Effect of π-Conjugated Length of Bridging Ligand on the Optoelectronic Properties of Platinum(II) Dimers

Two-Dimensional Metal-Organic Frameworks as Ultrahigh-Performance Electrocatalysts for the Fuel Cell Cathode: A First-Principles Study

Except for metal-organic frameworks (MOFs) with traditional metal-nitrogen sites, MOFs with metal-oxygen sites may also possess good oxygen reduction reaction (ORR) catalytic activity due to their unique electronic structures. Herein, using density functional theory methods, the ORR performances of a series of M₃(HHTT)₂ (where M is a 3d, 4d, or 5d transition metal and HHTT is 2,3,7,8,12,13-hexahydroxytetraazanaphthotetraphene)) catalysts are explored. The binding energy (ΔE_species) results suggest that the binding energy of *OH (ΔE_*OH) shows a good linear relationship with the binding energies of *O and *OOH (ΔE_*O and ΔE_*OOH, respectively), indicating that ΔE_*OH can serve as a descriptor to reflect the catalytic activity of M₃(HHTT)₂. In addition, the volcano plot suggests that M₃(HHTT)₂ catalysts with a moderate binding strength of the intermediate *OH (0.6 eV < ΔE_*OH < 0.9 eV) show relatively high ORR activity. Therefore, four highly active ORR catalysts are screened out, namely, Fe₃(HHTT)₂, Co₃(HHTT)₂, Rh₃(HHTT)₂, and Ir₃(HHTT)₂, which possess very small overpotentials of 0.35, 0.24, 0.31, and 0.29 V, respectively. Their potential-determining step is the reduction of O₂ to the intermediate *OOH. It is encouraging that the theoretically lowest overpotential of this kind of catalyst is 0.21 V, which is superior to that on Pt(111). Moreover, Co₃(HHTT)₂ has excellent poisoning-tolerance ability for impurity gases (CO, NO, and SO₂) as well as fuel molecules (CH₃OH and HCOOH).

Surface-Doped Quasi-2D Chiral Organic Single Crystals for Chiroptical Sensing

Chiral organic optoelectronics using circularly polarized light (CPL) as the key element in the photonic signal has recently emerged as a next-generation photonic technology. However, it remains challenging to simultaneously achieve high polarization selectivity and superior optoelectronic performance. Supramolecular two-dimensional (2D) chiral organic single crystals may be good candidates for this purpose due to their defect-free nature, molecular diversity, and morphologies. Here, quasi-2D single crystals of chiral perylene diimides with parallelogram and triangle/hexagon morphologies have been selectively fabricated via self-assembly using different cosolvent systems. These materials exhibit amplified circular dichroism (CD) spectral signals, due to their molecular packing modes and supramolecular chirality. Through molecular surface n-doping using hydrazine, chiral single crystals exhibit electron mobility surpassing 1.0 cm² V^-1 s^-1, which is one of the highest among chiral organic semiconductors, and excellent optoelectronic functions. Theoretical calculations reveal that the radical anions formed by n-doping increase the electron affinity and/or reduce the energy gap, thus facilitating electron transport. More importantly, the doped organic chiral crystals selectively discriminate CPL handedness with a high anisotropy factor of photoresponsivity (∼0.12). These results demonstrate that surface-doped quasi-2D chiral organic single crystals are highly promising for chiral optoelectronics.

End-capped group manipulation of indacenodithienothiophene-based non-fullerene small molecule acceptors for efficient organic solar cells

As the key component of organic solar cells (OSCs), the acceptor plays key roles in determining the power conversion efficiency (PCE). Based on the famous non-fullerene acceptor ITIC, a series of acceptors (A1-A5) were designed by introducing fused-ring units (phenanthrene, pyrene, benzopyrazine, dibenzo[a,c]phenazine, and phenanthro[4,5-abc]phenazine) as the end groups. Theoretical calculations showed that A1-A5 display improved solubility and redshifted absorption spectra compared with ITIC. More importantly, the newly designed acceptors exhibit much higher electron mobility, where the electron mobility of A5_h (similar to A5 but with the same hexyl side chain as ITIC) is about four orders of magnitude larger than that of ITIC. The computed binding energies of the donor PBDB-TF with the acceptor ITIC and A5_h are -2.52 eV and -3.75 eV, indicating much stronger interface interactions in PBDB-TF/A5_h. In terms of charge-transfer (CT) mechanism, we found that both PBDB-TF/ITIC and PBDB-TF/A5_h can generate CT states through direct excitation and hot excitons, meanwhile there exist more opportunities of producing CT states via the intermolecular electric field (IEF) mechanism in PBDB-TF/A5_h. Our results not only offer a set of promising ITIC-based acceptors, but also provide new insights into the donor/acceptor interface properties, which are closely related to the PCE of OSCs.

