Effect Of Positional Isomerism Research Articles

Positional isomeric effect: A simple and feasible strategy for constructing efficient red TADF materials

In order to investigate the effect of positional isomerization on the photoelectric properties of thermally activated delayed fluorescence (TADF) emitters, thereby fully stimulating the potential of the molecular backbone, herein, two red TADF isomers, oTPA-PPP and mTPA-PPP, were developed and synthesized by linking triphenylamine (TPA) donor into different positions of the pyrido [2′,3′:5,6] pyrazino [2,3-f] [1,10] phenanthroline (PPP). Their photoluminescent quantum yields (PLQYs) and external quantum efficiencies (EQEs) were significantly different by manipulating the substitution position of the donor. Compared with mTPA-PPP, oTPA-PPP exhibited higher PLQY benefiting from intramolecular hydrogen bonding and larger fluorescence radiative decay rate, as confirmed by both theoretical and experimental analyses. As a result, oTPA-PPP-based organic light-emitting diode (OLED) realized high EQEmax of 19.2 % with red emission at 603 nm, whereas mTPA-PPP achieves an EQEmax of 7.9 % at 596 nm. This work provides a simple and feasible molecular design strategy to design and select red TADF emitters with excellent properties.

Role of peripheral substitution on electronics and self-assembly of discotic semiconductors: The case of diazatruxenone

In this paper we present two sets of diazatruxenones functionalized at the 3,8 or 2,7 positions with two phenyl rings substituted at the para positions with groups of different electronic nature. With the aim to shed light on the role of the positional isomeric effect and of the electronic nature of the attached peripheral substituents on the final properties of these systems, we have performed a joint experimental and theoretical investigation linking thermal analysis, UV–Vis spectroscopy, electrochemistry and SCLC measurements with DFT calculations. The donor–acceptor character of these molecules not only confers them an interesting amphoteric redox behaviour but also creates a significant in-plane dipole moment. We have found that the different functionalization has only a slight impact on the electronic properties of these systems but exerts a significant influence on the strength and directionality of their dipole moment with strong implications in their self-assembly. Particularly, derivatives functionalized with electron acceptors, present the highest dipole moments within the series and form stable columnar mesophases, probably driven by the antiparallel dipole–dipole arrangement of neighbouring molecules. DFT calculations confirms that cofacially stacked dimers with their dipoles opposed allow for efficient electronic couplings helping to rationalize the favourable hole mobilities determined for the 3,8-disubstituted diazatruxenones with electron-acceptor groups by means of the space charge–limited current technique.

Positional isomeric effect of nitro group substituted indoles on the electropolymerization and the capacitance performances of their polymers

AbstractThe isomers of conducting polymers usually have different properties, however, there are still few studies on the isomeric effect of conducting polymers in supercapacitors field. In this work, four isomers (4‐nitroindole, 5‐nitroindole, 6‐nitroindole, and 7‐nitroindole) were selected as the research objects to study the positional isomeric effect of nitro group substituted indoles on the electropolymerization and the capacitance performances of their polymers. The results show that the prepared poly(5‐nitroindole) (5‐PNI) and poly(6‐nitroindole) (6‐PNI) are in nanowires structure, poly(7‐nitroindole) (7‐PNI) is in dense structure, while poly(4‐nitroindole) (4‐PNI) fails to be prepared. In addition, the as‐prepared 5‐PNI, 6‐PNI nanowires and dense 7‐PNI exhibit very different electrochemical properties and capacitance performances. Taking into account the specific capacitance (364 F g−1 at 5 mV s−1), rate capability (58.5%) and cyclic stability (94% capacitance retention after 1000 cycles test), it can be concluded that 5‐PNI is the most suitable electrode material in the field of supercapacitors.

Weak noncovalent interactions in two positional isomers of acrylonitrile derivatives: inputs from PIXEL energy, Hirshfeld surface and QTAIM analyses.

