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Through-space donor–alkyl bridge–acceptor multifunctional organic single molecules that simultaneously displayed white light emission, thermally activated delayed fluorescence, room temperature dual phosphorescence and optical wave-guiding properties.

Observation of light-triggered anomalous effects on a growing crystal is important from both fundamental and technological perspectives. Our experiments focus on the aggregation of a model photoiso...

A combination of flexibility and room temperature phosphorescence (RTPR) in organic crystals is in high demand due to various applications from bio-medical to organic photonic circuit technologies. However, flexible RTPR crystals are scarce. We report the design and synthesis of novel flexible microcrystals of (Z)-3-(4-(10H-phenothiazin-10-yl)phenyl)-2-(3,5-bis(trifluoromethyl)phenyl)acrylonitrile (PTX-2CF3), exhibiting a phosphorescence lifetime of 658 μs and λmax ≈ 530 nm. The structural basis for the mechanical flexibility and mechanophotonic aspects of the PTX-2CF3 crystals is studied in detail.

Flexible organic single crystals are evolving as new materials for optical waveguides that can be used for transfer of information in organic optoelectronic microcircuits. Integration in microelectronics of such crystalline waveguides requires downsizing and precise spatial control over their shape and size at the microscale, however that currently is not possible due to difficulties with manipulation of these small, brittle objects that are prone to cracking and disintegration. Here we demonstrate that atomic force microscopy (AFM) can be used to reshape, resize and relocate single-crystal microwaveguides in order to attain spatial control over their light output. Using an AFM cantilever tip, mechanically compliant acicular microcrystals of three N-benzylideneanilines were bent to an arbitrary angle, sliced out from a bundle into individual crystals, cut into shorter crystals of arbitrary length, and moved across and above a solid surface. When excited by using laser light, such bent microcrystals act as active optical microwaveguides that transduce their fluorescence, with the total intensity of transduced light being dependent on the optical path length. This micromanipulation of the crystal waveguides using AFM is non-invasive, and after bending their emissive spectral output remains unaltered. The approach reported here effectively overcomes the difficulties that are commonly encountered with reshaping and positioning of small delicate objects (the "thick fingers" problem), and can be applied to mechanically reconfigure organic optical waveguides in order to attain spatial control over their output in two and three dimensions in optical microcircuits.

Through-space donor-alkyl bridge-acceptor (D-σ-A) luminogens are developed as new organic single-molecule white light emitters (OSMWLEs) involving multiple higher lying singlet (S

Ambient pressure chemical vapour deposition of 5,5'-bis((2-(trifluoromethyl)phenyl)ethynyl)-2,2'-bithiophene provides ultrapure needle-shaped crystals. The crystal's supramolecular structure consists of an array of hydrogen bonds and π-π interactions leading to anisotropic arrangements. The cyan emitting crystals exhibit an optical waveguiding tendency with guided polarised optical emissions due to anisotropic molecular arrangements.

The advancement of nanoscience and technology relies on the development and utility of innovative techniques. Precise manipulation of photonic microcavities is one of the fundamental challenges in nanophotonics. This challenge impedes the construction of optoelectronic and photonic microcircuits. As a proof-of-principle, we demonstrate here that an atomic force microscopy cantilever and confocal microscopy can be used together to mechanically micromanipulate polymer-based whispering gallery mode microcavities or microresonators into well-ordered geometries. The micromanipulation technique efficiently assembles or disassembles resonators and also produces well-ordered dimer, trimer, tetramer, and pentamer assemblies of resonators in linear and bent geometries. Interestingly, an intricate L-shaped coupled-resonator optical waveguide (CROW) comprising a pentamer assembly effectively transduces light through a 90° bend angle. The presented new research direction, which combines mechanical manipulation and nanophotonics, is also expected to open up a plethora of opportunities in nano and microstructure-based research areas including nanoelectronics and nanobiology.

Time-dependent monitoring of aggregation-induced fluorescence of a model compound namely, (Z)-3-(3',5'-bis(trifluoromethyl)-[1,1'-biphenyl]-4-yl)-2-(4-bromophenyl)acrylonitrile unearth hitherto unknown molecular level events such as onset of molecular aggregation, their growth, size, and diffusion dynamics. The presented generalized approach can also be extended to in situ monitoring and controlling of various biological aggregation processes down to a single-cell level and all aspects of materials chemistry, as well.

Precise mechanical processing of optical microcrystals involves complex microscale operations viz. moving, bending, lifting, and cutting of crystals. Some of these mechanical operations can be implemented by applying mechanical force at specific points of the crystal to fabricate advanced crystalline optical junctions. Mechanically compliant flexible optical crystals are ideal candidates for the designing of such microoptical junctions. A vapor‐phase growth of naturally bent optical waveguiding crystals of 1,4‐bis(2‐cyanophenylethynyl)benzene (1) on a surface forming different optical junctions is presented. In the solid‐state, molecule 1 interacts with its neighbors via CH⋅⋅⋅N hydrogen bonding and π–π stacking. The microcrystals deposited at a glass surface exhibit moderate flexibility due to substantial surface adherence energy. The obtained network crystals also display mechanical compliance when cut precisely with sharp atomic force microscope cantilever tip, making them ideal candidates for building innovative T‐ and Δ‐shaped optical junctions with multiple outputs. The presented micromechanical processing technique can also be effectively used as a tool to fabricate single‐crystal integrated photonic devices and circuits on suitable substrates.

