickel doping on the growth of ZnO nanorods (79–123 nm diameter) on a p-type silicon substrate, exploring alterations in photovoltaic characteristics compared to the pure counterparts. The results reveal enhanced performances in devices with nickel doping ranging from 1% to 5%, exhibiting superior behavior across tested parameters. Despite consistent morphology and geometric aspects of the grown nanorods, the persistent presence of nickel was evident. Illumination from UV and visible light sources demonstrated increased current in I–V plots with rising doping levels, showcasing robust photovoltaic behavior at 0 V and enabling functionality as a self-powered photodetector. Under UV light, self-powered operation was observed at an intensity as low as 20 mW/cm2, extending beyond 50 mW/cm2 for visible light exposure. These devices exhibit applicability in detecting a broad spectrum of solar radiation, as evidenced by the influence of the wavelength and light intensity on the photocurrent response at zero bias. With pulsed frequencies of a 405 nm laser, changes in the photocurrent were observed with variations in operating frequency. Hence, a high-performance, wide spectral, self-powered photodetector capable of detecting minimal light intensity was fabricated