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In principle, polymerization tends to produce amorphous or poorly crystalline materials. Efficiently producing high-quality single crystals by polymerization in solvent remains as an unsolved issue in chemistry, especially for covalent organic frameworks (COFs) with highly complex structures. To produce μm-sized single crystals, the growth time is prolonged to >15 days, far away from the requirements in practical applications. Here, we find supercritical CO2 (sc-CO2) accelerates single-crystal polymerization by 10,000,000 folds, and produces two-dimensional (2D) COF single crystals with size up to 0.2 mm within 2~5 min. Although it is the fastest single-crystal polymerization, the growth in sc-CO2 leads to not only the largest crystal size of 2D COFs, but also higher quality with improved photoconductivity performance. This work overcomes traditional concept on low efficiency of single-crystal polymerization, and holds great promise for future applications owing to its efficiency, industrial compatibility, environmental friendliness and universality for different crystalline structures and linkage bonds., Rapid growth of highly crystalline Covalent organic framework (COF) materials remains challenging. Here, the authors accelerate single-crystal polymerization using supercritical CO2 and realize the fabrication of two-dimensional COF single crystals within several minutes.

Donor–acceptor dyads consisting of perylene bisimide (PBI) and trialkoxyphenyl–oligothiophene (TAPOT) units are reported that self-assemble into helical four-, six-, and seven-stranded hydrogen-bon...

Charge carrier mobility is an important figure of merit to evaluate organic semiconductor (OSC) materials. In aggregated OSCs, this quantity is determined by inter-chromophoric electronic and vibrational coupling. These key parameters sensitively depend on structural properties, including the density of defects. We have employed a new type of crystalline assembly strategy to engineer the arrangement of the OSC pentacene in a structure not realized as crystals to date. Our approach is based on metal–organic frameworks (MOFs), in which suitably substituted pentacenes act as ditopic linkers and assemble into highly ordered π-stacks with long-range order. Layer-by-layer fabrication of the MOF yields arrays of electronically coupled pentacene chains, running parallel to the substrate surface. Detailed photophysical studies reveal strong, anisotropic inter-pentacene electronic coupling, leading to efficient charge delocalization. Despite a high degree of structural order and pronounced dispersion of the 1D-bands for the static arrangement, our experimental results demonstrate hopping-like charge transport with an activation energy of 64 meV dominating the band transport over a wide range of temperatures. A thorough combined quantum mechanical and molecular dynamics investigation identifies frustrated localized rotations of the pentacene cores as the reason for the breakdown of band transport and paves the way for a crystal engineering strategy of molecular OSCs that independently varies the arrangement of the molecular cores and their vibrational degrees of freedom., Pentacene assembled into 1D arrays using a metal–organic framework (MOF) approach. This cofacial packing motif, which is not present in pentacene bulk, shows an interesting interplay of band-like and hopping-type transport.

Conjugated organic frameworks are an interesting class of functional porous organic materials having a π-conjugated backbone with permanent porosity. These materials are potential candidates for optoelectronic applications. Although there are several reports on the structure–property relationship between π-conjugated building blocks and optoelectronic performance, the influence of the linker position is hitherto unknown. We report two novel imine-linked 2D π-conjugated polymers which are positional isomers of each other consisting of pyrene and anthracene units. The polymers exhibited similar optical and electronic properties under ambient conditions. Upon I2 doping, one of the isomers exhibited high radical density and enhanced conductivity due to energetically favoured chemical oxidation. The linker position dramatically affects the optoelectronic performance of these polymers even though they have the same π-conjugated backbone.

