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Praveen V.K.,CNR Institute for Organic Syntheses and Photoreactivity | Ranjith C.,University of Milan | Bandini E.,CNR Institute for Organic Syntheses and Photoreactivity | Ajayaghosh A.,Indian National Institute for Interdisciplinary Science and Technology | Armaroli N.,CNR Institute for Organic Syntheses and Photoreactivity
Chemical Society Reviews | Year: 2014

Oligo(phenylenevinylene)s (OPVs) are extensively investigated π-conjugated molecules that exhibit absorption and fluorescence in the UV-Vis spectral region, which can be widely tuned by chemical functionalisation and external control (e.g. solvent, temperature, pH). Further modulation of the optoelectronic properties of OPVs is possible by supramolecular aggregation, primarily driven by hydrogen bonding or π-stacking interactions. In recent years, extensive research work has been accomplished in exploiting the unique combination of the structural and electronic properties of OPVs, most of which has been targeted at the preparation of molecules and materials featuring photoinduced energy transfer. This review intends to offer an overview of the multicomponent arrays and self-assembled materials based on OPV which have been designed to undergo energy transfer by means of a thorough choice of excitation donor-acceptor partners. We present a few selected examples of photoactive dyads and triads containing organic moieties (e.g. fullerene, phenanthroline) as well as coordination compounds (Cu(i) complexes). We then focus more extensively on self-assembled materials containing suitably functionalised OPVs that lead to hydrogen bonded aggregates, helical structures, gels, nanoparticles, vesicles, mesostructured organic-inorganic hybrid films, functionalised nanoparticles and quantum dots. In most cases, these materials exhibit luminescence whose colour and intensity is related to the efficiency and direction of the energy transfer processes. This journal is © the Partner Organisations 2014.


Babu S.S.,Indian National Institute for Interdisciplinary Science and Technology | Praveen V.K.,Indian National Institute for Interdisciplinary Science and Technology | Praveen V.K.,CNR Institute for Organic Syntheses and Photoreactivity | Ajayaghosh A.,Indian National Institute for Interdisciplinary Science and Technology
Chemical Reviews | Year: 2014

The large volume of research related to supramolecular π-gel chemistry indicates the potential of this area in the field of new functional materials useful for a variety of application, particularly to the fabrication of organic electronic devices. For improved electronic properties, it is necessary to avoid/reduce the content of insulating alkyl chains in the gelator molecules, which is the key point in balancing solubility and precipitation. This will improve the 1D ordering of the gelator and thereby the charge transport properties. Postpolymerization approaches and hybrid material assemblies of gels should be further explored to obtain stable structures that can overcome ambient conditions without loosing the electronic properties. π-gelators have great potential to the development of self-assembly based bulk heterojunction solar cells. For improved performance in this field, more appropriate D-A systems with absorption characteristics extendable to the near-IR and IR regions of the electromagnetic spectrum for more solar radiation coverage, improved stability and environmental compatibility are needed.


Varghese S.,Indian National Institute for Interdisciplinary Science and Technology | Das S.,Indian National Institute for Interdisciplinary Science and Technology
Journal of Physical Chemistry Letters | Year: 2011

The optical properties of π-conjugated organic molecules in their solid state are critically important in determining performance efficiencies of optoelectronic devices such as organic light-emitting diodes and organic thin-film transistors. This Perspective discusses some recent systematic explorations aimed toward arriving at an understanding of the role that molecular packing plays in determining these properties. © 2011 American Chemical Society.


