Quinacridone Research Articles

Theoretical study on charge transport of quinacridone polymorphs

AbstractThe charge carrier transporting ability in the polymorphism of quinacridone (QA) has been studied using density‐functional theory and Marcus charge transport theory. The theoretical results indicated quinacridone has good electron transport ability and electron mobilities of all the polymorphism are at 10−2 magnitude. But its hole mobility, which varied with the different molecular packing, is at range of 10−1–10−3 magnitude. The difference of charge carrier mobilities among the polymorphism is originated from the different packing mode. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Dimeric quinacridone cyclophanes: Synthesis, structures, and photophysical properties

Two novel quinacridone (QA) cyclophanes with intrinsic intramolecular dye-dye interactions have been designed and synthesized. X-ray crystal structures as well as detailed photophysical properties have been well demonstrated. These two dyes have a major advantage that efficient fluorescence quenching can be observed even in their dilute solutions. A comparison of photophysical properties between the dimeric QA cyclophane and its reference monomeric counterpart indicates that the dimerization is predominant for the fluorescence quenching of QA dyes in solution. This study provided some model QA derivatives with dimeric structures for understanding the fluorescence quenching of QA dyes in solutions.

Quinacridone-Based Molecular Donors for Solution Processed Bulk-Heterojunction Organic Solar Cells

New soluble quinacridone-based molecules have been developed as electron donor materials for solution-processed organic solar cells. By functionalizing the pristine pigment core of quinacridone with solubilizing alkyl chains and light absorbing/charge transporting thiophene units, i.e., bithiophene (BT) and thienylbenzo[c][1,2,5]thiadiazolethienyl (BTD), we prepared a series of multifunctional quinacridone-based molecules. These molecular donors show intense absorption in the visible spectral region, and the absorption range and intensity are well-tuned by the interaction between the quinacridone core and the incorporated thiophene units. The thin film absorption edge extends with the expansion of molecular conjugation, i.e., 552 nm for N,N'-di(2-ethylhexyl)quinacridone (QA), 592 nm for 2,9-Bis(5'-hexyl-2,2'-bithiophene)-N,N'-di(2-ethylhexyl)quinacridone (QA-BT), and 637 nm for 4-(5-hexylthiophen-2-yl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (QA-BTD). The change of molecular structure also influences the electrochemical properties. Observed from cyclic voltammetry measurements, the oxidation and reduction potentials (vs ferrocene) are 0.7 and -1.83 V for QA, 0.54 and -1.76 V for QA-BT, and 0.45 and -1.68 V for QA-BTD. Uniform thin films can be generated from both single component molecular solutions and blend solutions of these molecules with [6,6]-phenyl C70-butyric acid methyl ester (PC70BM). The blend films exhibit space-charge limited current (SCLC) hole mobilities on the order of 1×10(-4) cm(2) V(-1) S(-1). Bulk heterojunction (BHJ) solar cells using these soluble molecules as donors and PC70BM as the acceptor were fabricated. Power conversion efficiencies (PCEs) of up to 2.22% under AM 1.5 G simulated 1 sun solar illumination have been achieved and external quantum efficiencies (EQEs) reach as high as ∼45%.

Ultraviolet—Visible Absorption and Luminescence Properties of Quinacridone—Barium Sulfate Solid Mixtures

The absorption and emission spectral features of the dye quinacridone (QA) have been studied in solution and in the solid phase. In the solid phase, QA has been investigated as pure microcrystalline powder and mixed with barium sulfate (BaSO(4)) in different mass percentages. Two kinds of QA-BaSO(4) mixtures have been prepared: physical blends of the two microcrystalline powders, and mixtures with gum arabic as binder. The latter was used in painting mock-ups. Luminescence properties of the mixtures have been investigated using both steady-state and time-resolved techniques. The prepared samples have allowed the Kubelka-Munk correction model, formulated for the emission spectra, to be tested. Moreover, the luminescence decay profiles have been analyzed using the maximum entropy method (MEM) and the nonlinear least-squares method. All the results obtained highlight how physical (self-absorption) and chemical (composition of the microenvironment) factors can influence the spectral and kinetic properties of dyes. These factors should always be taken into account in the diagnostic activity applied to works of art.

Basket-shaped quinacridone cyclophanes: synthesis, solid-state structures, and properties

A series of basket-shaped quinacridone (QA) cyclophanes 1–6 has been synthesized and characterized. Single-crystal X-ray analysis of 5 shows no infinite π–π aggregation between QA cores, reflecting a significant isolated effect of the bridging tethers. Photophysical properties have been carefully investigated. All cyclophanes show much higher quantum yields in concentrated solutions compared to the non-bridged QA analogue 7. Further application of 1 as a green dopant in EL devices exhibits current efficiencies of 11.2 and 7.2 cd A−1 with doping concentrations of 0.5 and 3 wt%, respectively. QA cyclophanes maintain a high luminescent yield in both concentrated solution and high doping concentration EL devices, verifying that the basket-shaped functionalization is an ideal strategy for depressing fluorescence quenching of QA dyes in the condensed phase.