Self-assembled π-conjugated molecules exhibit switching between crystalline–amorphous nanostructures, attracting significant interest in the field of organic electronics, particularly memory devices. Herein, we report ferrocene-appended tetratolylporphyrin, H2TTP-Fc, which undergoes protonation in 1,2-dichloroethane via sonication and reverses to the original state by deprotonation with time, as confirmed by optical and electrochemical properties. Absorption spectra reveal the selectivity of reversible and irreversible protonation of H2TTP-Fc in halogenated solvents and mineral acids. Microscopic analysis suggested that H2TTP-Fc aggregates exhibit a crystalline flower-like morphology from the joining of 2D microsheets, whereas H4TTP-Fc forms nanospheres with an average diameter of 150–200 nm upon methanol vapor diffusion (MVD). Electrochemical properties of H4TTP-Fc films reveal the ease of oxidation when compared to that in the solution state as a result of high current generation at less work function. ...

Doping of organic semiconductors enhances the performance of optoelectronic devices. Although p-type doping is well studied and successfully deployed in optoelectronic devices, air stable ntype doping was still elusive. We succeeded with n-type doping of organic semiconductors using molecular dopant N-DMBI under ambient conditions. Strikingly, n-type doping accounts for a gigantic increase of the photoconductivity of doped thin films. Electrical and optical properties of the n-doped molecular semiconductor were investigated by temperature dependent conductivity, electron paramagnetic resonance (EPR), and flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements. A significant reduction and saturation in activation energy with increasing doping level clearly suggests the formation of an impurity band and enhancement in carrier density. Computational studies reveal the formation of a charge transfer complex mediated by hydrogen abstraction as the rate-determining step for the doping mechanism. The colossal enhancement of photoconductivity induced by n-doping is a significant step toward optoelectronic devices made of molecular semiconductors.

The rod-like configuration of conjugated polymer chains with its low energetic disorder is the key to utilizing the backbone as a highly electrically-conductive wire. An energetic disorder that is higher than 0.1 eV, coupled with vibronic modes of the chains, leads to the localization of charges. Herein, we have tracked precisely the rod-like transition of poly(p-phenyleneethynylene) (PPE) chains as a function of temperature in diluted solutions, and shown a steep increase in persistence length at 230 K. The resulting rod-like configuration of the PPE chains with its extended electronic conjugation exhibited an extremely small energetic disorder of ∼70 meV, and was stabilized by subsequent polymer aggregate formation.

Visible light driven hydrogen (H2) production from water is a promising strategy to convert and store solar energy as chemical energy. Covalent organic frameworks (COFs) are front runners among different classes of organic photocatalyst, owing to their tunable porosity, crystallinity, optical and electronic properties. Photocatalytic activity of COFs depends on numerous factors such as band gap, crystallinity, porosity, exciton migration, charge separation and transport, stability etc. However, it is challenging to fine tune all these factors simultaneously to enhance the photocatalytic activity. Hence, in this report, we have prioritized the key factors for efficient photocatalytic H2 production through structure–property–activity relationship combined with microwave spectroscopy and first–principles calculations. Careful molecular engineering allowed us to tune the light absorption (i.e. band gap), crystallinity, porosity, layer stacking and charge carrier generation and transport of a series of isoreticular COFs. We have assessed how these properties and the interplay between them impact photocatalytic activity of studied COFs. From the structure–property–activity relationship, we found that light absorption and charge carrier generation and transport are the prime factors, which influence the photocatalytic H2 production of COFs in much greater extent than other factors.

We report an unprecedented strategy to generate and amplify near-infrared (NIR) emission in an organic chromophore by mechanical stress or gelation pathways. A greenish-yellow emitting film of π-extended Bodipy-1, obtained from n-decane, became orange-red upon mechanical shearing, with a 15-fold enhancement in NIR emission at 738 nm. Alternatively, a DMSO gel of Bodipy-1 exhibited a 7-fold enhancement in NIR emission at 748 nm with a change in emission color from yellow to orange-red upon drying. The reason for the amplified NIR emission in both cases is established from the difference in chromophore packing, by single crystal analysis of a model compound (Bodipy-2), which also exhibited a near identical emission spectrum with red to NIR emission (742 nm). Comparison of the emission features and WAXS and FT-IR data of the sheared n-decane film and the DMSO xerogel with the single crystal data supports a head-to-tail slipped arrangement driven by the N–H⋯F–B bonding in the sheared or xerogel states, which facilitates strong exciton coupling and the resultant NIR emission.

