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The fabrication of a donor–acceptor based soluble porous organic polymer via smart tuning of the rigidity and flexibility for aqueous-organic biphasic photocatalytic hydrogen evolution.

Small organic luminogens, owing to their contrasting stimuli-responsive fluorescence in solution along with strong emission in aggregated and solidstates, have been employed in optoelectronic devices, sensors, and bioimaging. Pyrene derivatives usually exhibit strong fluorescence and concentration-dependent excimer/aggregate emission in solution. However, the impacts of microenvironments on the monomer and aggregate emission bands and their relative intensities in solution, solid, and supramolecular aggregates are intriguing. The present study delineates a trade-off between the monomer and aggregate emissions of a pyrene-benzophenone derivative (ABzPy) in solution, in the solid-state, and in nanoaggregates through a combined spectroscopic and microscopic approach. The impact of external stimuli (viscosity, pH) on the aggregate emission was demonstrated using steady-state and time-resolved spectroscopy, including fluorescence correlation spectroscopy and fluorescence anisotropy decay analysis. The aggregate formation was noticed at a higher concentration (10 μM) in solution, at 77 K (5 μM), and in the solid-state due to the π-π stacking interactions (3.6 Å) between two ABzPy molecules. In contrast, no aggregate formation was observed in the viscous medium as well as in a micellar environment even at a higher concentration of ABzPy (50 μM). The crystal structure analysis further shed light on the intermolecular hydrogen-bonding-assisted solid-state emission, which was found to be highly sensitive toward external stimuli like pH and mechanical forces. The broad emission band comprising both monomer and aggregate in the aqueous dispersion of nanoaggregates was used for the specific cellular imaging of lysosomes and lipid droplets, respectively.

Photocatalytic dehydrogenation of biomass derived ethanol: boosting bio-chemical economy.

The review unravels the order–disorder conundrum in porous organic polymers in view of task-specific applications through a comparative deliberation.

Strategizing the exploitation of renewable solar light could undoubtedly provide new insight into the field of biomass valorization. Therefore, for the first time, we reported the heterogeneous photocatalytic oxidation route of renewable furfural (FUR) to produce industrial feedstocks maleic anhydride (MAN) and 5-hydroxy-2(5H)-furanone (HFO) under simulated solar light (AM 1.5 G) using molecular oxygen (O2) as terminal oxidant and mesoporous graphitic carbon nitride (SGCN) as photocatalyst. SGCN showed an excellent photo-conversion (>95%) of FUR with 42 % and 33 % selectivity of MAN and HFO respectively. Moreover, an excellent selectivity towards MAN (66 %) under natural sunlight manifests a pioneering route for the sustainable production of MAN. In addition, the underlying mechanistic route of the FUR photo-oxidation was investigated via various experiments including scavenger studies, substrate studies, and electron spin resonance (ESR) studies which constructively proved the pivotal role of singlet oxygen (1O2) and holes (h+) in FUR photo-oxidation.

We delineated the underlying design strategies and photophysical pathways involved in multifunctional luminescent probes for intracellular sensing and imaging.

The electrochromic materials have received immense attention for the fabrication of smart optoelectronic devices. The alteration of the redox states of the electroactive functionalities results in the color change in response to electrochemical potential. Even though transition metal oxides, redox-active small organic molecules, conducting polymers, and metallopolymers are known for electrochromism, advanced materials demonstrating multicolor switching with fast response time and high durability are of increasing demand. Recently, two-dimensional covalent organic frameworks (2D COFs) have been demonstrated as electrochromic materials due to their tunable redox functionalities with highly ordered structure and large specific surface area facilitating fast ion transport. Herein, we have discussed the mechanistic insights of electrochromism in 2D COFs and their structure-property relationship in electrochromic performance. Furthermore, the state-of-the-art knowledge for developing the electrochromic 2D COFs and their potential application in next-generation display devices are highlighted.

