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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.

A p-n heterojunction based Ni3V2O8@g-CN nanocomposite acts as photocatalyst for selective activation of inert C(sp3)–H bonds of cyclohexane to form KA-oil.

Properties and functions of noncovalent interactions-driven fluorescent supramolecular self-assembly greatly depend on their evolution dynamics. Electron microscopy, atomic force microscopy, and confocal laser scanning microscopy have been used to elucidate...

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.

Deciphering the dynamics of intracellular organelles has gained immense attention due to their subtle control over diverse, complex biological processes such as cellular metabolism, energy homeostasis, and autophagy. In this context, molecular materials, including small-organic fluorescent probes and their supramolecular self-assembled nano-/microarchitectures, have been employed to explore the diverse intracellular biological events. However, only a handful of fluorescent probes and self-assembled emissive structures have been successfully used to track different organelle's movements, circumventing the issues related to water solubility and long-term photostability. Thus, the water-soluble molecular fluorescent probes and the water-dispersible supramolecular self-assemblies have emerged as promising candidates to explore the trafficking of the organelles under diverse physiological conditions. In this review, we have delineated the recent progress of fluorescent probes and their supramolecular self-assemblies for the elucidation of the dynamics of diverse cellular organelles with a special emphasis on lysosomes, lipid droplets, and mitochondria. Recent advancement in fluorescence lifetime and super-resolution microscopy imaging has also been discussed to investigate the dynamics of organelles. In addition, the fabrication of the next-generation molecular to supramolecular self-assembled luminogens for probing the variation of microenvironments during the trafficking process has been outlined.

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.

The advantages of the cage-to-network design strategy were demonstrated by knitting a waterwheel-like preporous molecular cage, noria, with a rigid aromatic linker to obtain a highly microporous organic polymer (NPOP, SBET: 748 ± 25 m2 g−1). The NPOP was employed for the catalytic conversion of CO2 to cyclic carbonates under solvent-free reaction conditions. Furthermore, a silver nanoparticle encapsulated NPOP exhibited remarkable catalytic activity for nitroarene reduction with excellent recyclability.

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.

The advantages of the cage-to-network design strategy were demonstrated by knitting a waterwheel-like preporous molecular cage, noria, with a rigid aromatic linker to obtain a highly microporous organic polymer (NPOP, SBET: 748 ± 25 m2 g-1). The NPOP was employed for the catalytic conversion of CO2 to cyclic carbonates under solvent-free reaction conditions. Furthermore, a silver nanoparticle encapsulated NPOP exhibited remarkable catalytic activity for nitroarene reduction with excellent recyclability.

Nanoporous organic polymers with distinct morphologies are of immense interest for a broad spectrum of applications ranging from catalysis to molecular separation, energy storage, and energy conversion. However, developing facile and versatile methodologies to obtain well-orchestrated morphologies along with high specific surface area pertinent to a specific application is still a formidable challenge. The design of the task-specific networks can be benefitted through further analysis of subtle variations in the polymerization conditions. Herein, we have critically examined the fabrication of triptycene-based hypercrosslinked polymers (HCPs), exhibiting contrasting morphologies developed through three distinct polymerization routes. Astonishingly, a remarkable variation of nanostructured morphology of irregular aggregates, nanospheres, and nanosheets was noticeable in the resultant network polymers through Friedel-Crafts crosslinking using dimethoxymethane as an external crosslinker, Scholl coupling, and solvent knitting using dichloromethane as an external crosslinker and solvent, respectively. The dramatic role of reaction temperature, catalysts, and solvents driving the formation of specific nanostructured HCPs was elucidated. Mechanistic investigations coupled with spectroscopic and microscopic studies revealed that the 2D-nanosheets of highly porous solvent-knitted HCP (SKTP, SBET: 2385 m2 g-1) evolved through the hierarchical self-assembly of rigid nanospheres into nanoribbons followed by the formation of nanosheets. We further demonstrated a structure-activity correlation of the pristine as well as post-synthetically sulfonated HCPs for the removal of a gamut of organic micropollutants from water. Solvent knitted triptycene polymer (SKTP) and its sulfonated derivative (SKTPS, SBET: 1444 m2 g-1) owing to high specific surface areas, excellent dispersity in water, and better accessibility of analytes through 2D-sheet like morphology exhibited ultrafast sequestration (30 s to 5 min) of an extensive array of persistent organic micropollutants, including ionic dyes, plastic components, steroids, antibiotic drugs, and herbicides with excellent recyclability. The current study holds the promise that a delicate control over the morphologies of nanoporous polymers by tuning the fabrication conditions paves the way for the development of advanced porous materials for environmental remediation.

