Electronic and Charge Transport Properties of <i>peri</i>-Xanthenoxanthene: The Effects of Heteroatoms and Phenyl Substitutions

The electronic and charge transport properties of <i>peri</i>-xanthenoxanthene (PXX) and its phenyl-substitued derivative (Ph-PXX) are explored via quantum chemical calculations. To gain a better understanding of the physical properties of PXX, a comparative study is performed for its analogue, that is, anthanthrene. By employing Marcus electron transfer theory coupled with an incoherent charge hopping and diffusion model, we estimate the charge mobilties of PXX and Ph-PXX. Our calculated results indicate that the introduction of a heteroatom (oxygen) at the reactive sites of anthanthrene can stabilize the extended π-system and improve the effiecient charge injection in electronic devices. The phenyl substitution of PXX makes a remarkable change of charge transport characteristics from a <i>p</i>-type semiconductor to an <i>n</i>-type semiconductor, which shed light on molecular design for an <i>n</i>-type semiconductor through simple chemical structural modification

Terminal Modulation of D−π–A Small Molecule for Organic Photovoltaic Materials: A Theoretical Molecular Design

A class of D−π–A–A type small-molecule donor materials used in heterojunction solar cell has been designed and investigated by means of quantum chemical calculations. A linear D−π–A molecule containing triphenylamine (TPA), ethynylbenzene (EB), and diketopyrrolopyrrole (DPP) is end-capped with various electron acceptors to further enhance its electron-accepting capability. To gain a better understanding of the effects of terminal acceptors on the modulation of electronic and optical properties of D−π–A molecule, the geometrical structures, light-absorbing capacities, frontier orbitals, exciton binding energies, intramolecular charge transfer (ICT) properties, and exciton dissociation rates at the interface are analyzed in detail to establish the structure–property relationships for D−π–A–A type materials. The calculated results indicate that the terminal modulation is an effective strategy to enhance light-absorbing capacities, ICT properties, and exciton dissociation at the heterojunction interface. The predicted power conversion efficiency (PCE) of designed molecules by Scharber diagram could reach up to more than 8%, which sheds light on the exploration of high-performance small-molecule donors for photovoltaic applications

Effects of Sulfur Oxidation on the Electronic and Charge Transport Properties of Fused Oligothiophene Derivatives

Comparative studies of a series of oligothiophenes and their oxidized compounds are carried out by means of quantum chemical calculations. Taking aim at the effects of chemical oxidation of thienyl sulfur on the modulation of electronic structures and charge transport properties of oligothiophenes, the geometrical structures, molecular reorganization energies upon gaining or losing electrons, molecular ionization potentials (IPs) and electron affinities (EAs), molecular aromaticities, frontier molecular orbitals, and charge mobilities are analyzed in detail to determine the structure–property relationships for the investigated oligothiophenes and their corresponding oxidized counterparts. The calculated results show that the oxidation of thienyl sulfur into the corresponding <i>S</i>,<i>S</i>-dioxide could possibly change the charge transport characteristics of fused oligothiophene from hole transporting materials to bipolar or electron transporting materials, shedding light on the exploration of n-type thiophene-based semiconductors

Modulation of Electron-Donating Ability in D–A–A Small Molecules for Application in Organic Solar Cells

Comparative studies of a class of dithienopyrrole (DTP)-based D–A–A type small-molecule donor materials used in heterojunction solar cell have been carried out by means of quantum chemical calculations. The chemical modification of DTP group will be expected to modulate the electron-donating ability of D–A–A small molecules. To gain a better understanding of the effects of structural modification of DTP on the photophysical properties and the photovoltaic performance, the geometrical and electronic structures, absorption spectra, energy loss, intramolecular charge transfer, exciton dissociation and charge recombination rates at the interface, and hole-transport properties are analyzed in detail to establish structure–property relationships for the investigated D–A–A molecules. This work provides an intuitive explanation why the modification of DTP could modulate the frontier orbital levels, light-absorbing capacities, intra- and intermolecular charge-transfer properties, and interfacial exciton dissociation and recombination. The calculated results also demonstrate that the fine tuning of the electron-donating ability of small-molecule donor material could be an effective approach to improving the cell performance. This study could give theoretical guidelines for molecular design and pave the way to synthesize efficient small-molecule donor materials

Dynamics-Driven Controlled Polymerization to Synthesize Fully Renewable Poly(ester–ether)s

Producing aromatic poly­(ester–ether)­s from completely renewable feedstocks is almost inaccessible via existing ring-opening polymerization or melt polycondensation methods. Herein, we report a practical strategy to synthesize fully bio-based poly­(ester–ether)­s in a one-pot/two-component manner via industrial melt polycondensation. The polymerization process was controlled by applying Sc­(OTf)3 as a catalyst and bio-based 2,5-furandicarboxylic acid and ethylene glycol as the substrate template to afford poly­(ester–ether)­s with a controlled oligoethylene glycol segment in the range from 10 to 92%. Studying the mechanism and model kinetics of Sc­(OTf)3-catalyzed etherification reactions provided complete insights into the formation process and impetus of poly­(ester–ether)­s, validating that a “butterfly effect” occurred in the reaction process. In contrast to flexible conventional polyethers, computational studies revealed that the unique rigidity of the etherification moiety leads to superior thermal and mechanical properties of poly­(ester–ether)­s. This synthetic protocol demonstrates applicability and versatility, exemplified by using various bio-based diacids/diesters to synthesize a series of poly­(ester–ether)­s. We envisage that this work will improve the privileged position that renewable poly­(ester–ether)­s hold as functional materials and broaden their applicability in diverse fields

