Tetracarboxylic Diimide Research Articles

Effect of biphenyl biimide structure on the thermal stability, flame retardancy and pyrolysis behavior of PET

At present, developing a flame-retardant unit to solve the flammability and melt-dripping of poly(ethylene terephthalate) (PET) still is a key issue. To endow PET with good flame retardancy and low smoke releasing, a third monomer, N, N′-bis(2-hydroxyethyl)-biphenyl-3,4,3′,4′-tetracarboxylic diimide (BPDI) containing biphenyl biimide and without any traditional flame-retardant elements, is synthesized and incorporated to the main chain of PET to obtain the P(ET-co-BP)n copolyester via melt polymerization. The thermal stability, combustion and pyrolysis behaviors of the obtained copolyesters have been well investigated. Thermogravimetric analysis (TGA) results demonstrate that introducing BPDI into PET obviously improves its thermal stability and the forming ability of char residue. LOI, vertical UL-94 and cone calorimeter measurements have been applied to investigate the combustion behaviors of P(ET-co-BP)n. The results prove that P(ET-co-BP)n copolyesters containing biphenyl biimide show better fire safety, reflected by lower fire growth rate (FIGRA) and low smoke production. SEM and Raman results suggest that the char layers of P(ET-co-BP)n become denser and mainly consist of polyaromatic species with small and uniform microstructures. The pyrolysis behaviors of the copolyesters are investigated by Py-GC/MS, and the results showed that the biphenyl biimide structure units can lead to rearrangement reactions at high temperature, ultimately forming the phenanthrene ring structures during combustion. Without traditional flame-retardant elements like halogen and phosphorus, this novel PET copolyester is environmentally friendly and more safety.

Effects of interfacial tension and molecular dipole moment on the electrical characteristics of low-voltage-driven organic electronic devices

In organic electronic/photonic devices, numerous types of interfaces and their properties exhibit profound correlation with device performance. For optimizing the performance of organic electronic/photonic devices, appropriate and effective interface engineering needs to be developed. In this study, a high dielectric constant material, hafnium dioxide (HfO2), and an organic semiconductor, N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13) were adopted as the dielectric and active layers, respectively, to fabricate low-voltage-driven organic thin-film transistors. Three kinds of insulating polymers were selected to serve as buffer layers (BLs) to modify HfO2. After the addition of BLs onto HfO2, the insulating properties of HfO2 and the microstructures of PTCDI-C13 active layers improved, resulting in considerably enhanced electrical characteristics and stability of the devices. Among different polymeric BLs, the BL polymer exhibiting smaller interfacial tension with PTCDI-C13 can induce PTCDI-C13 to form better microstructures and generate lower interfacial trap density despite the rougher topography of polymeric BL, leading to improved electrical characteristics of the corresponding device. However, we observed that BL polymer with larger dipole moment of side groups can yield better electrical stability of the corresponding device under continuous operation compared with polymers with smaller interfacial tension. During long-term operation, the dipoles can be aligned by an electric field and form a strong dipole layer to facilitate charge accumulation and alleviate device degradation caused by bias-stress-induced trap/defect states. We further adopted a BL polymer with both small interfacial tension and large dipole moment to fabricate low-voltage-driven organic complementary inverters. The inverter can exhibit high electrical characteristics and stability during continuous operation. Interfacial tension and molecular dipole moment are possible important issues for effective interface engineering.

Presence of Short Intermolecular Contacts Screens for Kinetic Stability in Packing Polymorphs.