A heptazine-based microporous polymeric network, HMP-TAPA was synthesised by direct coupling of trichloroheptazine and tris(4-aminophenyl)amine (TAPA). A high surface area of 424 m2 /g was achieved, which is the highest surface area among heptazine-based polymeric networks (HMPs). The tailored electron-donor and -acceptor units in HMP-TAPA give broad visible-light absorption. HMP-TAPA was employed as metal-free photocatalyst for oxidative coupling of amines to imines under visible light irradiation with 98 % selectivity. Furthermore, the surface basicity of HMP-TAPA was used to achieve metal-free heterogeneous base catalysis for Knoevenagel condensation under base-free conditions with >99 % conversion. In addition, HMP-TAPA showed extreme robustness over a wide pH range (1-14). The versatility and flexibility of the current material design is beneficial for understanding its photoactivity and surface basicity so as to design dual active (photo)catalyst materials for specific 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 temperature and polarity of the medium, along with the specific self-assembled pattern of molecular building units. 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, challenges are probing the evolution of molecular aggregates from a true solution and directing the self-assembly process in a pre-defined fashion. The structure of molecular aggregates in the solution can be predicted from fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS) analysis. On the other hand, the morphology of the aggregates can also be visualized through electron microscopy. Nevertheless, a direct correlation between emission from molecular aggregates in the aqueous dispersion and their morphology obtained through a solid-state characterization is missing. In the present study, we decipher the sequential evolution of molecular nanofibers from solution to spherical and oblong-shaped nanoparticles through the variation of solvent polarity, adjusting the hydrophobic-hydrophilic interactions. The intriguing case of molecular self-assembly is elucidated employing a newly designed π-conjugated thiophene derivative (TPAn) through a combination of steady-state absorption, emission measurements, FCS, and electron microscopy. The FCS analysis and microscopy results infer that small-sized nanofibers in the dispersion are further agglomerated, resulting in a network of nanofibers upon solvent evaporation. The evolution of organic nanofibers and subtle control over the self-assembly process demonstrated in the current investigation provides a general paradigm to correlate the size, shape, and emission properties of diverse fluorescent molecular aggregates in complex heterogeneous media, including a human cell.

We fabricated an inorganic–organic hybrid upconversion nanoprobe for the ratiometric detection of aliphatic biogenic amines in water. The hybrid nanoprobe comprises a thiophene-based acceptor–π-donor–π-acceptor organic fluorescent dye, TDPM, and near-infrared light-absorbing upconversion nanoparticles (UCNPs). The organic dye was loaded into a mesoporous silica-coated UCNP (UCNP@mSiO2) matrix to circumvent the issues of water insolubility and higher energy excitation. Yb3+ and Tm3+-doped UCNPs exhibited dual emission bands at 475 and 645 nm upon excitation with a 980 nm laser. The significant spectral overlap between the absorption and the emission bands of TDPM and UCNPs, respectively, at 475 nm led to resonance energy transfer (RET) from the UCNPs to TDPM resulting in the quenching of the UCNP emission. In contrast, ‘turn-on’ emission was noticeable with the addition of aliphatic biogenic amines due to an inhibition of the RET. The emission at 645 nm remained unaffected during the energy transfer process making the hybrid probe a versatile platform for the ratiometric detection of different aliphatic biogenic amines. Furthermore, we explored the sensing of aliphatic biogenic amines in adulterated milk and rotten fish. The unique material attributes demonstrated in the current study hold promise for further development of real-time sensors and switches based on hybrid upconversion nanoprobes.

