Aqueous Phase Phosphorescence: Ambient Triplet Harvesting of Purely Organic Phosphors via Supramolecular Scaffolding.

Ambient solution and amorphous state room temperature phosphorescence (RTP) from purely organic chromophores is rarely achieved. Remarkable stabilization of triplet excitons is realized to obtain deep red phosphorescence in water and in amorphous film state under ambient conditions by a unique supramolecular hybrid assembly between inorganic laponite clay and heavy atom core substituted naphthalene diimide (NDI) phosphor. Structural rigidity and oxygen tolerance of the inorganic template along with controlled molecular organization via supramolecular scaffolding are envisaged to alleviate the unprecedented aqueous phase phosphorescence.

Dynamic, conjugated microporous polymers: visible light harvesting via guest-responsive reversible swelling.

The light-harvesting properties of two fluorescent dynamic conjugated microporous organic polymers (Py-PP and Py-BPP) rendered with pyrene chromophores are described. The hydrophobic and dynamic nature of these porous frameworks allows the selective capture of various organic solvents by instantaneous swelling at room temperature. Moreover, the dynamic nature of these frameworks indicates the swelling process with visible volume expansion and enhanced fluorescence. This was further explored for the rapid encapsulation of various fluorescent chromophoric guests at room temperature and investigated for photoinduced energy transfer process. The resultant host-guest antenna materials showed efficient light-harvesting and funnelling of excitation energy of host framework towards the entrapped guest molecule. This process further yielded solid-state luminescent materials with tunable emission. This work holds a great promise on the design of smart porous organic solids from π-conjugated small molecules for optoelectronics, sensing and separation.

Redox-Active Metal-Organic Frameworks: Highly Stable Charge-Separated States through Strut/Guest-to-Strut Electron Transfer.

Molecular organization of donor and acceptor chromophores in self-assembled materials is of paramount interest in the field of photovoltaics or mimicry of natural light-harvesting systems. With this in mind, a redox-active porous interpenetrated metal-organic framework (MOF), {[Cd(bpdc)(bpNDI)]⋅4.5 H2 O⋅DMF}n (1) has been constructed from a mixed chromophoric system. The µ-oxo-bridged secondary building unit, {Cd2 (µ-OCO)2 }, guides the parallel alignment of bpNDI (N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) acceptor linkers, which are tethered with bpdc (bpdcH2 =4,4'-biphenyldicarboxylic acid) linkers of another entangled net in the framework, resulting in photochromic behaviour through inter-net electron transfer. Encapsulation of electron-donating aromatic molecules in the electron-deficient channels of 1 leads to a perfect donor-acceptor co-facial organization, resulting in long-lived charge-separated states of bpNDI. Furthermore, 1 and guest encapsulated species are characterised through electrochemical studies for understanding of their redox properties.

Supramolecular charge transfer nanostructures.

Supramolecular organization of π-conjugated chromophores into well defined nanostructures has gained much attention due to their promising role as active components in organic electronics. Charge-transfer (CT) nanostructures, in which aromatic donor (D) and acceptor (A) molecules are alternately arranged, (mixed stack) have emerged recently as prospective candidates in this direction, because they provide inherent, uniform doping conducive for excellent conducting properties. The present perspective highlights the importance of charge transfer (CT) based non-covalent interactions, with emphasis on supramolecular design principles, for construction of various CT nano-architectures. The whole article is divided into three parts themed on the type of interactions used for obtaining CT assemblies. Through some of our recent results, we have attempted to highlight the latent potential of this nascent field. Furthermore, we have presented our perspectives on the major challenges in this field which is expected to broaden the scope of this subject.

Supramolecular gating of ion transport in nanochannels.

Several covalent strategies towards surface charge-reversal in nanochannels have been reported with the purpose of manipulating ion transport. However, covalent routes lack dynamism, modularity and post-synthetic flexibility, and hence restrict their applicability in different environments. Here, we introduce a facile non-covalent approach towards charge-reversal in nanochannels (<10 nm) using strong charge-transfer interactions between dicationic viologen (acceptor) and trianionic pyranine (donor). The polarity of ion transport was switched from anion selective to ambipolar to cation selective by controlling the extent of viologen bound to the pyranine. We could also regulate the ion transport with respect to pH by selecting a donor with pH-responsive functional groups. The modularity of this approach further allows facile integration of various functional groups capable of responding to stimuli such as light and temperature to modulate the transport of ions as well as molecules.

Oxyberberine protects middle cerebral artery occlusion triggered cerebral injury through TLR4/NLRP3 pathway in rats.

