Latent Pigment Research Articles

Precursor polymorph determines the organic semiconductor structure formed upon annealing

Polymorph selection in thin films of quinacridone obtained by the soluble latent pigment precursor method is found to be driven by the crystalline form of the precursor in a combined low-frequency Raman spectroscopy and X-ray diffraction study.

High-Efficiency Synthesis and Properties of Latent Pigment Red 272DPP-BOC by Microwave Irradiation

A high-efficiency synthesis method for a latent pigment of red pigment diketo-pyrrolo-pyrrole (Pig. Red 272:272DPP), which is important as a functional organic pigment, was investigated, and the investigation results revealed that irradiation of microwaves (MWs) for several seconds to 272 DPP in NMP (N-methyl-2-pyrrolidone) solvent yielded DPP latent pigment (272DPP-BOC) at a high yield of 86.2%. Two kinds of latent-pigment crystals, namely, red and yellow, were obtained by recrystallization, and it was found that the fluorescence-emission properties of the two kinds differ significantly. Single-crystal X-ray structural analysis showed that the difference in the fluorescence-emission properties of the two types is derived from the difference in their crystal structures.

Preparation of Naphthalene Dianhydride Bithiophene Copolymers by Direct Arylation Polycondensation and the Latent Pigment Approach.

Invited for this month's cover are the collaborating groups of Prof. Luca Beverina from the University of Molani-Bicocca, Italy and Prof. Michael Sommer from Chemnitz University of Technology, Germany. The front cover shows the thermally induced transformation of a soluble and electron-rich naphthalene tetraester-bithiophene copolymer into the corresponding insoluble and electron-poor naphthalenetetraanhydride derivative. The combination of monochromatic squares, inspired by the work of Josef Albers, shows the color change involved in the transformation. Read the full text of the article at 10.1002/cplu.201900210.

Preparation of Naphthalene Dianhydride Bithiophene Copolymers by Direct Arylation Polycondensation and the Latent Pigment Approach.

An alternating naphthalene dianhydride bithiophene copolymer (PNDAT2) is prepared by a combined direct arylation polycondensation and the latent pigment approach. PNDAT2 is the first reported example of an alternating conjugated polymer containing naphthalene dianhydride, the oxo-analogue of naphthalene diimide often used in electron-acceptor conjugated polymers. PNDAT2 is resistant to organic solvents and can be generated directly as film by thermal treatment of the soluble tetraester precursor PNTET2. PNDAT2 is characterized by a LUMO level of -3.9 eV, similar to that of established naphthalene diimide containing soluble copolymers. This route to insoluble electron acceptor copolymers by thermal cleavage of soluble precursors is an alternative to classical cross-linking or orthogonal processing strategies.

A Diketopyrrolopyrrole‐Based Dimer as a Blue Pigment

1,4-Diketopyrrolo[3,4-c]pyrroles (DPPs) constitute a class of hydrogen-bonded pigments covering a color range from yellow-orange to dark violet. We report facile dimerization of a Boc-substituted 3,6-dithienyl-DPP. The formed dimer shows brilliantly blue color as a result of the expansion of the chromophore. The soluble dimer acts as latent pigment and is converted to the corresponding pigment either via thermocleavage or acidic deprotection of the Boc groups. The synthesized pigment is characterized by high migrational stability in a polymer matrix and a clear blue color.

Diketopyrrolopyrrole latent pigment-based bilayer solar cells

Abstract Two Diketopyrrolopyrrole based latent pigment donor materials were fabricated into thin film bilayer photovoltaic devices featuring PCBM as the acceptor. Thermal deprotection of the thin film, carried out at 200∘ C, returns the dye-like small molecule to the corresponding pristine pigment quantitatively. The connected evolution of electrical and morphological features of pure thin films and blends are examined. A significant decrease in extinction coefficient was noted and correlated both to intrinsic changes of the electronic structure upon cleavage and to an increase in internal scattering due to extensive crystallization. Power conversion efficiencies of 0.33% were achieved for bilayer devices, nearly doubling previous results with latent pigment DPP devices, under comparable experimental conditions.

(Invited) Organic Based Electrochromic and Thermochromic Materials: Design, Characterization and Integration in Flexible Devices