Polymorphism is pervasive in molecular solids. While computational predictions of the molecular polymorphic landscape have improved significantly, identifying which polymorphs are preferentially accessed and experimentally stable remains a challenge. We report a framework that correlates short intermolecular contacts with polymorphic stability. The presence of short contacts between neighboring molecules prevents structural rearrangement and stabilizes the packing arrangement, even when the stabilized polymorph is not enthalpically favored. In the absence of such intermolecular short contacts, the molecules have added degrees of freedom for structural rearrangement, and solid-solid polymorphic transformations occur readily. Starting with a series of core-halogenated naphthalene tetracarboxylic diimides, we establish this framework with the packing polymorphs of more than 20 compounds, ranging from molecular semiconductors to pharmaceutics and biological building blocks. This framework, widely applicable across molecular solids, can help refine computational predictions by identifying the polymorphs that are kinetically stable.

Donor-Acceptor Supramolecular Organic Nanofibers as Visible-Light Photoelectrocatalysts for Hydrogen Production.

Perylene tetracarboxylic diimide (PTCDI) derivatives have been extensively studied for one-dimensional (1D) self-assembled systems and for applications in photocatalysis. Herein, we constructed a PTCDI-based donor-acceptor (D-A) supramolecular system via in situ self-assembly on an indium tin oxide conductive glass surface. The self-assembled PTCDI nanostructures exhibit well-defined nanofibril morphologies and strong photocurrents. Interestingly, a strong and reversible electrochromic color change was observed during cyclic voltammetry. The color of the nanofibers changed from red to blue and then to violet as the reduction progressed to the radical anion and then to the dianion. This series of one-electron reductions was confirmed by UV absorption, electron paramagnetic resonance spectroscopy, and hydrazine reduction. Most importantly, these PTCDI nanofibers exhibit efficient photoelectrocatalytic hydrogen production with remarkable stability under xenon lamp illumination (λ ≥ 420 nm). Among the three nanofibers prepared, the fibers assembled from PTCDI molecule 2 were found to be the most effective catalyst with 30% Faradaic efficiency. In addition, the nanofibers produced hydrogen at a steady-state for more than 8 h and produced repeatable results in 3 consecutive testing cycles, giving them great potential for practical industrial applications. Under an applied bias voltage, the 1D intermolecular stacking along the long axis of the nanofibers affords efficient separation and migration of photogenerated charge carriers, which play a crucial role in the photoelectrocatalytic process. As a proof-of-concept, the D-A-structured PTCDI nanofibers presented herein may guide future research on photoelectrocatalysis based on self-assembled supramolecular systems by providing more options for material design of the catalysts to achieve greater efficiencies.

N-type organic field effect transistors based on naphthalene tetracarboxylic diimides derivatives containing halogen elements

Naphthalene tetracarboxylic diimides (NDIs) derivatives, functionalized with p-fluorophenyl (NDI-FAN), p-chlorophenyl (NDI-ClAN), p-fluorobenzyl (NDI-FBN), were synthesized and used to fabricated organic field effect transistors (OFETs) through vacuum evaporation. All materials display high decomposition temperature and low LUMO energy level facilitating air stable electron transport. OFETs devices based on N-octadecylphosphonic acid (ODPA) treated SiO2/Si substrate affords electron mobility up to 1.8 × 10−1 cm2v−1s−1 with high on/off ratio of 6.7 × 103 in air. Replaced the p-fluorophenyl by p-fluorobenzyl also leads to a comparable mobility reaching 1.1 × 10−1 cm2v−1s−1 with a low threshold voltage of 1.8 V. Microstructure and morphology of thin films were investigated to shed light on the reason for distinct electrical performance. These results demonstrate that fluorinated N-substituent is an alternative method to optimize molecular arrangement and device performance.

Printing technology based on isotropic liquid phase of naphthalene diimide derivatives for n-type organic transistors

Abstract Solution processes are well suited for large-scale production of thin films of organic active layers in transistors. However, environmentally hazardous chlorine-based solvents are required for conventional solution processes. Here we introduced a new wet-process approach, without the use of toxic solvents, for creating isotropic phases of several naphthalene tetracarboxylic acid diimide derivatives substituted at the N and N′ positions with long alkyl chains of varying lengths (NTCDI-Cn). Thin films of NTCDI-Cn were prepared by this process, the dependence of the device performance on the thickness of the thin films and the length of the NTCDI-Cn alkyl chains was investigated, and the process was optimized. The devices of NTCDI-Cn exhibited a relatively high electron mobility (∼0.1 cm2/V), and a maximum electron mobility of 0.38 cm2/V was obtained from the 50-nm-thick NTCDI-C13 TFT.