Quinacridone organic field effect transistors with significant stability by vacuum sublimation

Quinacridone (QA), a highly stable red dye, was investigated for the fabrication of organic field effect transistors (OFETs) by vacuum sublimation. Field effect mobilities for holes of 10 −6 to 10 −3 cm 2/Vs were found, depending on the purity of the QA and the substrate temperature during the sublimation. The latter influences the structural phase composition of the films. The temperature dependence of the mobilities exhibits a maximum ( μ = (1.5 ± 0.2) × 10 −3 cm 2/Vs) at ∼270 K. Over a period of 50 days, the mobilities are stable and even slightly increase, although the OFETs were exposed to air between measurements.

Self-assembly of luminescent twisted fibers based on achiral quinacridone derivatives

It is a great challenge to spontaneously assemble achiral molecules into twisted nanostructures in the absence of chiral substances. Here we show that two achiral centrosymmetric quinacridone (QA) derivatives, N,N′-di(n-hexyl)-1, 3, 8, 10-tetramethylquinacridone (C6TMQA) and N,N′-di(n-decyl)-1, 3, 8, 10-tetramethylquinac ridone (C10TMQA), can be employed as building blocks to fabricate well-defined twisted nanostructures by controlling the solvent composition and concentration. Bowknot-like bundles with twisted fiber arms were prepared from C6TMQA, whilst uniform twisted fibers were generated from C10TMQA in ethanol/THF solution. Spectroscopic characterization and molecular simulation calculations revealed that the introduction of ethanol into the solution could induce a staggered aggregation of C6TMQA (or C10TMQA) molecules and the formation of twisted nanostructures. Such twisted materials generated from achiral organic functional molecules may be valuable in the design and fabrication of new materials for optoelectronic applications.

Theoretical Analysis of the Intermolecular Interaction Effects on the Excitation Energy of Organic Pigments: Solid State Quinacridone

Quinacridones (QAs) are organic hydrogen-bonded pigments, which are yellow in solution and become reddish to violet in solid phase depending on the crystal structure. We have carried out regular and fragment molecular orbital (FMO) based time-dependent density functional theory (TDDFT) calculations of the alpha (I), beta, and gamma crystalline phases of QA to examine the origin of the spectral shift in the solid phase. On the basis of the TDDFT calculations, we have found that the spectral shift from gas to solid phase in QA is dominated by the interplay of the structural deformation, electrostatic potential (crystal field), and intermolecular interactions, and each contribution is of the same order of magnitude. The spectral shift induced by the structural deformation is mainly caused by the stretch of the CO bond. The individual intermolecular interactions contribute to bathochromic and hypsochromic shifts depending on the spatial orientation, and their sums result in the bathochromic shift overall.

Organic Field-Effect Transistor Devices Based on Latent Pigments of Unsubstituted Diketopyrrolopyrrole or Quinacridone

Organic field-effect transistors (FETs) based on unsubstituted diketopyrrolopyrrole (DPP) or quinacridone (QA) have been fabricated using their solvent-soluble precursors called latent pigments (t-BOC DPP and t-BOC QA) which can also be regenerated into their parent pigments by heating at about 200 °C. The use of latent pigments enables us to fabricate FETs by spin coating, offering a low-cost fabrication process rather than an expensive vacuum technology. The objective of the present investigation is to evaluate the performance of DPP- and QA-based FETs prepared using latent pigments. As a result, field effect mobilities of about 7.19×10-6 and 8.23×10-6 cm2 V-1 s-1 are obtained for FETs based on t-BOC DPP and QA, respectively. These values are almost equivalent to those of FETs prepared by the vacuum deposition of DPP and QA, namely 1.43×10-5 and 1.08×10-5 cm2 V-1 s-1, respectively. The present result leads us to conclude that latent pigment technology is an excellent low-cost process fabricating organic FETs.

