LUMO Research Articles

Optical properties of transition metals complex films derived from hydrazone oxime for optoelectronic devices

Hydrazone incorporating oxime nucleus and its Ni2+, Mn2+, Zn2+ and UO22+ metallic chelates have been prepared and completely characterized by different spectral, theoretical, and analytical techniques including NMR, FT-IR, mass, and EAS spectroscopy. The finding denoted that the Hydrazone ligand bonded as a dibasic tridentate chelator via deprotonated oximato nitrogen, enol carbonyl oxygen and hydrazono azomethine nitrogen atoms resultant in octahedral geometry for Ni2+, Mn2+, Zn2+ and UO22+. Theoretical studies by DFT/B3LYP/LANLDZ together with dipole moment, geometrical optimization, energetic parameters, and energy gap (HOMO–LUMO) were employed to support the geometrical structure of the synthetics. Additionally, these complexes were prepared in the form of thin film onto cleaned glass substrate by spin-coating technique. The values of the optical band gap (Eg) and film index of refraction (n) have been determined by many different methods. It was found that the hydrazone-oxime (OBBH2) film has the highest value of Eg (eV) where the UOBB complex film has the smallest value of Eg (2.56 eV). The latter is very close to the Eg value of ZnSe (2.58 eV). The refractive index changes with wavelengths show normal dispersion which is well discussed in terms of Sellmeier's dispersion model. Also, the nonlinear optical parameters viz. the first (χ(1)) and third (χ(3)) orders of nonlinear optical susceptibilities and the non-linear index of refraction (n2) have been studied. The complex dielectric constant (ε⌣=εr+iεi)), conductivity (σ⌣=σr+iσi), sheet resistance (Rs), and thermal have been investigated over the whole spectral range. According to the results of χ(1), χ(3) and n2 the complex films under study are candidates to be used in optical switching gadgets, optical modulators, and optical signal processing.

Theoretical study of the efficiencies of graphyne supported Mo single-atom catalyst (SAC) and Mo-Ni dual-atom catalyst (DAC) on hydrogen evolution reaction

In this work, by adding one molybdenum atom or two molybdenum and nickel atoms on the surface graphyne support, single atom catalyst (SAC) and dual atoms catalyst (DAC) were designed. The different spin multiplicities for both catalysts were analyzed by the relative energies, adsorption energies and frontier orbitals. The results showed in both case of SACs and DACs, the catalyst with spin multiplicity = 3 is desired. Then, the efficiency of these two catalysts as high-performance and cost-effective catalysts in the HER process was investigated theoretically. All calculations were performed using M06-2X/def2SV level of theory. In the HER mechanism, it has been found that the DAC has higher favorability than the SAC. Both steps (Volmer reaction and Tafel or Heyrovsky reaction) are more exothermic using DAC, and the difference between SAC and DAC is higher in the second step. The effect of solvent on these steps has been studied using water and methanol as two common solvents. The reactions are less exothermic in the solvent; but they are still highly exothermic and thermodynamically favorable. Moreover, despite the gas phase data, in both solvents, the use of DAC gives less favorable data versus the SAC. The data also showed the little preference of water versus the methanol as solvent.

Cobalt(II) Complex Constructed from Pyrazinecarboxamide and Aromatic Carboxylic Acid: Synthesis, Single Crystal XRD Along with Computational Study

A cobalt (II) mononuclear complex was synthesized by two-nitrobenzoic acid and pyrazine-two- carboxamide ligands in the presence of sodium bicarbonate and aqueous solution of cobalt acetate tetrahydrate. The synthesized cobalt(II) complex was characterized by single crystal X-rays diffraction. The coordination geometry of the cobalt complex was octahedral with water molecules occupying the axial sites. A lot of intermolecular interactions were in response to stabilize the supramolecular assembly which were inspected by Hirshfeld surface analysis. Enrichment ratios were calculated to find the pair of atoms having the highest propensity to form crystal packing interactions. Void analysis was conducted to forecast how the crystal would respond to applied stress. Interaction energy calculations were carried out using the B3LYP/6-31G(d,p) electron density model to identify which energy types most significantly contributed to the supramolecular assembly. Moreover, the energy data obtained from DFT calculations showed an average level of stability of the molecule. The moderate HOMO-LUMO energy gap suggested reactivity, while a high electrophilicity index indicates a strong tendency for electron-accepting reactions.