The advancement of nanoscience and technology relies on the development and utility of innovative techniques. Precise manipulation of photonic microcavities is one of the fundamental challenges in nanophotonics. This challenge impedes the construction of optoelectronic and photonic microcircuits. As a proof-of-principle, we demonstrate here that an atomic force microscopy cantilever and confocal microscopy can be used together to mechanically micromanipulate polymer-based whispering gallery mode microcavities or microresonators into well-ordered geometries. The micromanipulation technique efficiently assembles or disassembles resonators and also produces well-ordered dimer, trimer, tetramer, and pentamer assemblies of resonators in linear and bent geometries. Interestingly, an intricate L-shaped coupled-resonator optical waveguide (CROW) comprising a pentamer assembly effectively transduces light through a 90° bend angle. The presented new research direction, which combines mechanical manipulation and nanophotonics, is also expected to open up a plethora of opportunities in nano and microstructure-based research areas including nanoelectronics and nanobiology.

The dark-orange monomer single crystals of 1,1′-dioxo-1H-2,2′-biindene-3,3′-diyldidodecanoate (BIT-dodeca2) convert to a transparent single-crystalline polymer (PBIT-dodeca2) material via a single-...

Optical green emitting microresonators with high values of nonlinearity are desired for high optical up-conversion energy storage and lasing applications. Here we report on the synthesis of benzyla...

We observe experimentally multiphoton processes in active organic microres-onators with different shapes: spheres, squares, octahedrons and rods. Pronounced whispering gallery modes with Q-factor up to 700 and coupling induced mode splitting are demonstrated.

Organic micro-heterostructures (MHS) with dual optical emissions are essential to produce miniaturized optical waveguides for wavelength division multiplexing technologies. The bimolecular MHS produced by solution-based bottom-up self-assembly technique often leads to poor surface smoothness, edge imperfection, defects, and unwanted thin films deposits. Conversely, sequential sublimation technique at ambient pressure facilitates effective integration of α-perylene micro-square with dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran (DCM) microrods in an epitaxial manner to produce MHS. The obtained DCM/perylene MHS act as optical waveguides to produce red (λmax ≈670 nm) or/and yellow (λmax ≈607 nm) dual optical outputs via an energy transfer mechanism depending upon the heterostructures geometry and optical excitation positions. The presented dual-color emitting MHS optical waveguides are essential for the integrated nano-photonic and optoelectronic device structures.

Single dye based crystalline organic materials displaying molecular packing and conformation-dependent luminescent properties are attractive for opto-electronic and photonic applications. Hence, in this work the opto-structural analysis of two polymorphs (forms I and II) of a well-known coumarin-153 (C-153) dye is presented. Crystal structural analysis based on the syn or anti position of C-β1 and C-β2 carbons adjacent to nitrogen in the julolidyl moieties showed that form I and II polymorphs possess three and two molecular conformers, respectively. Optical excitation of single crystals of forms I and II radiated green and yellow fluorescence (FL) bands, respectively. The presence of different conformers, strong intermolecular π–π stacking, hydrogen bonding interactions, and charge transfer states was attributed to the energetically different emission bands of these polymorphs. Depending on the acetonitrile : water ratio, during self-assembly, C-153 formed polymorphic micro-crystalline rods, tubes and Japanese twin tubes on glass substrates. Analysis of the single-particle Raman spectra and FL life-time values of the rods, tubes and Japanese twin tubes clearly confirmed dissimilar molecular packing within the micro-solids. Single-particle microscopy studies revealed remarkable polymorphism-dependent FL emissions, optical waveguiding, and optical cavity and resonator effects of the rods, tubes and Japanese twin tubes. The yellow emitting hexagonal and rectangular tubes possibly supported whispering-gallery-modes (WGMs) and Fabry–Perot (FP) modes, respectively, while the blue-green emitting rods and Japanese twin tubes displayed FP-type cavity modes. Overall this work establishes a simple and economical self-assembly route for the fabrication of C-153 photonic micro-structures displaying polymorphism-dependent emission colours suitable for band-width tunable organic-based micro-lasers, opto-electronic and other polaritonic devices.

The present work describes the preparation of gold nanoparticles (AuNPs) under natural sunlight irradiation and their use in colorimetric detection of heavy metal ions. The AuNPs were prepared by an environmentally benign method using N-cholyl-l-valine (NaValC) as a self-reducing as well as stabilizing agent in aqueous medium. The size and shape of the particles were systematically controlled by varying the ratio of NaValC and Au3+ ions. The pH of the solution medium, sunlight irradiation and reaction time also influence the size and shape selectivity. The prepared NPs were thoroughly characterized by using UV-visible spectroscopy, TEM, DLS, EDX, XRD, XPS, FT-IR, cyclic voltammetry and TGA techniques. Natural solar energy acting as a driving force for the generation of AuNPs in aqueous medium makes the process eco-friendly, attractive and economical. As these NPs are highly reactive towards the surrounding environment the prepared AuNPs were effectively utilized for the colorimetric detection of Co2+ and Ni2+ ions in environmental samples.

