Xiao-Yu Cao

Electron-Deficient Poly(p-phenylene vinylene) Provides Electron Mobility over 1 cm2 V-1 s-1 under Ambient Conditions

Poly(p-phenylene vinylene) derivatives (PPVs) are one of the most widely investigated p-type polymers in organic electronics. PPVs generally exhibit electron mobilities lower than 10(-4) cm(2) V(-1) s(-1), thus hindering their applications in high-performance polymer field-effect transistors and organic photovoltaics. Herein, we design and synthesize a novel electron-deficient PPV derivative, benzodifurandione-based PPV (BDPPV). This new PPV derivative displays high electron mobilities up to 1.1 cm(2) V(-1) s(-1) under ambient conditions (4 orders of magnitude higher than those of other PPVs), because it overcomes common defects in PPVs, such as conformational disorder, weak interchain interaction, and a high LUMO level. BDPPV represents the first polymer that can transport electrons over 1 cm(2) V(-1) s(-1) under ambient conditions.

A BDOPV-Based Donor-Acceptor Polymer for High-Performance n-Type and Oxygen-Doped Ambipolar Field-Effect Transistors

An electron-deficient building block BDOPV is developed to construct a new donor-acceptor conjugated polymer BDOPV-2T for high-performance n-type and oxygen-doped ambipolar polymer field-effect transistors. A high electron mobility up to 1.74 cm(2) V(-1) s(-1) is demonstrated under ambient conditions. Furthermore, the oxygen-doping effect and possible mechanism are discussed.

A straightforward strategy toward large BN-embedded π-systems: Synthesis, structure, and optoelectronic properties of extended BN heterosuperbenzenes

A straightforward strategy has been used to construct large BN-embedded π-systems simply from azaacenes. BN heterosuperbenzene derivatives, the largest BN heteroaromatics to date, have been synthesized in three steps. The molecules exhibit curved π-surfaces, showing two different conformations which are self-organized into a sandwich structure and further packed into a π-stacking column. The assembled microribbons exhibit good charge transport properties and photoconductivity, representing an important step toward the optoelectronic applications of BN-embedded aromatics.

The Chemistry of Aromatic Osmacycles

Aromatic compounds, such as benzene and its derivatives, porphyrins, fullerenes, carbon nanotubes, and graphene, have numerous applications in biomedicine, materials science, energy science, and environmental science. Metalla-aromatics are analogues of conventional organic aromatic molecules in which one of the (hydro)carbon segments is formally replaced by an isolobal transition-metal fragment. Researchers have studied these transition-metal-containing aromatic molecules for the past three decades, particularly the synthesis and reactivity of metallabenzenes. Another focus has been the preparation and characterization of other metalla-aromatics such as metallafurans, metallapyridines, metallabenzynes, and more. Despite significant advances, remaining challenges in this field include the limited number of convenient and versatile synthetic methods to construct stable and fully characterized metalla-aromatics, and the relative shortage of new topologies. To address these challenges, we have developed new methods for preparing metalla-aromatics, especially those possessing new topologies. Our synthetic efforts have led to a large family of closely related metalla-aromatics known as aromatic osmacycles. This Account summarizes the synthesis and reactivity of these compounds, with a focus on features that are different from those of compounds developed by other groups. These osmacycles can be synthesized from simple precursors under mild conditions. Using these efficient methods, we have synthesized aromatic osmacycles such as osmabenzene, osmabenzyne, isoosmabenzene, osmafuran, and osmanaphthalene. Furthermore, these methods have also created a series of new topologies, such as osmabenzothiazole and osmapyridyne. Our studies of the reactivity of these osma-aromatics revealed unprecedented reaction patterns, and we demonstrated the interconversion of several osmacycles. Like other metalla-aromatics, osma-aromatics have spectroscopic features of aromaticity, such as ring planarity and the characteristic bond lengths between a single and double bond, but the osma-aromatics we have prepared also exhibit good stability towards air, water, and heat. Indeed, some seemingly unstable species proved stable, and their stability made it possible to study their optical, electrochemical, and magnetic properties. The stability of these compouds results from their aromaticity and the phosphonium substituents on the aromatic plane: most of our osma-aromatics carry at least one phosphonium group. The phosphonium group offers stability via both electronic and steric mechanisms. The phosphonium acts as an electron reservoir, allowing the circulation of electron pairs along metallacycles and lowering the electron density of the aromatic rings. Meanwhile, the bulky phosphonium groups surrounding the aromatic metallacycle prevent most reactions that could decompose the skeleton.