Supramolecular structure, DFT calculation and vibrational characterization of melamin-1-ium oxalurate monohydrate

Crystallization from an aqueous solution of melamine with parabanic acid was taken in a molar ratio of 1:1 leads to the formation of melamin-1-ium oxalurate monohydrate (MOX) crystals. The compound crystallizes in the centrosymmetric space group P21/n of the monoclinic system with four molecules per unit cell. The molecular geometry and vibrational frequencies of MOX in the ground state have been calculated by using the density functional hybrid function B3LYP 6–31+G(d) basis set. The results of optimized molecular structure are presented and compared with the experimental X-ray diffraction data. Furthermore, Fourier Transform Infrared (FT-IR) and Raman Spectra were used to conduct vibrational characterization to study the compound's structural groups. The calculated Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies show that charge transfer occurs in the molecule and other related electronic properties have also been calculated. Besides, Molecular Electrostatic Potential (MEP) was performed to identify the possible electrophilic and nucleophilic sites. First order hyperpolarizability results establish the nonlinear response of the grown MOX crystal with respect to the electric field. Further, the crystal packing behaviour of MOX was studied quantitatively with the aid of Hirshfeld surface analysis.

A Magnesium Organic Framework Fluorescent Sensor for Selective Detection of Nitrofuran Antibiotics and Inorganic Pollutants

ABSTRACTA novel 3D magnesium‐based metal organic framework (Mg‐MOF) has been solvothermally synthesized using 5‐(pyridin‐4‐yl)isophthalic acid. The ligand has demonstrated to preserve two types of coordination modes depending on the connection mode of the pyridine group. The uncoordinated pyridine groups provide Lewis base sites (LBSs), whereas the coordinated ones promote to form a rarely reported eight‐connected tetranuclear Mg clusters. Benefiting from the multinuclearity with high number of connections, the framework keeps good performance of high thermal stability until 500°C. Furthermore, the framework exhibits potential open metal sites (OMSs) benefiting from the terminal coordinated water groups of the metal clusters. Owing to the abundant active sites, the Mg‐MOF exhibits good sensitivity to nitrofuran antibiotics and Cr2O72−, with high KSV (at 104 M−1 level) and low limit of detection (LOD) values (∼10−6 M). Density functional theory (DFT) investigation reveals that the interchange of the HOMO–LUMO energy levels of the framework and antibiotics is responsible for the sensing activity. In addition, the Mg‐MOF is greatly recyclable in five cycles while maintaining the structural rigidity and sensing activity, making it a promising luminescence probe material.

Enhancing Magnetic Ordering in Two-Dimensional Metal-Organic Frameworks via Frontier Molecular Orbital Engineering.

Two-dimensional (2D) metal-organic frameworks (MOFs) have promise for use in lightweight permanent magnets in contrast to inorganic solid- or molecule-based magnets, but the realization of 2D MOF magnets with a high ordering temperature is limited by the typically weak spin exchange interactions. Here, we have proposed a frontier molecular orbital engineering strategy for modulating magnetism in 2D MOFs. It shows that the magnetic ground state can be mediated by two intra-atomic spin exchange pathways in organic ligands, akin to the Bloch and Heisenberg models, depending on the shape of the frontier orbitals of the organic ligands. By engineering the shape of the lowest unoccupied molecular orbital (LUMO) via chemical hydrogenation, we achieved a nearly 11-fold increase in the ordering temperature. In particular, a quantitative analysis shows that the ordering temperature increases linearly with the orbital delocalization index of the ligands' LUMO. This work suggests a general frontier orbital engineering approach for modulating the spin exchange interaction in 2D MOF magnets.