Synthesis, Characterization and Computational studies of new Perylene Tetracarboxylic Diimides

Synthesis, Characterization and Computational studies of new Perylene Tetracarboxylic Diimides

Work function and temperature dependence of electron tunneling through an N-type perylene diimide molecular junction with isocyanide surface linkers.

Conducting probe atomic force microscopy (CP-AFM) was employed to examine electron tunneling in self-assembled monolayer (SAM) junctions. A 2.3 nm long perylene tetracarboxylic acid diimide (PDI) acceptor molecule equipped with isocyanide linker groups was synthesized, adsorbed onto Ag, Au and Pt substrates, and the current-voltage (I-V) properties were measured by CP-AFM. The dependence of the low-bias resistance (R) on contact work function indicates that transport is LUMO-assisted ('n-type behavior'). A single-level tunneling model combined with transition voltage spectroscopy (TVS) was employed to analyze the experimental I-V curves and to extract the effective LUMO position εl = ELUMO - EF and the effective electronic coupling (Γ) between the PDI redox core and the contacts. This analysis revealed a strong Fermi level (EF) pinning effect in all the junctions, likely due to interface dipoles that significantly increased with increasing contact work function, as revealed by scanning Kelvin probe microscopy (SKPM). Furthermore, the temperature (T) dependence of R was found to be substantial. For Pt/Pt junctions, R varied more than two orders of magnitude in the range 248 K < T < 338 K. Importantly, the R(T) data are consistent with a single step electron tunneling mechanism and allow independent determination of εl, giving values compatible with estimates of εl based on analysis of the full I-V data. Theoretical analysis revealed a general criterion to unambiguously rule out a two-step transport mechanism: namely, if measured resistance data exhibit a pronounced Arrhenius-type temperature dependence, a two-step electron transfer scenario should be excluded in cases where the activation energy depends on contact metallurgy. Overall, our results indicate (1) the generality of the Fermi level pinning phenomenon in molecular junctions, (2) the utility of employing the single level tunneling model for determining essential electronic structure parameters (εl and Γ), and (3) the importance of changing the nature of the contacts to verify transport mechanisms.

Spectroscopic, electrochemical and photovoltaic properties of Pt(ii) and Pd(ii) complexes of a chelating 1,10-phenanthroline appended perylene diimide.

In this study, a bis-chelating bridging perylene diimide ditopic ligand, namely N,N'-di(1,10-phenanthroline)-1,6,7,12-tetrakis-(4-methoxyphenoxy)perylene tetracarboxylic acid diimide (1), was synthesized and characterized. Further reactions of 1 with d8 metal ions such as Pt(ii) and Pd(ii) having preferential square-planar geometry afforded the novel triads [(Cl2)M(ii)-(1)-M(ii)(Cl2)] where M(ii) = Pt(ii) (2), and Pd(ii) (3), respectively. The isolated triads and the key precursor were fully characterized by FT-IR, 1D-NMR (1H NMR and 13C DEPT NMR), 2D-NMR (1H-1H COSY, 1H-13C HSQC, 1H-13C HMBC), MALDI-TOF mass and UV/Vis spectroscopy. The electrochemical properties of 1, 2 and 3 were investigated by cyclic voltammetry as well as in situ spectroelectrochemistry and also in situ electrocolorimetric measurements. These compounds were shown to exhibit net colour changes suitable for electrochromic applications. The compounds exhibited remarkably narrow HOMO-LUMO gaps, leading to their ease of reduction at low negative potentials. More importantly, dye-sensitized solar cells (DSSCs) were also fabricated using 1-3 to clarify the potential use of these complexes as a sensitizer. Analysis of the experimental data indicated that 2 has good potential as a sensitizer material for DSSCs.