A Metal-Bridged Tricyclic Aromatic System: Synthesis of Osmium Polycyclic Aromatic Complexes†

Aromaticity is one of the most important concepts in organic chemistry. A variety of metalla-aromatic compounds have been recently prepared and in most of those examples, the metal participates only in a monocyclic ring. In contrast, metal-bridged bicyclic aromatic molecules, in which a metal is shared between two aromatic rings, have been less developed. Herein, we report the first metal-bridged tricyclic aromatic system, in which the metal center is shared by three aromatic five-membered rings. These metalla-aromatics are formed by reaction between osmapentalyne and arene nucleophiles. Experimental results and theoretical calculations reveal that the three five-membered rings around the osmium center are aromatic. In addition, the broad absorption bands in the UV/Vis absorption spectra of these novel aromatic systems cover almost the entire visible region. This straightforward synthetic strategy may be extended to the synthesis of other metal-bridged polycyclic aromatics.

Corannulene derivatives as non-fullerene acceptors in solution-processed bulk heterojunction solar cells

Corannulene derivatives were used in organic solar cells for the first time. Using Cor-PI and Cor-NI as acceptors, we achieved power conversion efficiencies up to 0.32% and 1.03%, suggesting potential applications of these fullerene segments as non-fullerene acceptors.

Conversions of osmabenzyne and isoosmabenzene.

We report herein the first example of the conversion of metallabenzyne II and isometallabenzene III. The osmium hydride vinylidene complex 1 reacts with HC≡CCH(OEt)(2) to give osmabenzyne 3 via isoosmabenzene 2. Compound 3 exhibits high thermal stability in air. Nonetheless, nucleophilic attack at 3 provides isoosmabenzenes 4 a and 4 b, or opens the ring to produce 5 a and 5 b. We propose mechanisms to disclose the intrinsic connection between the six-membered metallacycles, and carry out DFT calculations to rationalize the regioselectivity of the nucleophilic addition reactions.

Lewis Acid Mediated Reactions of Zirconacyclopentadienes with Aldehydes: One‐Pot Synthetic Route to Indene and Cyclopentadiene Derivatives from Aldehydes and Benzyne or Alkynes

One-pot procedures for the preparation of highly substituted indenes, tetrahydroindenes, and cyclopentadienes have been developed by using a combination of zirconocene-mediated Cbond;C-bond-forming reactions with Lewis acid mediated activation of carbonyl groups. The carbonyl groups of aldehydes were deoxygenated in the reaction and behaved formally as a one-carbon unit. A variety of Lewis acids were checked and showed different reactivities in this reaction.

Benzo‐Fused Double [7]Carbohelicene: Synthesis, Structures, and Physicochemical Properties

A benzo-fused double [7]carbohelicene (D7H) was synthesized through a regioselective cyclodehydrogenation of a tetranaphthyl-p-terphenyl-based precursor. The twisted (D7H-1) and anti-folded (D7H-2) conformers of D7H were separated by recrystallization, and their double helicene structures with overlapping terminal benzene rings were unambiguously elucidated by X-ray crystallography. A record-high isomerization barrier (46.0 kcal mol-1 ) in double helicenes was estimated based on density functional theory (DFT) calculation, which resulted in the excellent conformational stability of D7H. The physicochemical properties of D7H-1 and D7H-2 were investigated by UV/Vis absorption spectroscopy and cyclic voltammetry, displaying the variation of electronic structure upon conformational changes. The optical resolution of the racemic D7H-1 was carried out by chiral HPLC, offering enantiopure D7H-1-(P,P) and D7H-1-(M,M), which were further characterized by circular dichroism spectroscopy.

A corannulene-based donor–acceptor polymer for organic field-effect transistors

For the first time, the corannulene unit was incorporated directly into the backbone of conjugated polymers. A new donor–acceptor (D–A) copolymer PICBT using imide-fused corannulene as acceptor was synthesized and its performance in organic field-effect transistors (OFETs) was tested. PICBT exhibited ambipolar transporting property with a hole mobility of 0.025 cm2 V−1 s−1 and electron mobility of 7.45 × 10−5 cm2 V−1 s−1 when the substrates were treated with octyltrimethoxysilane (OTS). If the substrates were not modified with OTS, PICBT showed lower device performances with a hole mobility of 4.62 × 10−3 cm2 V−1 s−1 and electron mobility of 1.54 × 10−4 cm2 V−1 s−1. The device performances are competitive among the amorphous materials. This work paved the way for incorporating the corannulene unit into conjugated materials.