Manickam Jayakannan

Single Polymer Photosensitizer for Tb3+ and Eu3+ Ions: An Approach for White Light Emission Based on Carboxylic-Functionalized Poly(m-phenylenevinylene)s

Here, we have demonstrated a facile molecular approach to generate white light emission by combining carboxylic functionalized poly(m-phenylenevinylene)s polymeric architectures with lanthanide beta-diketonate complexes. The new class of carboxylic functional conjugated polymeric materials was custom-designed from phenyl propanoic and acetic acids and structurally characterized by NMR, FT-IR, and MALDI-TOF spectroscopic techniques. The designed conjugated polymers were employed for the synthesis of lanthanide complexes in the presence of acetyl acetone (acac) as coligand and investigated their photophysical properties. For comparison, carboxylic-anchored oligo-phenylenevinylene (OPV) was also designed, characterized, and utilized for the synthesis of lanthanide complexes in the presence of acetyl acetone as coligand. Investigations revealed that carboxylic functionalized polymeric material with Eu(3+)-beta-diketonate complex exhibits unique magenta emission when excited at 310 nm. On the other hand, carboxylic functionalized polymeric material with Tb(3+)-beta-diketonate complex shows bright sky-blue emission. Interestingly, when Eu(3+) and Tb(3+) were incorporated into polymer backbone in equimolar ratio along with acetyl acetone as coligand, exhibited a white emission with CIE 1976 color coordinates x = 0.28, y = 0.34. The intrinsic quantum yield and lifetime of Ln(3+) complexes have been evaluated. The singlet and triplet energy levels of the antenna chromophore ligands have been calculated and the probable energy transfer mechanisms in Ln(3+) complexes have also been discussed. The effect of polymer structure and spacer effect on the photosensitizing of Tb(3+) and Eu(3+) ions was also investigated.

Dextran vesicular carriers for dual encapsulation of hydrophilic and hydrophobic molecules and delivery into cells.

Dextran vesicular nanoscaffolds were developed based on polysaccharide and renewable resource alkyl tail for dual encapsulation of hydrophilic and hydrophobic molecules (or drugs) and delivery into cells. The roles of the hydrophobic segments on the molecular self-organization of dextran backbone into vesicles or nanoparticles were investigated in detail. Dextran vesicles were found to be a unique dual carrier in which water-soluble molecules (like Rhodamine-B, Rh-B) and polyaromatic anticancer drug (camptothecin, CPT) were selectively encapsulated in the hydrophilic core and hydrophobic layer, respectively. The dextran vesicles were capable of protecting the plasma-sensitive CPT lactone pharmacophore against the hydrolysis by 10× better than the CPT alone in PBS. The aliphatic ester linkage connecting the hydrophobic tail with dextran was found to be cleaved by esterase under physiological conditions for fast releasing of CPT or Rh-B. Cytotoxicity of the dextran vesicle and its drug conjugate were tested on mouse embryonic fibroblast cells (MEFs) using MTT assay. The dextran vesicular scaffold was found to be nontoxic to living cells. CPT loaded vesicles were found to be 2.5-fold more effective in killing fibroblasts compared to that of CPT alone in PBS. Confocal microscopic images confirmed that both Rh-B and CPT loaded vesicles to be taken up by fibroblasts compared to CPT alone, showing a distinctly perinuclear localization in cells. The custom designed dextran vesicular provides new research opportunities for dual loading and delivering of hydrophilic and hydrophobic drug molecules.

Stimuli-Responsive Poly(caprolactone) Vesicles for Dual Drug Delivery under the Gastrointestinal Tract

We report the first example of carboxylic functionalized poly(caprolactone) (PCL) block copolymer vesicles as a novel dual drug delivery pH responsive vehicle for oral administration under the gastrointestinal (GI) tract. A new carboxylic functionalized caprolactone monomer was custom designed through multistep organic reactions and polymerized under controlled ROP using polyethylene glycol (PEG-2000) to produce amphiphilic diblocks, PEG-b-CPCLx, with x = 25, 50, 75, and 100. These carboxylic PCL block copolymers were self-organized into 100-250 nm vesicular assemblies in water. The size and shape of the vesicular assemblies were confirmed by light scattering, zeta potential, and electron microscopes. These vesicles were capable of loading both hydrophilic molecules (Rhodamine B, Rh-B) and hydrophobic drugs such as ibuprofen (IBU) and camptothecin (CPT) in the core and layer, respectively. These pH-responsive PCL vesicles were stable in strong acidic conditions (pH < 2.0, stomach) and ruptured to release the loaded cargoes under neutral or basic pH (7.0 ≤ pH, similar to that of small intestine). The drug release kinetics under simulated GI tract revealed that the individual drug loaded vesicles followed the combination of diffusion and erosion pathway, whereas the dual drug loaded vesicles predominantly followed the diffusion controlled process. Thus, the custom designed PCL vesicles open up new area of pH stimuli responsive polymer vehicles for delivering multiple drugs in oral drug delivery which are yet to be explored for biomedical applications.

Recent Developments in Polyether Synthesis

Review: Polyethers, both aliphatic, such as poly(ethylene oxide), poly(propylene oxide), etc., and wholly aromatic ones, such as poly(phenylene oxide)s, are commercially important materials. Polymers belonging to the former class are primarily synthesized via a ring-opening polymerization route, while those belonging to the latter are prepared via either oxidative coupling or nucleophilic aromatic substitution approaches. Polyethers that contain both aromatic and aliphatic units in their backbone are far less common. This review will discuss some of the recent advances in the preparation of polyethers, primarily focussing on those where the ether linkage is generated during polymerization. Although the standard ring-opening polymerization (ROP) route toward aliphatic polyethers has witnessed several interesting developments in recent years, it will not be covered in this review. The last section deals with a new melt-transetherification approach for the preparation of poly(xylylene alkylene ether)s developed in our laboratory.