Photoelectrochemical processes in organic semiconductor: Ambipolar perylene diimide thin film

A thin film of N,N′-dioctadecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C18) is spin-coated on indium tin oxide (ITO) glass. Using the PTCDI-C18/ITO electrode, we fabricate a photoelectrochemical cell with the ITO/PTCDI-C18/Redox Electrolyte/Pt configuration. The electrochemical properties of this device are investigated as a function of hydroquinone (HQ) concentration, bias voltage, and wavelength of light. Anodic photocurrent is observed at V ≥ −0.2 V vs. Ag/AgCl, indicating that the PTCDI-C18 film acts as an n-type semiconductor as usual. However, when benzoquinone (BQ) is inserted into the electrolyte system instead of HQ, cathodic photocurrent is observed at V ≤ 0.0 V, displaying that PTCDI-C18 abnormally serves as a p-type semiconductor. Hence the overall results reveal that the PTCDI-C18 film can be an ambipolar functional semiconductor depending on the redox couple in the appropriate voltage.

Reflection of Molecular Twist in Unoccupied Molecular Orbitals in PTCDI Derivatives: A Density Functional Study

In this work, the structural and electronic properties of perylene tetracarboxylic diimide (PTCDI) derivative molecules have been calculated using density functional theory simulations. Here, we have obtained the equilibrium geometry for certain PTCDI derivatives and calculated their occupied and unoccupied density of states separately for molecular orbitals lying in-plane (σ type) and orthogonal to the plane (π type) of the molecules. We have also simulated the X-ray absorption spectroscopy (XAS) spectra for these molecules separately for π- and σ-type orbitals. A comparison between the unoccupied density of states and XAS data has been made because both provide a description of the molecular orbitals above the Fermi level. We have observed the presence of shallow-lying σ orbitals in twisted molecules and have obtained an almost linear relationship between the abundance of these orbitals and the degree of molecular twist. Additionally, we have shown the possibility of an experimentally viable stereoisomerism in PTCDI-C3.

Analyzing the n-Doping Mechanism of an Air-Stable Small-Molecule Precursor.

Efficient n-doping of organic semiconductors requires electron-donating molecules with small ionization energies, making such n-dopants usually sensitive to degradation under air exposure. A workaround consists in the usage of air-stable precursor molecules containing the actual n-doping species. Here, we systematically analyze the doping mechanism of the small-molecule precursor o-MeO-DMBI-Cl, which releases a highly reducing o-MeO-DMBI radical upon thermal evaporation. n-Doping of N,N-bis(fluoren-2-yl)-naphthalene tetracarboxylic diimide yields air-stable and highly conductive films suitable for application as electron transport layer in organic solar cells. By photoelectron spectroscopy, we determine a reduced doping efficiency at high doping concentrations. We attribute this reduction to a change of the precursor decomposition mechanism with rising crucible temperature, yielding an undesired demethylation at high evaporation rates. Our results do not only show the possibility of efficient and air-stable n-doping, but also support the design of novel air-stable precursor molecules of strong n-dopants.

Photoconductance from Exciton Binding in Molecular Junctions

We report on a theoretical analysis and experimental verification of a mechanism for photoconductance, the change in conductance upon illumination, in symmetric single-molecule junctions. We demonstrate that photoconductance at resonant illumination arises due to the Coulomb interaction between the electrons and holes in the molecular bridge, so-called exciton-binding. Using a scanning tunneling microscopy break junction technique, we measure the conductance histograms of perylene tetracarboxylic diimide (PTCDI) molecules attached to Au-electrodes, in the dark and under illumination, and show a significant and reversible change in conductance, as expected from the theory. Finally, we show how our description of the photoconductance leads to a simple design principle for enhancing the performance of molecular switches.

