Gaole Dai

Antiaromatic bisindeno-[n]thienoacenes with small singlet biradical characters: syntheses, structures and chain length dependent physical properties

Recent studies demonstrated that aromaticity and biradical character play important roles in determining the ground-state structures and physical properties of quinoidal polycyclic hydrocarbons and oligothiophenes, a kind of molecular materials showing promising applications for organic electronics, photonics and spintronics. In this work, we designed and synthesized a new type of hybrid system, the so-called bisindeno-[n]thienoacenes (n = 1–4), by annulation of quinoidal fused α-oligothiophenes with two indene units. The obtained molecules can be regarded as antiaromatic systems containing 4n π electrons with small singlet biradical character (y0). Their ground-state geometry and electronic structures were studied by X-ray crystallographic analysis, NMR, ESR and Raman spectroscopy, assisted by density functional theory calculations. With extension of the chain length, the molecules showed a gradual increase of the singlet biradical character accompanied by decreased antiaromaticity, finally leading to a highly reactive bisindeno[4]thienoacene (S4-TIPS) which has a singlet biradical ground state (y0 = 0.202). Their optical and electronic properties in the neutral and charged states were systematically investigated by one-photon absorption, two-photon absorption, transient absorption spectroscopy, cyclic voltammetry and spectroelectrochemistry, which could be correlated to the chain length dependent antiaromaticity and biradical character. Our detailed studies revealed a clear structure–aromaticity–biradical character–physical properties–reactivity relationship, which is of importance for tailored material design in the future.

Incorporating TCNQ into Thiophene-Fused Heptacene for n-Channel Field Effect Transistor

Incorporation of electron-deficient tetracyanoquinodimethane (TCNQ) into electron-rich thiophene-fused heptacene was successfully achieved for the purpose of stabilizing longer acenes and generating new n-type organic semiconductors. The heptacene-TCNQ derivative 1 was found to have good stability and an expected electron transporting property. Electron mobility up to 0.01 cm(2) V(-1) s(-1) has been obtained for this novel material in solution processed organic field effect transistors.

Z-Shaped Pentaleno-Acene Dimers with High Stability and Small Band Gap

Acene-based materials have promising applications for organic electronics but the major constrain comes from their poor stability. Herein a new strategy to stabilize reactive acenes, by fusion of an anti-aromatic pentalene unit onto the zigzag edges of two acene units to form a Z-shaped acene dimer, is introduced. The Z-shaped acene dimers are extremely stable and show a small energy gap resulting from intramolecular donor-acceptor interactions. X-ray crystallographic analysis revealed their unique geometry and one-dimensional slip-stack columnar structure. Besides optical and electrochemical characterizations, solution-processed field-effect transistors were also fabricated.

Stable 7,14-disubstituted-5,12-dithiapentacenes with quinoidal conjugation.

Two 7,14-disubstituted-5,12-dithiapentacenes (1 and 2) with quinoidal conjugation were synthesized. Their ground-state quinoidal structures were proven by X-ray crystallographic analysis. They showed very different electronic and optical properties from those of the corresponding pentacene derivatives with diene conjugation, and their stability was significantly improved. Organic field effect transistors based on solution processed thin films of 1 and 2 exhibited a hole mobility of up to 0.032 cm(-2) V(-1) s(-1).

Thienoacene‐Fused Pentalenes: Syntheses, Structures, Physical Properties and Applications for Organic Field‐Effect Transistors

Three soluble and stable thienoacene-fused pentalene derivatives (1-3) with different π-conjugation lengths were synthesized. X-ray crystallographic analysis and density functional theory (DFT) calculations revealed their unique geometric and electronic structures due to the interaction between the aromatic thienoacene units and antiaromatic pentalene moiety. As a result, they all possess a small energy gap and show amphoteric redox behaviour. Time dependent (TD) DFT calculations were used to explain their unique electronic absorption spectra. These new compounds exhibited good thermal stability and ordered packing in solid state and thus their applications in organic field-effect transistors (OFETs) were also investigated. The highest field-effect hole mobility of 0.016, 0.036 and 0.001 cm(2)  V(-1)  s(-1) was achieved for solution-processed thin films of 1-3, respectively.

Dithieno-naphthalimide based copolymers for air-stable field effect transistors: synthesis, characterization and device performance

A new thiophene-fused naphthalimide building block, 9-(2-decyltetradecyl)-8H-dithieno-[3′,2′:3,4; 2′′,3′′:5,6]benzo[1,2-f]isoindole-8,10(9H)-dione (4), was synthesized and three novel conjugated copolymers P1–P3 based on this building block and electron-rich units such as 4,4′-didodecyl-2,2′-bithiophene (for P1), benzo[1,2-b:4,5-b′]dithiophene (for P2) and 3,6-didodecylthieno[3,2-b]thiophene (for P3) were prepared by Stille coupling polymerization. The optical, electrochemical and thermal properties of polymers P1–P3 were studied and their applications in organic field effect transistors (OFETs) were also investigated. These new polymers have good solubility in common organic solvents and exhibit good thermal stability. Polymers P1 and P3 entered nematic liquid crystalline phases above 213 and 313 °C, respectively. The average field-effect hole mobilities were evaluated to be 0.15, 3 × 10−3 and 0.05 cm2 V−1 s−1 for P1, P2 and P3, respectively, under ambient conditions, with a high on/off ratios of 105–107. All the OFETs based on these polymers showed good environmental stability when stored in air.

TCNQ-embedded heptacene and nonacene: synthesis, characterization and physical properties

Incorporation of 7,7,8,8-tetracyanoquinodimethane (TCNQ) moieties into the acene backbone has been successfully achieved and two heptacene-TCNQ derivatives and one nonacene-TCNQ derivative have been synthesized and well characterized. Two TCNQ moieties have been embedded into heptacene and nonacene backbones for the first time. All the three compounds have good stability and solubility due to the presence of TCNQ moieties. Single crystal analysis revealed a bent butterfly-like conformation of these molecules. Their charge transport properties have been characterized using organic field effect transistors (OFETs).