Electrochromism and thermocromism are amongst the most promising chromogenic phenomena having real technological appeal. In particular, Organic electrochromic materials (OEMs) - the focus of the first part of the talk -offer a low power input and low cost solution for applications like smart windows, electrochromic sunglasses, electrochromic paper and displays. 1-3 Depending on the specific application, suitable OEMs should offer a wide color palette, high electrochromic contrast, fast switching, low cost and high stability. Relevant applications like sunglasses and automotive additionally require that the transmitted light experiences negligible color distortion in both device’s limiting states. The Donor-Acceptor (D-A) polymers concept so far gave best results on this very challenging topic. Indeed, the preparation of copolymers constituted by alternating electron rich and electron poor groups leads to devices having brown and even grey low transmittance states. Such result comes at the expenses of a somewhat limited transmittance in the bleached state (T ≈ 60 %). 2 Multichromophoric polymers (MCPs) represent a viable alternative to the D-A concept. Typical MCPs feature a PEDOT conjugated backbone, side chain functionalized with small molecule electrochromic derivatives acting as contrast enhancers and color tuning additives. 4 The most performing MCP so far reported, a naphthalenediimide containing cross-linked PEDOT, features a transmittance level above 80 % all over the visible region in the bleached state, along with a grey (T < 20 %) colored state. Cycling stability in the excess of 1000 cycles was also demonstrated. 5,6 We will discuss the synthesis and characterization of two new MCPs based upon specifically designed small molecule contrast enhancers pertaining to the class of Weitz electrochromes. The resulting side chain PEDOT polymers are able to reversibly switch between a brown and a colorless state, both of them complying with the performance of photochromic lenses. Figure 1a shows a representative example of an electrochromic devices based on said materials. In the second part of the talk we will focus on a particular use of organic thermochromic materials: Time Temperature Indicators for food safety. The spontaneous spoilage of fresh goods – milk might probably be the best everyday life example – due to inappropriate handling and storage, particularly during long distance delivery, is an acknowledged treat for public health, even more serious than adulteration. As such, there is a relevant technological interest towards the development of simple and low-cost smart labels that can be integrated into packages giving information on their whole thermal history. The current Time Temperature Indicator (TTI) 7-9 devices include two classes: a) Integrated circuits featuring data loggers and radio frequency identification chips, and b) simpler color indicators relying on chemical reactions such as enzymatic reactions. The second class is inexpensive and attractive for the packaging industry. We will show a new class of irreversible thermochromic molecular materials whose chemical transformation from a colorless state to a strongly colored one depends upon temperature, chemical substitution and substrate. The selection of the appropriate active molecule/substrate combination provides sensitivity to different targeted time/temperature regimes. 10 The key process providing the required irreversible color change is connected with the “latent pigment” approach. 11 Figure 1b shows one example of the two limiting states of demonstrator smart labels based upon latent squaraine pigments. Figure 1. a) Bleached (left) and colored (right) limiting states of an electrochromic device having the structure PET-ITO/organic electrochrome/electrolyte polymer membrane /Prussian blue/PET-ITO. b) bottom: comparison between a reference and a smart label based on a thermochromic material after 3 h at 4°C and at 25 °C; top: pictures taken at regular intervals of a TTI based on the molecule shown at 25°C. References. 1. J. Jensen, M. Hösel, A. L. Dyer, and F. C. Krebs, Adv. Funct. Mater., 25, 2073–2090 (2015). 2. P. M. Beaujuge, C. M. Amb, and J. R. Reynolds, Accounts Chem. Res., 43, 1396–1407 (2010). 3. P. M. Beaujuge and J. R. Reynolds, Chem. Rev., 110, 268–320 (2010). 4. L. Beverina, G. A. Pagani, and M. Sassi, Chem. Commun., 5413–5430 (2014). 5. M. Sassi et al., Adv. Funct. Mater., 26, 5240–5246 (2016). 6. M. Sassi et al., Adv. Mater., 24, 2004–2008 (2012). 7. M. Cavallini and M. Melucci, ACS Appl. Mater. Interfaces, 7, 16897–16906 (2015). 8. E. Shimoni, E. M. Anderson, and T. P. Labuza, J Food Science, 66, 1337–1340 (2001). 9. M. Riva, L. Piergiovanni, and A. Schiraldi, Packag. Technol. Sci., 14, 1–9 (2001). 10. D. Galliani et al., Advanced Optical Materials, 3, 1164–1168 (2015). 11. J. Zambounis, Z. Hao, and A. Iqbal, Nature, 388, 131–132 (1997). Figure 1

A latent pigment strategy for robust active layers in solution-processed, complementary organic field-effect transistors

A latent pigment approach enables solution-processing of small molecule films that are insoluble in aggressive solvents upon thermal cleavage of solubilizing groups.

Synthesis and Properties of Latent Pigment Nano- and Micro-encapsulated in High-durability Inorganic Capsules

Synthesis and Properties of Latent Pigment Nano- and Micro-encapsulated in High-durability Inorganic Capsules

First Demonstration of the Applicability of the Latent Pigment Approach to Plastic Luminescent Solar Concentrators

AbstractPlanar luminescent solar concentrators are slabs of high optical quality materials doped with luminophores. Such devices enable the collection of solar light over a large area, followed by concentrated emission at the slab edges due to total internal reflection. The luminophore plays a central role as it is responsible for light absorption over the largest possible fraction of the solar spectrum and efficient emission. We show how the latent pigment approach makes it possible to prepare bulk‐polymerized single‐layer luminescent solar concentrators doped with the high performance pigments quinacridone and perylenediimide. The process is advantageous in terms of overall synthetic efficiency for both quinacridone and perylendiimide. In the former case a sizeable improvement in photostability is also demonstrated.

Photoinduced Pigmentation Using Base-reactive Indigo Precursors in a Polymer Film

Abstract Organic pigments can be distinguished from dyes because of their insolubility. We have synthesized a soluble base-reactive indigo precursor as a latent pigment, which regenerates an indigo molecule by a base-catalyzed reaction. We also report here the pigmentation of indigo molecules regenerated by the basic species from photobase generator in a polystyrene film.