Halide exchange studies of novel Pd(ii) NNN-pincer complexes

Palladium(ii) complexes with an NNN type pincer ligand (pip2NNN = 2,6-bis(piperdyl-methyl)pyridine) are synthesized and characterized. Electronic and 1H NMR spectra point to decreasing filled/filled repulsions between the dπ(Pd) orbitals and the halide lone pair orbitals along the Cl < Br < I series. For all complexes, the most downfield α-piperidyl resonance of the pip2NNN ligand is sensitive to changes in the coordinated halide while the meta-pyridyl and benzylic resonances are sensitive to changes in the counter anion. This sensitivity is utilized to study halide association and exchange at the fourth coordination site. Conductivity and 1H NMR spectroscopy confirm the interaction between the exogenous anion (Cl-, Br-, BF4 -) and Pd(pip2NNN)X+ (X = Cl, Br).

Theoretical investigation of the electronic structure and photophysical properties of a series of Ir(iii) complexes bearing pentafluorosulfanyl groups

The electronic structure, absorption and emission spectra, charge injection/transport ability and phosphorescence quantum efficiency of a series of cyclometalated iridium(iii) complexes with different ancillary ligands are studied using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods.

Rigidified and expanded N-annulated perylenes as efficient donors in organic sensitizers for application in solar cells

Quantum calculations on rigidified and expanded NP-based dyes were carried out to establish the structure–property relationship.

Towards an efficient blue emission cationic Ir(iii) complex with azole-type ancillary ligands: a joint theoretical and experimental study

A highly efficient blue emitting cationic Ir(iii) complex based on 1,2,4-triazole-pyridine ligands modified by a simple methyl moiety is reported.

QM/MD simulations on the role of SiO2 in polymeric insulation materials

SiO₂ is an efficient electron-injection material and can help stabilize polyethylene in electric insulation materials.

The influence of numbers and ligation positions of the triphenylamine unit on the photophysical and electroluminescent properties of homoleptic iridium(III) complexes: a theoretical perspective

A DFT/TDDFT investigation was carried out on a series of homoleptic triphenylamine-featured Ir(iii) complexes [: (fac-tris[2-phenyl-4-(2-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2-phenyl-4-(3-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2-phenyl-4-(4-(N,N-diphenylamino)phenyl)pyridine]iridium(iii))] with one triphenylamine unit in the 2-phenylpyridine (ppy) ligand and [: (fac-tris[2,4-bis(2-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2,4-bis(3-(N,N-diphenylamino)phenyl)pyridine]iridium(iii)); : (fac-tris[2,4-bis(4-(N,N-diphenylamino)phenyl)pyridine]iridium(iii))] with two triphenylamine units in the ppy ligand, respectively, aiming to gain insight into the influence of number and ligation position of triphenylamine units on the photophysical and electronic properties of the studied complexes. Complexes have been synthesized recently. For comparison, the parent complex Ir(ppy)3 was also investigated. The calculated results reveal that the introduction of the triphenylamine unit leads to enhanced charge-injection abilities and a balanced charge-transfer process compared with Ir(ppy)3. The different ligation positions of triphenylamine unit have an obvious effect on the absorption intensities for these complexes. The emissions of and undergo significant red shift with the introduced triphenylamine unit in ppy ligands compared with that of Ir(ppy)3, while the extent of red shift shows an apparent dependence on the number of triphenylamine units. The factors that might affect the quantum yield have been discussed.

[M(rac-N-benzyl Asp)(H2O)] (M = Co, Ni): noncentrosymmetric coordination polymeric chains with racemic chiral ligands

The hydrothermal reaction of fumaric acid, benzylamine, and metal salts yielded M[(rac-N-benzyl-Asp)(H(2)O)] (M = Co, Ni), 1 and 2, and Ni[(rac-N-benzyl-Asp)(H(2)O)(3)]·H(2)O 3. Under mild hydrothermal conditions, Michael addition of benzylamine to fumaric acid led to the formation of a racemic mixture of N-benzyl aspartic acid enantiomers. The noncentrosymmetric structures of 1 and 2 consist of one-dimensional polymeric chains in which metal cations are bridged by d- and l-N-benzyl aspartate anions alternating along the chain. The centrosymmetric structure of 3 is composed of discrete Ni[(rac-N-benzyl-Asp)(H(2)O)(3)] units that are connected by hydrogen bonds into layers. The single layers are homochiral but are hydrogen bonded to similar homochiral layers that contain the N-benzyl aspartate with the opposite handedness. Compounds 1 and 2 showed second harmonic generation (SHG), and their magnetic and thermodynamic properties are described.