π-Gels are a promising class of functional soft materials formed out of short π-conjugated molecules. By utilizing the chemistry of noncovalent interactions, researchers have created a wide range of π-gels that are composed of supramolecular polymers. During the last two decades, supramolecular gel chemistry has been pursued with the hope of developing new materials for applications in, for example, organic electronics, energy harvesting, sensing, and imaging. The high expectations for π-gels were centered mainly around their electronic properties, such as tunable emission, energy transfer, electron transfer, charge transport, and electrical conductivity; such properties are amenable to modulation through size and shape control of molecular assemblies. Although a large number of exciting publications have appeared, a major technological breakthrough is yet to be realized. In this review, we analyze the recent advancements in the area of functional π-gels and their scope in future applications.

The very concept of dye and pigment chemistry that was long known to the industrial world underwent a radical revision after the discovery and commercialization of dyes such as mauveine, indigo, and so on. Apart from their conventional role as coloring agents, organic dyes, and pigments have been identified as indispensable sources for high-end technological applications including optical and electronic devices. Simultaneous with the advancement in the supramolecular chemistry of π-conjugated systems and the divergent evolution of organic semiconductor materials, several dyes, and pigments have emerged as potential candidates for contemporary optoelectronic devices. Of all the major pigments, diketopyrrolopyrrole (DPP) better known as the ‘Ferrari Pigment’ and its derivatives have emerged as a major class of organic functional dyes that find varied applications in fields such as industrial pigments, organic solar cells, organic field–effect transistors, and in bioimaging. Since its discovery in 1974 by Farnum and Mehta, DPP-derived dyes gained rapid attention because of its attractive color, synthetic feasibility, ease of functionalization, and tunable optical and electronic properties. The advancement in supramolecular polymerization of DPP-based small molecules and oligomers with directed morphological and electronic features have led to the development of high performing optoelectronic devices. In this review, we highlight the recent developments in the optoelectronic applications of DPP derivatives specifically engineered to form supramolecular polymers.

Organic semiconductors with variable charge carrier polarity are required for optoelectronic applications. Herein, we report the synthesis of three novel diketopyrrolopyrrole (DPP)-based D–A molecules having three different terminal groups (amide, ester, and dicyano) and study their electronic properties. An increase in electron acceptor strength from amide to dicyano leads to a bathochromic shift in absorption. Photoconductivity and field effect transistor (FET) measurements confirmed that a small increase in acceptor strength can result in a large change in the charge transport properties from p-type to n-type. The molecule with an amide group, DPP–amide, exhibited a moderate p-type mobility (1.3 × 10–2 cm2 V–1 s–1), whereas good n-type mobilities were observed for molecules with an ester moiety, DPP–ester (1.5 × 10–2 cm2 V–1 s–1), and with a dicyano group, DPP–DCV (1 × 10–2 cm2 V–1 s–1). The terminal functional group modification approach presented here is a simple and efficient method to alter the cha...

A π-conjugated amphiphilic diketopyrrolopyrrole (PDPP-Amphi) forms crystalline 2D supramolecular nanosheets in water when compared to that from methyl cyclohexane. These nanosheets exhibit high fluorescence quantum yield in the solid-state with anisotropic charge-carrier mobility of 0.33 cm2 V-1 s-1 .

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO2 and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO2 powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO2 powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH4)2Ce(NO3)6 and urea. The grain size achieved by the hydrothermal technique is ∼7 nm which is smaller than that of commercial nano CeO2 powders. Conventional or microwave sintering was used to prepare dense Ce0.8Gd0.2O1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd2O3 as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400 °C is 1 × 10−2 and 2.4 × 10−2 S/cm at 700 °C and 800 °C respectively.

