Pyromellitic diimides: minimal cores for high mobility n-channel transistor semiconductors

Three pyromellitic diimides were synthesized in high yields by one conventional reaction between pyromellitic dianhydride and various amines. The films made from these pyromellitic diimides derivatives exhibit a mobility up to 0.079 cm2/(V.s). In addition, the on/off ratios of n-channel devices are as high as 1 000 000.     

Selenium-containing core-expanded naphthalene diimides for high performance n-type organic semiconductors

The incorporation of heavy atoms into molecular backbone is an extremely straightforward strategy for fine-tuning the optoelectronic properties of organic semiconductors. However, it is rarely studied in n-type small molecules. Herein, by selenium substitution of NDI3 HU-DTYM2, two Se-decorated core-expanded naphthalene diimides(NDI) derivatives DTYM-NDI3 HUDSYM(1) and NDI3 HU-DSYM2(2) were synthesized. In comparison with the reference S-containing compound NDI3 HUDTYM2, the highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) energy levels of 1 and 2 were fine-tuned with ?HOMO of about 0.2 e V, ?LUMO of 0.1 e V and the narrowed HOMO-LUMO gaps. More surprisingly, the as-spun organic thin film transistors(OTFTs) based on 1 and 2 both showed μe,satvalues as high as1.0 cm~2 V~(-1) s~(-1), which are 2-fold higher than that of NDI3 HU-DTYM2 with the same device structure and measurement conditions. In addition, the single crystal OFET devices based on Se-containing compound NDI2 BO-DSYM2 showed a highμe,satvalue of 1.30 cm~2 V~(-1) s~(-1). The molecular packing of NDI2 BO-DSYM2 in single crystals(two-dimensional supramolecular structure formed by intermolecular Se···Se interactions) is quite different from that of a S-containing compound NDI-DTYM2(one dimensional supramolecular structure formed by intermolecular π-π stacking). Therefore, the Se substitution can cause dramatic change about molecular stacking model, giving rise to high n-type OTFT performance. Our results demonstrated an effective strategy of the heavy atom effect for designing novel organic semiconductors.     

Nitrogen-rich oligoacenes: candidates for n-channel organic semiconductors

The successive replacement of CH moieties by nitrogen atoms in oligoacenes (benzene to hexacene) has been studied computationally at the B3LYP/6-311+G(d,p)//6-31G(d) level of theory, and the effects of different heteroatomic substitution patterns on structures, electron affinities, excitation, ionization, and reorganization energies are discussed. The calculated tendencies are rationalized on the basis of molecular orbital arguments. To achieve electron affinities of 3 eV, a value required to allow for efficient electron injection from common metal electrodes, at least seven nitrogen atoms have to be incorporated into tetracenes or pentacenes. The latter require rather small reorganization energies for electron transfer (<0.20 eV) making these compounds promising candidates for n-channel semiconducting materials. Particularly interesting are heptaazapentacenes 5 and 6 in which the nitrogen atoms are arranged to form self-complementary systems with a maximum number of intermolecular CH-N contacts in planar oligomers. These interactions are expected to facilitate the formation of graphite-like sheet structures with cofacial arrangements of the pi systems and short interlayer distances due to attractive N-C(H) interlayer interactions. This should not only be ideal for charge transfer but also might contribute to improved air stability of these semiconductors. Self-complementarity is maintained in azaacenes containing two cyano groups in the terminal rings. These compounds require lower reorganization energies than the unsubstituted heterocycles (0.13-0.14 eV), show high electron affinities (3.3 eV), and are thus promising candidates for materials applications.     

High-performance floating-gate organic phototransistors based on n-type core-expanded naphthalene diimides

In the field of organic phototransistor, achieving both broad-spectral and high photosensitivity has always been a big challenge. The innovation of device structure has previously proven to be a possible solution to this problem. Here in this study, a novel organic phototransistor based on a high mobility n-type small molecule as the conducting layer and an isolated bulk heterojunction light-absorbing layer as the floating gate has been demonstrated in this study. With the special designed device structure, the phototransistor shows extremely high sensitivity to broad spectral and weak light irradiation, and the photoresponsivity and photocurrent/dark-current ratio of the device can reach up to 4840 mA/W and 1.8 × 10⁵ respectively. For conclusion, this study suggests a potential way to obtain high-performance phototransistors at room temperature, which will further promote the commercial application of organic phototransistors.     