Covalent organic frameworks (COFs) having layered architecture with open nanochannels and high specific surface area are promising candidates for energy storage. However, the low electrical conductivity of two-dimensional COFs often limits their scope in energy storage applications. The conductivity of COFs can be enhanced through post-synthetic modification with conducting polymers. Herein, we developed polyaniline (PANI) modified triazine-based COFs via in situ polymerization of aniline within the porous frameworks. The composite materials showed high conductivity of 1.4-1.9×10-2 S cm-1 at room temperature with a 20-fold enhancement of the specific capacitance than the pristine frameworks. The fabricated supercapacitor exhibited a high energy density of 24.4 W h kg-1 and a power density of 200 W kg-1 at 0.5 A g-1 current density. Moreover, the device fabricated using the conducting polymer-triazine COF composite could light up a green light-emitting diode for 1 min after being charged for 10 s.

Covalent organic frameworks (COFs) with layered architecture with open nanochannels and high specific surface areas are promising candidates for energy storage. However, the low electrical conductivity of two-dimensional COFs often limits their scope in energy storage applications. The conductivity of COFs can be enhanced through post-synthetic modification with conducting polymers. Herein, we developed polyaniline (PANI) modified triazine-based COFs via in situ polymerization of aniline with the porous frameworks. The composite materials showed high conductivity of 1.4-1.9 x 10-2 S cm-1 at room temperature with 10-fold enhancement in specific capacitance than the pristine frameworks. The fabricated supercapacitor exhibited a high energy density of 24.4 W h kg-1 and a power density of 200 W kg-1 at 0.5 A g-1 current density. Moreover, the device fabricated using the conducting polymer-triazine COF composite can light up a green light-emitting diode for 1 min after being charged for 10 s.

Supramolecular cavitands and organic cages having a well-defined cavity and excellent host-guest complexing ability have been explored for a myriad of applications ranging from catalysis to molecular separation to drug delivery. On the other hand, porous organic polymers (POPs) having tunable porosity and a robust network structure have emerged as advanced materials for molecular storage, heterogeneous catalysis, water purification, light harvesting, and energy storage. A fruitful marriage between guest-responsive discrete porous supramolecular hosts and highly porous organic polymers has created a new interface in supramolecular chemistry and materials science, confronting the challenges related to energy and the environment. In this mini-review, we have addressed the recent advances (from 2015 to the middle of 2020) of cavitand and organic cage-based porous organic polymers for sustainable development, including applications in heterogeneous catalysis, CO2 conversion, micropollutant separation, and heavy metal sequestration from water. We have highlighted the "cavitand/cage-to-framework" design strategy and delineated the future scope of the emerging new class of porous organic networks from "preporous" building blocks.

Semiconductor nanocrystals are promising for display and lighting devices. Herein, we report a facile one-pot synthetic route to fabricate white light emitting CdSexSy nanocrystals with enhanced quantum yield using CdO, S powder, and Se powder as precursors. The 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 molar ratio of Se/S. The emission of pristine CdSexSy nanocrystals covered a broad visible range from 400 to 750 nm. The CdSexSy nanocrystals (Se/S = 0.4) exhibited white-light emission with quantum yield of 50 ± 3 % and Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.30, 0.31). The band-edge (~400-450 nm) to trap-state (~550-750 nm) emissions was tuned by controlling the Se/S ratio, and the different shades of white light were obtained. Furthermore, the quantum yield and CIE coordinates of the CdSexSy nanocrystals (Se/S = 0.4) were found to be similar even after 30 days of fabrication, showing the high stability of nanocrystals. The white light emission was retained in nanocrystals-embedded poly(methyl methacrylate) (PMMA) thin film and also in the hydrogel matrix. The one-pot, low-cost, scalable fabrication of white light emitting CdSexSy nanocrystals demonstrated in the present study offers promising scope in the solid-state display applications.