A single crystal X-ray diffraction analysis was performed on two positional isomers (m-tolyl and p-tolyl) of acrylonitrile derivatives, namely, (Z)-3-(4-(pyridin-2-yl) phenyl)-2-(m-tolyl) acrylonitrile (1) and (Z)-3-(4-(pyridin-2-yl)phenyl)-2-(p-tolyl) acrylonitrile (2). Compound 1 crystallized in the monoclinic P21/n space group with two crystallographically independent molecules. Compound 2 also possesses two crystallographically independent molecules and crystallized in the triclinic P-1 space group. The Hirshfeld surface analysis revealed that, in both isomers, intermolecular H⋅⋅⋅H/C/N contacts contribute significantly to the crystal packing. More than 40% of the contribution arises from intermolecular C-H⋅⋅⋅C(π) contacts. In both compounds, the relative contribution of these contacts is comparable, indicating that the positional isomeric effects are marginal. The structures in which these isomers are arranged in the solid state are very similar, and the lattice energies are also comparable between the isomers. The Coulomb-London-Pauli-PIXEL (CLP-PIXEL) energy analysis identified the energetically significant dimers. The strength of the intra- and intermolecular interactions was evaluated using the quantum theory of atoms in molecules approach. The UV-Vis absorbance in three different solvents (chloroform, ethanol, and ethyl acetate) for isomers 1 and 2 are very similar. This result is in good agreement with the time-dependent density-functional theory (TD-DFT) calculations.

Understanding the interaction mechanism of CO2 and position isomeric organic absorbents by density functional theory

The effect of position isomerism on absorbent-CO2 interaction for CO2-philic absorbents, ethers, ketones, and esters, were investigated at the molecular level by density functional theory simulation. It is found that C1OC7 and C1COC6 show superior CO2 absorption potential as their three-armed structure of the methyl group weakens the spatial resistance of the main absorbent molecule and enhances the Lewis acid-base interaction. The addition of carbonyl or ether group to form the corresponding ester usually results in decreased interaction energy. Notably, the stable configuration like the C4COOC3-CO2 system in claw-like structure as well as the C1COOC6-CO2 system containing hydrogen atoms with hyperconjugation shows enhanced Lewis acid-base interaction and weak hydrogen bonding. Unlike ethers and ketones, esters with high symmetric structure, such as C3COOC4 and C4COOC3, exhibit superior CO2 absorption intensity. The findings are beneficial to the design of specific physical absorbents, especially position isomers for CO2 capture.

Impact of Positional Isomerism on Melting Point and Stability in New Energetic Melt-Castable Materials

For an energetic material with a definite composition, the substituent position is the most crucial factor to influence its physicochemical properties. Thus, it is becoming increasingly important to understand the impact of positional isomerism on multidimensional properties differences. Herein, we reported two new potential energetic melt-castable molecules, a pair of positional isomers (4-MMDNP and 5-MMDNP). These two explosives exhibit obviously different properties, including densities (Δρ = 0.03 g cm–3), melting point (ΔTm = 47.2 °C), decomposition temperature (ΔTd = 27.3 °C), stability (IS = 20 J, FS = 160 N vs IS = 10 J, FS = 40 N), etc., even though they share similar compositions and structures. Simultaneously, by analyzing crystal packing, intermolecular interactions, and monomolecular parameters, we were able to uncover the roots of property differences. Altogether, our results provide comprehensive molecular and crystal level insight into the effect of positional isomerism, which may be useful for new molecular design.

Effect of positional isomerism on the excited state charge transfer dynamics of anthracene-based D-π-A systems.