Chemistry of naphthalene diimides

This tutorial review surveys recent developments in the chemistry of naphthalene diimides (NDIs) and explores their application in the fields of material and supramolecular science. It begins with a discussion of their general uses, methods of syntheses and their electronic and spectroscopic properties. Of interest to their application in the fields of conducting thin films and molecular sensors is the structure-function relationships that exist either as co-components of supramolecular ensembles as in the case of "nanotubes", or as the sole components in molecular wires. Also discussed are advances in NDI research within the areas of energy and electron transfer (covalent and non-covalent systems) and in host-guest chemistry including foldamer, mechanically-interlocked and ligand-gated ion channel examples. Finally, we explore the developments in the recent field of core-substituted NDIs, their photophysical properties and applications in artificial photosynthesis. We conclude with our views on the prospects of NDIs for future research endeavours.     

Valence electronic properties of n-channel organic materials based on fluorinated derivatives of perylene diimides

The valence electronic states of three kinds of fluorinated derivatives of perylene diimides, D2MFPP, D3MFPP, and D4MFPP, on Cu(110) and SiO(2)Si surface were studied by photoemission and density functional calculations. When these organic molecules were deposited on the Cu(110) and thermally oxidized SiO(2) surfaces, five well-resolved photoemission features originating from the molecules were observed. On Cu(110) surface, two emission features with pi-like character increased their binding energy with increasing the coverage of organic molecule, indicating a strong interaction between the organic molecules and Cu substrate. The density functional calculations suggest flat-lying adsorption geometry for D3MFPP and D4MFPP on Cu(110) surface.     

One-pot synthesis of core-expanded naphthalene diimides: enabling N-substituent modulation for diverse n-type organic materials

A mild and versatile one-pot synthesis of core-expanded naphthalene diimides has been developed, which undergoes a nucleophilic aromatic substitution reaction and then an imidization reaction, allowing an easy and low-cost access to diverse n-type organic materials. Some newly synthesized compounds by this one-pot operation exhibited high electron mobility of up to 0.70 cm(2) V(-1) s(-1) in ambient conditions.     

Self-assembly of naphthalene diimides into cylindrical microstructures

We have designed two rod-shaped compounds each incorporating a naphthalene diimide core and two terminal carboxylic acids. Both molecules aggregate in aqueous solution and spontaneously organize into cylindrical microstructures on the surface of solid substrates. Presumably, hydrogen bonds between the carboxylic acid termini and hydrophobic contacts between the naphthalene diimide cores are mainly responsible for the formation of these supramolecular arrays. Indeed, extended stacks of molecules self-assemble with close contacts between their aromatic cores in single crystals grown from polar solvents.     

Highly soluble perylene tetracarboxylic diimides and tetrathiafulvalene–perylene tetracarboxylic diimide–tetrathiafulvalene triads

Two donor-σ-acceptor-σ-donor triads incorporating tetrathiafulvalene (TTF) and 3,4,9,10-perylene tetracarboxylic diimides (PDI) units were synthesized. The structures of the triads and their intermediates were characterized by ¹H NMR, ¹³C NMR, MS, IR. The results of UV–vis and cyclic voltammetry (CV) of the triads indicated negligible intramolecular charge transfer (ICT) interaction in their ground states. The fluorescence and fluorescence lifetimes of the triads were reduced compared to PDIs, which evidently indicated that photoinduced electron transfer (PET) interaction occurred from the TTF unit to the PDI unit in the excited state. The fluorescence intensity of the triads could be reversibly modulated by sequential oxidation and reduction of the TTF unit using the chemical methods. Therefore two new fluorescence molecular switches based on TTF and PDI units were established.     

p-Channel organic semiconductors based on hybrid acene-thiophene molecules for thin-film transistor applications

