Room-temperature phosphorescence from organic materials in aqueous media.

In recent years, organic materials with room-temperature phosphorescence (RTP) features have gained significant attention due to their wide applications in the fields of bioimaging, light-harvesting materials, encryption technology, etc. Although several examples of organic RTP materials in the crystalline state and polymer-based systems have been reported in the last decade or so, achieving organic RTP in the solution phase, particularly in the aqueous phase has remained a challenging task. Herein in this review, we summarize the progress in this direction by highlighting design strategies based on supramolecular scaffolding and host-guest complexation and the applications of such aqueous organic RTP materials in bioimaging, sensing, etc.

Metal Ion Responsive Luminescent Bio-Templated Co-Assemblies: Label-Free Detection of Multi-Metal Ions in Aqueous Media.

Recently, anionic bio-templates have emerged as promising platforms for designing dynamic and stimuli-responsive chromophoric assemblies capable of light harvesting in aqueous media thereby mimicking natural photosynthesis. Here, we present multi-metal ion-responsive luminescent co-assemblies between cationic pyrene-imidazolium amphiphile and anionic bio-templates (ATP, heparin, and DNA) in aqueous media. The anionic bio-templates enhance Förster resonance energy transfer (FRET) in the co-assemblies, with pyrene serving as an excellent donor for generating tunable multi-luminescent materials with embedded acceptor dyes.

pH-tunable phosphorescence and light harvesting in cucurbit[8]uril host-guest assemblies.

Host-guest assemblies of halo-phenyl pyridine derivatives and cucurbit[8]uril (CB[8]) exhibited pH-responsive room temperature phosphorescence (RTP) in aqueous media. Moreover, they acted as efficient light-harvesting systems demonstrating triplet-singlet energy transfer to various acceptor dyes.

ATP-Enhanced Multistimuli-Responsive Förster Resonance Energy Transfer in Organic Coassemblies.

In recent years, ATP has emerged as an anionic biocomponent for the design of dynamic and stimuli-responsive supramolecular assemblies. Herein, we present ATP-enhanced Förster resonance energy transfer (FRET) in the coassemblies of pyrene-imidazolium amphiphiles with pyrene acting as an excellent donor for the coembedded acceptor dyes to generate tunable multiluminescent materials in aqueous solutions and in polymer and solid films. We achieved high energy transfer efficiency up to 95% even at a donor/acceptor (D/A) ratio of 100:1.

Contrasting luminescence in heparin and DNA-templated co-assemblies of dimeric cyanostilbenes: efficient energy transfer in heparin-based co-assemblies.

Dimeric cationic cyanostilbenes with peripheral alkyl chains demonstrated aggregation in aqueous media depending on the length of the hydrophobic segment and produced luminescent spherical nano-assemblies in the case of long alkyl chain derivatives. In the presence of heparin, a bio-polyanion that is routinely used as an anticoagulant, the self-assembled structures obtained from the amphiphilic dimers showed the formation of higher-order structures whereas the non-assembling dimers exhibited heparin-induced supramolecular structure formation. In both cases, a significant enhancement in the emission was observed.

Efficient light harvesting in self-assembled organic luminescent nanotubes.

Luminescent organic nanotubes derived from the co-assembly of cyanostilbene (CS) based cationic supramolecular polymers and bio-polyanion heparin, a known anticoagulant, have been utilized as highly efficient FRET (fluorescence resonance energy transfer) donors in aqueous media resulting in amplified acceptor emission in the orange-red and near-infrared (NIR). Energy transfer efficiencies higher than 80% and an ultra-high antenna effect of 150 were achieved even at high donor/acceptor ratios (500 : 1-100 : 1) translating to emission quenching of several hundred donors by one acceptor. Utilizing the temperature responsiveness of the FRET process, these systems were employed as ratiometric emission thermometers in the temperature range 20-90 °C.

Cascade Energy Transfer in Biopolymer-Templated Multi-Chromophoric Assemblies: Ratiometric Temperature Sensing.

Natural light-harvesting complexes collect energy from sunlight and transfer it to the reaction center through a cascade of energy and electron transfer steps. Artificial light-harvesting systems functioning in aqueous media mimic natural photosynthetic systems. However, their design remains a challenging task as closely packed antenna chromophores often undergo severe self-quenching.

Heparin-Induced Dual Mode Luminescence Modulation of Organic Nanoparticles and Efficient Energy Transfer.

