A new series of Fe(II) and Co(II) complexes of sterically modulated 2,3,7,8-tetrahydroacridine-4,5(1H,6H)-diimine by substituted aryl rings are synthesized. The complex synthesis is achieved through a one-pot methodology by reacting one equivalent of 2,3,7,8-tetrahydroacridine-4,5(1H,6H)-dione with two equivalents of required aniline derivatives together with Fe or Co salt in boiling acetic acid. The single-crystal X-ray analyses of Fe and Co complexes bearing a 2,6-diisopropyl-substituted ligand, (N,N′E,N,N′E)-N,N′-(2,3,7,8-tetrahydroacridine-4,5(1H,6H)-diylidene)bis(2,6-diisopropylaniline), show a distorted trigonal-bipyramidal geometry for the metal center, a deviation from square-pyramidal geometry due to the opening up of the coordination sphere originating from structural rigidity of the carbonyl carbon atom achieved through cyclization. All the complexes show high activity toward ethylene activation when treated with methylaluminoxane as a cocatalyst. The ortho substituents of the aryl rings and the type of metal have a significant effect on ethylene activation and specifically on product distribution. The Fe complex with a 2,6-diisopropyl-substituted bis(imino)tetrahydroacridyl ligand produced polyethylene of moderate molecular weight (18 000). On changing the ortho substitution of the ligand from 2,6-diisopropyl to 2,6-dimethyl, the Co complexes produce polyethylene waxes and oligomers of predominantly α-olefins simultaneously, obeying Schulz−Flory distribution. The Co complexes bearing ligands with less sterically hindered substituents at the ortho position behave exclusively as dimerization catalysts.

No abstract

A series of dual stimuli responsive synthetic polymer bioconjugate chimeric materials, poly(N-isopropylacrylamide)55-block-poly(L-histidine)n [p(NIPAM)55-b-p(His)n] (n=50, 75, 100, 125), have been synthesized by employing reversible addition-fragmentation chain transfer polymerization of NIPAM, followed by ring-opening polymerization of α-amino acid N-carboxyanhydrides. The dual stimuli responsive properties of the resulting biocompatiable and membrenolytic p(NIPAM)55-b-p(His)n polymers are investigated for their use as a stimuli responsive drug carrier for tumor targeting. Highly uniform self-assembled micelles (∼55 nm) fabricated by p(NIPAM)55-b-p(His)n polymers display sharp thermal and pH responses in aqueous media. An anticancer drug, doxorubicin (Dox), is effectively encapsulated in the micelles and the controlled Dox release is investigated in different temperature and pH conditions. Antitumor effect of the released Dox is also assessed using the HepG2 human hepatocellular carcinoma cell lines. Dox molecules released from the [p(NIPAM)55-b-p(His)n] micelles remain biologically active and have stimuli responsive capability to kill cancer cells. The self-assembling ability of these hybrid materials into uniform micelles and their efficiency to encapsulate Dox makes them a promising drug carrier to cancer cells. The new chimeric materials thus display tunable properties that can make them useful for a molecular switching device and controlled drug delivery applications needing responses to temperature and pH for the improvement of cancer chemotherapy.

No abstract

The inferior long-term stability of polymer-based solar cells needs to be overcome for their commercialization to be viable. In particular, an abrupt decrease in performance during initial device operation, the so-called 'burn-in' loss, has been a major contributor to the short lifetime of polymer solar cells, fundamentally impeding polymer-based photovoltaic technology. In this study, we demonstrate polymer solar cells with significantly improved lifetime, in which an initial burn-in loss is substantially reduced. By isolating trap-embedded components from pristine photoactive polymers based on the unimodality of molecular weight distributions, we are able to selectively extract a trap-free, high-molecular-weight component. The resulting polymer component exhibits enhanced power conversion efficiency and longterm stability without abrupt initial burn-in degradation. Our discovery suggests a promising possibility for commercial viability of polymer-based photovoltaics towards real solar cell applications.