In an enduring quest to develop highly efficient display and lighting devices over the decades, semiconductor nanocrystals have recently emerged as favorable candidates. However, developing a prudent and viable methodology to fabricate high-quality semiconductor nanocrystals exhibiting tunable luminescence, including single-component white light emission, is challenging. Herein, we report a facile one-pot synthetic route to fabricate white light emitting CdSeₓSy nanocrystals demonstrating high quantum yield using CdO, S powder, and Se powder as precursors. A phosphine-free route was adopted, employing paraffin oil as the reducing agent and solvent for the fabrication. The optical properties can be effectively tailored by controlling the reaction time and the Se/S molar ratio. The pristine CdSeₓSy nanocrystals exhibited a broad visible range emission from 400 to 750 nm. The CdSeₓSy nanocrystals (Se/S = 0.4) displayed white light emission with Commission Internationale de l’Eclairage (CIE) chromaticity coordinates of (0.30, 0.31) and quantum yield of 50 ± 3%. Moreover, by manipulating the Se/S ratio effectively, the band-edge (∼400–450 nm) to trap-state (∼550–750 nm) emission was tuned, and the distinct shades of white light were obtained. The white light emission was retained in nanocrystals-embedded poly(methyl methacrylate) (PMMA) thin film and also in the hydrogel matrix. Furthermore, white light emission characteristics from CdSeₓSy nanocrystals (Se/S = 0.4), PMMA thin film, and thin film coated white light emitting devices were found to be similar even after months of fabrication, indicating the high stability of the nanocrystals and sustainability of the materials derived from nanocrystals. The one-pot, low-cost fabrication route demonstrated in the present study offers the promising scope of white light emitting CdSeₓSy nanocrystals in solid-state display applications.

Supramolecular self-assembly of small organic molecules has emerged as a powerful tool to construct well-defined micro- and nanoarchitecture through fine-tuning a range of intermolecular interactions. The size, shape, and optical properties of these nanostructures largely depend on the specific assembly of the molecular building units, temperature and polarity of the medium, and external stimuli. The engineering of supramolecular self-assembled nanostructures with morphology-dependent tunable emission is in high demand due to the promising scope in nanodevices and molecular machines. However, probing the evolution of molecular aggregates from the solution and directing the self-assembly process in a pre-defined fashion are challenging. In the present study, we have deciphered the sequential evolution of supramolecular nanofibers from solution to spherical and oblong-shaped nanoparticles through the variation of solvent polarity, tuning the hydrophobic–hydrophilic interactions. An intriguing case of molecular self-assembly has been elucidated employing a newly designed π-conjugated thiophene derivative (TPAn) through a combination of steady-state absorption, emission measurements, fluorescence correlation spectroscopy (FCS), and electron microscopy. The FCS analysis and microscopy results revealed that the small-sized nanofibers in the dispersion further agglomerated upon solvent evaporation, resulting in a network of nanofibers. Stimuli-responsive reversible interconversion between a network of nanofibers and spherical nanoaggregates was probed both in dispersion and solvent-evaporated state. The evolution of organic nanofibers and a subtle control over the self-assembly process demonstrated in the current investigation provide a general paradigm to correlate the size, shape, and emission properties of fluorescent molecular aggregates in complex heterogeneous media, including a human cell., Supramolecular nanofiber evolution in solution and solid-state, including stimuli-responsive reversible interconversion among diverse nanoarchitectures, was probed through a combined spectroscopic and microscopic approach.

A π-conjugated porous organic polymer (BCzBz) was fabricated employing N,N'-bicarbazole and benzothiadiazole as molecular building units exhibiting broad visible light absorption. The photostable, water-dispersible, and cytocompatible BCzBz was demonstrated as an efficient probe for intracellular reactive oxygen species generation under photoirradiation.

An intriguing case of intramolecular and intervalence charge transfer-driven multistate electrochromism and electrofluorochromism in dibenzophenazin-(phenyl)methanone and arylamine-based redox-active donor-acceptor-donor molecules was elucidated. Tunable absorption from UV to NIR and on-off switching of fluorescence in a single-component all-organic molecular material by a subtle variation of electric potentials were demonstrated.

Nanostructured hypercrosslinked porous organic polymers have triggered immense research interest for a broad spectrum of applications ranging from catalysis to molecular separation. However, it still remains a challenge to tune their nanoscale morphology. Herein, we demonstrated a remarkable variation of morphologies of triptycene-based hypercrosslinked microporous polymers starting from irregular aggregates (FCTP) to rigid spheres (SCTP) to two-dimensional nanosheets (SKTP) from three distinct polymerization methodologies, Friedel-Crafts knitting using an external crosslinker, Scholl reaction, and solvent knitting, respectively. Further, the dramatic role of reaction temperatures, catalysts, and solvents resulting in well-defined morphologies was elucidated. Mechanistic investigations coupled with microscopic and computational studies revealed the evolution of 2D nanosheets of a highly porous solvent-knitted polymer (SKTP, 2385 m

Controlling the nonradiative deactivation of triplet states and tuning the singlet–triplet energy gap are the major challenges in developing materials that exhibit thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). Additionally, the conformational flexibility/rigidity around the donor–acceptor bond and the π-spacer unit significantly alters the charge transfer efficiency, subsequently impacting the relative propensity of TADF and RTP. Herein, we propose a new class of multichromophoric tridonor–acceptor (D3–A) compounds with rigid and flexible π-spacers having N-rich pyridoquinoxaline and pyridopyrazine acceptor cores, respectively. The molecule with carbazole donors meta to the quinoxaline nitrogen of the rigid pyridoquinoxaline core exhibits TADF, whereas the variation of the linkage position of carbazole to the pyridoquinoxaline as well as the twisted and flexible pyridopyrazine core shows predominantly RTP due to a relatively higher singlet–triplet energy gap. Increasing the donor strength with phenoxazine in the pyridopyrazine system leads to TADF and RTP simultaneously. Furthermore, we demonstrate the promising scope of the all-organic triplet harvesting materials in solid-state security encryption.