Study on Electrophoretic Deposition of Size-Controlled Quinacridone Nanoparticles

We have prepared quinacridone (QA) colloids with various particle sizes (25−120 nm) and different crystalline phases by nanosecond laser ablation of its microcrystalline powder dispersed in water and fabricated the prepared colloidal particles into homogeneous films on an indium-tin-oxide electrode by an electrophoretic deposition (EPD) method. The nanoparticle-assembled films consist of closely packed nanoparticles and many nanosized pores. We evaluated the porous nature of the film by scanning electron microscopy observation and by measuring the film thickness dependence of the absorption. It was found that the film morphology is sensitive to the applied bias, and the optimum bias for the QA colloid was determined to be about 10 V/cm. We also demonstrated that organic thin films with different grain sizes and crystalline phases can be fabricated arbitrarily by combining the EPD method with nanoparticle preparation by laser ablation.

Supramolecular Self‐Assembly Initiated by Solid–Solid Wetting

We present a preparation method for self-assembled supra-molecular monolayers of unsubstituted organic semiconductors and pigments on a solid substrate, applicable under ambient conditions. The deposition is based on a solid-solid wetting phenomenon, whereas the subsequent layer growth proceeds according to standard models. Molecular adsorption results from direct contact of the compound in a nanocrystalline state with the solid surface. Based on complementary force field calculations, we propose that molecules disintegrate from the crystalline state and adsorb on the surface because of a gain in binding energy. The preparation method is exemplified by means of a linear hydrogen-bonded system, namely quinacridone (QAC) on graphite. In addition, the chosen system allows us to actively guide the self-assembly after deliberate removal of molecules from a predefined area.

Organic FET devices based upon latent pigments of unsubstituted diketopyrrolopyrrole or quinacridone

Organic FETs based upon unsubstituted diketopyrrolopyrrole (DPP) or quinacridone (QA) have been fabricated, using their solvent-soluble precursors called latent pigments (t-BOC DPP and t-BOC QA) that can be also regenerated into their parent pigments by heating around 200 °C. Use of latent pigments enables us to fabricate FET devices by means of spin coating, offering a low-cost fabrication process rather than an expensive vacuum technology. The objective of the present investigation is to evaluate the performance of DPP- and QA-based FETs prepared by latent pigments. As a result, the field effect mobilities of about 7.19×10−6 and 8.23×10−6 cm2/Vs have been obtained for FET devices based upon t-BOC DPP and QA, respectively. These values are almost equivalent to those of the FETs prepared by vacuum deposition of DPP and QA: 1.43×10−5 and 1.08×10−5 cm2/Vs, respectively. The present result leads us to conclude that the latent pigment technology is a promising low-cost process to fabricate organic FETs.

High efficiency small molecule white organic light-emitting devices with a multilayer structure

In this paper, a new white organic light-emitting device (WOLED) with multilayer structure has been fabricated. The structure of devices is ITO/ N, N -bis-(1-naphthyl)- N , N ′ -diphenyl-1, 1′-biphenyl-4, 4′-diamine (NPB) (40 nm)/NPB: QAD (1%): DCJTB (1%) (10 nm) /DPVBi (10 nm) /2, 9-dimethyl, 4, 7-diphenyl, 1, 10-phenanthroline (BCP) ( d nm)/tris-(8-hydroxyquinoline) aluminium (Alq 3)(50- d nm)/LiF (1 nm)/Al (200 nm). In our devices, a red dye 4-(dicyanomethylene)-2-t-butyl-6 (1, 1, 7, 7-tetramethyl julolidyl-9-enyl)-4H-pyran (DCJTB) and a green dye quinacridone (QAD) were co-doped into NPB. The device with 8 nm BCP shows maximum luminance of 12 852 cd/m 2 at 20 V. The current efficiency and power efficiency reach 9.37 cd/A at 9 V and 3.60 lm/W at 8 V, respectively. The thickness of the blocking layer permit the tuning of the device spectrum to achieve a balanced white emission with Commission International de’Eclairage (CIE) chromaticity coordinates of (0.33,0.33). The CIE coordinates of device change from (0.3278, 0.3043) at 5 V to (0.3251, 0.2967) at 20 V that are well in the white region, which is largely insensitive to the applied bias.

Quinacridone sub-monolayer as efficient emitter in OLEDs

Efficient electroluminescence (EL) was obtained in organic light-emitting devices (OLEDs) using a Quinacridone (QAD) sub-monolayer as emitter, which was inserted in a narrow excitons formation Alq 3 layer. For the structure-optimized devices, efficient QAD emission almost without Alq 3 EL was observed, and a highest efficiency of 7.2 cd/A was attained by inserting 0.02-nm-thick QAD layer in the middle of 10-nm-thick Alq 3 layer which neighbored a blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The performance improvement was attributed to the application of the narrow excitons formation zone, in which both electrons and holes were confined, and resulted in efficient collision capture for the excitons formation. Confinement of excitons induces enhanced energy transfer from Alq 3 to QAD and weak emission from the Alq 3.