Supramolecular Liquid Crystalline π-Conjugates: The Role of Aromatic π-Stacking and van der Waals Forces on the Molecular Self-Assembly of Oligophenylenevinylenes

Here, we report a unique design strategy to trace the role of aromatic π-stacking and van der Waals interactions on the molecular self-organization of π-conjugated building blocks in a single system. A new series of bulky oligophenylenevinylenes (OPVs) bearing a tricyclodecanemethylene (TCD) unit in the aromatic π-core with flexible long methylene chains (n = 0-12 and 16) in the longitudinal position were designed and synthesized. The OPVs were found to be liquid crystalline, and their enthalpies of phase transitions (also entropies) showed odd-even oscillation with respect to the number of carbon atoms in alkyl chains. OPVs with an even number of methylene units in the side chains showed higher enthalpies with respect to their highly packed solid structures compared to odd-numbered ones. Polarized light microscopic analysis confirmed the formation of cholesteric liquid crystalline (LC) phases of fan shaped textures with focal conics in OPVs with 5 ≤ n ≤ 9. OPVs with longer alkyl chains (OPV-10 to OPV-12) produced a birefringence pattern consisting of dark and bright ring-banded suprastructures. The melting temperature followed a sigmoidal trend, indicating the transformation of molecular self-organization in OPVs from solid to ring-banded suprastructures via cholesteric LC intermediates. At longer alkyl chain lengths, the van der Waals interactions among the alkyl chains became predominant and translated the mesogenic effect across the lamellae; as a consequence, the lamellae underwent twisted self-organization along the radial growth direction of the spherulites to produce bright and dark bands. Scanning electron microscope (SEM) analysis of cholesteric LC and ring-banded textures strongly supported the existence of twisted lamellae in the OPVs with ring-banded textures. Variable temperature X-ray diffraction analysis confirmed the reversibility of the molecular self-organization in the solid state and also showed the existence of the higher ordered lamellar structure in ring-banded OPVs. Photophysical characterizations such as excitation, emission, and time resolved fluorescence decay measurements were employed to trace molecular self-organization in their liquid crystalline phases. The emission spectra of the OPV samples showed odd-even oscillation in their emission wavelengths with respect to the length of alkyl chains. Highly packed even-OPVs showed more blue shift compared to that of less crystalline odd-OPVs. Time dependent fluorescence decay of OPVs followed a biexponential fit, and their lifetimes (τ(1) and τ(2) values) revealed that the decay is faster for odd-OPVs compared to even-OPVs. Among all the OPVs, the τ(2) values for OPV-8 and OPV-12 were found to be much higher, indicating their high luminescent characteristics. In a nut shell, bulky liquid crystalline OPV chromophores were cleverly utilized, for the first time, to probe the aromatic π-stacking versus van der Waals interactions on the molecular self-organization of π-conjugated system.

π-Conjugated polymer–Eu3+ complexes: versatile luminescent molecular probes for temperature sensing

We report π-conjugated polymer–Eu3+ ion complexes as new potential luminescent thermo-sensitive molecular probes. Carboxylic acid functionalized segmented π-conjugated polymers having oligophenylenevinylene (OPV) chromophores in the poly(ethyleneoxide) or polymethylene backbones were custom designed, synthesized and utilized as efficient photosensitizers for Eu3+ ions. These π-conjugated polymer–Eu3+ ion complexes were found to be thermo-sensitive and behaved as reversible ‘turn-on’ or ‘turn-off’ luminescent switches in solution and in solid state. Luminescent decay studies revealed that the red-emission from the Eu3+ ion excited state was highly sensitive to temperature which drove the functioning of optical switches. The decay rate constants followed a typical Arrhenius trend over a wide temperature range having similar activation energies. Both the nature as well as length of the segmented polymer chain that tied the OPV optical chromophores in the backbone determine the temperature range of the luminescent on–off process. The emission characteristics of the oligomer–Eu3+ ion complex were found to be non-thermosensitive which emphasized the need for the segmented π-conjugated polymer ligand structure for the probes based on Eu3+ ion complexes. The present strategy opens up new concept and molecular design principles for π-conjugated polymer–lanthanide ion complexes as potential candidates for temperature sensitive luminescent molecular probes.

Effect of branching on the thermal properties of novel branched poly(4‐ethyleneoxy benzoate)

Poly(4-ethyleneoxy benzoate) (PEOB) was synthesized by the self-condensation of ethyl 4-(2-hydroxyethoxy) benzoate (E4HEB) under transesterification conditions. Branched PEOB was prepared by the condensation of E4HEB with an

Synthesis and thermal analysis of branched and “kinked” poly(ethylene terephthalate)

AB_2

Enzyme and Thermal Dual Responsive Amphiphilic Polymer Core–Shell Nanoparticle for Doxorubicin Delivery to Cancer Cells

monomer, ethyl 3,5-bis(2-hydroxyethoxy) benzoate (EBHEB), under similar conditions. Varying amounts of branching (0–50%) were introduced into the linear polymer by changes in the composition of the comonomers in the feed. The solution viscosity of the polymers indicated that they had reasonable molecular weights; the extent of branching in these copolymers was established from their

CH/π‐Interaction‐Guided Self‐Assembly in π‐Conjugated Oligomers

^1H