Understanding the dynamics of the back electron transfer (BET) rate of ion pairs from the electronically excited state of donor-acceptor systems is crucial for developing materials for organic electronics. The structure-property relationships in the organic molecular architectures play a key role in controlling the BET rate and have been utilized as a criterion to design systems with a reduced BET rate. Here, we examine the influence of isomerism on the BET rate in anthracene based systems, viz., (E)-2-(2-(anthracen-9-yl)vinyl)benzonitrile (ortho-CN) and (E)-3-(2-(anthracen-9-yl)vinyl)benzonitrile (meta-CN) with N,N-diethylaniline (DEA) in methylcyclohexane using time-resolved spectroscopy. The radical cation (DEA˙+) and the radical anion (ortho-CN˙- or meta-CN˙-) generated after photoexcitation show synchronous decay kinetics, and the rate constant of back electron transfer (kBET) for the DEA/ortho-CN pair was 6.6 × 104 s-1, which is ca. 2 orders of magnitude lower compared with the DEA/meta-CN pair. The role of isomerism in providing resonance stabilization for the organic radicals is expected to have implications for strategies that retard charge recombination in photovoltaics. The role of the molecular structural features that dictate the kinetics for charge recombination has been further identified using quantum calculations.

Sensing the ortho Positions in C6Cl6 and C6H4Cl2 from Cl2- Formation upon Molecular Reduction.

The geometrical effect of chlorine atom positions in polyatomic molecules after capturing a low-energy electron is shown to be a prevalent mechanism yielding Cl2−. In this work, we investigated hexachlorobenzene reduction in electron transfer experiments to determine the role of chlorine atom positions around the aromatic ring, and compared our results with those using ortho-, meta- and para-dichlorobenzene molecules. This was achieved by combining gas-phase experiments to determine the reaction threshold by means of mass spectrometry together with quantum chemical calculations. We also observed that Cl2− formation can only occur in 1,2-C6H4Cl2, where the two closest C–Cl bonds are cleaved while the chlorine atoms are brought together within the ring framework due to excess energy dissipation. These results show that a strong coupling between electronic and C–Cl bending motion is responsible for a positional isomeric effect, where molecular recognition is a determining factor in chlorine anion formation.

Knotting Two Donor−π-Acceptor AIEgens Using a Nonconjugated Linker: Tunable and Switchable Fluorescence and Fingerprinting and Live Cell Imaging Applications

Aggregation-induced emissive fluorophores (AIEgens) have drawn widespread attention over the years because of their structure-controlled tunable and external-stimuli-responsive solid-state fluorescence, which have stimulated rapid development in the optoelectronics and biomedical fields. However, precise control of organic π-conjugated molecular fluorescence remains a great challenge and depends on the molecular structure and organization. Herein, we have interlinked two triphenylamine-based donor−π acceptor (D−π-A) AIEgens using a nonconjugate spacer (xylene) and explored the effect of interlinking, positional isomerism, and acceptor structure on the tunable and switchable solid-state fluorescence. A change of the acceptor group resulted in tuning of fluorescence between 534 and 614 nm. Interestingly, interspacing modulation from o-xylene (1) to the meta (2) and para isomers (3) showed a decrease of fluorescence efficiency in the solid state. A closer spacing between the AIEgens and tighter molecular packing could restrict the intramolecular rotation in ortho isomers that resulted in enhanced fluorescence in comparison to para isomers. In contrast, more spatial freedom in para isomers allowed the molecules to respond to external pressure and produced mechanofluorochromism (MFC) in comparison to ortho isomers. Strong tunable solid-state fluorescence of ortho isomers was used to obtain clear latent fingerprinting images on three different surfaces with tunable fluorescence color. 1a,b,e (orange, green, and red, respectively) were further utilized for live cell imaging applications using E. coli cells that demonstrated clear labeling of the cell membrane and cytoplasm with strong green/red fluorescence in the cell structures. In vitro and in vivo toxicity studies of 1a,b,e confirmed the nontoxic nature of these fluorophores and indicated their potential for live cell imaging applications.

