Latent pigments activated by heat

Hydrogen-bonded organic semiconductor micro- and nanocrystals: from colloidal syntheses to (opto-)electronic devices

Organic pigments such as indigos, quinacridones, and phthalocyanines are widely produced industrially as colorants for everyday products as various as cosmetics and printing inks. Herein we introduce a general procedure to transform commercially available insoluble microcrystalline pigment powders into colloidal solutions of variously sized and shaped semiconductor micro- and nanocrystals. The synthesis is based on the transformation of the pigments into soluble dyes by introducing transient protecting groups on the secondary amine moieties, followed by controlled deprotection in solution. Three deprotection methods are demonstrated: thermal cleavage, acid-catalyzed deprotection, and amine-induced deprotection. During these processes, ligands are introduced to afford colloidal stability and to provide dedicated surface functionality and for size and shape control. The resulting micro- and nanocrystals exhibit a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near-infrared. Due to excellent colloidal solubility offered by the ligands, the achieved organic nanocrystals are suitable for solution processing of (opto)electronic devices. As examples, phthalocyanine nanowire transistors as well as quinacridone nanocrystal photodetectors, with photoresponsivity values by far outperforming those of vacuum deposited reference samples, are demonstrated. The high responsivity is enabled by photoinduced charge transfer between the nanocrystals and the directly attached electron-accepting vitamin B2 ligands. The semiconducting nanocrystals described here offer a cheap, nontoxic, and environmentally friendly alternative to inorganic nanocrystals as well as a new paradigm for obtaining organic semiconductor materials from commercial colorants.

25th anniversary article: progress in chemistry and applications of functional indigos for organic electronics

Indigo and its derivatives are dyes and pigments with a long and distinguished history in organic chemistry. Recently, applications of this 'old' structure as a functional organic building block for organic electronics applications have renewed interest in these molecules and their remarkable chemical and physical properties. Natural-origin indigos have been processed in fully bio-compatible field effect transistors, operating with ambipolar mobilities up to 0.5 cm(2) /Vs and air-stability. The synthetic derivative isoindigo has emerged as one of the most successful building-blocks for semiconducting polymers for plastic solar cells with efficiencies > 5%. Another isomer of indigo, epindolidione, has also been shown to be one of the best reported organic transistor materials in terms of mobility (∼2 cm(2) /Vs) and stability. This progress report aims to review very recent applications of indigoids in organic electronics, but especially to logically bridge together the hereto independent research directions on indigo, isoindigo, and other materials inspired by historical dye chemistry: a field which was the root of the development of modern chemistry in the first place.

Fluorescent materials for pH sensing and imaging based on novel 1,4-diketopyrrolo-[3,4-c]pyrrole dyes†Electronic supplementary information (ESI) available: NMR and MS spectra, further sensor characteristics and sensor long-time performance. See DOI: 10.1039/c3tc31130aClick here for additional data file

New optical pH-sensors relying on 1,4-diketopyrrolo-[3,4-c]pyrroles (DPPs) as fluorescent pH-indicators are presented. Different polymer hydrogels are useful as immobilization matrices, achieving excellent sensitivity and good brightness in the resulting sensor. The operational pH can be tuned over a wide range (pH 5-12) by selecting the fine structure of the indicator and the matrix. A ratiometric sensor in the form of nanoparticles is also presented. It is suitable for RGB camera readout, and its practical applicability for fluorescence imaging in microfluidic systems is demonstrated. The indicators are synthesized starting from the commercially available DPP pigments by a straightforward concept employing chlorosulfonation and subsequent reaction with amines. Their sensitivity derives from two distinct mechanisms. At high pH (>9), they exhibit a remarkable alteration of both absorption and fluorescence spectra due to deprotonation of the lactam nitrogen atoms. If a phenolic group is introduced, highly effective fluorescence quenching at near-neutral pH occurs due to photoinduced electron transfer (PET) involving the phenolate form.

Synthesis and Spectroscopic Studies of N,N'-dialkyl Derivatives of Antisymmetrical 2H,5H-Dihydropyrrolo[3,4-c]pyrrole-1,4-diones

2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione derivatives (DPP) are chemically stable, fluorescent molecules, known as High Performance Pigments. Preparation of the soluble derivatives of DPPs provides great advantage in designing the optic sensor for new and existing applications and overcoming aggregation problems in solid matrices. For this purpose, the synthesis of antisymmetric DPPs and the formation of new organic dyes through N,N'-dialkylation and their spectroscopic studies have been carried out both in solutions and in solid phase.

