Edamana Prasad

Bio: Edamana Prasad is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Dendrimer & Ether. The author has an hindex of 27, co-authored 100 publications receiving 2263 citations. Previous affiliations of Edamana Prasad include Texas Tech University & Indian Institutes of Technology.

Luminescent micro and nanogel formation from AB3 type poly(aryl ether) dendron derivatives without conventional multi-interactive gelation motifs

Abstract: We report the synthesis, gelation and photophysical properties of luminescent AB3 type poly(aryl ether) dendron derivatives in the absence of conventional multi-interactive gelation motifs. The gelation process is controlled through employing partial polar solvent milieu, which significantly enhances the propensity of π–π interaction between the aryl units present in the system. The self-assembly leads to unprecedented gelation through entrapping solvent molecules in the fibrillar arrangement of poly(aryl ether) units. The strategy was further utilized to prepare an excimer based photoluminescent gel through incorporating anthracene units in the dendrons. The close proximity between the anthracene units in the gel renders the formation of anthracene excimers at room temperature, resulting in the emission of bright green light from the gel, upon UV excitation. The study suggests that the size and packing of the self-assembled fibre can be controlled by the generation and functional groups present in the dendron. Furthermore, the strategy envisages an easy approach to generate fluorescent Low Molecular-mass Organic Gelator (LMOG) through incorporating poly cyclic aromatic hydrocarbon units to the poly(aryl ether) dendrons, since the self-assembly is largely guided by π–π interactions.

A mixed ligand approach towards lanthanide-based gels using citric acid as assembler ligand: white light emission and environmental sensing

Abstract: Fine tuning the optical properties of lanthanide-based gels using low molecular weight gelators has several advantages over the polymeric gelator analogues. Herein, we have prepared a lanthanide-based gel using low molecular weight citric acid as the assembler ligand and the optical properties of the gel were fine-tuned, utilizing a mixed ligand approach, enabling white light emission and environmental sensing (pH and temperature). The coligand utilized in the study was 4'-(4-bromophenyl)-2,2':6',2''-terpyridine. The resultant mixed-ligand gel exhibited green and red emissions in the presence of Tb(iii) ions and Eu(iii) ions, respectively. White light emission was achieved, with CIE coordinates (0.33, 0.32), in the bimetallic Tb/Eu metallogel formed by the precise control over Tb/Eu ratio. The correlated color temperature (CCT) for white-light-emitting gel was calculated, and the value of 5473 K suggests that the system generates cool white light. While most of the reported low molecular weight gelators exhibit on-off responses to stimulus at a particular value, the present system is capable of gradually monitoring changes for stimuli such as pH and temperature over a wide range (pH from 4-11 and temperature from 20 to 70 °C). The unique design strategy of the gel and the characteristic physicochemical properties of the lanthanide ions resulted in the unprecedented ability of the system to monitor changes in environmental stimuli over a considerable range.

Photoinduced Electron Transfer Reactions by SmI2 in THF: Luminescence Quenching Studies and Mechanistic Investigations

Abstract: Photoluminescence quenching studies of SmI 2 in dry THF were carried out in the presence of five different classes of compounds: ketone, alkyl chloride, nitrile, alkene and imine. The free energy change (AG°) of the photoinduced electron transfer (PET) reactions was calculated from the redox potentials of the donor (SmI 2 ) and acceptors. The bimolecular quenching constants (k q ) derived from the Stern-Volmer experiments parallel the free energy changes of the PET processes. The observed quenching constants were compared with the theoretically derived electron transfer rate constants (k e t ) from Marcus theory and found to be in good agreement when a value of λ=167 kJ mol - 1 (40 kcal mol - 1 ) was used for the reorganization energy of the system. A careful comparison of the excited state dynamics of Sm I I in the solid state to the results obtained in solution (THF) provides new insight in to the excited states of Sm I I in THF. The activation parameters determined for the PET reactions in SmI 2 /1-chlorobutane system are consistent with a less ordered transition state and high degree of bond reorganization in the activated complex compared to similar ground state reactions. Irradiation studies clearly show that SmI 2 acts as a better reductant in the excited state and provides an alternative pathway for rate enhancement in known and novel functional group reductions.

Intrinsic luminescence properties of ionic liquid crystals based on PAMAM and PPI dendrimers

Abstract: The photophysical properties of ionic liquid crystals based on poly(amidoamine) {PAMAM} and poly (propyleneimine) (PPI) dendrimers were examined both in solutions and in thin solid films. The dendrimers were peripherally modified by decanoic, 4-octyloxybenzoic, and 3,4,5-trioctyloxybenzoic acids to generate dendrimer based ionic liquid crystals of smectic and columnar phases. The liquid crystalline properties of these compounds were examined by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The dendrimer based ionic liquid crystals exhibited blue emission upon excitation at 370 nm. The emission intensity was found to be enhanced by an order of magnitude in solution when ionic liquid crystals are made from higher generation dendrimers. The steady state and time resolved fluorescence experiments suggest that optical properties of the liquid crystals are originated from the intrinsic emission properties of amine terminated PAMAM and PPI dendrimers. The findings presented here show for the first time that PAMAM and PPI based mesogenic structures can exhibit intrinsic emission in the visible region without incorporating conventional fluorophores.

Principles Of Fluorescence Spectroscopy

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Self-Healing Hydrogels

Abstract: Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self-healing and self-recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self-healing hydrogels generally either possess mechanically robust or rapid self-healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self-healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self-healing hydrogels are reviewed. Specifically, methods to test self-healing efficiencies and recoveries, mechanisms of autonomous self-healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self-heal better also achieve self-healing faster, as compared to gels that only partially self-heal. Recommendations to guide future development of self-healing hydrogels are offered and the potential relevance of self-healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.

Fluorescence and colorimetric chemosensors for fluoride-ion detection.

Abstract: Detection Ying Zhou,†,‡ Jun Feng Zhang, and Juyoung Yoon*,† †Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea ‡Key Laboratory of Medicinal Chemistry for Natural Resource, School of Chemical Science and Technology, Yunnan University, Kunming, 650091, P. R. China College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650500, P. R. China

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

Abstract: Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N