LUMO Research Articles

Meso-β, β-β' trifused porphyrins: synthesis, spectral, electrochemical and DFT studies and their femtosecond third-order nonlinear optical properties.

Meso-β, β-β' trifused porphyrins incorporating two distinct active methylene groups (MN = malononitrile and IND = 1,3-indanedione) and their corresponding metal complexes with Cu(II) and Zn(II) have been synthesized with good to excellent yields and characterized by various spectroscopic techniques and spectrometric methods. Single crystal X-ray analysis of the Zn(II) complex ZnTFPMB(MN)2 (where TFP = trifused porphyrin and MB = mono benzo) revealed a ruffled nonplanar 'armchair' type conformation with a twist angle of 24.10°. The absorption spectra showed a significant bathochromic shift in both the B- and Q-bands, extending into the near-infrared (NIR) region, particularly for π-extended trifused porphyrins. The cyclic voltammograms of MN-appended trifused porphyrins revealed unusual redox behavior, likely due to chemical reactions occurring at the electrode surface during electroreduction. The HOMO-LUMO energy gap for the π-extended porphyrins (MTFPMB(VCN)2) was effectively reduced to ≤1.5 V, compared to ∼2.23 V for the parent porphyrins. Additionally, the femtosecond third-order nonlinear optical properties of the synthesized trifused porphyrins and reported Ni(II) complexes were investigated using the Z-scan technique. Most of the studied porphyrins exhibited promising three-photon absorption coefficients and cross-section values, suggesting their potential applications in optical limiting, bio-imaging, and advanced optoelectronics.

Modulation of Molecular Quadrupole Moments by Phenyl Side-Chain Fluorination for High-Voltage and High-Performance Organic Solar Cells.

The ground-state charge generation (GSCG) in photoactive layers determines whether the photogenerated carriers occupy the deep trap energy levels, which, in turn, affects the device performance of organic solar cells (OSCs). In this work, charge-quadrupole electrostatic interactions are modulated to achieve GSCG through a molecular strategy of introducing different numbers of F atom substitutions on the BTA3 side chain. The results show that 8F substitution (BTA3-8F) and 16F substitution (BTA3-16F) lead to different patterns of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy level changes. The perfluorination of the phenyl side chain endows BTA3-16F with a LUMO energy level similar to that of BTA3, ensuring a high VOC. Besides, BTA3-16F features a large charge-quadrupole moment, promoting strong electrostatic interactions between neighboring molecules along the π-π stacking direction, which then induces the GSCG in photoactive components. This efficient GSCG directly makes a significant impact on the subsequent kinetics of photogenerated exciton dissociation, recombination, and transport over longer time periods, as well as on nonradiative recombination over larger spatial scales. Benefiting from the favorable GSCG and suitable energy level arrangement, PTQ10/BTA3-16F achieves a VOC of 1.302 V and a PCE of 11.14%, setting the world record for OSCs performance with a VOC greater than 1.3 V. In addition, BTA3-16F is an effective guest molecule to improve the performance of ternary OSCs, and PM6/L8-BO/BTA3-16F-based ternary device achieves the highest PCE of 19.82%. This result emphasizes the important role of GSCG between photoactive components in OSC performance and demonstrates that modulation of molecular quadrupole moments is an effective means of designing efficient acceptors.

Selective Recognition of Oncogene Promoter C-Myc G-Quadruplex: Design, Synthesis, and In Vitro Evaluation of Naphthalimide and Imidazo[1,2-a]pyrazines for Their Anticancer Activity.