Coordinative layer-by-layer assembly of electrochromic thin films based on metal ion complexes of terpyridine-substituted polyaniline derivatives

Preparation, metal ion complexation, and coordinative assembly into organized electro-chromic films of a polyaniline derivative P1 substituted with tert-butyloxycarbonyl (boc) and terpyridine (tpy) substituent groups in alternating sequence are described. Cleavage of the boc groups after processing into thin films is also described. P1 is prepared upon Pd-catalyzed polycondensation of N-tert-butyloxycarbonyl-4,4'-dibromodiphenylamine and 4'(4-aminophenyl)-2,2':6,2''-terpyridine. The molecular weight is in the range of oligomers, the tetramer and pentamer being the most abundant species. P1 is soluble in common organic solvents. Solutions are pale yellow with blue or green fluorescence depending on the solvent. Fluorescence quantum yields up to 68% are found. P1 is able to complex divalent metal salts such as zinc(II) chloride, for example. Titration experiments indicate the formation of 2:1 tpy:metal ion complexes. Layer-by-layer (LbL) assembled films of metal ion complexes of P1 can be prepared, if negatively charged substrates are alternately dipped into solutions of metal(II) hexafluorophosphates and P1. Films of the zinc and nickel ion complex of P1 are lemon yellow in the neutral state and change color into greenish gray upon anodic oxidation, while Co-containing films are purple and change color into grayish blue upon oxidation. All color changes are reversible under ambient conditions. ATR-IR studies indicate that thermal treatment of the films at 180 °C, or acid treatment, e.g. with 5% aqueous trifluoroacetic acid solution, results in cleavage of the boc groups. P1 is transformed into the polyaniline derivative P2 with tpy substituent groups at every second N atom in the backbone. Films of metal ion complexes of P2 are also electrochromic albeit the colors differ slightly from those of P1. For example, the absorption maximum of the Zn-P2 film is at 456 nm, whereas it is at 446 nm for the corresponding Zn-P1 film. Prior to cleavage of the boc group, electrochromic switching times are 1.1 to 2.0 s for 30 to 40 nm thick films, while after the cleavage 0.5 to 1.2 s are found. The contrast is 13 to 19%, and not affected by the cleavage. Because of high stability, fast switching, and high contrast, the films might be useful as active materials in electrochromic devices.

Organic photoresponse materials and devices

Organic photoresponse materials and devices are critically important to organic optoelectronics and energy crises. The activities of photoresponse in organic materials can be summarized in three effects, photoconductive, photovoltaic and optical memory effects. Correspondingly, devices based on the three effects can be divided into (i) photoconductive devices such as photodetectors, photoreceptors, photoswitches and phototransistors, (ii) photovoltaic devices such as organic solar cells, and (iii) optical data storage devices. It is expected that this systematic analysis of photoresponse materials and devices could be a guide for the better understanding of structure-property relationships of organic materials and provide key clues for the fabrication of high performance organic optoelectronic devices, the integration of them in circuits and the application of them in renewable green energy strategies (critical review, 452 references).

Conjugated polymers containing diketopyrrolopyrrole units in the main chain

Research activities in the field of diketopyrrolopyrrole (DPP)-based polymers are reviewed. Synthetic pathways to monomers and polymers, and the characteristic properties of the polymers are described. Potential applications in the field of organic electronic materials such as light emitting diodes, organic solar cells and organic field effect transistors are discussed.

Nonlinear organic reactions to proliferate acidic and basic molecules and their applications

Acid amplifiers derived from a certain class of sulfonates suffer from autocatalytic decomposition in the presence of a strong acid to give corresponding sulfonic acids, which catalyze the decomposition of the parent sulfonates, leading to the liberation of more of the same sulfonic acids in an exponential manner. Five types of acid amplifiers displaying acid proliferation reactions are presented. A certain type of carbamate exhibits autocatalytic fragmentation to give the corresponding aliphatic amine and olefin together with carbon dioxide, whereas the generated amine is able to act as a catalyst for the fragmentation so that the carbamates are referred to as base amplifiers. Applications of acid and base amplifiers to photofunctional materials, including photoresists, are described as a consequence of the combination of the molecular amplifiers with photoacid as well as photobase generators. Practical applications of acid proliferation reactions in polymer films are discussed.