Naphthalene diimide self-assembled ribbons with high electrical conductivity and mobility without doping

The thermally activated electrical conductivity and charge transfer properties of self-assembled naphthalene diimide molecule have been studied with N,N’di(hexadecyl)naphthalene tetracarboxylic diimide (HD-NDI) derivative. The self-assembly of HD-NDI has been resulted in one-dimensional large micron-size ribbons. The aggregate formation and self-assembling property have been extensively studied by absorption, fluorescence and X-ray diffraction analysis. Absorption and fluorescence measurements were taken in variety of solvents in fresh and aged samples, and the study suggested J-type aggregation for self-assembly formation. The electrical conductivity of self-assembled HD-NDI material was measured as a function of temperature where the conductivity increased with temperature and the highest conductivity (1 × 10−5 S/cm) was obtained at 250 °C. SEM images clearly show the formation of ribbons of micron size. Further the electron transport property of HD-NDI was also evaluated by SCLC method at room temperature by fabricating electron-only devices with annealing the film at ~ 200 °C. HD-NDI shows excellent electron mobility (1.8 × 10−3 cm2 V−1 s−1) because of effective channel formation due to self-assembly of HD-NDI molecules, and this material may find potential application in variety of electronic devices.

J–V and C–V investigation of the effect of small molecular fullerene and non-fullerene acceptors for CH3NH3PbI3 perovskite solar cell

To find the ideal acceptors for perovskite solar cells (PSCs) and get insight into the dielectric property at the interface between perovskite and acceptor, series of small molecular fullerene and non-fullerene acceptors were comparatively investigated. Fullerene acceptors based PSCs show higher performance than non-fullerene acceptors based PSCs. However, the perylene tetracarboxylic diimide based PSC has achieved a ηPCE of 4.70%, implying that it is a promising acceptor candidate for PSCs because of its suitable energy level, high electron mobility, and smooth surface. By employing double acceptors of (6,6)-phenyl-C61-butyric acid methyl ester (PCBM)/C60 or PCBM/3,4,9,10-perylenetetracarboxylic bisbenzimidazole, the PSC stability is greatly improved even without performance enhancement. The perovskite (Pero)/PCBM film shows smooth surface, suggesting that PCBM penetrates into the Pero layer. The hydrophobicity trend of Pero/acceptor composite films is same as the device performance by judging from the water contact angle, and Pero/PCBM as well as Pero/C60 show higher hydrophobicity than other Pero/small-molecular-acceptor composite films. Capacitance–voltage characteristics of the series of single and double acceptor based PSCs were measured. The double acceptor based PSCs show larger depletion layer width (Wd) than single acceptor based PSCs. Meanwhile, the defect density (NA) in Pero layer for single acceptor based PSCs is larger than that for double acceptor based PSCs, implying better n-doping of Pero layer by using a single acceptor.

Comparative study of long alkyl chain substituted naphthalene diimide derivatives as n-type organic thin-film transistor materials

In this study, vacuum-evaporated thin films of several naphthalene tetracarboxylic acid diimide derivatives substituted at the N and N′ positions with long normal alkyl chains of varying lengths (NTCDI-Cn) were evaluated as active materials for n-type organic thin-film transistors (TFTs). The electron mobility (μe) of the TFTs increased with increasing chain length from octyl (NTCDI-C8) to pentadecyl (NTCDI-C15); those of NTCDI-C15 and C18 TFTs were of 0.262 ± 0.016 and 0.222 ± 0.016 cm2 V−1 s−1, respectively. However, the threshold voltage of the TFTs increased with increasing chain length.

Real Space Demonstration of Induced Crystalline 3D Nanostructuration of Organic Layers.