c-Myc is a transcription factor that is overexpressed in most human cancers. Despite its challenging nature, we have developed a series of naphthalimide-imidazopyrazine conjugates to target c-Myc. The library of synthesized derivatives was tested for their anticancer activity against a nine-panel of cancer cell lines. Compound 8eb showed excellent cytotoxicity against all the tested cancer cell lines, with the range of growth inhibition from -98.79% to 96.62% at a single-dose concentration of 10-5 M. Further, 8eb was employed for a 5-dose assay against the same cancer cell lines, which showed efficacy at varying concentrations with an MG-MID GI50 value of 2.61 μM. Biophysical studies were performed to explore the interaction of 8eb with c-Myc Pu27 over ct-DNA, oncogene promotor Pu22, and human telomere, with a binding constant value of 1.3 × 107 M-1. Additionally, experiments were performed to get insights into the interaction mechanism between 8eb and the c-Myc oncogene promoter. A molecular docking study unveiled the stacking of the compound with G4 DNA through groove binding, where very few reports are available, with a favorable binding energy of -9.2 kcal/mol. Moreover, the pharmacokinetic study and HOMO-LUMO energy gap analysis underscored the potency of the active candidate. The compound's binding ability toward HSA was also assessed, where results suggested effective binding of the compound to HSA, revealing its potential for easy delivery to the target site. The above findings suggested that these newly synthesized candidates with potent anticancer activity offer a promising avenue as G4 DNA c-Myc stabilizers.

Designing pillar-layered metal-organic frameworks with photo-induced electron transfer interactions between ligands for enhanced photodynamic sterilization and photocatalytic degradation of dyes and antibiotics.

Pollution caused by antibiotics, bacteria, and organic dyes presents global public health challenges, posing serious risks to human health. Consequently, new, efficient, fast, and simple photocatalytic systems are urgently required. To this end, 2,7-di(pyridin-4-yl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NDI)-an electron acceptor-is introduced as a connecting column into a porphyrin-based metal-organic layer (2DTcpp) with excellent photocatalytic activity; this modification yields a three-dimensional pillar-layered metal-organic framework (MOF, 3DNDITcpp) with superior photocatalytic reactive oxygen species (ROS) generation capability. Introducing NDI enlarges the pore cavity of 3DNDITcpp creating active sites and boosting type II ROS production. The orderly arrangement of the electron donor (porphyrin layer) and acceptor (NDI) within 3DNDITcpp promotes photo-induced electron transfer (PET) interactions-as confirmed by density functional theory calculations-substantially boosting type I ROS production. Specifically, the energy levels of the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of the porphyrin derivative ligand are -0.122252 and -0.185307eV, respectively. The energy levels of the LUMO and HOMO of the NDI ligand are -0.15977 and -0.221199eV, respectively. The HOMO energy level of the porphyrin ligand is between the HOMO and LUMO of NDI, and higher than the HOMO orbital energy level of NDI, proving that the porphyrin derivative ligand can act as an electron donor and carry out an efficient PET process with the electron acceptor NDI. Various ROS indicators demonstrate the superior ROS generation ability of 3DNDITcpp under light irradiation. Using activated 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) as an indicator of total ROS, the fluorescence enhancement factors of 2DTcpp, 3DPyTcpp, and 3DNDITcpp were 42.13, 48.24 and 94.21 times, respectively. Both the degradation curve and degradation rate of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) demonstrated that the order of 1O2 production ability was 3DNDITcpp (rate up to 0.312min-1)>3DpyTcpp (0.158min-1)≈2DTcpp (0.155min-1). In addition, dihydrorhodamine 123 (DHR 123) and hydroxyphenyl fluorescein (HPF) were used as specific indicators of O2- and OH to monitor the generation of type I ROS of 2DTcpp, 3DPyTcpp, and 3DNDITcpp, respectively. The fluorescence enhancement factors of DHR 123 and HPF aqueous solutions containing 3DNDITcpp were as high as 47.70 and 192.19 times, respectively. The fluorescence enhancement factors of DHR 123 and HPF containing 2DTcpp and 3DPyTcpp were 19.65/63.07 (2DTcpp) and 27.97/134.19 times (3DPyTcpp), respectively. Photocurrent response (3DNDITcpp is 1.2 and 2.7 times better than 3DPyTcpp and 2DTcpp, respectively) and electrochemical impedance (3DNDITcpp is 1.9 and 2.9 times smaller than 3DPyTcpp and 2DTcpp, respectively) measurements confirming its excellent type I ROS production capability. Under low-power light irradiation (60mW·cm-2, 5min), ROS generated by 3DNDITcpp effectively inactivates Escherichia coli and Staphylococcus aureus, with an inhibition zone diameter of approximately 4.00cm. Furthermore, 3DNDITcpp rapidly degrades various colored dyes and antibiotics within 30min, achieving degradation rates as high as 0.095 and 0.054min-1, outperforming most traditional photosensitizers (PSs). To our knowledge, this is the first instance when differences in the electron clouds of mixed ligands are leveraged to induce PET interactions within pillar-layered MOFs, yielding excellent porous PSs. Overall, our study offers a new approach for developing porous PSs with enhanced ROS generation capacity and advances MOFs crystal engineering based on mixed ligands.