Amphiphilic di-cationic fumaronitrile derivatives with peripheral n-alkyl chains formed organic nanoparticles (NPs) through self-assembly in aqueous media. The NPs exhibited enhanced luminescence in both steady-state and delayed mode in comparison to their molecularly dissolved state. Due to the presence of the multivalent array of positive charges on their surface, they were found to bind heparin, a bio-polyanion which is routinely employed during surgery as an anticoagulant.

Luminescence Sensing of Biomacromolecules Heparin and Protamine in 100% Human Serum and Plasma by Supramolecular Polymeric Assemblies.

Heparin, an anionic biomacromolecule, is routinely used as an anticoagulant during medical surgery to prevent blood clot formation and in the treatment of several heart, lung, and circulatory disorders having a higher risk of blood clotting. We herein report supramolecular polymeric nanoassemblies of cationic pyrene-tagged bis-imidazolium amphiphiles for heparin detection with high sensitivity and selectivity in aqueous buffer, plasma, and serum media. The nano-assemblies exhibited cyan-green excimeric emission in aqueous media, and their multivalent array of positive surface charges allowed them to form co-assemblies with heparin, resulting in significantly enhanced emission.

Multicolor-Luminescence Including White Light by Photomodulation of Supramolecular Assemblies in Aqueous Media.

Photo-responsive supramolecular systems offer intriguing functional aspects which have led to their applications in diverse fields such as optoelectronics and biomedicine. However, the modulation of the luminescence output in a spatiotemporal fashion by photo-controlled transformation still remains a challenging task. Herein, we report the controlled regulation of the emission color of supramolecular assemblies of amphiphilic cyanostilbenes (CSs) in water through in situ photomodulation employing UV and sunlight.

Cucurbituril Based Luminescent Materials in Aqueous Media and Solid State.

Cucurbit[n]urils, the pumpkin shaped macrocyclic host molecules possessing a hydrophobic cavity and two identical carbonyl portals, have drawn a lot of attention in recent years due to their high-affinity yet dynamic molecular recognition properties in water. The reversible and stimuli-responsive nature of their host-guest complexes imparts "smart" features leading to materials with intriguing optical, mechanical and morphological properties. In this review, we focus on the design of cucurbituril based luminescent materials in aqueous media as well in solid or film state.

Highly sensitive and ratiometric luminescence sensing of heparin through templated cyanostilbene assemblies.

The assembly of organic dyes on bio-molecular templates is an attractive strategy for the creation of bio-materials with intriguing optical properties. This principle is exploited here for the detection of polyanion heparin, a known anticoagulant, by employing di-cationic cyanostilbene derivatives with inherent aggregation induced emission (AIE) features. The cyanostilbene derivatives exhibited weak cyan-blue monomeric emissions in solutions but upon electrostatic co-assembly with heparin, formed highly luminescent clusters on the polyanion surface.

Selective recognition of ATP by multivalent nano-assemblies of bisimidazolium amphiphiles through "turn-on" fluorescence response.

Bisimidazolium receptors, tagged with chromophoric pyrene at one end and linked to an -alkyl chain at the other, underwent self-assembly in aqueous media depending on the length of the alkyl segment. The amphiphilic derivatives having -decyl or longer chains, formed nano-assemblies with cyanic-green emission resulting from the stacked pyrene chromophores in the aggregates. The presence of positive surface charges on the multivalent aggregates led to ATP binding which was accompanied by a significant increase in the excimeric emission intensity.

Sources and atmospheric processing of brown carbon and HULIS in the Indo-Gangetic Plain: Insights from compositional analysis.

We present here spectroscopic compositional analysis of brown carbon (BrC) and humic-like substances (HULIS) in the Indian context under varying conditions of source emissions and atmospheric processing. To this end, we study bulk water-soluble organic matter (WSOM), neutral- and acidic-HULIS (HULIS-n and HULIS-a), and high-polarity (HP)-WSOM collected in the eastern Indo-Gangetic Plain (IGP) with respect to UV-Vis, fluorescence, FT-IR, H NMR and C characteristics under three aerosol regimes: photochemistry-dominated summer, aged biomass burning (BB)-dominated post-monsoon, and fresh BB-dominated winter. Absorption coefficients (b; Mm) of WSOM and HULIS fractions increase by a factor of 2-9 during winter as compared to summer, with HULIS-n dominating total HULIS + HP-WSOM absorption (73-81%).

A Remarkable Fluorescence Quenching Based Amplification in ATP Detection through Signal Transduction in Self-Assembled Multivalent Aggregates.