Exploring Spectral and Electrochemical Behavior of Hydroxy‐N‐Benzylideneanilines by Integrated Theoretical and Experimental Approaches

ABSTRACTThe present work explored the effect of –OH group substitution (o/p) on the spectral and electrochemical behavior of N‐benzylideneaniline. The geometry optimization of unsubstituted and (o/p)‐OH‐substituted analogs revealed the coplanarity of the molecules. The vibrational spectra of the compounds were computed using density functional theory (DFT) and compared with the experimental data. The observed bands were assigned based on total energy distribution (TED). Predicted electronic absorption spectra from time‐dependent density functional theory (TD‐DFT) calculation were compared with the UV–visible spectra of the molecules. The analysis of the lowest spin‐allowed (singlet‐singlet) excited states divulged possible electronic transition. The o‐substituted benzylideneaniline possessed the lowest highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap among the substituted and unsubstituted analogs. The intramolecular contacts were interpreted using natural bond orbital and localized molecular orbital analysis. The –CH=N– linkage was investigated as a bridge for the electron delocalization from the donor to acceptor moieties. The manifestation of a reduction peak in the cyclic voltammetric studies confirmed the electrochemical behavior in the –OH‐substituted molecule, which was diffusion‐controlled. The discrepancy in the electrochemical property concerning the position of the –OH substituent of the candidate molecules was put forward.

N-phenethyl-2-(1H-1,2,3-triazol-1-yl)acetamide derivatives: Synthesis, crystal structure and molecular docking studies against SARS-CoV-2

Novel N-phenethyl-2-(1H-1,2,3-triazol-1-yl)acetamide derivatives were synthesized via Copper(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition, commonly known as CuAAC. These triazoles were then characterized using Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), and Mass Spectrometry (MS). The crystal structures of ten compounds were elucidated through single-crystal X-ray diffraction (SCXRD). Computational calculations, based on Density Functional Theory (DFT), were employed to optimize the molecular structures. The energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were also determined. Additionally, molecular docking studies revealed the binding interactions of the most potent triazole with the active sites of key molecular targets. The findings indicated that the newly synthesized triazoles exhibit promising inhibitory activity against SARS-CoV-2 proteases 3-chymotrypsin-like protease (3CLpro), papain-like protease (PLpro), and helicase, outperforming the co-crystallized ligand.

Synthesis, spectral characterization, anti-cancer activity evaluation, and molecular docking of substituted 1,2-bis(3-butyl-2,6-diphenylpiperidin-4-ylidiene)hydrazone derivatives

A series of 1,2-bis(3‑butyl‑2,6-diphenylpiperidin-4-ylidiene)hydrazone derivatives of the substituted compounds 1–7, were confirmed by the characterization of IR & 1H-, NMR spectrum, together with X-ray crystallography and Mass spectroscopy also incredibly revealed. Docking analysis of the synthesized compounds employed under the protein from PDB code as 5cqh1, 4i40, 5fan, 7nud, 6Ya1 offers more inhibition values from 2D and 3D structures of the compounds, followed by Anti-cancer activity of the carcinoma cell line displayed that, highly potent to be active in nature. The in-vitro performance of -Cl substituted compound 6 (high anticancer activity) was in good correlation with its protein binding behaviour (strong binding). The increasing order of anticancer effect was 5>7>1>2>4>3>6 and the increasing order of binding ability on proteins were 7>3>4>1>2>5>6. The computational investigations were aligned with experimental techniques using Density Functional Theory (DFT) with a 6–31 G (d, p) basis set. Calculated Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies revealed Mulliken charges and charge transfer phenomena occurring within the molecule. Analysis of the Molecular Electrostatic Potential (MEP) unveiled reactive sites, with high electron density regions depicted in red and low electron density regions in blue.