Structural, Electronic, and Magnetic Properties of Neutral Borometallic Molecular Wheel Clusters.

Atomic clusters exhibit properties that fall between those found for individual atoms and bulk solids. Small boron clusters exhibit planar and quasiplanar structures, which are novel materials envisioned to serve as a platform for designing nanodevices and materials with unique physical and chemical properties. Through past research advancements, experimentalists demonstrated the successful incorporation of transition metals within planar boron rings. In our study, we used first-principles calculations to examine the structure and properties of neutral boron clusters doped with transition metals, denoted as TMBn and TMB2n, where TM = Ti, Cr, Mn, Fe, Co, Nb, or Mo and n=8-10. Our calculations show that the TMB2n structures, which involve sandwiching metal atoms between two rings (called the drum configuration), and clusters with the single ring configuration, TMBn, are stable. These clusters typically have relatively large HOMO-LUMO energy gaps, suggesting high kinetic stability and low chemical reactivity. Moreover, the clusters display interesting magnetic properties, determined not only by the metal atoms but also by the induced magnetism of the boron rings. These structures have potential applications in spintronics and sensing. This work also provides a basis for studying magnetism in the one-dimensional limit.

Resonantly Enhanced Hybrid Wannier-Mott-Frenkel Excitons in Organic-Inorganic Van Der Waals Heterostructures.

Hybrid excitons formed via resonant hybridization in 2D material heterostructures feature both large optical and electrical dipoles, providing a promising platform for many-body exciton physics and correlated electronic states. However, hybrid excitons at organic-inorganic interface combining the advantages of both Wannier-Mott and Frenkel excitons remain elusive. Here, hybrid excitons are reported in the copper phthalocyanine/molybdenum diselenide (CuPc/MoSe2) heterostructure (HS) featuring strong molecular orientation dependence by low-temperature photoluminescence and absorption spectroscopy. The hybrid Wannier-Mott-Frenkel excitons exhibit a large oscillator strength and display signatures of the Frenkel excitons in CuPc and the Wannier-Mott excitons in MoSe2 simultaneously through the delocalized electrons. The density functional theory (DFT) calculations further confirm the strong hybridization between the lowest unoccupied molecular orbital (LUMO) of CuPc and the conduction band minimum (CBM) of MoSe2. The out-of-plane molecular orientation is further employed to tune the hybridization strength and tailor the hybrid exciton states. The results reveal the hybrid excitons at the CuPc/MoSe2 interface with tunability by molecular orientation, suggesting that the organic-inorganic HS constitutes a promising platform for many-body exciton physics such as exciton condensation and optoelectrical applications.

Identifying Carbon-Carbon Triple Bonds from Double Bonds via Single-Molecule Conductance.

Molecular-scale electronics focuses on understanding and utilizing charge transport through individual molecules. A key issue is the charge transport capability of a single molecule characterized by current decay. We visualize the on-site formation of conjugated polymers with varying carbon-carbon bond orders by using scanning tunneling microscopy and noncontact atomic force microscopy. Although carbon-carbon double bonds and triple bonds exhibit similar electronic characteristics, single-molecule conductance measurements reveal distinct features based on different levels of conjugation. These findings, supported by density functional theory calculations, indicate that a higher bond order results in greater electron density and more symmetric molecular orbitals, leading to larger transmission rates and more rigid frontier orbitals. Consequently, this contributes to a higher conductance and a lower decay constant. These findings enhance the understanding of bond orders in molecular electronics and should facilitate the development of single-molecule devices and the applications of nanoscale circuitry.

Merging SOMO activation with transition metal catalysis: Deoxygenative functionalization of amides to β-aryl amines.