Cerebral ischemia is a life-threatening health concern that leads to severe neurological complications and fatalities worldwide. Although timely intervention with clot-removing agents curtails serious post-stroke neurological dysfunctions, no effective neuroprotective intervention is available for addressing post-recanalization neuroinflammation. Herein, for the first time we studied the effect of oxyberberine (OBB), a derivative of berberine, on transient middle cerebral artery occlusion (MCAO)-generated neurological consequences in Sprague-Dawley rats. The MCAO-operated rats exhibited significant somatosensory and sensorimotor dysfunctions in adhesive removal, foot fault, paw whisker, and rotarod assays at 1 and 3 days post-surgery. These MCAO-generated neurological deficits were prevented in OBB-treated (50 and 100 mg/kg) rats, and also coincided with a smaller infarct area (in 2,3,5-triphenyl tetrazolium chloride staining) and decreased neuronal death (in cresyl violet staining) in the ipsilateral hemisphere of these animals. The immunostaining of neuronal nuclear protein (NeuN) and glial-fibrillary acidic protein (GFAP) also echoes the neuroprotective nature of OBB. The increased expression of neuroinflammatory and blood-brain barrier tight junction proteins like toll-like receptor 4 (TLR4), TRAF-6, nuclear factor kappa B (NF-κB), pNF-κB, nNOS, ASC, and IKBα in the ipsilateral part of MCAO-operated rats were restored to normal following OBB treatment. We also observed the decline in plasma levels/mRNA transcription of TNF-α, IL-1ß, NLRP3, IL-6, and matrix metalloproteinase-9 and increased expression of occludin and claudin in OBB-treated rats. These outcomes imply that OBB may prevent the MCAO-induced neurological consequences and neuroinflammation by interfering with TLR4 and NLRP3 signaling in rats.

Adaptive pores: charge transfer modules as supramolecular handles for reversible pore engineering of mesoporous silica.

We introduce a non-covalent pore engineering approach to achieve exceptional reversibility of functionalization in SBA-15 through viologen-pyranine charge transfer (CT) modules. By employing alkyl derivatives of pyranine as donors, we could exploit the strong CT interactions between pyranine and viologen to reversibly modify the pore size and philicity. The fast binding of the donors enables quick and facile functionalization within minutes at room temperature. The modularity of the approach enables modification of pores with custom-designed compositions, components, and functions. The high selectivity exhibited by viologen on the pore wall facilitated its use in a CT affinity column.

Supramolecular alternate co-assembly through a non-covalent amphiphilic design: conducting nanotubes with a mixed D-A structure.

Mixing it up! The supramolecular alternate co-assembly of extended π-conjugated donor (D) and acceptor (A) molecules (i.e., oligo(phenylenevinylene) and perylenebisimide, respectively), to 1-D nanotubes with an unprecedented mixed stack D-A molecular structure is presented, through a non-covalent amphiphilic design strategy, which results in the formation of hydrogels with remarkable mechanical properties (see scheme).

Exciplex formation and energy transfer in a self-assembled metal-organic hybrid system.

Exciting assemblies: A metal-organic self-assembly of pyrenebutyric acid (PBA), 1,10-phenanthroline (o-phen), and Mg(II) shows solid-state fluorescence originating from a 1:1 PBA-o-phen exciplex. This exciplex fluorescence is sensitized by another residual PBA chromophore through an excited-state energy-transfer process. The solvent polarity modulates the self-assembly and the corresponding exciplex as well as the energy transfer, resulting in tunable emission of the hybrid (see figure).

Guest-responsive reversible swelling and enhanced fluorescence in a super-absorbent, dynamic microporous polymer.

A swell idea! The guest-responsive reversible swelling and fluorescence enhancement of a dynamic, microporous polymer network is presented. Guest-induced breathing of hydrophobic pores imparts multi-functional properties, such as super-absorbency, phase-selective swelling of oil from water and encapsulation of C(60) (see figure), to this soft micro-porous organic polymer.

Light-harvesting hybrid assemblies.

Light-harvesting hybrids have gained much importance as they are considered as potential mimics for photosynthetic systems. In this Concept article we introduce the design concepts involved in the building up of light-harvesting hybrids; these resemble the well-studied organic-based assemblies for energy transfer. We have structured this article into three parts based on the strategies adopted in the synthesis of hybrid assemblies, as covalent, semicovalent, and noncovalent procedures. Furthermore, the properties and structural features of the hybrids and analogous organic assemblies are compared. We also emphasize the challenges involved in the processability of these hybrid materials for device applications and present our views and results to address this issue through the design of soft-hybrids by a solution-state, noncovalent, self-assembly process.

Dynamic self-assembly of charge-transfer nanofibers of tetrathiafulvalene derivatives with F4TCNQ.

One-dimensional charge-transfer nanostructures were constructed by the supramolecular coassembly of amphiphilic (Amph-TTF) and hydrophobic (TDD-TTF) tetrathiafulvalene (TTF) donor derivatives with the acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ), in appropriate solvent composition mixtures. Microscopic analyses show that TDD-TTF retains its self-assembled fibrillar morphology even in the charge-transfer state, whereas Amph-TTF undergoes a spherical to nanorod transition upon coassembly. Time-dependent optical spectroscopy studies have shown a spontaneous change in molecular organization in TDD-TTF-based donor-acceptor costacks, which suggests a dynamic behavior, in contrast to the kinetically stable amphiphilic TTF assemblies. We have also tried to get an insight into the observed time-dependent change in molecular packing of these nanostructures through spectroscopic analyses by commenting on whether the TTF-TCNQ pair is cofacially arranged or present in the classical herringbone (orthogonal) fashion. Furthermore, our two-probe electrical measurements showed that these charge-transfer fibers are conducting. A supramolecular approach that yields 1D charge-transfer nanostructures of donor and acceptor molecules will be an alternative to existing crystalline substances with high conductivity and hence can be a viable tool for nanoelectronics.

