Role of Electron-Donating and Electron-Withdrawing Groups in Tuning the Optoelectronic Properties of Difluoroboron–Napthyridine Analogues

Five napthyridine-based fluorine–boron (BF₂–napthyridine) conjugated compounds have been theoretically designed, and subsequently, their photophysical properties are investigated. The influence of electron-donating and electron-withdrawing groups attached with the N^∧C^∧O moiety of BF₂–napthyridine molecule has been interpreted. The optoelectronic properties, including absorption spectra and emission spectra of the BF₂–napthyridine derivatives are studied using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) based methods. Different characteristics, such as HOMO–LUMO gap, molecular orbital density, ionization potential, electron affinity, and reorganization energy for hole and electron, are calculated. All these molecules show excellent π-electron delocalization. TD-DFT results illustrate that the amine-substituted BF₂–napthyridine derivative has the highest absorption and emission maxima; it also shows a maximum Stoke shift. These results are well-correlated with the structural parameters and calculated HOMO–LUMO gap. Moreover, it is found that introduction of an electron-donating group into the BF₂–napthyridine complex improves the hole transport properties and provides useful clues in designing new materials for organic light emitting diodes (OLED). As a whole, this work demonstrates that electron-donating and electron-withdrawing groups in BF₂ derivatives can extend their effectiveness toward designing of OLED materials, vitro cellular studies, ex vivo assays, and in vivo imaging agents

A Perspective on Designing Chiral Organic Magnetic Molecules with Unusual Behavior in Magnetic Exchange Coupling

A total of nine diradical-based organic chiral magnetic molecules with allene and cumulene couplers have been theoretically designed, and subsequently, their magnetic property has been studied by density functional theory. It is found that with an increase in length of the coupler, a remarkable increase in spin density within the coupler takes place. An increase in the length of the coupler reduces the energy of LUMO, and a smaller HOMO–LUMO gap facilitates stronger magnetic coupling and thereby a higher magnetic exchange coupling constant (<i>J</i>). This observation is supported by the occupation number of natural orbitals

Charge-Transfer-Induced Magnetism in Mixed-Stack Complexes

Explanation of the ferromagnetic anomaly in two recently synthesized mixed-stack charge-transfer (CT) complexes (1) (HMTTF)­[Ni­(mnt)₂] (HMTTF = bis­(trimethylene)-tetrathiafulvalene, mnt = maleonitrile dithiolate) and (2) (ChSTF)­[Ni­(mnt)₂] (ChSTF = 2,3-cyclohexylenedithio-1,4-dithia-5,8-diselenafulvalene) is the cornerstone of this investigation. Because these systems are reported to achieve magnetic properties through charge transfer from the neutral organic donor to the neutral organometallic acceptor stack, their magnetic interaction is assessed through the charge-transfer energy and the spin densities on the concerned sites following one of our recent formalisms. The positive value of <i>J</i> obtained in this way is found to be in good agreement with that evaluated through ab<i> </i>initio and density functional theory (DFT). In DFT framework, broken symmetry (BS) approach is adopted to evaluate <i>J</i> using spin-projection technique. No overlap between singly occupied molecular orbitals (SOMOs) suggests a through-space ferromagnetic interaction between the donor and the acceptor in the ground state of the complexes. Apart from the ground state, the magnetic status of the molecules is studied by varying interlayer distance <i>d</i>, the extent of slippage (slipping distance <i>r</i>, <i>r</i>^/, and deviation angle α), and rotational angle θ, which play a crucial role in magneto-structural correlation. Furthermore, it is categorically observed that the ferromagnetic interaction reaches its zenith at minimum energy crystallographic stacking mode resulting in maximum value of coupling constant in the ground state

Regiocontrolled Nitration of 4-Quinolones at Ambient Conditions

<div><p></p><p>Regiocontrolled nitration of 4-quinolone, the highly privileged scaffold, has been developed at ambient conditions. The nitro group can selectively be introduced at diverse positions simply by tuning the reactivity of the moiety. Discrimination is being achieved through the selective functionalization of the free N-H group. The functional group has been screened theoretically with the help of Fukui function and local softness calculation. Theoretical predictions are synchronized well with the experimental findings. Finally, this nitration technique allows quick access to the structurally diverse 4-quinolones.</p></div

Performance of the Widely Used Minnesota Density Functionals for the Prediction of Heat of Formations, Ionization Potentials of Some Benchmarked First Row Transition Metal Complexes

We have computed and investigated the performance of Minnesota density functionals especially the M05, M06, and M08 suite of complementary density functionals for the prediction of the heat of formations (HOFs) and the ionization potentials (IPs) of various benchmark complexes containing nine different first row transition metals. The eight functionals of M0X family, namely, the M05, M05-2X, M06-L, M06, M06-2X, M06-HF, M08-SO, and M08-HX are taken for the computation of the above-mentioned physical properties of such metal complexes along with popular Los Alamos National Laboratory 2 double-ζ (LANL2DZ) basis set. Total 54 benchmark systems are taken for HOF calculation, whereas the 47 systems among these benchmark complexes are chosen for the calculation of IPs because of lack of experimental results on rest of the seven systems. The computed values of HOFs and IPs are compared with the experimental results obtained from the literature. The deviation of these computed values from the actual experimental results is calculated for each eight different M0X functionals to judge their performances in evaluating these properties. Finally, a clear relationship between the exchange correlation energy of eight M0X functionals and their efficiency are made to predict the different physical properties

Probing the Effects of Ligand Field and Coordination Geometry on Magnetic Anisotropy of Pentacoordinate Cobalt(II) Single-Ion Magnets

In this work, the effects of ligand field strength as well as the metal coordination geometry on magnetic anisotropy of pentacoordinated Co^II complexes have been investigated using a combined experimental and theoretical approach. For that, a strategic design and synthesis of three pentacoordinate Co^II complexes [Co­(bbp)­Cl₂]·(MeOH) (<b>1</b>), [Co­(bbp)­Br₂]·(MeOH) (<b>2</b>), and [Co­(bbp)­(NCS)₂] (<b>3</b>) has been achieved by using the tridentate coordination environment of the ligand in conjunction with the accommodating terminal ligands (i.e., chloride, bromide, and thiocyanate). Detailed magnetic studies disclose the occurrence of slow magnetic relaxation behavior of Co^II centers with an easy-plane magnetic anisotropy. A quantitative estimation of ZFS parameters has been successfully performed by density functional theory (DFT) calculations. Both the sign and magnitude of ZFS parameters are prophesied well by this DFT method. The theoretical results also reveal that the α → β (SOMO–SOMO) excitation contributes almost entirely to the total ZFS values for all complexes. It is worth noting that the excitation pertaining to the most positive contribution to the ZFS parameter is the d_<i>xy</i> → d_{<i>x</i>²–<i>y</i>²} excitation for complexes <b>1</b> and <b>2</b>, whereas for complex <b>3</b> it is the d_<i>z</i>² → d_{<i>x</i>²–<i>y</i>²} excitation