We report the structural and electrical characterization of two new p-channel organic semiconductors, 5,5'-bis(2-tetracenyl)-2,2'-bithiophene (1) and 5,5'-bis(2-anthracenyl)-2,2'-bithiophene (2). Both compounds exhibited a high degree of thermal stability with decomposition temperatures of 530 degrees C and 425 degrees C for 1 and 2, respectively. The thin-film structures of 1 and 2 were examined using wide-angle X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscopy (AFM). Films of 1 and 2 pack in similar triclinic unit cells with the long axes of the molecules nearly perpendicular to the substrate. Thin-film transistors (TFTs) based on 1 and 2 exhibit contact-corrected linear regime hole mobility as high as 0.5 cm2/Vs and 0.1 cm2/Vs, respectively. The specific contact resistance at high gate voltages for gold top contacts was 2 x 10(4) Ohms cm and 3 x 10(4) Ohms cm for 35 nm thick films of 1 and 2, respectively. Long-term air stability tests revealed less degradation of the electrical properties of 1 and 2 in comparison to pentacene. Variable temperature measurements revealed activation energies as low as 22 and 27 meV for 1 and 2, respectively. The temperature and gate voltage dependence of the mobility are discussed in terms of a double exponential distribution of trap states and a model accounting for the layered structure of the organic films. The enhanced air and thermal stability over pentacene, combined with good electrical performance characteristics, make 2 a promising candidate for future organic TFT applications.     

Stepwise cyanation of naphthalene diimide for n-channel field-effect transistors

Stepwise cyanation of tetrabromonaphthalenediimide (NDI) 1 gave a series of cyanated NDIs 2-5 with the monocyanated NDI 2 and dicyanated NDI 3 isolated. The tri- and tetracyano- NDIs 4 and 5 show intrinsic instability toward moisture because of their extremely low-lying LUMO energy levels. The partially cyanated intermediates can be utilized as air-stable n-type semiconductors with OFET electron mobility up to 0.05 cm(2) V(-1) s(-1).     

Naphthalene and perylene diimides for organic transistors

The development of ambient stable organic n-channel semiconductor molecules for thin-film transistors has experienced a tremendous impetus in the last decade to close the gap in performance in comparison to that of their p-channel counterparts. Especially naphthalene and perylene tetracarboxylic diimides (NDI and PDI) have shown to be the most valuable building blocks to achieve this challenging goal and to gain insight into the molecular structure-transistor performance relationship. Remaining challenges and new emerging research fields for these n-type semiconductors are the optimization of their deposition on flexible substrates, the control of their long term ambient stability and their implementation in complementary transistor circuits, display and sensor devices.     

Syntheses and properties of 1,6 and 1,7 perylene diimides and tetracarboxylic dianhydrides

Via Sonogashira cross-coupling with different alkynes, 1,6 and 1,7 perylene diimides (PDIs) and perylene tetracarboxylic dianhydrides (PTCDs) were synthesized from the corresponding regioisomeric mixture of 1,6/1,7-dibromo precursors. Both bulky triphenyl propyne (TPP) groups and nonbulky hexyl groups allow for facile chromatographic separation. The optical properties of these compounds are discussed. Neutral bay substituents hypsochromically shift both the absorption and emission through deformation from planarity of the perylene core.     

Facile synthesis of chiral unsymmetric perylene tetracarboxylic diimides involving α-amino acids

A facile synthesis of chiral unsymmetric perylene tetracarboxylic diimides (PDIs) has been developed and the first two nonracemic chiral amphiphilic PDIs have been synthesized. The key building blocks, AB bifunctional 3,4,9,10-perylenetetracarboxylic-3,4-anhydride-9,10-imides, were prepared conveniently from enantiomerically pure α-amino acids, which were introduced as the steric and stereochemical controlling units. Such building blocks allow the incorporation of sterically and stereochemically controlled PDI moieties into both terminal and inner positions.     

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.     

Siloxanes with pendent naphthalene diimides: synthesis and fluorescence quenching

Cyclic siloxanes with pendent naphthalene diimide groups were synthesized via hydrosilylation to form amorphous electron-accepting compounds. Photophysical measurements and >99.9% fluorescence quenching of well-known p-type polymers by the siloxanes demonstrate that these siloxanes form a new class of highly efficient n-type materials that provide some control over intermolecular interactions.     

