Tetracarboxylic Diimide Research Articles

Architecturally Diverse Nanostructured Foldamers Reveal Insightful Photoinduced Single-Molecule Dynamics

Single molecule fluorescence spectroscopy has been used to probe architecturally diverse and unique model oligomers containing exactly two or four perylene tetracarboxylic diimide (PTDI) units: linear foldamers lin2 and lin4, monocyclic complement cyc2, and concatenated foldable rings cat4. Linear, cyclic, and concatenated foldamers reveal that photoabsorption and excitation induces unfolding and refolding, generating colorful spectral switching from one spectral type to another. Foldamer architectures dictate the unfolding and refolding processes, and hence the spectral dynamics. As a result, linear tetramer exhibits active frame-to-frame spectral switching accompanying dramatic changes in colors, but a concatenated tetramer displays a multicolored composite spectrum with little or no spectral switching. Excited state dynamics causes spectral switching: an electronically decoupled PTDI monomer emits green fluorescence while electronically coupled PTDI pi-stacks emit red fluorescence, with longer pi-stacks emitting redder fluorescence. A key question we address is the excited-state delocalization length, or the exciton coherence length, in the pi-stacks, which has been proven difficult to measure directly. Using foldamers having controlled sequences, structures, and well-defined length and chromophore numbers, we have mapped out the exciton coherence length in pi-stacks. Single molecule fluorescence studies on chromophoric foldamers reveal that the maximum domain length is delocalized across just four pi-stacked PTDI dyes and no new pure color can be found for oligomers beyond the tetramer. Therefore, the range of fluorescent colors in pi-stacks is a function of the number of chromophores only up to the tetramer.

Temperature-Dependent Statistical Behavior of Single Molecular Conductance in Aqueous Solution

We have combined molecular dynamics simulations with first principles calculations to study electron transport in a single molecule of perylene tetracarboxylic diimide (PTCDI) sandwiched between two gold electrodes with an aqueous electrolyte. This combination has for the first time allowed one to reveal statistical behavior of molecular conductance in solution at different temperatures and to produce conductance histograms that can be directly compared with experiments. Our calculations show that experimentally observed temperature-dependent conductance can be attributed to the thermal effect on the hydrogen bonding network around the molecule and can be described by the radial distribution of water molecules surrounding the oxygen atom in the PTCDI molecule.

Electrospray Deposition of C60 on a Hydrogen-Bonded Supramolecular Network

An electrospray technique has been successfully used to deposit C60 onto a hydrogen-bonded supramolecular template held in an ultrahigh vacuum environment. Characterization of the surface by in situ scanning tunneling microscopy shows the size-selective trapping of C60 dimers and heptamers within a 3,4,9,10-perylene tetracarboxylic diimide (PTCDI)/melamine network. We demonstrate that ultrahigh vacuum electrospray deposition (UHV-ESD), where energetic molecules impact onto a substrate, is compatible with surfaces which have been functionalized through the incorporation of hydrogen-bonded templates.

X-shape oligo(thiophene)s as donor materials for vacuum-deposited organic photovoltaic cells

The films of two x-shape oligo(thiophene)s, 3, 4-dibithienyl-2, 5-dithienylthiophene (7T) and 2, 5-dibithienyl-3, 4-ditrithienylthiophene (11T), which are prepared by vacuum evaporation, have been investigated as novel electron donor layers in two-layer photovoltaic cells. UV-Vis absorptions show red-shifted and broadened absorptions of the vacuum-evaporated films as compared with those of the corresponding solutions and spin-coating films, which is beneficial for photovoltaic properties. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements show that the vacuum-evaporated films are almost amorphous. Two-layer photovoltaic cells have been realized by the thermal evaporation of 7T and 11T as donors and N, N′—bis(1-ethylpropyl)-3, 4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) as an acceptor. An energy conversion efficiency (ECE) of 0.18% of the cell based on 7T with an irradiation of white light at 100 mw/cm2 has been demonstrated by the measurements of current (I)- voltage (V) curves of the cells to be higher than the ECE of the reference system based on donor dihexylterthienyl (H3T) that is linear and without α, β linkage.