Singly occupied molecular orbital (SOMO) activation of in situ generated enamines has achieved great success in (asymmetric) α-functionalization of carbonyl compounds. However, examples on the use of this activation mode in the transformations of other functional groups are rare, and the combination of SOMO activation with transition metal catalysis is still less explored. In the area of deoxygenative functionalization of amides, intermediates such as iminium ions and enamines were often generated in situ to result in the formation of α-functionalized amines. In contrast, the direct deoxygenation of amides to β-functionalized amines is highly appealing yet remains scarcely investigated. Here, a deoxygenative arylation of amides with aryl halides was developed via multicatalysis of iridium/photoredox/nickel/iridium, affording β-aryl amines in high efficiency. The key to the success of this reaction is the SOMO activation of enamine in synergy with a Ni-catalyzed arylation, which is in conjunction with two compatible Ir-catalyzed reduction processes.

Dual-Emissive Iridium(III) Complex with Aggregation-Induced Emission: Mechanistic Insights into Electron Transfer for Enhanced Hypoxia Detection in 3D Tumor Models.

Accurate oxygen detection and measurement of its concentration is vital in biological and industrial applications, necessitating highly sensitive and reliable sensors. Optical sensors, valued for their real-time monitoring, nondestructive analysis, and exceptional sensitivity, are particularly suited for precise oxygen measurements. Here, we report a dual-emissive iridium(III) complex, IrNPh2, featuring "aggregation-induced emission" (AIE) properties and used for sensitive oxygen sensing. IrNPh2 exhibits dual emissions at 450 and 515 nm, with 515 nm triplet-state emission demonstrating remarkable oxygen sensitivity due to its long-lived excited state (12.12 μs) and high quantum yield (68%). Stern-Volmer analysis reveals a notable quenching constant (Ksv = 12.44%-1) and an ultralow detection limit of 0.0397%, emphasizing its superior performance. The oxygen quenching mechanism is driven by electron transfer (ET), supported by computational studies showing the lowest-unoccupied molecular orbital (LUMO) alignment of IrNPh2 with the πg* orbitals of triplet oxygen, leading to superoxide radical (O2•-) formation. Electron paramagnetic resonance (EPR) studies further confirm this pathway. Biological evaluations using a three-dimensional (3D) U87-MG glioma spheroid model highlight the ability of IrNPh2 to detect hypoxic regions, with significant fluorescence enhancement under hypoxia and minimal cytotoxicity (>80% viability at 100 μM). With high sensitivity, low detection limits, and biocompatibility, IrNPh2 emerges as a promising candidate for oxygen sensing in environmental and biomedical applications, especially tumor hypoxia detection.

Construction of N−E bonds via Lewis acid-promoted functionalization of chromium-dinitrogen complexes

Direct conversion of dinitrogen (N2) into N-containing compounds beyond ammonia under ambient conditions remains a longstanding challenge. Herein, we present a Lewis acid-promoted strategy for diverse nitrogen-element bonds formation from N2 using chromium dinitrogen complex [Cp*(IiPr2Me2)Cr(N2)2]K (1). With the help of Lewis acids AlMe3 and BF3, we successfully trap a series of fleeting diazenido intermediates and synthesize value-added compounds containing N−B, N−Ge, and N−P bonds with 3 d metals, offering a method for isolating unstable intermediates. Furthermore, the formation of N−C bonds is realized under more accessible conditions that avoid undesired side reactions. DFT calculations reveal that Lewis acids enhance the participation of dinitrogen units in the frontier orbitals, thereby promoting electrophilic functionalization. Moreover, Lewis acid replacement and a base-induced end-on to side-on switch of [NNMe] unit in [(Cp*(IiPr2Me2)CrNN(BEt3)(Me)] (8) are achieved.

Simultaneous Ring-Opening and Dehydrogenation of Diarylethene Induced by Tunneling Electrons.