Varughese S.,Indian National Institute for Interdisciplinary Science and Technology
Journal of Materials Chemistry C | Year: 2014

Switching and tuning solid state luminescence properties of molecular materials by modulating molecular packing through non-covalent routes is an attractive prospect. This strategy further makes it feasible to expand the utility of molecules of interest by obtaining a large array of solids - polymorphs, solvates, amorphous phase, nano/micro-crystals and as multi-component systems - with distinct fluorophore arrangement and hence emission characteristics. Because non-covalent interactions that determine the fluorophore arrangements in polymorphs or supramolecular complexes are weak and flexible, their making and breaking become more realistic under ambient conditions, thus having potential to achieve reversible transformations and hence external-stimuli-responsive and switchable molecular fluorescent materials. Recent advances in this context are highlighted in this review with the aid of illustrative examples and further emphasize the scope and relevance of interdisciplinary and multitechnique approaches to unravel the structure-optical property relationships and also to augment the foundations of factual knowledge. This journal is © the Partner Organisations 2014.


Sivakumar S.,Indian National Institute for Interdisciplinary Science and Technology | Reddy M.L.P.,Indian National Institute for Interdisciplinary Science and Technology
Journal of Materials Chemistry | Year: 2012

Luminescent lanthanide complexes (Eu 3+ (1) or Tb 3+ (2)) involving a highly fluorinated aromatic carboxylate, namely, 3,5-bis(perfluorobenzyloxy)benzoic acid which acts as an antenna chromophore and sensitizes the visible emitting lanthanides, have been synthesized and characterized and their photophysical properties investigated. The results demonstrated that the replacement of high-energy C-H vibrations with fluorinated phenyl groups in the 3,5-bis(benzyloxy)benzoate effectively improves the luminescence intensity and lifetimes of lanthanide complexes. It is interesting to note that the designed fluorinated carboxylate is well suited for the sensitization of Tb 3+ emission (Φ sen = 52%), thanks to a favorable position of the triplet state of the ligand as investigated in the Gd 3+ complex. On the other hand, the corresponding Eu 3+ complex shows weak luminescence efficiency (Φ sen = 24%) due to poor match of the triplet state of the ligand with the emissive excited states of the metal ion. In the present work, efforts have also been made to isolate luminescent molecular terbium plastic materials by combining the unique optical properties of lanthanides with the mechanical characteristics, thermal stability, flexibility and film-forming tendency of polymers (PMMA). The photoluminescence quantum yields of polymer-lanthanide hybrid materials are significantly enhanced (53-65%) as compared to that of the Tb 3+-3,5-bis(perfluorobenzyloxy)benzoate complex. © The Royal Society of Chemistry 2012.


Anees P.,Indian National Institute for Interdisciplinary Science and Technology | Sreejith S.,Indian National Institute for Interdisciplinary Science and Technology | Ajayaghosh A.,Indian National Institute for Interdisciplinary Science and Technology
Journal of the American Chemical Society | Year: 2014

Design of selective sensors for a specific analyte in blood serum, which contains a large number of proteins, small molecules, and ions, is important in clinical diagnostics. While metal and polymeric nanoparticle conjugates have been used as sensors, small molecular assemblies have rarely been exploited for the selective sensing of a protein in blood serum. Herein we demonstrate how a nonspecific small molecular fluorescent dye can be empowered to form a selective protein sensor as illustrated with a thiol-sensitive near-IR squaraine ( Sq) dye (λabs= 670 nm, λem= 700 nm). The dye self-assembles to form non fluorescent nanoparticles (Dh = 200 nm) which selectively respond to human serum albumin (HSA) in the presence of other thiol-containing molecules and proteins by triggering a green fluorescence. This selective response of the dye nanoparticles allowed detection and quantification of HSA in blood serum with a sensitivity limit of 3 nM. Notably, the Sq dye in solution state is nonselective and responds to any thiol-containing proteins and small molecules. The sensing mechanism involves HSA specifi c controlled disassembly of the Sq nanoparticles to the molecular dye by a noncovalent binding process and its subsequent reaction with the thiol moiety of the protein, triggering the green emission of a dormant fluorophore present in the dye. This study demonstrates the power of a self-assembled small molecular fluorophore for protein sensing and is a simple chemical tool for the clinical diagnosis of blood serum. © 2014 American Chemical Society.