Effect of positional isomerism on the functional properties of carbazole-phenanthroimidazole-triphenylamine triads

A series of bipolar 2, 6 or 2, 7 substituted carbazole-based isomeric hybrids featuring phenanthroimidazole as acceptor and N-phenylcarbazole or triphenylamine as donor are synthesized. Structure-property relationship of these blue-emitting materials is established by detailed investigation of physiochemical, thermal and electroluminescence characteristics. The materials showed tunable absorption and emission spectra depending upon nature and position of chromophores attached to carbazole core. The triphenylamine substituted isomers exhibited red-shifted absorption and emission spectra when compared to their respective N-phenylcarbazole-based analogs. It is attributed to the increased intramolecular charge transfer (ICT) in the electron-rich triphenylamine derivatives as further confirmed in solvatochromism studies. However, the N-phenylcarbazole derivatives showed less solvent dependence in spectra attesting less polar ground and excited state due to comparatively poor donor strength of N-phenylcarbazole. Similarly, dyes containing electron-rich chromophores showed facile removal of electron with low oxidation potentials. The thermal robustness of the compounds was attested by high thermal decomposition temperatures (Td) which varied from 438 to 481 οC. The EL performance of 3 wt% doped device fabricated with emitter derived from 2,7-disubstituted carbazole featuring N-phenylcarbazole and PI chromophores showed deep-blue CIE coordinates of (0.16, 0.06) and maximum external quantum efficiency of 5.3%.

An effect of positional isomerism of benzoic acid derivatives on antibacterial activity against Escherichia coli.

This study demonstrated the effect of positional isomerism of benzoic acid derivatives against E. coli ATCC 700728 with the serotype O157. The addition of hydroxyl and methoxyl substituents weakened the effect of acids against E. coli with respect to benzoic acid (except 2-hydroxybenzoic). The connection of the hydroxyl group at the second carbon atom in the benzoic ring reduced the time needed to kill bacterial cells. Phenolic acids with methoxyl substitutes limited the biofilm formation by E. coli to a greater extent than hydroxyl derivatives. The most significant influence on the antibacterial activity of phenolic acids has the type of substituent attached to the benzoic ring, their number, and finally the number of carbon atoms at which the functional group is located.

Positional isomeric effect of acyclic hosts on supramolecular recognition of anionic guests

• Anion coordinated neutral/charged self-assemblies of positional isomeric receptors. • Acyclic positional isomeric receptor with different functionalities is discussed. • Anion-coordinated different types of molecular assemblies are summarized. • Aerial CO 2 uptake, extraction, transport phenomena are also discussed. Two or more supramolecular hydrogen-bonding receptor scaffolds having identical molecular formulas act as positional isomers only when the position of a substituent or a receptor arm or double/triple bond of one isomer differ from another isomer. The review summarizes the research on anion coordination chemistry of last decade affected by the positional isomeric acyclic receptors. The detailed and comprehensive account of reported examples of one or more anionic guest/hydrated-anionic guest assisted self-assemblies (neutral or charged) of artificial acyclic isomers (monopodal or linear, dipodal, triodal, hexapodal), affected by the terminal aryl substituents or the receptor arms with respect to central aryl spacer are systematically incorporated in the review. The review specifically consolidates the underexplored broad area of anion recognition chemistry affected by positional isomerism of acyclic amine, amide, urea, thiourea functionalized receptors/sensors in solid as well as in solution state. These substituent dependent isomeric systems could provide insights into the fundamental hydrogen-bonded anion-receptor chemistry and also useful for understanding the biological and environmental processes followed by the crystal engineering as well as extraction, aerial CO 2 fixation, sensing or transport phenomena of anions. Discussions relating to the construction of some typical examples of anion-coordinated self-assembled supramolecular architectures such as molecular capsules, barrels, helicates, foldamer, tetrahedral cages and mechanically interlocked systems by these positional isomeric podands are also included in this review.