Understanding the reversible transformation between two isomeric states of organic molecules under external stimulation is essential for advancing single-molecule device development. Photochromic diarylethene (DAE) derivatives are promising candidates for single molecular switching elements. This study investigates the single-molecule reactions of the closed-form isomer of a DAE derivative on Cu(111) using scanning tunneling microscopy (STM). A novel ring-opening pathway, distinct from the well-known photochromic isomerization, was discovered. Electron injection into the lowest unoccupied molecular orbitals induces the sequential anchoring of molecules to the substrate through the dehydrogenation of a methyl group at the 2-position of the thiophene ring. This mechanism was revealed by density functional theory calculations and STM simulations. The adsorption configurations for singly and doubly dehydrogenated DAEs were identified. Based on these findings, a new reaction mechanism extending beyond reversible isomeric reactions is proposed for DAE on Cu(111). The present work establishes a novel framework for future studies on single-molecule switching phenomena on metal substrates.

ThCTi@Cs(6)-C82: Th═C Double Bond in a Mixed Actinide-Transition Metal Cluster.

A thorium-carbon double bond that corresponds to the sum of theoretical covalent double bond radii has long been sought after in the study of actinide-ligand multiple bonding as a synthetic target. However, the stabilization of this chemical bond remains a great challenge to date, in part because of a relatively poor energetic matching between 5f-/6d- orbitals of thorium and the 2s-/2p- frontier orbitals of carbon. Herein, we report the successful synthesis of a thorium-carbon double bond in a carbon-bridged actinide-transition metal cluster, i.e., [Th═C═Ti], encapsulated inside a fullerene cage of C82. ThCTi@Cs(6)-C82 was successfully synthesized by a modified arc discharging method and characterized by mass spectrometry, single-crystal X-ray crystallography, various spectroscopy, and theoretical calculations. X-ray crystallographic analysis reveals a bent μ2-bridged carbide cluster with a Th-C distance of 2.123(18) Å, which is the shortest reported to date in an isolable compound and is comparable to the sum of the covalent Th═C double bond radii (2.10 Å). In addition, Th═C═Ti takes an unexpected nonlinear configuration with a bond angle of 133.0(10)°. The combined experimental and theoretical investigation further revealed the bonding nature of Th═C, which is polarized toward the bridged carbon but has a notably higher covalency than the Th-C bonds reported previously for organometallic compounds. Moreover, pronounced cage-to-metal donation appears to be stabilizing the encapsulated Th═C═Ti cluster. This work offers a deeper understanding of the bonding behavior of thorium and features the unique ability of fullerene cages to stabilize bonding motifs containing different types of metal-ligand multiple bonds.

Thiazolidinone-Based Electron-Collecting Monolayers for n-i-p Perovskite Solar Cells.

The development of efficient electron-collecting monolayer materials is desired to lower manufacturing costs and improve the performance of regular (negative-intrinsic-positive, n-i-p) type perovskite solar cells (PSCs). Here, we designed and synthesized four electron-collecting monolayer materials based on thiazolidinone skeletons, with different lowest-unoccupied molecular orbital (LUMO) levels (rhodanine or thiazolidinedione) and different anchoring groups to the transparent electrode (phosphonic acid or carboxylic acid). These molecules, when adsorbed on indium tin oxide (ITO) substrates, lower the work function of ITO, decreasing the energy barrier for electron extraction at the ITO/perovskite interface and improving the device performance. The shift of work function, rather than the LUMO levels of the molecules themselves, was found to be correlated with the performance of the perovskite solar cells.

Electronic absorption of ferricenium derivatives: an unexpected twist

Our results revealed that the introduction of either electron-donating or electron-withdrawing group(s) on the cyclopentadienyl rings leads to a substantial red shift of the lowest energy ligand-to-metal charge transfer (LMCT) band, generally known as 2E2g → 2E1u, relative to that of the parent ferricenium complex. The observed stabilization of the lowest unoccupied molecular orbitals (LUMO), i.e. e2g orbitals, in the electron-deficient system, was ascribed to the δ back donation from the iron atom into the antibonding molecular orbitals of the ligand rings. A series of DFT calculations reproduce the experimental trend highlighting the shift in energies of the molecular orbitals involved in the charge transfer transition. The direct relationship between the location of the LMCT band and reduction potential for specific class of substituents is also presented which allows for more informed structural modifications in the development of these complexes.

Prediction of Thermodynamic Properties of C60-Based Fullerenols Using Machine Learning.

