Investigation of Guest-Induced Flexibility in Pyrazine Derivative of ALFFIVE MOF via Molecular Simulation

One of the important understandings of porous solids like metal-organic frameworks (MOFs) is their flexibility. Therefore, there are certain computational studies on flexible MOFs in the literature, primarily concentrating on MIL-53, UiO-66, and DUT-49. Here, investigation of another class of MOF, that is, [Ni(1,4-pyrazine)₂(AlF₅)]_n, was shown to have guest-induced flexible characteristics; nevertheless, the mechanism for the emergence of flexibility is uncertain. We simulated the structural flexibility of [Ni(1,4-pyrazine)₂(AlF₅)]_n, named ALFFIVE-Ni-pyr-TBP, upon adsorption of a guest molecule based on force fields using the molecular dynamics (MD) method and Monte Carlo (MC) simulations. As the first step towards understanding guest-induced flexibility, the MC simulations were performed by relaxing the framework and then further comparing it with the rigid framework. Subsequently, MD simulations were executed on the ALFFIVE-Ni-pyr-TBP framework with and without the guest molecules. In the case of moisture adsorption, the MOF system was identified to undergo a geometric transformation from trigonal bipyramidal to square bipyramidal geometry due to the strong interaction of oxygen of the water with the metal aluminum. However, some tilting in the pyrazine ligand was observed in the presence of all the guest molecules. Therefore, the detailed guest-induced flexibility described in this work could support the ALFFIVE series to be explored for future adsorption applications.

Design and development of Imidazo[4,5-f] [1,10] phenanthroline-Zn (II) based fluorescent probes for specific recognition of ATP with tunable optical responses and probing the enzymatic hydrolysis of ATP by alkaline phosphatase

The development of chemosensors for selective detection of specific biologically important analytes continues to be of great attention in contemporary analytical chemistry. Among the several biologically important analytes, selective detection...

Why trans and not cis? – Molecular Dynamics and DFT study on selective separation of dihaloethene isomers using perethylated pillar[5]arene

The separation of mixtures of isomers is a daunting task. It is found that perethylated pillar[5]arene can separate trans-dichloroethene from its cis isomer. This work deals with the host-guest interactions...

Oxidation State-Dependent Electronic Properties of Sulfur-Containing Thermally Activated Delayed Fluorescence Molecules

Comparative studies of a series of sulfur-containing thermally activated delayed fluorescence (TADF) molecules and their oxidized compounds are carried out by means of electronic structure calculations. Aiming at investigating the effects of oxidation of bridged sulfur on the modulation of electronic structures of sulfur-containing TADF molecules, their geometrical structures, singlet (S₁) and triple (T₁) energies and their gap (ΔE_ST), the transition dipole moment, the spin-orbit coupling (SOC) between S₁ and T₁ states, the ionization potentials, and electron affinities are analyzed in detail to determine the structure-property relationships in these investigated TADF molecules and their corresponding oxidized counterparts. The electronic structure calculations show that the oxidation of bridged sulfur into the corresponding sulfoxide and sulfone significantly changes the electronic properties of TADF molecules. Interestingly, a substantial reduction in the singlet-triplet energy difference is possible with an increase in the oxidation state of the sulfur atom in the core. Moreover, the sulfone-containing molecules exhibit both S₁ and T₁ states having a large charge transfer (CT) excitation characteristic, which helps reduce the singlet-triplet energy gap and facilitates the reverse intersystem crossing (RISC) from the triplet state to the singlet state. SOC values increase with an increase in the oxidation state of the sulfur atom. Particularly, a sulfoxide-containing core moiety exhibits higher SOC values when compared with the sulfone-containing acceptor core.

Two-acceptor one-donor random terpolymers comprising thiophene- and phenyl-capped diketopyrrolopyrrole for organic photovoltaics

A series of random terpolymers comprising two electron deficient phenyl (PDPP) and thiophene (ThDPP)-capped diketopyrrolopyrrole (DPP) in conjugation with the electron-donating thiophene moiety are synthesised using Stille coupling.