P3HT/ZnO bulk-heterojunction solar cell sensitized by a perylene derivative

In this work, a soluble perylene-derivative dye, N, N′-didodecyl-3,4,9,10-perylene tetracarboxylic diimide (PDI), was used to improve the photovoltaic performance of poly(3-hexylthiophene) (P3HT)/ZnO bulk heterojunction cells through blending with the composite. Results show that by incorporation of PDI in the P3HT/ZnO composite, the light absorption and exciton separation can be significantly improved. The photocurrent under white-light irradiation can be increased from 6.35 to 9.55 mA/cm 2. Solar decay experiment shows that V OC of the ITO/PEDOT:PSS/P3HT:ZnO:PDI/Al device decreases rapidly to almost zero in 1 h under persistent white-light illumination. After placing a 420 nm cutoff filter between the cell and the xenon lamp, the stability of the cell can be significantly improved. The device performance can maintain about 80% of the original value within 30 h and I SC degraded to zero after 142 h. The addition of PDI into the P3HT/ZnO device up to 5 wt% does not show observable effect on the solar cell decay behavior.

N-type organic thin-film transistor using N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimides grown by organic vapor deposition

We have studied the dependence of grain size of n-type organic semiconductor on the electrical performance of n-type organic thin-film transistor (N-OTFT) operated in air. The bottom-contact type N-OTFT based on N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimides (PTCDI-C8), which is unstable in air, is grown by organic vapor deposition to obtain large PTCDI-C8 grain. Even though PTCDI-C8 is unstable in air, the field-effect mobility of 5.6×10−3cm2/Vs and on/off current ratio of ∼106 were obtained in ambient air. The PTCDI-C8 layer was patterned by oxygen plasma etching with the passivation layer of parylene-C. In spite of the degradation in the electrical performance, the n-type OTFT still operated in air after the patterning process. These results show the possibility of organic complementary metal-oxide-semiconductor (O-CMOS) devices with large scale integration without shadow mask.

Synthesis and properties of a tetrathiafulvalene–perylene tetracarboxylic diimide–tetrathiafulvalene dyad

A donor–acceptor–donor dyad 4 involving 2-sulfur-3-methylthio-6,7-bis(hexylthio)tetrathiafulvalene (TTF) as a donor attached directly to N,N′-dibutylperylene-3,4,9,10-tetracarboxylic diimide (PDI) as an acceptor was synthesized by condensation of N,N′-dibutyl-1,6-dibromo-3,4,9,10-perylenetetracarboxylic diimide and 2-(2-cyanoethylthio-3-methylthio-6,7-bis(hexylthio)tetrathiafulvalene. The cyclic voltammetric (CV) data implied significant intramolecular interaction and the absorption spectrum indicated that there was an intramolecular charge transfer (ICT) interaction between TTF and PDI moieties in dyad 4. Comparing with PDI 13, the fluorescence emission intensity of dyad 4 was quenched almost quantitatively, which might result from the photo-induced electron transfer (PET) interaction between the PDI and TTF moieties in dyad 4. The fluorescence intensity of dyad 4 could be reversibly modulated by sequential oxidation and reduction of the TTF unit using chemical methods. Thus dyad 4 can be regarded as a new reversible fluorescence-redox dependent molecular switch.

Air-stable n-channel organic thin-film transistors with high field-effect mobility based on N,N′-bis(heptafluorobutyl)-3,4:9,10-perylene diimide

The thin-film transistor characteristics of n-channel organic semiconductor, N,N′-bis(2,2,3,3,4,4,4-heptafluorobutyl)-perylene tetracarboxylic diimide, are described. The slip-stacked face-to-face molecular packing allows a very dense parallel arrangement of the molecules, leading to field-effect mobility as high as 0.72cm2V−1s−1. The mobility only slightly decreased after exposure to air and remained stable for more than 50days. Our results reveal that molecular packing effects such as close stacking of perylene diimide units and segregation effects imparted by the fluorinated side chains are crucial for the air stability.

Degradation and segregation: Thermal stability and highly ordered epitaxial thin films of large aromatic molecules

The authors present an investigation of highly ordered epitaxial thin films of large organic molecules, namely quaterrylene derivatives. Even though the raw material quaterrylene tetracarboxylic diimide (QTCDI) starts to decompose below its sublimation temperature, epitaxial monolayers could be grown. By modifying the preparation procedure, highly ordered domains of quaterrylene dicarboxylic monoimide, being the main decomposition product of QTCDI, could also be produced. Although both molecules bear strong similarities, they grow in a dissimilar fashion influenced by their substituents and molecular dipole and quadrupole moments. The structures are characterized by scanning tunneling microscopy and, in case of QTCDI, low energy electron diffraction.

Relationship between Film Structure and Electric Performance of Organic Field-Effect Transistors Based on Perylene Tetracarboxylic Diimide Derivatives

We have fabricated organic field-effect transistors (OFETs) based on three derivatives of perylene tetracarboxylic diimide (PTCDI). The electron mobility more than 8 × 10−2 cm2V−1s−1 has been obtained in both vacuum and air for N,N′-bis(4-fluorobenzyl)perylene-3,4,9,10-tetracarboxylic diimide. The study of the film structures suggests that the flat-layer structures near the SiO2 surfaces induce the high electron mobilities.