Traditional machine learning methods face significant challenges in predicting the properties of highly symmetric molecules. In this study, we developed a machine learning model based on graph neural networks (GNNs) to accurately and swiftly predict the thermodynamic and photochemical properties of fullerenols, such as C60(OH)n (n = 1 to 30). First, we established a global method for generating fullerenol isomers through isomer fingerprinting, which can generate all possible isomers or produce diverse structural types on demand. Significantly, by incorporating interpretable descriptors such as atomic labels, bond lengths, and bond angles from highly symmetric isomers, our multilayer GNN model achieved over 90% accuracy in predicting the thermodynamic stability of fullerenols. The model also performed excellently in predicting electronic properties, including the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and the energy gap. Overall, this work demonstrates a new strategy using interpretable descriptors for accurately predicting the properties of highly symmetric structures, offering theoretical chemists a valuable tool for studying these materials.

Toward High-Performance Pure-Green Tandem Organic Light-Emitting Diodes by Employing Barrier-Free Strategies in the Charge Generation Layer.

Charge generation layers (CGLs) play crucial roles in determining the electroluminescence (EL) performance of tandem organic light-emitting diodes (OLEDs). However, acquiring negligible voltage drops across the CGL unit and high-efficiency multiplications remains challenging. Here, we propose barrier-free strategies to compose a high-performance p-i-n type CGL intermediate by introducing a Yb/HI-9 modification at the heterojunction and a novel n-dopant, Yb:1,3-bis(9-phenyl-1,10-phenanthrolin-2-yl)benzene (mdPPhen), as the n-CGL. Mechanism analysis confirms that the Yb/HI-9 modification efficiently eliminates the intrinsic energy mismatch at the n-CGL/p-CGL interface, while the lowest unoccupied molecular orbital (LUMO) of the n-dopant can be aligned to the electron transport layer of adjacent EL units, creating improved electron transport. Consequently, the resulting 2-EL unit tandem OLEDs exhibited no voltage drops across the CGL intermediate with excellent efficiency multiplications. Notably, the barrier-free CGL strategy worked efficiently in the sensitized fluorescence tandem OLED with low operating voltage, extremely high efficiency (current efficiency of 267.2 cd/A, external quantum efficiency of 62.6%), and operational stability (95% of the initial luminance at 3000 cd/m2, T95 of 4713 h) with pure-green emission (CIEy coordinate of over 0.68), showing the best tandem OLED among reported CGLs to satisfy commercial demands.

Exploring the Impact of Structural Modifications of Phenothiazine-Based Novel Compounds for Organic Solar Cells: DFT Investigations.

This paper explores a novel group of D-π-A configurations that has been specifically created for organic solar cell applications. In these material compounds, the phenothiazine, the furan, and two derivatives of the thienyl-fused IC group act as the donor, the π-conjugated spacer, and the end-group acceptors, respectively. We assess the impact of substituents by introducing bromine atoms at two potential substitution sites on each end-group acceptor (EG1 and EG2). With the donor and π-bridge held constant, we have employed density functional theory and time-dependent DFT simulations to explore the photophysical and optoelectronic properties of tailored compounds (M1-M6). We have demonstrated how structural modifications influence the optoelectronic properties of materials for organic solar cells. Moreover, all proposed compounds exhibit a greater Voc exceeding 1.5 V, a suitable HOMO-LUMO energy gap (2.14-2.30 eV), and higher dipole moments (9.23-10.90 D). Various decisive key factors that are crucial for exploring the properties of tailored compounds-frontier molecular orbitals, transition density matrix, electrostatic potential, open-circuit voltage, maximum absorption, reduced density gradient, and charge transfer length (Dindex)-were also explored. Our analysis delivers profound insights into the design principles of optimizing the performance of organic solar cell applications based on halogenated material compounds.

Theoretical elucidation of the effect of the linkage and orientation of carbazole and naphthalenediimide on the TADF and RTP propensities.

Thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) are most promising processes for harvesting triplet excitons in organic light-emitting diodes. In this work, the effect of the linkage between the carbazole (Cz) donor (D) and the naphthalenediimide (NDI) acceptor (A) on the TADF and RTP propensities is elucidated using density functional theory computations employing D-A, D-A-D, D-π-A, and D-π-A-π-D structural designs. The effects of the dihedral angle between the donor and acceptor units on the energy difference between the singlet and triplet excited states (ΔEST), the spin-orbit coupling (SOC) constants, and radiative (kr), intersystem crossing (kISC) and reverse intersystem crossing (kRISC) rates are unravelled. The molecules possessing a direct linkage between Cz and NDI exhibit large ΔEST values due to substantial overlap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). However, the insertion of a phenyl spacer between the Cz and NDI units led to disjoint HOMO and LUMO and consequently resulted in a small ΔEST. Furthermore, the presence of two donors with and without a phenyl spacer on NDI resulted in a high-lying triplet state (T2) that is energetically lower than the lowest singlet excited state (S1), hence providing additional channels to the TADF and RTP processes. Also, the orientation of Cz and NDI in the ortho-positions of the phenyl unit resulted in a T1 state with dominant LE character which led to moderate spin-orbit coupling constants and highest kr rates compared to the analogous meta- and para-linked derivatives. Thus, the ortho-derivatives possessed small ΔEST, charge transfer dominated S1, joint holes and electrons for the T1 state, characteristic of local excitation, high SOC, and promising rISC and kr rates. Overall, the phenyl linked derivatives possess TADF characteristics, while the directly linked analogues show RTP propensity.

Unveiling the molecular mechanism of Mn and Zn-catalyzed Ullmann-type C-O cross-coupling reactions.

A detailed theoretical study delving into the molecular mechanisms of the Ullmann-type O-arylation reactions catalyzed by manganese and zinc metal ions has been investigated with the aid of the density functional theory (DFT) method. In contrast to the redox-active mechanisms proposed for classical Ullmann-type condensation reaction, a redox-neutral mechanism involving σ-bond metathesis emerged as the most appealing pathway for the investigated high-valent Mn(II) and Zn(II)-catalyzed O-arylation reactions. The mechanism remains invariant with respect to the nature of the central metal, ligand, base, etc. This unusuality in the mechanism has been dissected by considering three cases: ligand-free and ligand-assisted Mn(II)-catalyzed O-arylation reaction and ligand-assisted Zn(II)-catalyzed O-arylation reactions. In each class, a metal phenoxide species was identified as the active catalyst. The unusual mechanistic trends observed in these C-O cross-coupling reactions could be attributed to the stable electronic configurations (d5, d10) combined with the higher oxidation states of the catalytic metal centers (Mn(II), Zn(II)). The exploration into the electronic effects of functional groups in controlling the reaction feasibility within each metal variant disclosed a consistent trend irrespective of the transition metal catalyst involved in the reaction. It was found that the introduction of electron-withdrawing groups at the para-position of organic halide lowers the energy of their lowest unoccupied molecular orbitals (LUMO), thereby lowering the HOMO-LUMO gap between the coupling partners. This study thereby revealed a comprehensive understanding of the fundamental mechanisms exhibited by high-valent first-row transition metal catalysts that could foster the development of eco-friendly protocols for preparing biaryl ether moieties.

Nanoring interactions with bio-relevant molecule: A quantum chemical approach to C18 and B9N9 systems.

This study investigates the interaction of a synthetic bio-relevant molecule with C18 and B9N9 nanorings, exploring their potential applications in sensing and drug delivery. Employing Density Functional Theory (DFT) at the ωB97XD level with the 6-31G(d,p) basis set, we computed the adsorption and electronic properties of the resulting nanocomplexes. A total of ten distinct configurations were identified for the interactions, with adsorption energies ranging from -6.75 to -12.62kcal/mol for the C18@target molecule and -9.01 to -18.46kcal/mol for the B9N9@target molecule. Notably, alterations in the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) upon interaction suggest an enhancement in electrical conductivity. The effect of aqueous media was also examined, revealing an increase of approximately 2.0 Debye in the dipole moments of the most stable nanocomplexes. Additional analyses, including reduced density gradient (RDG), UV-Vis spectroscopy, and Quantum Theory of Atoms in Molecules (QTAIM), were conducted in both gas and aqueous phases. Our findings indicate that C18 and B9N9 nanorings exhibit significant promise as candidates for drug delivery and sensing applications, particularly due to their enhanced electronic properties upon interaction with the bio-relevant molecule.