The role of sulfur oxidation in controlling the electronic properties of sulfur-containing host molecules for phosphorescent organic light-emitting diodes

In this study a series of dibenzothiophene (DBT) derivatives having different valence states of sulfur atoms have been reported as host materials for blue phosphorescent organic light-emitting diodes. Their electronic properties have also been thoroughly investigated to develop structure-property relationships which include the consideration of the effect of various oxidation states of the sulfur atom in the core moiety and linking (C-N linkage) of subunits with the core at different positions. The results obtained from the electronic structure calculations highlight that the triplet energy (E_T), singlet-triplet energy difference (ΔE_ST), reorganization energy for the hole and the injection barrier for the electron decrease with an increase in the oxidation state of the sulfur atom in DBT. On the other hand, the injection barrier for the hole and the reorganization energy for the electron increase upon increasing the oxidation state of the sulfur atom present in the DBT.

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium(III) complex, bis[2',6'-difluorophenyl-4-formylpyridinato-N,C4']iridium(III) (picolinate) (IrC), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN(-) on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed IrC was authenticated by single-crystal X-ray diffraction. Notably, the iridium(III) complex exhibits intense red phosphorescence in the solid state at 298 K (ΦPL = 0.16) and faint emission in acetonitrile solution (ΦPL = 0.02). The cyanide anion binding properties with IrC in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV-vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium(III) complex in acetonitrile (c = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of IrC at 480 nm was dramatically enhanced ∼5.36 × 10(2)-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10(-8) M. The cyanohydrin formation mechanism is further supported by results of a (1)H NMR titration of IrC with CN(-). As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with IrC for the trace detection of CN(-) in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium(III) complex probe and its cyanide adduct.

Design of medium band gap random terpolymers containing fluorene linked diketopyrrolopyrrole and thiophene co-monomers: an experimental and theoretical study

Six different random terpolymers were synthesised and their optoelectronic properties were fine-tuned by varying the thiophene strength.

Quantum chemical design of carbazole- and pyridoindole-based ambipolar host materials for blue phosphorescent OLEDs

Structure–property relationship of carbazole- and pyridoindole-type host materials for blue PhOLEDs using quantum chemical calculations.

Monolayer to interdigitated partial bilayer smectic C transition in thiophene-based spacer mesogens: X-ray diffraction and (13)C nuclear magnetic resonance studies

Mesophase organization of molecules built with thiophene at the center and linked via flexible spacers to rigid side arm core units and terminal alkoxy chains has been investigated. Thirty homologues realized by varying the span of the spacers as well as the length of the terminal chains have been studied. In addition to the enantiotropic nematic phase observed for all the mesogens, the increase of the spacer as well as the terminal chain lengths resulted in the smectic C phase. The molecular organization in the smectic phase as investigated by temperature dependent X-ray diffraction measurements revealed an interesting behavior that depended on the length of the spacer vis-a-vis the length of the terminal chain. Thus, a tilted interdigitated partial bilayer organization was observed for molecules with a shorter spacer length, while a tilted monolayer arrangement was observed for those with a longer spacer length. High-resolution solid state (13)C NMR studies carried out for representative mesogens indicated a U-shape for all the molecules, indicating that intermolecular interactions and molecular dynamics rather than molecular shape are responsible for the observed behavior. Models for the mesophase organization have been considered and the results understood in terms of segregation of incompatible parts of the mesogens combined with steric frustration leading to the observed lamellar order.

Intramolecular charge transfer interactions and molecular order of rod like mesogens

Photophysical studies, VT-XRD and¹³C solid state NMR investigation of three ring based dimethylamino mesogens reveal intramolecular charge transfer, smectic A_dmesophase and molecular order.

Structural investigation of resorcinol based symmetrical banana mesogens by XRD, NMR and polarization measurements

The structural characterization of two bent-core mesogens DBPPD and DBPPDO which differ in terminal chains reveals B₂ and B₇ mesophases while the orientational order parameter for DBPPD is found to be 0.84 with a bent angle of 120.5°.