Signal transduction is essential for the survival of living organisms, because it allows them to respond to the changes in external environments. In artificial systems, signal transduction has been exploited for the highly sensitive detection of analytes. Herein, a remarkable signal transduction, upon ATP binding, in the multivalent fibrillar nanoaggregates of anthracene conjugated imidazolium receptors is reported.

High affinity heparin detection by multivalent supramolecular polymers through aggregation induced emission.

Amphiphilic di-cationic cyanostilbene derivatives with aggregation induced emission (AIE) features formed luminescent supramolecular polymers in aqueous media. They bind bio-polyanion heparin, a known anticoagulant, in a multivalent fashion through the formation of co-assemblies with highly enhanced greenish-yellow emission. Heparin detection in nanomolar concentrations in buffer and in medically relevant concentrations in human serum and plasma was achieved.

Tunable multi-color luminescence from a self-assembled cyanostilbene and cucurbit[7]uril in aqueous media.

Amphiphilic cyanostilbene 12CS12 underwent self-assembly in aqueous media and exhibited bright greenish-yellow emission in its aggregated state. Macrocyclic host cucurbit[7]uril (CB[7]) was found to encapsulate 12CS12 and the host-guest complex was an efficient bluish-cyan emitter. Variation of the 12CS12 and CB[7] ratio in their mixture generated multiple emission colors including near white light through the color mixing of these two emitting species.

Tb(III) functionalized vesicles for phosphate sensing: membrane fluidity controls the sensitivity.

We report a modular design of vesicular chemosensors by co-embedding a Tb(III) complex and a receptor-sensitizer conjugate in phospholipid vesicles. The binding of phosphate anions to the vesicle surface in aqueous media is detected by a decrease in Tb(III) phosphorescence. The sensory response can be modulated by a variation in the membrane fluidity.

Molecular imprinting of luminescent vesicles.

Applying molecular imprinting techniques to the surface of functionalized unilammelar fluid vesicles allows the preparation of specific and high-affinity luminescent chemosensors. We have photopolymerized diacetylene containing vesicles in the presence of small peptides as templates yielding imprinted polydiacetylene (PDA) patches in the membrane. They serve as multivalent receptor sites with significantly increased rebinding affinity for the template.

A self-assembled, luminescent europium cholate hydrogel: a novel approach towards lanthanide sensitization.

We propose a new self-assembly based strategy for the design of novel lanthanide based luminescent materials. In this approach a europium hydrogel is prepared and sensitization is achieved by doping the gel with pyrene in a non-coordinated fashion.

Structural relationships in 2,3-bis-n-decyloxyanthracene and 12-hydroxystearic acid molecular gels and aerogels processed in supercritical CO(2).

Supercritical carbon dioxide is used to prepare aerogels of two reference molecular organogelators, 2,3-bis-n-decyloxyanthracene (DDOA) (luminescent molecule) and 12-hydroxystearic acid (HSA). Electron microscopy reveals the fibrillar morphology of the aggregates generated by the protocol. SAXS and SANS measurements show that DDOA aerogels are crystalline materials exhibiting three morphs: (1) arrangements of the crystalline solid (2D p6m), (2) a second hexagonal morph slightly more compact, and (3) a packing specific of the fibers in the gel.

Role of Src protein tyrosine kinases in late preconditioning against myocardial infarction.

Although Src protein tyrosine kinases (PTKs) have been shown to be essential in late preconditioning (PC) against myocardial stunning, their role in triggering versus mediating late PC against myocardial infarction remains unclear. Four groups of conscious rabbits were subjected to a 30-min coronary occlusion on day 2, with or without PC ischemia on day 1. Administration of the Src PTK inhibitor lavendustin A (LD-A; 1 mg/kg iv) before the PC ischemia on day 1 (group III, n = 7) failed to block the delayed protective effect against myocardial infarction 24 h later.

Use of atropine to maintain higher heart rate after exercise during treadmill stress echocardiography.

The sensitivity of treadmill stress echocardiography (SE), which is extensively used as a noninvasive test to detect myocardial ischemia, is contingent on the rapid acquisition of 2-dimensional echocardiographic (2D) images immediately after exercise, before a substantial decrease in heart rate (HR). This test is technically challenging and needs proficient sonographers to obtain the images rapidly. This study was designed to determine whether administration of atropine at peak exercise would maintain a higher HR longer after exercise, thereby facilitating acquisition of images.