The Main Boundary Thrust (MBT) Zone in the Darjeeling foothills, Eastern Himalaya exhibits northerly dipping fault splays, named here as MBT-1 and MBT-2, with Proterozoic Daling Group in the MBT-1 hanging wall, Upper Paleozoic Gondwana rocks between the MBT-1 and the MBT-2, and Neogene Siwalik Group in the footwall of the MBT-2. On the basis of reduced stress tensors from fault-slip analysis and their grouping relative to different stratigraphic units in the MBT zone that crops out over a strike length of ∼20 km, the following successive stress regimes have been interpreted. The earliest brittle deformation recorded only in the basal part of the Gondwana succession was controlled by a pre-Himalayan NW-SE extensional regime. The Himalayan deformation under sustained N-S compressive regime developed in three stages: (a) thrust displacement along the MBT-1, juxtaposing folded Daling rocks against the Lower Gondwana rocks; (b) tilting and fracturing of Lower Gondwana succession and thrust transport over the Siwalik rocks along the MBT-2; (c) strike-slip regime with NW- and NE-trending faults affecting both the Lower Gondwana and Siwalik strata, developed possibly due to increased tectonic loading. The tensor solutions under N-S compressional regime are consistent with the modern plate convergence, supporting a foreland propagating thrust system in the Eastern Himalaya. In addition, an E-W extensional regime led to apparent orogen-parallel extension.

A novel approach for the fabrication of a solution processable conjugated porous organic polymer (CzBDP) involving a flexible core composed of carbazole and boron dipyrromethene was developed. The red emitting soluble polymer was found to be an excellent probe for the generation of both singlet oxygen and superoxide anion radicals under visible light irradiation.

The intramolecular charge transfer-driven emission properties of T and V-shaped donor-acceptor-donor molecules involving a new acceptor core of pyridoquinoxaline were demonstrated. The T-shaped molecule exhibits a large Stokes shift, red emission in the solid state and remarkable viscosity and temperature-dependent tunable fluorescence including a thermally-induced single-component near white-light emission.

The present study demonstrates the tuning of iconic optical features of pyrene through its judicious assembly with a C3-symmetric triaminoguanidinium ion, leading to the development of a unique multifunctional luminescent material PYTG. By fine tuning the concentration and the external stimuli, such as temperature, the addition of analytes led to a dramatic change in the fluorescence of PYTG, providing an excellent platform for the exploration of the dynamic and static excimer formation. Recently, white-light-emitting molecular probes have received considerable attention from the scientific community due to their great potentials in display devices. Tripodal PYTG was employed as a pure white-light emitter consisting of blue emission from monomers and orange emission from excimers both in solution and thin film with Commission Internationale de l’Eclairage (CIE) coordinates of (0.33, 0.34) and (0.33, 0.38), respectively. The formation of a dynamic excimer along with monomer fluorescence at higher concentrations of PYTG led to tunable emission. Additionally, the rich electronic properties of PYTG allowed efficient detection of trivalent metal ions by turn-on fluorescence and colorimetric sensing of fluoride ions. PYTG selectively detected Fe3+ and Al3+ with nanomolar sensitivity in a semi-aqueous solution via a chelation-enhanced fluorescence response in the orange-red region (λem = 588 nm) by static excimer formation. The ‘on–off’ fluorescence switching by the consecutive addition of trivalent cations and a chelating ligand EDTA makes PYTG a promising fluorescent molecular switch. A simple and cost-effective strategy, leading to the development of a versatile fluorescent probe and an in-depth exploration of the structure–property relationship as delineated in the present manuscript, will pave the way for the emergence of novel task-specific molecular optical materials.