The current study demonstrates a simple and economical synthetic approach for the development of a multifunctional Schiff base compound (NRSB) through the condensation reaction between 2-hydroxynaphthaldehyde and a five-membered heterocycle 3-aminorhodanine. The rhodanine unit was chosen due to the presence of an active electron-deficient carbonyl group. A facile chemical transformation from the closed to the open form was noticeable for rhodanine derivatives in the presence of a suitable nucleophile or an electron-rich system. Such a unique feature was invoked to develop a versatile molecular platform for the colorimetric sensing of methanol and the fluorometric detection of Al3+ ions. The nucleophilic attack by methanol on NRSB led to the formation of an open-ring compound, NRSB-O, with a distinct change in color from colorless to yellow. NRSB showed noticeable sensitivity towards methanol and the detection limit was found to be 0.43 wt%. The methanol-induced chemical transformation from NRSB to NRSB-O was probed through X-ray diffraction studies. The strong CH–π interaction between the methylene protons of the rhodanine unit and the π-electron cloud of the naphthalene unit (3.03 A) and the π–π interaction between naphthalene and the rhodanine moiety (3.51 A and 3.55 A) lead to a two-dimensional (2D) supramolecular structure in the NRSB crystal. NRSB-O possesses strong CH–π interactions between molecules with an intermolecular distance of 2.49 A, leading to 2D-supramolecular self-assembly. The crystal structure revealed the scope of the chelation of NRSB-O with metal ions due to the presence of different N, O, and S donor centers. Interestingly, NRSB-O exhibited a turn-on fluorescence response specifically towards Al3+ through the chelation-enhanced fluorescence (CHEF) mechanism over other competitive metal ions. The turn ‘on–off’ fluorescence switching was demonstrated for multiple cycles through the alternative addition of Al3+ and EDTA. The low-cost, simple design strategy of NRSB and NRSB-O as delineated in the current study would contribute to further development of task-specific molecular sensors and switches.

Control of nonradiative deactivation of triplet states and tuning the singlet-triplet energy gap (ΔEST) are the major challenges to develop materials exhibiting thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP). Herein, we propose a new class of multichromophoric tridonor-acceptor (D3-A) compounds with rigid and flexible π-spacer having N-rich pyridoquinoxaline (PQ) and pyridopyrazine (PZ) acceptor core, respectively. The molecule with carbazole (Cz) donors at meta to quinoxaline (QX) nitrogen of rigid PQ core exhibits TADF. Whereas, the variation of the linkage position of Cz to PQ as well as twisted and flexible PZ core show predominantly RTP due to relatively higher singlet-triplet energy gap (ΔEST). Increasing the donor strength with phenoxazine (PO) in PZ system leads to simultaneous TADF and RTP. Further, we demonstrate the promising scope of all-organic triplet harvesting materials in solid-state security encryption.

The excited-state intramolecular proton transfer (ESIPT)-based molecular probes have drawn significant attention owing to their environment-sensitive fluorescence properties, large Stokes shift, and emerged as building blocks for the development of molecular sensors and switches. However, most of the ESIPT-based fluorophores exhibit weak emission in the solid state limiting the scope of real-time applications. Addressing such issues, herein, we presented a C

Tuning the fluorescence of π-conjugated small organic molecules through the structural modifications and in the presence of external stimuli have found immense applications ranging from sensing, switching, optoelectronics to bioimaging. Herein, we demonstrated a simple design strategy for the synthesis of a pyrene-cyanostyrene-pyridine molecular triad (PYBNP) using a cost-effective, one-step Knoevenagel condensation between 1-pyrenecarboxaldehyde and 2-(4-(pyridin-4-yl)phenyl)acetonitrile. PYBNP exhibited strong solid-state emission having a quantum yield of ∼ 36 ± 3% due to the deactivation of nonradiative decay channels through the restriction of intramolecular rotations and reduced π-π stacking interactions as revealed from the crystal structure analysis. Similarly, PYBNP was found to be highly emissive in the constrained environments like viscous medium and aggregated state. The optical properties of PYBNP could be tuned by the UV light-mediated dynamic Z/E-isomerization as elucidated through fluorescence spectroscopy and NMR analysis. Additionally, the pyridinic nitrogen centre allowed the fabrication of methylated analog (PYBNPM; a new cationic photoresponsive species). The cationic PYBNPM showed a better solvatochromic behavior contrary to PYBNP due to the efficient intramolecular charge transfer (ICT). The different crystal packing of PYBNP and that of hexafluorophosphate salts of PYBNPM led to distinct fluorescent properties in the solid-state. As a preliminary exploration, the cationic PYBNPM(PF6) was employed for the specific imaging of the mitochondria through multiple fluorescence channels in an aqueous medium. The cost-effective and viable design strategy demonstrated for the fabrication of a simple molecular triad holds the promise for the emergence of new functional fluorescent molecules to molecular materials for task-specific applications.