Jing-Shuang Dang

From Mononuclear to Dinuclear Iridium(III) Complex: Effective Tuning of the Optoelectronic Characteristics for Organic Light-Emitting Diodes

Phosphorescent dinuclear iridium(III) complexes that can show high luminescent efficiencies and good electroluminescent abilities are very rare. In this paper, highly phosphorescent 2-phenylpyrimidine-based dinuclear iridium(III) complexes have been synthesized and fully characterized. Significant differences of the photophysical and electrochemical properties between the mono- and dinuclear complexes are observed. The theoretical calculation results show that the dinuclear complexes adopt a unique molecular orbital spatial distribution pattern, which plays the key role of determining their photophysical and electrochemical properties. More importantly, the solution-processed organic light-emitting diode (OLED) based on the new dinuclear iridium(III) complex achieves a peak external quantum efficiency (η(ext)) of 14.4%, which is the highest η(ext) for OLEDs using dinuclear iridium(III) complexes as emitters. Besides, the efficiencies of the OLED based on the dinuclear iridium(III) complex are much higher that those of the OLED based on the corresponding mononuclear iridium(III) complex.

Thiazole-based metallophosphors of iridium with balanced carrier injection/transporting features and their two-colour WOLEDs fabricated by both vacuum deposition and solution processing-vacuum deposition hybrid strategy

New phosphorescent iridium(III) cyclometallated complexes bearing thiazole-based ligands (IrTZ1 and IrTZ2) have been developed. The functionalized organic ligands derived by combining the thiazolyl moiety and triphenylamino group have conferred not only favorable hole-injection/hole-transporting (HI/HT) features but also more balanced charge carrier injection/transporting traits to the as-prepared iridium(III) metallophosphors. Owing to the unique electronic structures afforded by the ligand, the orange organic light-emitting devices (OLEDs) made from IrTZ1 can furnish peak external quantum efficiency (ηext) of 14.82%, luminance efficiency (ηL) of 39.97 cd A−1 and power efficiency (ηp) of 34.95 lm W−1. Inspired by its outstanding electroluminescence (EL) performance, the orange IrTZ1 phosphor complemented with a blue phosphor FIrpic was employed to fabricate highly efficient white organic light-emitting devices (WOLEDs) with a single emission layer. Despite their simple device configuration, the optimized WOLEDs can still maintain decent electroluminescence (EL) ability with ηext of 7.20%, ηL of 18.07 cd A−1 and ηp of 19.57 lm W−1. With the aim to simplify the fabrication process of multi-layered WOLEDs, two-component WOLEDs were obtained through a novel solution processing–vacuum deposition hybrid method with the doped blue fluorescent emission layer deposited by a solution process and the orange phosphorescent emission layer made by vacuum deposition. The WOLEDs prepared using such exploratory approach can show an attractive EL performance with ηext of 9.06%, ηL of 22.72 cd A−1 and ηp of 17.28 lm W−1. All these data have indicated not only the great potential of the orange phosphor in monochromatic and white OLEDs, but also the importance of the hybrid method for simplifying WOLED fabrication.

Versatile phosphorescent color tuning of highly efficient borylated iridium(III) cyclometalates by manipulating the electron-accepting capacity of the dimesitylboron group

Several phosphorescent IrIII ppy-type complexes (ppy = 2-phenylpyridine anion) bearing dimesitylboron (B(Mes)2) units have been designed and some of them have been newly prepared. By changing the substitution positions with different electronic characters that can manipulate the electron-accepting ability of the attached B(Mes)2 moieties, the direction of the metal-to-ligand charge transfer (MLCT) process for these IrIII complexes can be either retained or shifted, which can provide a new strategy toward phosphorescent color tuning. Through computational studies, shifting the substitution position of the B(Mes)2 moiety on the organic ligand, some electronic features, such as the electron injection/electron transporting (EI/ET) properties and charge transport balance, can also be conferred to the phosphorescent IrIII complexes to give excellent electroluminescent (EL) characteristics. Highly efficient red phosphorescent bis(5-(dimesitylboryl)-2-phenylpyridinato)iridium(acetylacetonate) (Ir-B-1) based on the above notion shows a very good compatibility with the choice of host materials which can furnish maximum current efficiency (ηL) of 22.2 cd A−1, external quantum efficiency (ηext) of 14.7% and power efficiency (ηP) of 21.4 lm W−1 for the devices constructed with the conventional host materials. So, these exciting results will not only provide both the systematic guidelines for the phosphorescent color variation on the IrIII complexes with B(Mes)2 units as well as a deeper insight into the conventional color-tuning approach on ppy-type IrIII complexes, but also offer a simple outlet to afford unique electronic features to these phosphorescent emitters to show admirable EL performance.