Unraveling the Marked Differences of the Excited-State Properties of Arylgold(III) Complexes with C^∧N^∧C Tridentate Ligands

Three structurally similar gold(III) complexes with C∧N∧C tridentate ligands, [1; C∧N∧C = 2,6-diphenylpyridine], [2; C∧N∧C = 2,6-diphenylpyrazine], and [3; C∧N∧C = 2,6-diphenyltriazine], have been investigated theoretically to rationalize the marked difference in emission behaviors. The geometrical and electronic structures, spectra properties, radiative and nonradiative decay processes, as well as reverse intersystem crossing and reverse internal conversion (RIC) processes were thoroughly analyzed using density functional theory (DFT) and time-dependent DFT calculations. The computed results indicate that there is a small energy difference ΔET1−T1′ between the lowest-energy triplet state (T1) and the second lowest-energy triplet state (T1′) of complexes 2 and 3, suggesting that the excitons in the T1 state can reach the emissive higher-energy T1′ through the RIC process. In addition, the non-emissive T1 states of gold(III) complexes in solution can be ascribed to the easily accessible metal-centered (3MC) state or possibly tunneling into high-energy vibrationally excited singlet states for nonradiative decay. The low efficiency of 3 is attributed to the deactivation pathway via the 3MC state. The present study elucidates the relationship between structure and property of gold(III) complexes featuring C∧N∧C ligands and providing a comprehensive understanding of the significant differences in their luminescence behaviors

Theoretical Study of Isomerism/Phase Dependent Charge Transport Properties in Tris(8-hydroxyquinolinato)aluminum(III)

The charge carrier transporting ability in the polymorphism of tris(8-hydroxyquinolinato)aluminum(III) (Alq3) has been studied using density functional theory (DFT) and Marcus charge transport theory. α- and β-Alq3 composed of mer-Alq3 molecules have stronger electron-transporting property (n-type materials) compared with their hole-transporting ability. In contrast, γ- and δ-Alq3 formed by fac-Alq3 molecules possess stronger hole-transporting character than their electron-transporting ability. The detailed theoretical calculations indicate the reason lies in the differences of HOMO and LUMO distribution states of the two kinds of isomers, and the different molecular packing modes of charge-transporting pathways for different phases

2‑(2-Hydroxyphenyl)benzimidazole-Based Four-Coordinate Boron-Containing Materials with Highly Efficient Deep-Blue Photoluminescence and Electroluminescence

Two novel four-coordinate boron-containing emitters <b>1</b> and <b>2</b> with deep-blue emissions were synthesized by refluxing a 2-(2-hydroxyphenyl)­benzimidazole ligand with triphenylborane or bromodibenzoborole. The boron chelation produced a new π-conjugated skeleton, which rendered the synthesized boron materials with intense fluorescence, good thermal stability, and high carrier mobility. Both compounds displayed deep-blue emissions in solutions with very high fluorescence quantum yields (over 0.70). More importantly, the samples showed identical fluorescence in the solution and solid states, and the efficiency was maintained at a high level (approximately 0.50) because of the bulky substituents between the boron atom and the benzimidazole unit, which can effectively separate the flat luminescent units. In addition, neat thin films composed of <b>1</b> or <b>2</b> exhibited high electron and hole mobility in the same order of magnitude 10^–4, as determined by time-of-flight. The fabricated electroluminescent devices that employed <b>1</b> or <b>2</b> as emitting materials showed high-performance deep-blue emissions with Commission Internationale de L’Eclairage (CIE) coordinates of (<i>X</i> = 0.15, <i>Y</i> = 0.09) and (<i>X</i> = 0.16, <i>Y</i> = 0.08), respectively. Thus, the synthesized boron-containing materials are ideal candidates for fabricating high-performance deep-blue organic light-emitting diodes

Synthesis and Assembly with Mesoporous Silica MCM-48 of Platinum(II) Porphyrin Complexes Bearing Carbazyl Groups: Spectroscopic and Oxygen Sensing Properties

The synthesis and spectroscopic characterization of a series of luminescent platinum meso-tetrakis{3,5-di[(N-carbazyl)n-alkyloxyphenyl]}porphyrin (Pt-8Cn-TPP, n-alkyl = (CH2)n, n = 4, 6, and 8) are presented. The protonated platinum porphyrins ([Pt-8Cn-TPPH8]8+) were assembled with mesoporous silica MCM-48 resulting in the assembly materials [Pt-8Cn-TPPH8]8+/MCM-48. The luminescence of [Pt-8Cn-TPPH8]8+/MCM-48 can be extremely quenched by molecular oxygen with very high sensitivity (I0/I100 > 5000) and rapid response time (0.04 s) suggesting that the [Pt-8Cn-TPPH8]8+/MCM-48 system can be employed to develop high performance oxygen sensors. Among this assembly system, [Pt-8C8-TPPH8]8+/MCM-48 exhibits the highest sensitivity. Even if the concentration of oxygen is 0.1%, the luminescence intensity of [Pt-8C8-TPPH8]8+/MCM-48 can be quenched by 86%