Babu S.S.,Indian National Institute for Interdisciplinary Science and Technology | Prasanthkumar S.,Indian National Institute for Interdisciplinary Science and Technology | Ajayaghosh A.,Indian National Institute for Interdisciplinary Science and Technology
Angewandte Chemie - International Edition | Year: 2012

Nature excels at engineering materials by using the principles of chemical synthesis and molecular self-assembly with the help of noncovalent forces. Learning from these phenomena, scientists have been able to create a variety of self-assembled artificial materials of different size, shapes, and properties for wide ranging applications. An area of great interest in this regard is solvent-assisted gel formation with functional organic molecules, thus leading to one-dimensional fibers. Such fibers have improved electronic properties and are potential soft materials for organic electronic devices, particularly in bulk heterojunction solar cells. Described herein is how molecular self-assembly, which was originally proposed as a simple laboratory curiosity, has helped the evolution of a variety of soft functional materials useful for advanced electronic devices such as organic field-effect transistors and organic solar cells. Highlights on some of the recent developments are discussed. All gelled together: Solvent-assisted gelation of functional organic molecules leading to one-dimensional fibers is an area of great interest. Recent developments in molecular self-assembly-assisted gelation of π systems into soft functional materials and their potential application in organic electronic devices, such as organic field-effect transistors and organic solar cells, are reviewed (see picture). © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


George J.,Indian National Institute for Interdisciplinary Science and Technology | George Thomas K.,Indian National Institute for Interdisciplinary Science and Technology
Journal of the American Chemical Society | Year: 2010

(Figure Presented) Au nanoparticles grown on D- and L-isomers of diphenylalanine peptide nanotubes showed a bisignated CD signal at their surface plasmon frequency with positive and negative couplets, respectively. The surface plasmon coupled CD signal in these hybrid systems originates from the asymmetric organization of Au nanoparticles on peptide nanotubes. Mirror image relationship in the CD spectra clearly indicates that the chiral molecules on the nanotubes drive the organization of nanoparticles in two different ways. Copyright © 2010 American Chemical Society.


Kartha K.K.,Indian National Institute for Interdisciplinary Science and Technology | Babu S.S.,Indian National Institute for Interdisciplinary Science and Technology | Srinivasan S.,Indian National Institute for Interdisciplinary Science and Technology | Ajayaghosh A.,Indian National Institute for Interdisciplinary Science and Technology
Journal of the American Chemical Society | Year: 2012

Detection of explosives is of utmost importance due to the threat to human security as a result of illegal transport and terrorist activities. Trinitrotoluene (TNT) is a widely used explosive in landmines and military operations that contaminates the environment and groundwater, posing a threat to human health. Achieving the detection of explosives at a sub-femtogram level using a molecular sensor is a challenge. Herein we demonstrate that a fluorescent organogelator exhibits superior detection capability for TNT in the gel form when compared to that in the solution state. The gel when coated on disposable paper strips detects TNT at a record attogram (ag, 10 -18 g) level (∼12 ag/cm 2) with a detection limit of 0.23 ppq. This is a simple and low-cost method for the detection of TNT on surfaces or in aqueous solutions in a contact mode, taking advantage of the unique molecular packing of an organogelator and the associated photophysical properties. © 2012 American Chemical Society.


Reddy M.L.P.,Indian National Institute for Interdisciplinary Science and Technology | Sivakumar S.,Indian National Institute for Interdisciplinary Science and Technology
Dalton Transactions | Year: 2013

On account of their intrinsic chemical and spectroscopic properties, luminescent lanthanide molecular materials find potential applications in lighting, optical communications, photonics and biomedical devices. This perspective article summarizes some recent seminal research work on luminescent properties and structural aspects of a series of lanthanide benzoate complexes featuring Eu3+ and Tb3+ ions. In particular, when modified with light-harvesting moieties, benzoates have proven to be efficient sensitizers for lanthanide ions. The photoluminescence properties of the various lanthanide benzoate coordination compounds have also been correlated with the electronic states of the newly designed antenna molecules. © 2013 The Royal Society of Chemistry.

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