Thermally Activated Electron Transport in Single Redox Molecules

We have studied electron transport through single redox molecules, perylene tetracarboxylic diimides, covalently bound to two gold electrodes via different linker groups, as a function of electrochemical gate voltage and temperature in different solvents. The conductance of these molecules is sensitive to the linker groups because of different electronic coupling strengths between the molecules and electrodes. The current through each of the molecules can be controlled reversibly over 2-3 orders of magnitude with the gate and reaches a peak near the redox potential of the molecules. The similarity in the gate effect of these molecules indicates that they share the same transport mechanism. The temperature dependence measurement indicates that the electron transport is a thermally activated process. Both the gate effect and temperature dependence can be qualitatively described by a two-step sequential electron-transfer process.

Spectroscopic Fingerprints of Amine and Imide Functional Groups in Self‐Assembled Monolayers

The electronic structures of naphthalene tetracarboxylic diimide (NTCDI) and 1,4-bis(4,6-diamino-1,3,5-triazin-2-yl)benzene (BDG) monolayer assemblies grown on Au(111) are investigated by photoemission spectroscopy, X-ray absorption, and density functional theory. The different spectroscopic features in the absorption and core-level photoemission spectra are understood in terms of contributions from different core and molecular levels at N- and O-atom sites. This study provides clear spectroscopic fingerprints for amine and imide functional end groups, which drive the self-organization process in a number of planar, pi-conjugated molecular structures.

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.

Solvent and electric field dependence of the photocurrent generation in donor:acceptor blend system

This paper reports that the blend films of poly (2-methoxy-5–(2'-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) and N,N'-bis(1-ethylpropyl)-3,4: 9,10-perylene bis (tetracarboxyl diimide) (EP-PDI) with the weight ratio of 1:2.5 have been prepared by spin-coating from chloroform (CF) and chlorobenzene (CB) solutions respectively. The absorption spectra and the morphology of the blend films show that large crystal-like EP-PDI aggregates are formed in film prepared from CB solution, which corresponds to a new absorption shoulder near 590 nm, while there is no shoulder around 590 nm in the UV–Vis absorption spectra of the blend film from CF solution. The electric-field dependence spectra of the photocurrent generation quantum yield of the film from CB solution shows that at weak electric field the EP-PDI aggregates act as more efficient sensitizers, but at strong electric field the quantum yields become almost invariable over the entire spectral range no matter what the state of EP-PDI, monomer or aggregate. At strong electric field, the photocurrent generation yields of both films from CF and CB solution saturate and their yield spectra become spectrally similar, mentioning that at strong electric field the photoexcitons dissociate efficiently and the free charges are collected by the electrodes almost completely.

Vibrational Spectroscopy Reveals Electrostatic and Electrochemical Doping in Organic Thin Film Transistors Gated with a Polymer Electrolyte Dielectric

We apply attenuated total internal reflection Fourier transform infrared (ATR-FTIR) spectroscopy to directly probe active layers in organic thin film transistors (OTFTs). The OTFT studied uses the n-type organic semiconductor N-N'-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) and a polymer electrolyte gate dielectric made from poly(ethylene oxide) and LiClO4. FTIR spectroscopy of the device shows signatures of anionic PTCDI-C8 species and broad polaron bands when the organic semiconductor layer is doped under positive gate bias (VG). There are two distinctive doping regions: a reversible and electrostatic doping region for VG <or= 2 V and an irreversible and electrochemical doping regime for VG>2 V. On the basis of intensity loss of vibrational peaks attributed to neutral PTCDI-C8, we obtain a charge carrier density of 2.9 x 10(14)/cm2 at VG=2 V; this charge injection density corresponds to the conversion of slightly more than one monolayer of PTCDI-C8 molecules into anions. At higher gate bias voltage, electrochemical doping involving the intercalation of Li+ into the organic semiconductor film can convert all PTCDI-C8 molecules in a 30-nm film into anionic species. For comparison, when a conventional gate dielectric (polystyrene) is used, the maximum charge carrier density achievable at VG=200 V is approximately 4.5 x 10(13)/cm2, which corresponds to the conversion of 18% of a monolayer of PTCDI-C8 molecules into anions.