A simple method of separating metallic and semiconducting single-walled carbon nanotubes based on molecular charge transfer.

Interaction of as-prepared single-walled carbon nanotubes (SWNTs), containing a mixture of metallic and semiconducting species with the potassium salt of coronene tetracarboxylic acid, I, in an aqueous medium provides a simple method of separating semiconducting and metallic species. The metallic nanotubes precipitate out on interaction with I while the semiconducting nanotubes remain in solution. The method avoids centrifugation and is amenable for large-scale separation and can be used as a routine laboratory procedure. Interestingly, interaction with strong electron acceptor molecules brings about metal-semiconductor transitions in SWNTs.

Supramolecular Switching of Ion-Transport in Nanochannels.

Noncovalent approaches to achieve smart ion-transport regulation in artificial nanochannels have garnered significant interest in the recent years because of their advantages over conventional covalent routes. Herein, we demonstrate a simple and generic approach to control the surface charge in mesoporous silica nanochannels by employing π-electron-rich charged motifs (pyranine-based donors) to interact with the surface of mesoporous silica modified with π-electron-deficient motifs (viologen-based acceptors) through a range of noncovalent forces, namely, charge-transfer, electrostatic, and hydrophobic interactions. The extent of each of these interactions was independently controlled by molecular design and pH, while employing them in a synergistic or antagonistic fashion to modulate the binding affinity of the charged motifs. This enabled the precise control of the surface charge of the nanochannels to achieve multiple ion-transport states.

Validity of thyromental height test as a predictor of difficult laryngoscopy: A prospective evaluation comparing modified Mallampati score, interincisor gap, thyromental distance, neck circumference, and neck extension.

BACKGROUND AND AIMS: Thyromental height test (TMHT) is a recently described anatomical bedside screening tool in predicting difficult laryngoscopy. It has been shown to be more accurate than the modified Mallampati score, thyromental distance (TMD), and sternomental distance with regard to sensitivity and positive predictive value (PPV). Airway assessment studies based on the anatomic parameters of the upper airway are limited in the subcontinent population. We attempted this study to evaluate and validate the predictive value of TMHT at 50 mm in an Indian population in predicting difficult laryngoscopy. METHODS: This prospective observational study was conducted in a tertiary teaching hospital on 340 patients. TMHT along with other bedside predictors of difficult intubation, including modified Mallampati score, interincisor gap (IIG), TMD, neck circumference (NC), and neck extension were assessed. We compared the sensitivity, specificity, PPV, negative predictive value (NPV), and diagnostic accuracy of TMHT with other bedside tests such as the modified Mallampati score, IIG, TMD, NC, and neck extension individually in predicting difficult laryngoscopy. Any Cormack and Lehane's intubation grade II b and above was considered to be difficult laryngoscopy. RESULTS: TMHT had the highest sensitivity (84.62%) and specificity (98.97%), and had the most PPV (88%) and NPV (98.63%) when compared with the modified Mallampati score, IIG, TMD, NC, and neck extension. TMHT was followed by the modified Mallampati score and IIG. CONCLUSION: TMHT appears promising as a single anatomical measure to predict the risk of difficult laryngoscopy, however, validation will require further studies in more diverse patient populations.

Raven's matrices and working memory: a dual-task approach.

Raven's Matrices Test was developed as a "pure" measure of Spearman's concept of general intelligence, g. Subsequent research has attempted to specify the processes underpinning performance, some relating it to the concept of working memory and proposing a crucial role for the central executive, with the nature of other components currently unclear. Up to this point, virtually all work has been based on correlational analysis of number of correct solutions, sometimes related to possible strategies. We explore the application to this problem of the concurrent task methodology used widely in developing the concept of multicomponent working memory. Participants attempted to solve problems from the matrices under baseline conditions, or accompanied by backward counting or verbal repetition tasks, assumed to disrupt the central executive and phonological loop components of working memory, respectively. As in other uses of this method, number of items correct showed little effect, while solution time measures gave very clear evidence of an important role for the central executive, but no evidence for phonological loop involvement. We conclude that this and related concurrent task techniques hold considerable promise for the analysis of Raven's matrices and potentially for other established psychometric tests.

Highly pure solid-state white-light emission from solution-processable soft-hybrids.

Highly pure and solution processable white-light-emitting hybrids are presented. These soft-hybrids are designed by an organic-inorganic supramolecular co-assembly in water. White-light emission is achieved by partial energy transfer (ET) between donor and acceptor molecules anchored on the inorganic component. The unique and remarkable processability feature of these hybrids is demonstrated by painting/writing onto large glass and flexible plastic substrates.