A simple and cost-effective methodology employing environmentally benign substances for the fabrication of white-light emitting materials is important for practical applications in the field of lighting and display devices. Designing purely organic-based white-light-emitting systems with high quantum efficiency in aqueous media is an unmet challenge. With this objective, a new class of pyridoindole-based hydrophobic fluorophore 6,7,8,9-tetrapropylpyrido[1,2-a]indole-10-carbaldehye (TPIC) was introduced. A strategy of self-assembly using nonionic surfactants was employed to enhance the fluorescence of TPIC in an aqueous medium and was exploited as energy donor. The steady-state and time-resolved emission spectra analysis revealed the micelle-mediated energy transfer from TPIC to Nile red (energy acceptor) leading to tunable fluorescence along with white-light emission. The white-light emitting aqueous solution was obtained with the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.33, 0.36) and significantly high quantum yield of 37 %. Solid-state white-light emission was achieved retaining the assembly of fluorophores in the form of a gel having the high quantum efficiency of 33 % with CIE coordinates of (0.32, 0.36); close to that of pure white light. The bright white luminescence of the inscription prepared using white-light emitting gel on a solid substrate offers promising applications for full-color flat panel displays.

The origin of reddening of granitoid is controversial. Red granitoids, occurring spatially with grey granitoids with a thin transitional zone is a volumetrically significant litho-type in the Bundelkhand Craton, north central India. Using detailed petrography and microstructure study, and phase compositions and elemental X-ray maps, we demonstrate for the first time that pervasive infiltration of Fe-Mg-Na-K-rich fluid caused re-equilibration of ~2.5 Ga grey monzogranite during both brittle and ductile deformation in the craton. The reddening of granitoid is attributed to replacement and precipitation of tiny Fe-rich particles in porous feldspars by the high temperature Fe-Mg-Na-K-rich fluid (~950°C), plausibly from crust–mantle depths. The Fe-Mg-Na-K-rich fluid with high to moderately high FeO (≤27 wt%), MgO (≤19 wt%), Al2O3 (≤20 wt%), Na2O (

A new core of [1,2,5]-thiadiazolo-[3,4-c]-pyridine was employed for the fabrication of microporous organic polymers exhibiting a very high CO2 uptake of 5.8 mmol g−1 (25.5 wt%) at 273 K and 1 bar. The presence of CO2-philic active sites and microporosity confer the high uptake and superior selectivity (61) towards CO2 over N2.

Schiff base condensation and C–C coupling between a biologically important heterocycle pyrido[1,2-a]indole (PI) and aggregation induced emission active tetraphenylethylene (TE) led to the formation of weakly fluorescent PITE1 and strongly fluorescent PITE2, respectively. The photophysical phenomenon was rationalized by crystal structure analysis; PITE2 was found to exhibit strong fluorescence in solution, nanoparticles and solid state.

A versatile fluorescent probe, PITE, based on alkyl-substituted pyridoindole (PI) and tetraphenylethylene (TE), which exhibits facile pH-induced fluorescence switching in solution, as nanoparticles, and in the solid state, is presented. Strong fluorescence in the solid state, as well as in solution and the aggregated state, allow sensing of toxic acid vapors. Fluorescence "off-on" switching of PITE through exposure to trifluoroacetic acid and triethylamine vapor is visualized by the naked eye. A unified picture of the switchable fluorescence of PITE is obtained by comprehensive spectroscopic investigations coupled with quantum mechanical calculations. Strong fluorescence, a large Stokes shift, high photostability, and biocompatibility of PITE make it a viable probe for subcellular imaging. Extensive fluorescence microscopic studies by employing organisms including lower and higher eukaryotes reveal specific localization of PITE to lipid droplets (LDs). LDs are dynamic subcellular organelles linked to various physiological processes and human diseases. Hence, the specific detection of LDs in diverse organisms is important to biomedical research and healthcare. Isolation of LDs and subsequent colocalization studies ascertain selective targeting of LDs by the easily affordable, lipophilic bioprobe, PITE. Thus, PITE is a promising multifunctional probe for chemosensing and the selective tracking of LDs.

An ultra-bright fluorescence probe comprising conjugated polymer nanoparticles is developed for biological imaging. Highly blue fluorescent polyfluorene nanoparticles (PF-NPs) stabilized by sodium dodecylsulfate with an average diameter of 100 nm are prepared by a miniemulsion technique. A folate-conjugated cationic triblock copolymer is employed to coat negatively charged PF-NPs via electrostatic interaction for specific cell imaging of folate receptor over-expressing cancer cells. The coated PF-NPs show a similar size and morphology to the pristine PF-NPs, while the fluorescence intensity is enhanced. Such surface-functionalized PF-NPs are demonstrated to be suitable probes for efficient cell imaging of folate receptor over-expressing KB cells by CLSM and flow cytometry.