Electrophosphorescent Heterobimetallic Oligometallaynes and Their Applications in Solution-Processed Organic Light-Emitting Devices

By combining the iridium(III) ppy-type complex (Hppy=2-phenylpyridine) with a square-planar platinum(II) unit, some novel phosphorescent oligometallaynes bearing dual metal centers (viz. Ir(III) and Pt(II)) were developed by combining trans-[Pt(PBu(3))(2)Cl(2)] with metalloligands of iridium possessing bifunctional pendant acetylene groups. Photophysical and computational studies indicated that the phosphorescent excited states arising from these oligometallaynes can be ascribed to the triplet emissive Ir(III) ppy-type chromophore, owing to the obvious trait (such as the longer phosphorescent lifetime at 77 K) also conferred by the Pt(II) center. So, the two different metal centers show a synergistic effect in governing the photophysical behavior of these heterometallic oligometallaynes. The inherent nature of these amorphous materials renders the fabrication of simple solution-processed doped phosphorescent organic light-emitting diodes (PHOLEDs) feasible by effectively blocking the close-packing of the host molecules. Saliently, such a synergistic effect is also important in affording decent device performance for the solution-processed PHOLEDs. A maximum brightness of 3,356 cd m(-2) (or 2,708 cd m(-2)), external quantum efficiency of 0.50% (or 0.67%), luminance efficiency of 1.59 cd A(-1) (or 1.55 cd A(-1)), and power efficiency of 0.60 Lm W(-1) (or 0.55 Lm W(-1)) for the yellow (or orange) phosphorescent PHOLEDs can be obtained. These results show the great potential of these bimetallic emitters for organic light-emitting diodes.

Dimetallic sulfide endohedral metallofullerene Sc2S@C76: Density functional theory characterization

In terms of density functional theory combined with statistic mechanics computations, we investigated a dimetallic sulfide endohedral fullerene Sc2S@C76 which has been synthesized without any characterization in experiments. Our theoretical study reveals that Sc2S@Td(19151)‐C76 which satisfies the isolated‐pentagon rule (IPR) possesses the lowest energy, followed by three non‐IPR structures (Sc2S@C2v(19138)‐C76, Sc2S@Cs (17490)‐C76, and Sc2S@C1(17459)‐C76). To clarify the relative stabilities of those isomers at high temperatures, enthalpy–entropy interplay has been taken into consideration. Calculation results indicate that three species Sc2S@Td(19151)‐C76, Sc2S@C2v(19138)‐C76, and Sc2S@C1(17459)‐C76 have noticeable molar fractions at the fullerene‐formation temperature region (500–3000K), and the Sc2S@C1(17459)‐C76 with one pentagon pair becomes the most predominant isomer above 1800 K, suggesting that the unexpected non‐IPR structure is thermodynamically favorable at elevated temperatures. In addition, the structural characteristics, electron features, UV‐vis‐NIR adsorptions, and 13C NMR spectra of those three stable structures are introduced to assist experimental identification and characterization in future.

Regioselective Derivatization of C84 by Diels–Alder Reactions: Applications to Photovoltaic Solar Cells and Fullerene Polymerization

Regioselective properties of a D2d-C84 in multistep [4 + 2] cycloadditions and the applications of bis-functional C84 derivatives were investigated. Density functional calculations demonstrate that an indene-C84 bisadduct is a promising electron acceptor in organic solar cells and a C84-bis-anthracene copolymer can be utilized as a charge-transfer material.

