An easily accessible donor-π-acceptor-conjugated small molecule from a 4,8-dialkoxybenzo[1,2-b:4,5-b']dithiophene unit for efficient solution-processed organic solar cells.

A new donor-acceptor-conjugated organic small molecule, BDT(TBT)(2), comprised of benzo[1,2-b:4,5-b']dithiophene and 2,1,3-benzothiadiazole units was designed and synthesized. The small molecule BDT(TBT)(2) in its thin film showed an absorption band in the range of 300-700 nm with an absorption edge at 650 nm and an optical band gap of 1.90 eV. As estimated from the cyclic voltammetry measurements, the HOMO and LUMO energy levels of BDT(TBT)(2) were -5.44 and -3.37 eV, respectively. The spin-coated thin film of BDT(TBT)(2) exhibited p-channel output characteristics with a hole mobility of 2.7 × 10(-6). BDT(TBT)(2), when explored as an electron-donor material in solution-processed bulk-heterojunction organic solar cells in conjunction with a PC(71)BM acceptor with an active layer thickness of 50-55 nm, generated a power conversion efficiency (PCE) of 1.18%. A more impressive PCE of ~2.9% with a short-circuit current density (J(sc)) of 7.94 mA cm(-2) and an open-circuit voltage (V(oc)) of 0.89 V was achieved when the active layer of the cell was annealed at higher temperature (~180 °C).

Development of naphtho[1,2-b:5,6-b']dithiophene based novel small molecules for efficient bulk-heterojunction organic solar cells.

Two new small molecules with a rigid planar naphtho[1,2-b:5,6-b']dithiophene (NDT) unit were designed and synthesized. Solution processed bulk-hetereojunction organic solar cells based on blends of the small molecules and [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) exhibited promising photovoltaic device performance with a maximum power conversion efficiency up to 2.20% under the illumination of AM 1.5G, 100 mW cm(-2).

Drug solubilization by amino acid based polymeric nanoparticles: Characterization and biocompatibility studies.

Three novel amino acid based amphiphilic copolymers, poly(sodium N acryloyl-L-aminoacidate-co-dodecylacrylamide) (where aminoacidate=glycinate, leucinate, and phenylalaninate) were synthesized and characterized. These hydrophobically modified polyelectrolytes (HMPs) formed spheroidal nanoparticular aggregates above a critical aggregation concentration with average diameter 20-200nm and overall negative charges as indicated by dynamic light scattering (DLS) and zeta-potential (ζ≈-10.2 to -25.2) measurements, respectively. The size and shape of the nanostructures was confirmed by transmission electron microscopic images. The micropolarity and microviscosity of the nanosize aggregates were investigated by fluorescence probe method using extrinsic probes like N-phenyl-1-naphthylamine, pyrene, and 1,6-diphenyl-1,3,5-hexatriene. The stability of the copolymer micelles was investigated as a function of pH and temperature using fluorescence and DLS techniques. Both fluorescence probe and DLS data suggest that the copolymer micelles are highly stable under physiological condition (pH 7.4, 37.4°C). These HMP micelles were evaluated primarily as a drug delivery system. The ability of the copolymers to encapsulate hydrophobic drug was investigated using a poorly water-soluble antifungal drug, griseofulvin. Biocompability of the HMPs were examined by hemolytic and cytotoxicity assay. All three HMPs were non-hemolytic up to the tested concentration of about 1.0g/L. In vitro biological assay indicated that these new copolymers were also less toxic against 3T3 mammalian cell line. The studies suggest that these newly conceived amino acid based biocompatible polymeric nanoparticles might have potential application as injectible drug delivery systems which can enhance the therapeutic index of poorly water-soluble clinically challenging drugs.

Nanostructure formation in aqueous solution of amphiphilic copolymers of 2-(N,N-dimethylaminoethyl)methacrylate and alkylacrylate: Characterization, antimicrobial activity, DNA binding, and cytotoxicity studies.