The controlled 3D nanostructuration of molecular layers of the semiconducting molecules C22H14 (pentacene) and N,N'-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) is addressed. A tip-assisted method using atomic force microscopy (AFM) is developed for removing part of the organic material and relocating it in up to six layer thick nanostructures. Moreover, unconventional molecular scale imaging combining diverse friction force microscopy modes reveals the stacking sequence of the piled layers. In particular, we unambiguously achieve epitaxial growth, an issue of fundamental importance in thin film strategies for the nanostructuration of more efficient organic nanodevices.

Novel derivatives of regioisomerically pure 1,7-disubstituted perylene diimide dyes bearing phenoxy and pyrrolidinyl substituents: Synthesis, photophysical, thermal, and structural properties

Two new isomerically pure 1,7-substituted perylene-bisimide derivatives namely; 1,7-Di(4-tert-butylphenoxy)-N,N′-bis[2-(diethylamino)ethyl]-3,4,9,10-perylene-tetracarboxylic diimide (6) and 1,7-Di(pyrrolidinyl)-N,N′-bis[2-(diethylamino)ethyl]-3,4,9,10-perylene- tetracarboxylic diimide (7), have been synthesized and their electronic absorption, steady-state fluorescence, and thermal properties were studied. Both compounds show good solubility in a range of organic solvents. Attachment of two electron donating tert-butyl-phenoxy groups at the 1,7-positions in (6) resulted in a red shifted absorption band with absorption maximum at 543nm. UV–visible absorption spectrum of (7) shows a broad absorption band within the red region. Absorption maximum of lowest energy transition now shifts to 704nm. Both compounds (6) and (7) exhibit low fluorescence quantum yields of 0.133 and 0.007, respectively. Density functional theory (DFT) calculations revealed that the attachment of electron donating groups at 1,7-positions of PDIs, results in an increase in frontier orbitals energy levels. Observed energy increase in HOMO is larger in each case, compared to the energy increase in LUMO levels. Calculated band gaps for (6) and (7) are 2.462 and 2.128eV respectively.

Electronic Transport and Light Response of Air-Stable n-Type Organic Chlorophenyl-Substituted Perylene Diimide Microribbons

We report a new n-type single-crystalline microribbon based on a chlorophenyl-substituted perylene tetracarboxylic diimide derivative via solution-phase self-assembly. Electronic transport, environmental stability, and photoresponse properties of these microribbons are studied using field-effect transistors. Transistors based on a network of the as-prepared microribbons have moderate electron mobilities and ON/OFF current ratios on the order of $10^{-3}$ cm2/ $\text {V}\cdot \text {s}$ and $10^{3}$ – $10^{4}$ , respectively. The lifetime test of microribbon devices under various humidity conditions is found to be very sustainable over 100 days. Moreover, illuminating these microribbons could profoundly induce photocurrents in the visible light range, presenting good responsivity of 9.5 A/W and a high external quantum efficiency up to 2000% under 1.9 mW/cm2. In addition, these microribbon devices are processed from solution-phase at temperatures below 100 °C, making the technology a viable candidate for low-cost and plastic-based organic optoelectronic applications.

Dual photo-electrochromic diimides derived from aliphatic aminothiols and π-electron deficient aromatic dianhydrides

The reaction of aliphatic 2-aminothiols with pyromellitic and benzophenone-3,3′,4,4'-tetracarboxylic dianhydrides endowed dual-response diimides with photo- and electrochromic properties in concentrated sulfuric acid solution. Upon stimulation, the yellow color photo-isomeric materials turned in a few seconds to dark blue or red color and subsequently reverted back within a few minutes. The color change was ascribed to the generation of radical-cation species which may be formed through a reversible photo-induced electron-transfer process from the thiol group to the proton-activated dianhydride moiety. Spectroelectrochemistry measurements in concentrated H2SO4 solution of the specified diimides were accompanied by a quite similar UV-vis spectral response as observed in photochromic process, indicating the equality of the created chromic centre in both phenomena. The two chromic activities showed a great sensitivity to the structure of the donor-acceptor couples.