Mechanistic and thermodynamic studies on directing group-assisted copper-catalyzed α-C(sp2)−H amination of aryl amines with alkylamines

In mechanistic, three possible pathways of α-C(sp[2])−H functionalization amination of picolinamide with morpholine catalyzed by Cu(OAc)2/O2 in p-xylene were studied. Through theoretical calculations, it was found that the pathway involving the radical-cation intermediates produced by the subsequent single electron transfer (SET) was proved to be the most favorable. Then, we also discussed the solvation and substituent effects of three key steps, including N − H bond deprotonation, C − N bond formation rate-determining step and C − H bond deprotonation step, so as to fully understand the mechanism of directing group-assisted copper-catalyzed α-C − H functionalization of aniline and the screening of substrates and solvents. In thermodynamic, the SET process plays a crucial role in the entire catalytic cycle. Therefore, we further studied the reduction potential (Ered) values of Cu(II) radical-cation intermediates involved in the SET process, reflecting the occurrence trend of SET from the thermodynamic point of view, and studied the substituent effects and structure-activity relationships on Ered values of Cu(II) complexes derivatives formed by different Cu(Ⅱ) catalysts, different directing groups, different alkylamines and aromatic amines substrates. It is also found that there are many quantitative structure-activity relationships between Ered and the singly occupied molecular orbital (SOMO) energy, Hammett substituent constant σ+ and other structural parameters.

Synthesis and evaluation of the anti-TB activity of novel 7-(2-(4-substituted-phenyl)-4,5-diphenyl-1H-imidazol-1-yl)-4-methyl-2H-chromen-2-one derivatives and their DFT studies for NLO application

A series of novel 7-(2-(4-substituted-phenyl)-4,5-diphenyl-1H-imidazol-1-yl)-4-methyl-2H-chromen-2-one derivatives 5(a-g) have been synthesized and reported as anti-TB activity and non-linear optical applications. The activity results show that compounds 5b, 5c, 5d, 5f, and 5g exhibited excellent efficacy with a MIC value of 3.12 μg/mL, one-fold greater than the reference standard streptomycin (6.26 μg/mL). An in silico molecular docking study was performed against InhA protein and the results were consistent with the experimental results. Computational studies were performed using the DFT method and results reveal that the presence of greater electronegativity atoms increases the HOMO-LUMO energy gap. The NLO properties show that the presence of stronger electron-donating substituents increases the ICT, charge delocalization and β0 values. The NBO analysis shows significant interactions between LP (Lone pair), π* and σ* in compounds account for the high polarization and enhanced NLO activity.

Photo- and Electrocatalytic Hydrogen Evolution by Heteroleptic Dirhodium(II,II) Complexes: Role of the Bridging and Diimine Ligands.

A series of heteroleptic Rh2(II,II) complexes, cis-[Rh2(μ-DPhF)2(μ-bncn)2]2+ (1; bncn = benzo[c]cinnoline), cis-[Rh2(μ-DPhF)(μ-OAc)(μ-bncn)2]2+ (2), and cis-[Rh2(μ-OAc)2(μ-bncn)2]2+ (3), is presented, and the excited state and redox properties of each complex was characterized for the photo- and electrocatalytic production of H2. The oxidation potentials shift anodically from 1 to 3, consistent with a highest occupied molecular orbital (HOMO) with significant metal-ligand mixing, Rh2(δ*)/DPhF(π/nb). In contrast, modest differences in the first two bncn-localized reversible reduction potentials were observed in 1 - 3. The lowest energy metal/ligand-to-ligand charge transfer (1ML-LCT) transition, Rh2(δ*)/DPhF(π/nb) → bncn(π*), shifts from 633 nm in 1 to 553 nm in 2, and the metal-to-ligand charge transfer (1MLCT) Rh2(π*) → bncn(π*) absorption in 3 appears at 462 nm in CH3CN. Although the 3ML-LCT excited state of 2 is shorter lived than that of 1, 2.7 ns as compared to 19 ns, respectively, photocatalytic hydrogen generation is observed for the former upon 595 nm irradiation in the presence of 0.1 M TsOH (p-tolylsulfonic acid) and 0.1 M BNAH (1-benzyl-1,4-dihydronicotinamide). The temperature dependence of the 3ML-LCT lifetimes of 1 and 2 shows the presence of a thermally accessible deactivating state. In addition, the singly reduced intermediate, [2]-, is photoactive and able to generate hydrogen in the presence of TsOH. Importantly, the electrocatalytic currents generated by equimolar concentrations of 1 - 3 in CH3CN are nearly identical, consistent with a mechanism of catalysis that is localized on the bncn ligand and does not require a Rh-H hydride intermediate. This finding can be used to develop earth-abundant first-row transition metal complexes for photo- and electrocatalytic H2 production.