Size and Phase Control in Quinacridone Nanoparticle Formation by Laser Ablation in Water

Quinacridone (QA) nanoparticles were formed by nanosecond laser ablation of QA microcrystalline powder dispersed in water. The particle size and phase were examined at two different excitation wavelengths of 355 and 580 nm. At a fluence of 95 mJ/cm2, the mean sizes of the formed nanoparticles were approximately 22 and 50 nm at 355 and 580 nm excitations, respectively. The absorption spectra of the nanoparticles prepared by 355 nm laser pulses showed the caracteristic bands of the initial β-form QA in the fluence range from 30 to 120 mJ/cm2. On the other hand, 580 nm laser pulses with fluences of 50 to 118 mJ/cm2 caused the spectra to become similar to that of γ-form QA. We demonstrate that the crystalline phase and mean size of QA nanoparticles can be controlled by tuning the intensity and wavelength of laser pulses.

Efficient Electroluminescence from a Quinacridone sub-monolayer inserted in a narrow exciton formation zone confined by a blocking layer

Efficient electroluminescence (EL) was obtained from quinacridone (QA) sub-monolayer inserted in a tris(8-quinolinolato) aluminum (ALQ) layer which was confined by a blocking layer 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The thickness of the confined ALQ layer was optimized and the highest EL current efficiency of 7.2 cd/A was obtained by inserting a 0.02 nm-thick QA layer in the 10-nm thick ALQ layer, we attribute it to the narrow exciton formation zone, in which both electron and hole carriers were confined and resulted in efficient collision capture in the exciton formation process. In addition, exciton confinement led to improved energy transfer from ALQ to QA and weaken the emission from the ALQ itself. The two factors are simultaneously operating in efficiency enhancement.

Preparation and Characterization of Organic Light Emitting Devices Using QD Dopant

Two types of the organic light-emitting devices (OLEDs) with different emission structures were prepared using Alq3 (aluminum tris 8-hydroxyquinoline) host material and quinacridone (QD) dopant at the emission layer. One is the OLED device with emission layer consisting of Alq3 host material doped with QD dopant ("codoped OLED"). The another one has a seperated QD dopant film in the Alq3 emission layer ("undoped OLED"). The maximum brightness of the codoped and undoped OLEDs were 3207 cd/m2 and 1570 cd/m2, respectively. The wavelength of the maximum emission peak in the undoped sample was 527 nm and shifted slightly toward longer wavelength with the value of 540 nm for the codoped OLED sample. The maximum luminous efficiency of the undoped OLED was about 1.4 lm/W and increased to 7.0 lm/W for the codoped sample.

ORGANIC WHITE LIGHT EMITTING DEVICES WITH AN RGB STACKED MULTILAYER STRUCTURE

White organic light emitting devices (OLEDs) with an RGB stacked multilayer structure are demonstrated. In RGB staked OLEDs, blue emitting 1,4-bis[2,2-diphenylvinyl]biphenyl (DPVBi), green emitting quinacridone (QD), and red emitting [2,6-bis[2-[5-(dibutylamino)phenyl]vinyl]-4H-pyran-4-ylidene]propanedinitrile (DADB) were used. Through the optimization of the device structure, the pure white light emission with CIE coordinates of (0.33,0.33) at 20 mA/cm2 was obtained, at which the color temperature and color rendering index were 5560 K and 79, respectively. Its maximum luminance was 14,000 cd/m2 at 12.6 V, and the luminance efficiency was 1.34 lm/W at 100 cd/m2.

Refinement of the crystal structure of 5,7,12,14-tetrahydro[2,3-b]-quinolinoacridine (γ-form), C20H12N2O2, at 223 Κ

Article Refinement of the crystal structure of 5,7,12,14-tetrahydro[2,3-b]-quinolinoacridine (γ-form), C20H12N2O2, at 223 Κ was published on December 1, 2002 in the journal Zeitschrift für Kristallographie - New Crystal Structures (volume 217, issue 1).

Improvement of efficiency and color purity utilizing two-step energy transfer for red organic light-emitting devices

We present organic red light-emitting devices with improved optical and electrical characteristics utilizing the two-step energy transfer. N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine and tris-(8-hydroxyquinoline) aluminum (Alq) are used as hole and electron-transporting layers, respectively. Quinacridone (QAD) and 4-(dicyanomethylene)-2-t- butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) are codoped into the Alq emitting layer. Compared with devices where the emitting layer is only composed of Alq and DCJTB, the emitting characteristics such as emission efficiency and purity of emission color are greatly improved, and the turn-on voltage is decreased as much as 4 V. We attribute these improvements to the assistant dopant (QAD), which leads to the more efficient energy transfer from Alq to DCJTB.