Three amphiphilic random copolymers poly(2-(dimethylaminoethyl)methacrylate-co-alkylacrylate) (where, alkyl = hexyl, octyl, dodecyl) with 16 mol% hydrophobic substitution were synthesized. Surface tension, viscosity, fluorescence probe, dynamic light scattering (DLS), as well as transmission electron microscopic (TEM) techniques were utilized to investigate self-assembly formation by the hydrophobically modified polymers (HMPs) in pH 5. Formation of hydrophobic domains through inter-polymer chain interaction of the copolymer in dilute solution was confirmed by fluorescence probe studies. Average hydrodynamic diameter of the copolymer aggregates at different polymer concentration was measured by DLS studies. The copolymer with shorter hydrophobic chain exhibits larger hydrodynamic diameter in dilute solution, which decreased with either increase of concentration or increase of hydrophobic chain length. TEM images of the dilute solutions of the copolymers with shorter as well as with longer hydrophobic chain exhibit spherical aggregates of different sizes. The antimicrobial activity of the copolymers was evaluated by measuring the minimum inhibitory concentration value against one Gram-positive bacterium Bacillus subtilis and one Gram-negative bacterium Escherichia coli. The copolymer with the octyl group as pendent hydrophobic chain was found to be more effective in killing these microorganisms. The interaction of the cationic copolymers with calf-thymus DNA was studied by fluorescence quenching method. The polymer-DNA binding was found to be purely electrostatic in nature. The hydrophobes on the polymer backbone were found to have a significant influence on the binding process. Biocompatibility studies of the copolymers in terms of cytotoxicity measurements were finally performed at different concentrations of the HMPs to evaluate their potential application in biomedical fields.

Amino acid based amphiphilic copolymer micelles as carriers of non-steroidal anti-inflammatory drugs: solubilization, in vitro release and biological evaluation.

Three novel amino acid based anionic amphiphilic copolymers poly(sodium N-acryloyl-l-valinate-co-alkylacrylamide) (where, alkyl=octyl and dodecyl) with either 9 or 16 mol% hydrophobic substitution were synthesized. These hydrophobically modified polyelectrolytes (HMPs), above a critical concentration, self-assemble in aqueous solution through inter-chain hydrophobic aggregation, forming micelle-like aggregates having hydrodynamic diameter in the range of 50-200 nm. The HMPs were found to undergo conformational changes with the change in solution pH, electrolyte and additive concentration, and temperature. The polymeric micelles were observed to be stable under biological conditions (pH 7.4, [NaCl]=150 mM and temperature (37°C)). The solubilization capacity of the polymeric micelles for six important non-steroidal anti-inflammatory drugs of different hydrophobicity was evaluated. Depending upon the hydrophobicity the solubilities of the drugs were observed to increase ca. 2-10 times in the presence of 1.0 g/L copolymers. The in vitro release kinetics of the loaded drug was studied under physiological pH. To explore their potential application in pharmaceutical industries hemocompatibility and cytotoxicity studies were carried out using hemolytic and MTT assay, respectively. The anionic HMPs were found to be not directly toxic to mammalian cells.

Amphiphilic polymer nanoparticles: characterization and assessment as new drug carriers.

An amino-acid-based hydrophobically modified biocompatible copolymer, poly[(sodium N-acryloyl-L-valinate)-co-(N-octylacrylamide)] was synthesized and characterized. Techniques such as fluorescence probes, DLS, and TEM were used to investigate its aggregation behavior in aqueous solution. The copolymer was observed to form micellar aggregates having diameters in the nanometer range in aqueous solution (pH = 8) through inter-chain hydrophobic association. This behavior was found to be similar to that of poly[(sodium N-acryloyl-L-valinate)-co-(N-dodecylacrylamide)]. The compact micellar nanostructures were observed to be stable with respect to changes of pH and temperature. The encapsulation and release of griseofulvin, a hydrophobic model drug, was studied.