Optimizing non-fullerene acceptor molecules constituting fluorene core for enhanced performance in organic solar cells: a theoretical methodology.

Looking for novel outstanding performance materials suitable for organic solar cells, we constructed a range of non-fullerene acceptors (NFAs) evolved from the recently synthesized acceptor molecule identified as DICTIF, structured around fluorene core where 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene) propanedinitrile presented the terminals end-groups. Employing density functional theory (DFT) and time dependent-DFT (TD-DFT) simulations, we have simulated the impact of altering the end groups of DICTIF molecule by five assorted acceptors molecules, for the purpose of exploring their opto-electronic properties and their performance in organic solar cell (OSC) applications. We proved that the designed non-fullerene acceptors provide enhanced efficiency compared to the synthesized molecule, such as planar geometries and narrower energy gap ranging from 1.51 to 1.95 eV. A red shift in absorption was observed for all tailored molecules (λmax = 583.5-711.4 nm) as compared to the reference molecule (λmax = 578 nm).Various decisive factors such as frontier molecular orbitals (FMOs), exciton binding energy (EB), absorption maximum (λmax), open circuit voltage (VOC), reorganization energies (RE), transition density matrix (TDM), reduced density gradient (RDG), and electron-hole overlap have also been computed for analyzing the performance of NFAs. Low reorganizational energy values facilitate charge mobility which improves the conductivity of all the designed molecules. This study showed that our novel tailored molecules might be suitable candidates for the fabrication of highly efficient photovoltaic materials. After testing various hybrid functionals, optimized geometries were assigned using DFT HSEH1PBE/6-31G(d) level of theory. Electronic excitations and absorption spectra were investigated using the TD-DFT MPW1PW91/6-31G(d) level of theory. We ascertained that HSEH1PBE/6-31G(d) level of theory yield the closest calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the DICTIF to the corresponding experimental ones and that TD-MPW1PW91//6-31G(d) was the most suitable level of theory for exploring electronic excitations and finding the maximum of absorption (λmax).

DFT insights into the nonlinear optical properties of azulene-stilbene dyads for photonics and optoelectronics

The present study aims to investigate the nonlinear optical characteristics of a series of azulene-stilbene chromophores through the utilization of density functional theory (DFT). Various acceptor substitution techniques were used to enhance first, second, and third order static and dynamic polarizabilities of the parent azulene-stilbene dyad (AS). The natural transition orbitals and UV-Visible absorption spectra were analyzed using time dependent-density functional theory (TD-DFT). Theoretical computations were performed to analyze the structural, electronic, and charge transfer properties of all designed compounds. The energy gap separating the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the designed moieties was observed to decrease in the new compounds compared to the parent compound. Analysis of the nonlinear optical (NLO) data among the designed compounds (AS1-AS10) revealed that AS2, AS3, AS4, and AS10 exhibit promising second and third order NLO characteristics, with AS6 exhibits suitability as a second order NLO material and AS8 and AS9 display third order NLO responses. The computed static and dynamic NLO parameters and maximum absorption wavelength closely match the experimentally reported data in the literature, suggesting these derivatives are excellent candidates for photonic and optoelectronic applications in the future.

Effect of Electron-Donating Substituents and an Electric Field on the ΔEST of Selected Imidazopyridine Derivatives: A DFT Study.