Effect of Positional Isomerism on Some Alcohol Based Drug towards Anti-Viral Activity against SARS-Cov-2: A Molecular Modeling Based Investigation

The severe acute respiratory syndrome coronavirus 2, better known as COVID-19, has become a major health concern worldwide. It has challenged the global healthcare sector like anything. It appeared in Wuhan, China, around November 2019, had spread to almost 187 countries due to its highly contagious nature. Quarantine, isolation, mask, and other precautionary measures remain the sole obliging strategy to decline the person-to-person transmissions. Amidst the pandemic, drug repurposing by identifying therapeutically potent molecule from the collection of pre-existing molecules by molecular docking and DFT methods are certainly fast and handy. Herein, this paper is dealing with 5 hydroxy based drugs such as 5-isopropyl-2-methylphenol (Carvacrol), 3-isopropyl-6-methylbenzene-1,2-diol, 2-isopropyl-5-methylbenzene-1,4-diol, 5-isopropyl-2-methylbenzene-1,3-diol, 2-isopropyl-5-methylbenzene-1,3-diol to discover the new possible COVID-19 inhibitors. The proteases PDB, e.g., 5r7y is used as hosts to calculate the interactions with hydroxy-based drugs as guests. Our research shows that 5-isopropyl-2-methylbenzene-1,3-diol is the most active, having binding energy –6.46 kcal/mol against 5r7y of SARS-CoV-2. Hence it is assumed that increasing number of alcohol group make the system more preferable towards SARS-CoV-2 protease protein 5r7y. It was also observed that relative binding energy among these alcohol-based drugs is further tuned by their positional isomerism property.

Positional Isomeric Effects on the Optical Properties, Multivalent Glycosidase Inhibition Effect, and Hypoglycemic Effect of Perylene Bisimide-deoxynojirimycin Conjugates.

Although multivalent glycosidase inhibitors have shown enhanced glycosidase inhibition activities, further applications and research directions need to be developed in the future. In this paper, two positional isomeric perylene bisimide derivatives (PBI-4DNJ-1 and PBI-4DNJ-2) with 1-deoxynojirimycin conjugated were synthesized. Furthermore, PBI-4DNJ-1 and PBI-4DNJ-2 showed positional isomeric effects on the optical properties, self-assembly behaviors, glycosidase inhibition activities, and hypoglycemic effects. Importantly, PBI-4DNJ-1 exhibited potent hypoglycemic effects in mice with 41.33 ± 2.84 and 37.45 ± 3.94% decreases in blood glucose at 15 and 30 min, respectively. The molecular docking results showed that the active fragment of PBI-4DNJ-1 has the highest binding energy (9.649 kcal/mol) and the highest total hydrogen bond energy (62.83 kJ/mol), which were related to the positional isomeric effect on the hypoglycemic effect in mice. This work introduced a new means to develop antihyperglycemic agents in the field of multivalent glycomimetics.

Positional isomeric effect of monobrominated ending groups within small molecule acceptors on photovoltaic performance.