Open-Shell Triplet Character of #6094C68: Spherical Aromaticity, Thermodynamic Stability, and Regioselective Chlorination

The recently captured fullerene (#6094)C68 was found to exhibit a more aromatic character than originally assumed via density functional theory calculations. Such an inconsistency was attributed to the unexpected triplet ground state of pristine (#6094)C68. The equilibrium concentrations of C68 isomeric system reveal that (#6094)C68 is thermodynamically favorable at elevated temperatures with respect to the fullerene formation. The regioselective chlorination process of the open-shell C68 was discussed as well to elucidate the formation of octachlorinated derivative C68Cl8 experimentally.

Role of four-membered rings in C32 fullerene stability and mechanisms of generalized Stone-Wales transformation: a density functional theory investigation

Density functional theory (DFT) methods have been applied to study C(32) fullerenes built from four-, five-, and six-membered rings. The relative energies of pure C(32) fullerenes have been evaluated to locate three most stable structures, 32:D(4d) with two squares, 1:D(3) without square and 5:C(s) with one square. Structural analysis reveals that there is a rearrangement pathway between the lowest energy classical isomer 1:D(3) and the lowest energy non-classical isomer 32:D(4d), and 5:C(s) behaves just as an intermediate between them. The kinetic processes of generalized Stone-Wales transformation (GSWT) with four-membered rings have been explored and two distinct reaction mechanisms are determined by all the transition states and intrinsic reaction coordinates with PBE1PBE/6-31G(d) approach for the first time. One mechanism is the concerted reaction with a rotating dimer closed to the cage surface and another is the stepwise reaction with a carbene-like sp(3) structure, whereas the latter is sorted into two paths based on four-membered ring vanishing before or after the formation of the carbene-like structure. It is indicated that there is no absolute preference for any mechanism, which depends on the adaptability of different reactants on the diverse mechanisms. Furthermore, its found that the interconversion process with the participation of squares is more reactive than the rearrangement between C(60)_I(h) and C(60)_C(2v), implying some potential importance of non-classical small fullerenes in the fullerene isomerization.

Theoretical prediction of the host-guest interactions between novel photoresponsive nanorings and C60: a strategy for facile encapsulation and release of fullerene.

A series of photoresponsive‐group‐containing nanorings hosts with 12∼14 Å in diameter is designed by introducing different number of azo groups as the structural composition units. And the host–guest interactions between fullerene C60 and those nanoring hosts were investigated theoretically at M06‐2X/6‐31G(d)//M06‐L/MIDI! and wB97X‐D/6‐31G(d) levels. Analysis on geometrical characteristics and host–guest binding energies revealed that the designed nanoring molecule (labeled as 7) which is composed by seven azo groups and seven phenyls is the most feasible host for encapsulation of C60 guest among all candidates. Moreover, inferring from the simulated UV‐vis‐NIR spectroscopy, the C60 guest could be facilely released from the cavity of the host 7 via configuration transformation between trans‐form and cis‐form of the host under the 563 nm photoirradiation. Additionally, the frontier orbital features, weak interaction regions, infrared, and NMR spectra of the C60@7 host–guest complex have also been investigated theoretically.

Metal-promoted restoration of defective graphene

A novel metal-participating rearrangement mechanism of graphene is elucidated via density functional calculations. Results show that the barrier for the elimination of Stone–Wales defects can be decreased by the adsorbed transition metal atoms. Molecular orbital composition analysis shows that the contribution from the metal atom to the frontier orbital in the transition state is a key factor for the distinct metal catalytic properties. Among the chosen elements (Cu, Ni, Fe, Cr, Mo, and W), tungsten can reduce the activation energy remarkably from 6.2 to 2.9 eV, and 1000 K is regarded as a favorable temperature to yield perfect hexagonal nanographene. In contrast to curved network structures in fullerenes and carbon nanotubes, the open and planar structure of graphene helped to accommodate kinetic transformations of the carbon skeleton and metal atoms in favorable pathways.