A series of thermally activated delayed fluorescent (TADF) molecules having an imidazopyridine acceptor, a benzene linker, and a 9,9-dimethyl-9,10-dihydroacridine donor are designed and examined using a quantum chemical approach. The above framework spatially separates the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), minimizing their overlap, ultimately resulting in a reduced energy gap between the excited singlet and triplet states (ΔEST). The impact of electron-donating substituents (-Me, -Et, -t-Bu, -OMe, and -NMe2) on the donor moiety of the parent molecule 2-(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)imidazo[1,2-a]pyridine-3,6-dicarbonitrile (Ac-CNImPy) is investigated. The calculated results revealed that for a given substituent, the para-substituted derivatives exhibit relatively less ΔEST, compared to that of the respective ortho- and meta derivatives. The value of ΔEST decreased with an increase in the electron-donating capacity of the substituent. Additionally, the ΔEST of the disubstituted derivatives is found to be less than that for the monosubstituted derivatives. The charge transport studies revealed that molecules with strong electron-donating substituents act as electron transporters. The effect of an external electric field (EEF) on ΔEST of the parent molecule Ac-CNIMPY and its derivative is also examined and revealed that the ΔEST can be further reduced by applying an electric field of appropriate strength in a direction perpendicular to the dipole moment of the molecule and in the plane of the acceptor moiety.

Quantitative analysis of the density of states distribution in N-type polymer filed-effect transistor

In the advancement of polymer field-effect transistors, both p-type and n-type polymer transistors are indispensable because they are the basic components of complementary metal oxide semiconductor (CMOS) logic circuitry. The scarcity of research on the interface properties of n-type polymer transistors, particularly regarding their density of state (DOS) distribution hinders the device modeling and further optimization of n-type polymer transistor. Consequently, the focus on understanding and investigating n-type polymer transistors interface properties holds substantial value and relevance, as it fills a critical knowledge gap in the polymer transistors. In view of this, an n-type poly((N,N0-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,50-(2,29-bisthiophene)) (N2200) polymer transistor was fabricated and a dynamic quantitative measurement method was utilized to investigate the DOS distribution of polymer transistors. Comparative analyses were conducted on the drain current (ID), carrier charge (Q), and DOS with varying pulse fall times (Tf). Variations in pulse fall times revealed significant differences in the DOS near the edge of the lowest unoccupied molecular orbital (LUMO), with a maximum DOS of 8 × 1013 cm−2 eV−1 observed at Tf = 1000 μs and a maximum of 2 × 1013 cm−2 eV−1 at Tf = 100 μs. By using different Tf, an effective method was successfully utilized for analyzing the effects of water and oxygen molecules on the DOS distribution of n-type polymer transistors.

The effect of fluorinated conjugated side chains on the photovoltaic performance of polymers based on benzodithiophene (BDT) and carbazolobistriazole (CTA)

Reasonable regulation of the structure-performance relationship is extremely crucial to enhancing the device performance of organic solar cells (OSCs). As a novel fused-benzotriazole (BTA) electron-accepting (A) unit, carbazolobistriazole (CTA) has excellent luminescent properties, and the alkyl chains on the three N atoms allow flexible modulation of polymer solubility. However, higher molecular energy levels and weak crystallinity restrict the enhancement of device performance. Herein, a new donor polymer PE97 with CTA as A unit and 4,8-bis(4-(2-ethylhexyl)-3,5-difluorophenyl)benzo[1,2-b:4,5-b’]dithiophene (BDT-P2F) as electron-donating (D) unit was designed and synthesized. In comparison with the first CTA-based polymer PE93 with 4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b’]dithiophene (BDT-TF) as D unit, PE97 realizes stronger molecular stacking conducive to modulation of the active layer morphology and a deeper highest occupied molecular orbital (HOMO) level, which are favorable to increase short-circuit current density (JSC) and open-circuit voltage (VOC) of OSCs. When paired with Y-series non-fullerene acceptor eC9-2F, PE97-based OSC devices have achieved a higher power conversion efficiency (PCE) of 15.5 %, with a VOC of 0.81 V, a JSC of 25.3 mA cm−2, and a fill factor (FF) of 75.7 %, which figures significantly surpass efficiency (13.6 %) of PE93-based devices. These results indicate that the BDT-P2F unit can excellently modulate the optoelectronic properties of CTA-based polymers. This highlights the potential of the BDT-P2F as a promising D unit for polymers with weak crystallinity and limited electron-withdrawing properties.