Tetrachlorinated tetraazaperopyrenes (TAPPs): highly fluorescent dyes and semiconductors for air-stable organic n-channel transistors and complementary circuits

A range of 2,9-perfluoroalkyl-substituted tetraazaperopyrene (TAPP) derivatives (1-5) was synthesised by reacting 4,9-diamino-3,10-perylenequinone diimine (DPDI) with the corresponding carboxylic acid chloride or anhydride in the presence of a base. The reaction of compounds 1-4 with dichloroisocyanuric acid (DIC) in concentrated sulphuric acid resulted in the fourfold substitution of the tetraazaperopyrene core, yielding the 2,9-bisperfluoroalkyl-4,7,11,14-tetrachloro-1,3,8,10-tetraazaperopyrenes 6-9, respectively. The optical and electrochemical data demonstrate the drastic influence of the core substitution on the properties. All compounds are highly luminescent (fluorescence quantum yields of up to Φ=0.8). The LUMO energies of the tetrachlorinated TAPP derivatives (determined by cyclic voltammetry and computed by DFT calulations) were found to be below -4?eV. In the course of this work the performance of TAPP derivatives in organic thin-film transistors (TFTs) was investigated, and their n-channel characteristics with field-effect mobilities of up to 0.14?cm(2) V(-1) s(-1) and an on/off current ratio of >10(6) were confirmed. Long-term stabilities of 3-4 months under ambient conditions of the devices were established. Complementary inverters and ring oscillators with n-channel TFTs based on compound 8 and p-channel TFTs based on dinaphtho-[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) were fabricated on a glass substrate.     

Stannyl derivatives of naphthalene diimides and their use in oligomer synthesis

2-Stannyl and 2,6-distannyl naphthalene diimides (NDIs) can be synthesized through the palladium-catalyzed reaction of the appropriate bromo derivatives with hexabutylditin. The utility of these precursors in palladium catalyzed cross-coupling reactions is demonstrated by the synthesis of bi- and ter-NDI derivatives, UV-vis, cyclic voltammetry, and n-channel organic field-effect transistor data for which are compared to those of the monomeric parent NDI.     

Gate dielectric chemical structure-organic field-effect transistor performance correlations for electron, hole, and ambipolar organic semiconductors

This study describes a general approach for probing semiconductor-dielectric interfacial chemistry effects on organic field-effect transistor performance parameters using bilayer gate dielectrics. Organic semiconductors exhibiting p-/n-type or ambipolar majority charge transport are grown on six different bilayer dielectric structures consisting of various spin-coated polymers/HMDS on 300 nm SiO(2)/p(+)-Si, and are characterized by AFM, SEM, and WAXRD, followed by transistor electrical characterization. In the case of air-sensitive (generally high LUMO energy) n-type semiconductors, dielectric surface modifications induce large variations in the corresponding OTFT performance parameters although the film morphologies and microstructures remain similar. In marked contrast, the device performance of air-stable n-type and p-type semiconductors is not significantly affected by the same dielectric surface modifications. Among the bilayer dielectric structures examined, nonpolar polystyrene coatings on SiO(2) having minimal gate leakage and surface roughness significantly enhance the mobilities of overlying air-sensitive n-type semiconductors to as high as approximately 2 cm(2)/(V s) for alpha,omega-diperfluorohexylcarbonylquaterthiophene polystyrene/SiO(2). Electron trapping due to silanol and carbonyl functionalities at the semiconductor-dielectric interface is identified as the principal origin of the mobility sensitivity to the various surface chemistries in the case of n-type semiconductors having high LUMO energies. Thiophene-based n-type semiconductors exhibiting similar film morphologies and microstructures on various bilayer gate dielectrics therefore provide an incisive means to probe TFT performance parameters versus semiconductor-dielectric interface relationships.     

Water soluble extended naphthalene diimides as pH fluorescent sensors and G-quadruplex ligands

Extended naphthalene diimides (NDIs) fused to 1,4-dihydropyrazine-2,3-dione, containing two solubilizing moieties, have been synthesized. Fluorescence spectra of the new NDIs were remarkably affected by pH, as the second deprotonation of the dihydropyrazinedione moiety (pK(a) 6.9) switched off the emission. Binding to a G-quadruplex folded oligonucleotide and stoichiometry were evaluated by FRET melting assay and CD analysis. G-quadruplex binding was strongly enhanced shifting from pH 7.4 to pH 6.0 as a consequence of the dihydropyrazinedione moiety protonation. Cytotoxicity studies using two human telomerase-positive cell lines (HT29 and A549) revealed that the best G-quadruplex ligand was very active against the colon cell line, with an EC(50) of 300 nM.