Crystallization and morphology of indanthrone converted from latent pigment in the solution with photo acid generator

The crystal phase, particle size, and morphology of organic pigments play an important role on the surface coating properties, such as substrate absorbency, surface smoothness, the light scattering properties, gloss, roughness, coating power, rheology and stability upon storage, etc. This paper aims to study the effect of photo acid generator (PAG) containing the stibium ion on the crystal structure and morphology of the regenerated pigment from the precursor of indanthrone in organic solvent. As measured from ultraviolet–visible spectroscopy and Fourier transform infrared spectroscopy, it was discovered that adding PAG accelerated the conversion of latent pigment to regenerated pigment. In addition, field emission scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis indicated that, as the amount of PAG increased, the regenerated pigment lost its crystal structure, which particle size is increased from 1 to 4 μm and morphology is changed from a bar like form to a cubic and spherical form.

Preparation and Optical Patterning of Organic-Inorganic Hybrid Color-Filter Films Using Latent Pigments by Utilizing Photo-Acid-Generator and Microwave Irradiation

Preparation and photo-patterning characteristics of organic-inorganic hybrid thin film containing latent pigment by using photo-acid-generator (PAG) and microwave irradiation have been investigated. The acrylic thin film modified with methoxysilane containing PAG was formed on a glass substrate and irradiated with ultraviolet rays to promote sol-gel reaction by catalytic action of acid which was generated from PAG. And then the film was hardened with microwave irradiation, yielding organic-inorganic hybrid polymer film having hardness, highly transparency and strong adhesion with a glass substrate. Since this reaction only occurred in the optically (UV) irradiated regions, by exploiting the difference between the adhesivenesses of these regions photo-irradiated through photomask with a glass substrate, it was possible to form a patterned film with pitch of 100 to 50 μm by a simple lift-off method. A pigment-containing film using latent pigments (with subtractive three primary colors of coloring materials) and a patterned film were prepared, and it was possible to make these films multi-colored by varying the mixing ratio of the pigments. This multi-colored film-preparation method is effective for simply and efficiently forming a color-filter film by applying optical and microwave irradiation.

Preparation and properties of sol-gel thin film containing quinacridone latent pigment by using laser irradiation

The synthesis of Ph-SiO2 film containing Qn-BOC latent pigment using the sol-gel method and the formation of thin film using laser irradiation have been investigated. The film is useful for a wavelength selective absorption film for displays and optical disk. Newly developed film formation technique using latent pigment and laser irradiation gives the excellent film having high transparency, excellent absorption characteristics and high durability. And also, this process is low cost process due to high speed film formation.

ラテント顔料含有有機無機ハイブリッド薄膜の合成と CO2 レーザによる高速成膜技術

ラテント顔料含有有機無機ハイブリッド薄膜の合成と CO2 レーザによる高速成膜技術

Pigmentation of Boc-indanthrone in Organic Solvent/Photopolymer through a Thermal Process

This work explores a pigment converted from a latent pigment in organic solvent and photopolymer through a thermal process. Measurements by thermogravimetric analysis (TGA), ultraviolet−visible (UV−vis) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy showed that regeneration of the pigment from boc-indanthrone in the solvent or photopolymer could be achieved by heating. X-ray diffraction (XRD) was employed to characterize the regenerated pigments. As shown in the results, the recrystallized structure is similar to the structure of the parent pigment. Analysis using field-emission scanning electron microscopy (FESEM) indicated that the particles of the re-formed pigment in the solvent were initially cubic, then aggregated into loose bars, and finally became firmly slated and flat for hydrogen-bonding and π−π stacking interactions. In addition, the morphology of the reproduced pigment was found to be cubic, as in the photopolymer.

Lessons on the Discovery and Assignment of Polymorphs, Highlighted by the Case of the Latent Pigment DPP-Boc

The latent pigment 1,4-diketo-2,5-di-t-butoxycarbonyl-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP-Boc) has three well-characterized polymorphic forms (denoted α, β, and γ) in the solid state, although some confusion exists in the literature concerning the assignment of these polymorphs. This paper clarifies the assignment of the three polymorphs of DPP-Boc, discusses various issues concerning the polymorphism of this material, and highlights several general issues regarding the characterization, discovery, and assignment of polymorphic systems.

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.

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 &#xB0;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&#xD7;10&#x2212;6 and 8.23&#xD7;10&#x2212;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&#xD7;10&#x2212;5 and 1.08&#xD7;10&#x2212;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.

Tert-Butyl 1,4-dioxo-3,6-diphenyl-1,2,4,5-tetrahydropyrrolo[3,4-c]pyrrole-2-carboxylate

The title compound, C23H20N2O4, is a soluble precursor (`latent pigment') of diketopyrrolo­pyrrole pigments. The tert-butoxy­carbonyl group is twisted by 78.5 (1)° with respect to the heterocyclic ring system. In the crystal structure, pairs of mol­ecules form centrosymmetric dimers through N—H⋯O intermolecular hydrogen bonds and are stacked in a herring-bone fashion along the a axis.