Influence of Multiple rISC Channels on the Maximum Efficiency and Roll-Off of TADF OLEDs.

In this work, we look into the detailed photophysical characterization of a multidonor-acceptor (D-A) family of thermally activated delayed fluorescent (TADF) emitters to find correlations with their device performance. Increasing the number of closely packed Ds around the A core leads to changes in dihedral angles between Ds and A, affecting the highest occupied molecular orbital (HOMO)/lowest unpccupied molecualar orbital (LUMO) separation and impacting the singlet-triplet energy gaps. Moreover, D-A dihedral angles change molecular conjugation affecting the spread of charge-transfer state energies as well as the energy of D local triplet states. The coupling between these triplet states and the dispersion in CT states lead to the appearance of multiple rISC channels, a phenomenon that is host-dependent, i.e., hosts with different rigidities twist the dihedral angles differently. We show that different subsets of rISC rates directly impact device performance, where faster rISC leads to external quantum efficiencies above 20% while slower rISC rates act as parasitic traps, severely affecting device roll-off. This explains why emitters with excellent peak external quantum efficiencies can also present very poor roll-off.

Investigation of heterocyclic azo dyes for dye-sensitized solar cells and non-linear optical properties: Synthesis and in-silico studies

Four thiophene-based donor-π-azo-acceptor dyes were designed and synthesized with benzoic and salicylic acids anchoring groups for dye-sensitized solar cells (DSSC). The results show that the orientation of the secondary donor significantly affects molecular planarity, which in turn affects the characteristics of charge transfer (CT) inside the backbones of thiophene-azo-benzoic or salicylic acids. These results have been confirmed by the time-dependent density functional theory (TD-DFT) study, which shows that the dyes' vertical absorption maximum increases as the secondary donors' providing strength increases. Photovoltaic parameters indicate an increase in DSSC performance from PG9 to PG12. Moreover, dye@TiO2 cluster investigations suggest that these dyes could combine with TiO2 to cause dye@TiO2 cluster absorbance to shift red.The synthesis of PG9 to PG12 confirms theoretical predictions, with initial absorption in dimethylformamide (DMF) and energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) following a pattern like that seen in density functional theory (DFT) investigations. According to TGA data, PG9 to PG12 have exceptional thermal stability, making them suitable for DSSCs. The built-in DSSCs had varying efficiencies; PG10 had the highest efficiency at 4.73 ± 0.1, and PG12 had the lowest at 1.72 ± 0.1. According to the theoretical and practical DSSC results, secondary donors are essential in defining molecular properties and device performance.

Large Orbital Moment and Dynamical Jahn-Teller Effect of AlCl-Phthalocyanine on Cu(100).

Submonolayer amounts of chloroaluminum-phthalocyanine on Cu(100) were studied with scanning tunneling spectroscopy. The molecule can be prepared in a fourfold symmetric state whose conductance spectrum exhibits a zero-bias feature similar to a Kondo resonance. In magnetic fields, however, this resonance splits far more than expected from the spin of a single electron. Density functional theory calculations reveal a charge transfer of 1.3 electrons to the degenerate lowest unoccupied molecular orbitals. These orbitals are mixed by the orbital momentum operator L[over ^]_{z} with a large matrix element corresponding to m_{L}≈2.7. Dehydrogenation of a ligand lifts the degerenracy of the lowest unoccupied molecular orbital, reduces the splitting in magnetic fields, and induces a polarity dependence of the spectra. Using model calculations of the spin, orbital, and vibrational degrees of freedom we show that a dynamical Jahn-Teller effect reproduces the main experimental observations.