This paper reports for the first time the attempted synthesis of SrO- and MgO-doped LaGaO 3 (La 1− x Sr x Ga 1− y Mg y O 3−0.5( x + y ) , LSGM) perovskite by an aqueous ‘regenerative’ solution route. This novel technique enabled recycling of the undesired product and subsequently yielded product with much better phase purity and density than that obtained from the solid-state route. La 0.8 Sr 0.2 Ga 0.85 Mg 0.15 O 2.825 (LSGM-2015) and LaGaO 3 were prepared using both the regenerative sol–gel (RSG) and conventional solid-state route at 1400 °C. Series of La 0.8 Sr 0.2 Ga 0.83 Mg 0.17 O 2.815 (LSGM-2017) pellets were also prepared by the RSG method at different sintering temperature (1200–1500 °C) and time. The effect of conventional and microwave sintering of samples obtained from both solid-state and regenerative route was also investigated. Microwave heating was carried out using SiC as a microwave susceptor. The LSGM pellets prepared by using different synthetic methods were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and pellet density was determined by pycnometry. The LSGM-2015 prepared by RSG route exhibited conductivity σ t = 0.066 and 0.029 S cm −1 at 800 and 700 °C, respectively, and activation energy of the bulk, grain-boundary, and total are E b = 0.97 eV, E gb = 1.03 eV and E t = 1.01 eV, respectively. The sintering temperature severely affected the grain size (

The formation of coaxial p-n heterojunctions by mesoscale alignment of self-sorted donor and acceptor molecules, important to achieve high photocurrent generation in organic semiconductor-based assemblies, remains a challenging topic. Herein, we show that mixing a p-type π gelator (TTV) with an n-type semiconductor (PBI) results in the formation of self-sorted fibers which are coaxially aligned to form interfacial p-n heterojunctions. UV/Vis absorption spectroscopy, powder X-ray diffraction studies, atomic force microscopy, and Kelvin-probe force microscopy revealed an initial self-sorting at the molecular level and a subsequent mesoscale self-assembly of the resulted supramolecular fibers leading to coaxially aligned p-n heterojunctions. A flash photolysis time-resolved microwave conductivity (FP-TRMC) study revealed a 12-fold enhancement in the anisotropic photoconductivity of TTV/PBI coaxial fibers when compared to the individual assemblies of the donor/acceptor molecules.

The tunable luminescent features along with the electrical conductivity (~2 × 10(-4) S m(-1)) exhibited by the gel fibers formed through supramolecular polymerisation of the N-annulated perylenedicarboxamide based π-gelator are reported.

Making large-scale, multifunctional, paper-like, free-standing membranes (FSM) and the FSM-based 3D macroscopic devices purely from long inorganic functional nanowires is challenging in many nanomaterials systems. Here we report synthesis of long nanowires of the catalytic titanate for direct fabrications of the FSM and the FSM-based 3D devices that are among the first to show unusual potentials in photocatalysis, write−erase−rewrite, microfiltration, and controlled release.

Sr2/3La1/3FeO3 is a perovskite-type oxide with formally 67% Fe4+ and 33% Fe3+ ions revealing a charge disproportionation of Fe4+ and concomitant Fe3+Fe3+Fe5+ charge ordering below its Neel temperature of ∼200 K. Co-doped materials Sr2/3La1/3Fe1−xCoxO3 (0.15⩽x⩽0.33) were synthesized and investigated by X-ray powder diffraction, 57Fe Mossbauer spectroscopy, magnetization measurements, and magnetotransport studies in order to explore the relation between charge ordering, magnetic properties, and magnetoresistance effects in this system. Cobalt substitution induces the formation of charge disordered ferromagnetic clusters (x=0.15, 0.24) and finally leads to complete suppression of the charge disproportionation (x=0.33). Spin-glass like magnetic properties are observed. Pronounced negative magnetoresistance effects up to −20% at 5 K and 7 T are attributed to reduced scattering of charge carriers due to parallel spin alignment of ferromagnetic regions in an applied magnetic field.