Fluorescent microporous organic polymers (MOPs) are an emerging class of porous organic materials with considerable technological relevance due to great promise in a range of applications, in addition to typical usage in gas storage and catalysis. In this respect, innovative optical materials have been developed based on MOPs. In this Concept article, a brief appraisal of the fabrication methodologies of fluorescent MOPs in the form of bulk solid as well as in nanoparticles, their optical attributes, and promising application potentials are presented.

A polyelectrolyte-assisted reprecipitation method is developed to fabricate nanoparticles of highly soluble molecules. The approach is demonstrated by using a zwitterionic diaminodicyanoquinodimethane molecule bearing remote ammonium functionalities with high solubility in water as well as organic solvents. Nanoparticles are prepared by injecting aqueous solutions of this compound containing an optimum concentration of sodium poly(styrenesulfonate) into methanol. The strong fluorescence exhibited by the compound in the aggregated state is reflected in the enhanced fluorescence of the polyelectrolyte complex in water. The nanoparticles formed in the colloidal state manifest even stronger fluorescence, which leads to an overall enhancement by about 90 times relative to aqueous solutions of the pure compound. The conditions for achieving the emission enhancement are optimized and a model for the molecular-level interactions and aggregation effects is developed through a range of spectroscopy, microscopy, and calorimetry investigations and control experiments.

A wide variety of amines are known to react with 7,7,8,8-tetracyanoquinodimethane (TCNQ) to yield push-pull diaminodicyanoquinodimethanes with a strongly zwitterionic structure and significant optical and nonlinear optical properties. A novel course of reaction is observed now with the amine 2-methyl-4-chloroaniline, which leads to three well-defined products, A-C, in a single pot. A and B are formed through the replacement of one cyano group in TCNQ by the amine; A is a carbon acid and B is its corresponding salt. C is the conventional product in which two cyano groups in TCNQ are replaced by the amine. The products are characterized structurally and spectroscopic studies reveal contrasting optical responses. A is nonfluorescent, whereas B and C show red and green emission, respectively, in the solution and solid states. The acid/conjugate-base pair A and B can be interconverted through facile, reversible, and repeated deprotonation/protonation cycles, which are accompanied by instantaneous switching of the fluorescence. The current study illustrates an interesting case of a single-pot reaction yielding different optical materials with attributes that can be switched through simple approaches such as protonation or tuned through modification of the push-pull characteristics.

Methodologies that we developed recently for the fabrication of molecular crystals with size variation in the nano to micro regime and polyelectrolyte templated mono and multilayer Langmuir-Blodgett films, are reviewed. The electronic absorption and strong fluorescence in the molecular nano/microcrystals are found to be size-dependent. Crystal structure and computational investigations provide a unified model to explain these observations. Role of polyelectrolyte templating in achieving stable and enhanced optical second harmonic generation response from LB films based on a hemicyanine amphiphile is highlighted.

The three fold symmetric molecule, tris(4-cyanophenyl)amine (TCPA) is synthesized from 4-fluorocyanobenzene by treatment with potassium carbonate in dimethylsulfoxide; the occurrence of the reaction without any amine reagent suggests the involvement of a novel self-assembly process. A reprecipitation strategy provides stable colloids containing highly monodisperse nano/microcrystals with well-defined cubic morphology and sizes tunable from 250 to 500 nm. The solution, colloid, and solid states of TCPA exhibit strong blue fluorescence; the colloid shows dual emission with an unusually small Stokes shift. Computational investigations are carried out on the molecule and supramolecular assemblies derived from the crystal structure. Coupled with detailed spectroscopic studies, they show that the emission in the colloidal and solid states can be attributed to energy levels resulting from the intermolecular interactions within different aggregation motifs in the condensed phase and energy cascades between them. The computations also reveal the presence of cooperative interactions in the molecular crystal contributing to its high thermal stability. The strong light emission exhibited by TCPA, concurrently in the solution, nano/microcrystal, and solid states establishes it as a novel molecular material of potential practical utility; it has led to the exploration of the underlying mechanism that describes the phenomena observed in the different physical states.

Well-defined nanoparticles composed of a tetraphenylmethane-based microporous polymer network with an average particle diameter of 30-60 nm were fabricated by a miniemulsion polymerization technique. Strong green emission was observed and efficient excitation energy transfer from nanoparticles to surface-bound dye molecules was explored.

A convenient protocol has been developed to fabricate well-defined nanorods of a photochromic molecule N-(3,5-di-tert-butylsalicylidene)-4-aminopyridine (DBSAP) by a laser ablation method. Reversible and fatigue-resistant optical switching and SHG activity were demonstrated. Interestingly, it was observed that DBSAP nanorods exhibit intermediate photochromic properties compared to solution and solid.