In this study, we report a simple and green method for the synthesis of l-tyrosine-stabilized silver (AgNPs) and gold nanoparticles (AuNPs) in aqueous medium under ambient sunlight irradiation. The nanoparticles (NPs) are characterized by UV–visible spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV), and dynamic light scattering (DLS) techniques. The size and shape of the metal NPs could be controlled by changing the concentration of the substrate, metal precursors, and pH of the medium. The synthesized AgNPs are found to be highly sensitive to Hg2+ and Mn2+ ions with the detection limit for both ions as low as 16 nM under optimized conditions. However AuNPs are found to be sensitive to Hg2+ and Pb2+ ions with a detection limit as low as 53 and 16 nM, respectively. The proposed method was found to be useful for colorimetric detection of heavy metal ions in aqueous medium.

One-pot photocatalytic synthesis of 2-substituted benzimidazoles from 2-nitroanilines with different alcohols by combined redox cyclization reaction using TiO2-P25 is reported. The reaction, when performed with ethanol, gives 2-methylbenzimidazole as a single product. However, in a mixture of ethanol and water (1:1), it gives both 2-methylbenzimidazole and 1-ethyl-2-methylbenzimidazole. The products have been characterized by Fourier transorm–infrared, 1H NMR, 13CNMR, and gas chromatography–mass spectrometry analysis. TiO2-P25 behaves as a combined redox photocatalyst by reducing 2-nitroaniline and oxidizing alcohols simultaneously under ultraviolet light. Easy product isolation under mild conditions and good yield make this one-pot synthesis ecofriendly.

Silver-loaded TiO2 (Ag–TiO2) and acidic clay (K10 montmorillonite) composite photocatalyst has been successfully applied for the light-induced conversion of o-phenylenediamine (OPD) and its derivat...

Luminescent carbon dots (CDs) are emerging as a potential eco-friendly alternative to standard metal-based semiconductor quantum dots. A solvatothermal method to prepare crystalline, nitrogen-rich, surface-passivated, and rare excitation wavelength-independent green-emitting (λmax ≈ 522 nm in solution and 536 nm in solid) CDs from a pyridine diamine precursor in ethanol solvent is reported here. In comparison to a neat thin film of CDs, a film of CD-doped polystyrene microspheres (PS-CDs) displays a remarkable enhancement of the photoluminescence emission intensity driven by optical cavity effect of the composite microspheres. Apart from downconversion one-photon luminescence, upon excitation with 800 nm femtosecond pulse laser, pure CDs and PS-CDs exhibit enhanced upconversion two-photon luminescence in the range of about 410–580 nm.

One-pot photocatalytic synthesis of 2-substituted benzimidazoles from 2-nitroanilines with different alcohols by combined redox cyclization reaction using TiO2-P25 is reported. The reaction, when performed with ethanol, gives 2-methylbenzimidazole as a single product. However, in a mixture of ethanol and water (1:1), it gives both 2-methylbenzimidazole and 1-ethyl-2-methylbenzimidazole. The products have been characterized by Fourier transorm–infrared, 1H NMR, 13CNMR, and gas chromatography–mass spectrometry analysis. TiO2-P25 behaves as a combined redox photocatalyst by reducing 2-nitroaniline and oxidizing alcohols simultaneously under ultraviolet light. Easy product isolation under mild conditions and good yield make this one-pot synthesis ecofriendly.

Aqueous solution containing two additives, silver nitrate (AgNO(3)) and sodium salt of N-cholyl amino acid were irradiated by sunlight for the synthesis of spherical shaped AgNPs without the need for an additional stabilizer or capping agent. Variations of N-cholyl amino acid concentration provided good control over the morphology of the AgNPs, while the carboxylate group of bile salt reduced the Ag(+) ions and the amide group binds strongly to the surface of the NPs. The optical properties, morphology of the AgNPs were characterized by UV-visible, transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies. The interaction of N-cholyl amino acid on the AgNPs surface was studied using cyclic voltammetry and FT-IR techniques. The reduction process was completed within 5 min and the synthesized AgNPs were stable for more than 6 months. The possible mechanism of N-cholyl amino acid on the reduction and stabilization of AgNPs is also discussed. The antimicrobial activity of N-cholyl amino acid capped AgNPs against Escherichia coli, Staphylococcus aureus and Pseudomonas aeroginosa using Mueller Hinton broth and the antifungal activity against Candida albicans, Candida krusei and Candida tropicalis using RPMI broth were determined by MIC studies as per CLSI guidelines.

The title catalyst is successfully applied to the synthesis of benzimidazoles using solar light or UV-A.