Beyond Exciton Theory: A Time-Dependent DFT and Franck−Condon Study of Perylene Diimide and Its Chromophoric Dimer

The diimide perylene motif exhibits a dramatic intensity reversal between the 0 --> 0 and 0 --> 1 vibronic bands upon pi-pi stacking; this distinct spectral property has previously been used to measure folding dynamics in covalently bound oligomers and synthetic biological hybrid foldamers. It is also used as a tool to assess organization of the pi-stacking, indicating the presence of H- or J-aggregation. The zeroth-order exciton model, often used to describe the optical properties of chromophoric aggregates, is solely a transition dipole coupling scheme, which ignores the explicit electronic structure of the system as well as vibrational coupling to the electronic transition. We have therefore examined the optical properties of gas-phase perylene tetracarboxylic diimide (PTCDI) and its chromophoric dimer as a function of conformation to relate the excited-state distributions predicted by exciton theory with that of time-dependent density functional theory (TDDFT). Using ground- and excited-state geometries, the Franck-Condon (FC) factors for the lowest energy molecular nature electronic transition have been calculated and the origin of the intensity reversal of 0 --> 0 and 0 --> 1 vibronic bands has been proposed.

Ultralong Nanobelts Self-Assembled from an Asymmetric Perylene Tetracarboxylic Diimide

Ultralong nanobelts (>0.3 mm) have been fabricated from an asymmetric perylene tetracarboxylic diimide (PTCDI) molecule via a seeded self-assembly processing. The long length of nanobelts facilitates the construction of two-electrode devices employing the nanobelt as channel material, and the long-range one-dimensional π−π molecular stacking allows for efficient conductivity modulation through surface doping. A combination of these two characters enables efficient electrical sensing of reducing VOCs using the nanobelt. As examined for hydrazine, more than 3 orders of magnitude increase in current was observed for a single nanobelt when exposed to the saturated vapor of hydrazine.

Palladium Complexes of Perylene Diimides: Strong Fluorescence Despite Direct Attachment of Late Transition Metals to Organic Dyes

We prepared the first sigma-bonded metal complexes of widely utilized organic dyes, perylene tetracarboxylic acid diimides (PDIs). These 1,7-dipalladium PDI complexes were synthesized by C-Br oxidative addition of 1,7-dibromo-N,N'-dicyclohexyl PDI (Br2PDI) to Pd(0) phosphine complexes bearing triphenylphosphine and bischelating 1,2-bis(diphenylphosphino)ethane (dppe). The structures of Pd-PDI complexes were elucidated by single-crystal X-ray analysis. Surprisingly, despite direct attachement of two late transition metal centers, Pd-PDI systems are highly fluorescent (Phi=0.65 and 0.22 for triphenylphosphine and dppe systems, respectively). This is rationalized in terms of weak electronic interactions between the metal centers and PDI pi-system, as revealed by TD-DFT calculations.

Fabrication and third-order nonlinearity of an ultrathin film containing perylene derivatives

An ultrathin composite film containing cationic tetra-pyridine perylene tetracarboxylic acid diimide (TPP-I) and an anionic tetra-sulfuric perylene tetracarboxylic acid diimide (TSP-Na) has been fabricated by the electrostatic layer-by-layer self-assembly technique. UV/Vis spectra showed a continuous and uniform deposition process of TPP-I/TSP-Na. The film structure was characterized by the small-angle X-ray diffraction measurement and atomic force microscopy image. We investigated the third-order nonlinearity of the ultrathin film sample at 532 nm. The film exhibited strong saturable nonlinear absorption. The nonlinear absorption coefficient and refractive index of the film sample are − 5.0 × 10 − 7 mW − 1 and − 1.2 × 10 − 14 m 2W − 1 , respectively.

Effect of solvent on the performance of poly(2-methoxy-5-(2-ethyl-hexyloxy)-p-phenylene vinylene): N, N′-bis(1-ethylpropyl)-3,4,9,10-perylene bis(tetracarboxyl diimide) solar cells

The effects of different solvents on the morphology of poly(2-methoxy-5-(2-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV): N,N′-bis(1-ethylpropyl)-3,4,9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) blend film and the performance of solar cells based on MEH-PPV: EP-PTC blend film were studied. The results show that the phase separation in the blend film using non-aromatic solvents is of micron (0.5—5 μm) size, which leads to low charge separation efficiency and consequently the low power conversion efficiency of the assembled solar cell; whereas the phase separation in the blend film using aromatic solvents is of nano-size, which increases the interface area of the two phases obviously and consequently increases the ratio of charge separation significantly. The power conversion efficiency of solar cells based on MEH-PPV: EP-PTC blend film using aromatic solvents is improved 30 times of magnitude compared with that of solar cell based on the blend film using non-aromatic solvents.