As an ending acceptor unit (A) within acceptor–donor–acceptor (A–D–A)-type small molecule acceptors (SMAs), monobrominated 1,1-dicyanomethylene-3-indanone (IC-Br) plays a critical role on developing high-performance SMAs and polymer acceptors from polymerizing SMAs. IC-Br is usually a mixture (IC-Br-m) consisting of positional isomeric IC-Br-γ and IC-Br-δ (bromine substituted on the γ and δ positions, respectively). The positional isomeric effect of these monobrominated ending groups has been witnessed to take an important role on regulating the photovoltaic performance. Fully investigating this isomeric effect of monobromination would be of great value for SMAs and even polymer acceptors. In this study, benefitting from the separation of IC-Br-γ and IC-Br-δ from IC-Br-m with high yields, bis(thieno[3,2-b]cyclopenta)benzo[1,2-b:4,5-b′]diselenophene (BDSeT) was chosen as the D unit and combined with IC-Br-γ, IC-Br-δ and IC-Br-m as A units, respectively. Three A–D–A type SMAs (BDSeTICBr-γ, BDSeTICBr-δ and BDSeTICBr-m) have thus been obtained. When blended with the representative donor polymer of PBDB-T-2Cl to construct bulk heterojunction (BHJ) polymer solar cells (PSCs), BDSeTICBr-γ, BDSeTICBr-δ and BDSeTICBr-m devices offered power conversion efficiencies (PCEs) of 9.42, 10.63, and 11.54% respectively. The result indicated the superior photovoltaic performance of the isomer mixture over the pure isomers, which was contrary to the reported ones that the pure isomers of SMAs used to give a better performance. The superior performance of the BDSeTICBr-m devices was mainly reflected in the improved carrier generation and transport as well as the carrier recombination suppression. In the three PBDB-T-2Cl:SMA BHJ films, a comparable intermixing phase and acceptor domain sizes were observed. Compared with BDSeTICBr-γ and BDSeTICBr-δ, BDSeTICBr-m showed a preferential face-on orientated packing with the closest π–π stacking in its BHJ film, probably accounting for its higher photovoltaic performance than those of the pure isomers. This study provides an alternative sight to develop efficient SMAs with suitably monobrominated IC ending groups for the strategy of polymerizing SMAs.

Co(II) and Mn(II) coordination polymers: Ligand functional and positional isomeric effects, structural diversities, luminescence sensing and magnetic properties

Two new isostructural 3D Co(II) and Mn(II) coordination polymers (CPs) [M(L1′)2] (M = Co(1) and Mn (2)) were prepared by reactions of metal salts and 2-connected 4-(4-(3-cyanophenyl)-[2,3′-bipyridin]-6-yl)benzoic acid ligand (HL1′). Interestingly, when simple modification of the ligand functional group (from the cyano to carboxylate group), other two new 3D Co(II) [Co(HL2′)2] (3) and Mn(II) [Mn(L2′)(H2O)] (4) CPs are constructed by using 3-connected 3-(6-(4-carboxyphenyl)-[2,3′-bipyridin]-4-yl) benzoic acid (H2L2′), which are ascribed to the change in ligand functionality (from the cyano to carboxylate group). Moreover, the variable positions of cyano group (or carboxylate group) at the ligand isomers also can tune structural diversities. Present and previous works indicate that the isomeric effects of the ligand isomers play important role in adjusting structures of the Co(II) CPs. 1–4 were fully characterized by IR, elemental analyses, TGA, PXRD, and single-crystal X-ray diffraction. Interestingly, 2 and 4 can serve as sensing materials for detecting Fe3+ and Cr2O72− ions. Furthermore, the magnetic properties of four CPs have been investigated. The present work provides a promising approach to design and construct CPs or MOFs by adjusting ligand functionality and positional isomeric effects.

Effect of positional isomerism on electron-transfer photochromism and photoluminescence of two pyromellitic diimide-based organic molecules

Two positional isomeric organic molecules, 2-PMPMD (1) and 4-PMPMD (2) (2/4-PMPMD = N, N′-bis(2/4-pyridylmethyl)-pyromellitic diimide) have been constructed by anchoring two pyridylmethyl groups at both sides of nitrogen positions in pyromellitic diimide (PMD), which are assembled into different supramolecular architectures through lone pair-π interactions. Noteworthy, 1 and 2 exhibit unique electron-transfer photochromic behaviors with completely different photoresponsive rate and coloration contrast, which are contributed to the distinct interfacial contacts of electron donors and acceptors. Interestingly, photoluminescence properties of two compounds show different changes during the coloration-decoloration process (the slightly red-shift and weakening of the fluorescence for 1vs. the almost completely quenching of the fluorescence for 2). The present study illustrates the influence of positional isomerism on the resultant supramolecular networks and photochromic behaviors accompanying adjustable photoluminescence properties.

Difluorinated Oligothiophenes for High‐Efficiency All‐Small‐Molecule Organic Solar Cells: Positional Isomeric Effect of Fluorine Substitution on Performance Variations

Three symmetrically difluorinated organic semiconductors (namely D5T2F‐P, D5T2F‐S, and D5T2F‐T) containing rhodanine‐flanked pentathiophene structures are synthesized and used as donors in all‐small‐molecule organic solar cells (ASM‐OSCs) prepared with the small‐molecule acceptor 2,2′‐((2Z,2′Z)‐((4,4,9,9‐tetrahexyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IDIC‐4F). The different substitutional positions of fluorine atoms (–F) in the conjugated backbone of the donor molecule lead to various material and photovoltaic properties being exhibited. Among the three isomers, the centrally fluorinated D5T2F‐P exhibits a redshifted absorption spectrum, downshifted highest occupied molecular orbital (HOMO) energy level, and improved miscibility with IDIC‐4F in the blend films, all of which result in superior device performance. The power conversion efficiency (PCE) of the ASM‐OSCs based on D5T2F‐P:IDIC‐4F reaches an impressive value of 9.36% with an open‐circuit voltage (VOC) value of 0.86 V and a short‐circuit current density (JSC) value of 16.94 mA cm−2, whereas those of D5T2F‐S (6.11%) and D5T2F‐T (5.42%) are much lower. In comparison, an ASM‐OSC based on the nonfluorinated analogue DRCN5T fabricated under the same conditions exhibits poorer performance (8.03% with IDIC‐4F), revealing 16% enhancement in the PCE achieved through backbone fluorination. The PCE of 9.36% may be one of the highest efficiencies of oligothiophene‐based ASM‐OSCs reported in the literature to date.

Investigating the effect of positional isomerism on the assembly of zirconium phosphonates based on tritopic linkers.

We report on the use of a novel tritopic phosphonic linker, 2,4,6-tris[3-(phosphonomethyl)phenyl]-1,3,5-triazine, for the synthesis of a layered zirconium phosphonate, named UPG-2. Comparison with the structure of the permanently porous UPG-1, based on the related linker 2,4,6-tris[4-(phosphonomethyl)phenyl]-1,3,5-triazine, reveals that positional isomerism disrupts the porous architecture in UPG-2 by preventing the formation of infinitely extended chains connected through Zr-O-P-O-Zr bonds. The presence of free, acidic P-OH groups and an extended network of hydrogen bonds makes UPG-2 a good proton conductor, reaching values as high as 5.7 × 10-4 S cm-1.

Modulation of Weak Interactions in Structural Isomers: Positional Isomeric Effects on Crystal Packing and Physical Properties and Solid-State Thin-Film Fabrication.

Selective formation of positional isomers and accordingly tuning the physicochemical properties of small conjugated organic molecules through structural isomers is an effective crystal engineering for a fascinating successful delivery of thermally stable and photophysically exciting compounds. By small structural skeleton changes, the single crystal of the naphthalenemaleonitrile isomers is found to exhibit a drastic change in crystal packing array, which in turn is found to tune the thermal and physicochemical properties. The α-isomer (A) forms the “herringbone packing” (HP) due to peri-interaction-sensitive C–H···(Ar)π (Ar = naphthalene ring) interactions, and the β-isomer (B) forms the “bricklayer packing” (BP) due to π(C≡N)···π(Ar) stacking interactions. These two positional isomers have revealed insight of molecular packing-dependent structure–property relationship. In this report, we show that a simple modification of relatively less common weak interactions, such as C–H···π(Ar) ↔ π(C≡N)···π(Ar), through the preparation of isomers, can lead to a drastic change in crystal packing (HP ↔ BP). Also, this report demonstrates that by a small structural diversity, one can obtain significant changes in the physicochemical properties like melting behavior, enthalpy, entropy, and electrical properties in the solid state. Therefore, it transpires from this study that structural isomer provides a useful complement to intermolecular nonbonding interactions as a tool to design new promising materials.