Application of polysaccharide biopolymers as natural adsorbent in sample preparation.

Preparing samples for analyses is perhaps the most important part to analyses. The varied functional groups present on the surface of biopolymers bestow them appropriate adsorption properties. Properties like biocompatibility, biodegradability, presence of different surface functional group, high porosity, considerable absorption capacity for water, the potential for modification, etc. turn biopolymers to promising candidates for varied applications. In addition, one of the most important parts of determination of an analyte in a matrix is sample preparation step and the efficiency of this step in solid phase extraction methods is largely dependent on the type of adsorbent used. Due to the unique properties of biopolymers they are considered an appropriate choice for using as sorbent in sample preparation methods that use from a solid adsorbent. Many review articles have been published on the application of diverse adsorbents in sample preparation methods, however despite the numerous advantages of biopolymers mentioned; review articles in this field are very few. Thus, in this paper we review the reports in different areas of sample preparation that use polysaccharides-based biopolymers as sorbents for extraction and determination of diverse organic and inorganic analytes.

Conformationally restricted dynamic supramolecular catalysts for substrate-selective epoxidations.

A second generation of a substrate-selective dynamic supramolecular catalytic system consisting of a catalyst part and a receptor part, connected by a hydrogen-bonding motif, has been realized based on rational design. The results from analyses of the equilibrium mixture of the species generated by the components of the first generation system led us to selectively lock the cisoid conformation of the catalyst part to increase the amount of the substrate-selective catalytic cavity in the equilibrium mixture. This was realized by strapping the catalyst part by organic synthesis. This strapping led to an increase in substrate selectivity in the pair-wise competitive epoxidations of pyridyl- vs. phenyl-appended styrenes and pyridyl- vs. phenyl-appended stilbenes of both Z- and E- configuration compared to the first generation system, reaching 3.4 : 1 as the highest substrate selectivity for Z-mono-pyridyl-stilbene (27a) vs. the corresponding all-carbon analogue (28a) and for E-dipyridyl-stilbene (26b) vs. the corresponding all-carbon analogue (28b), respectively.

Dye-sensitized solar cells based on Fe N-heterocyclic carbene photosensitizers with improved rod-like push-pull functionality.

A new generation of octahedral iron(ii)-N-heterocyclic carbene (NHC) complexes, employing different tridentate C^N^C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push-pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well as directional charge-transfer displacement of the lowest excited state towards the semiconductor substrate in accordance with the push-pull design. Prototype DSSCs based on one of the new Fe NHC photosensitizers demonstrate a power conversion efficiency exceeding 1% already for a basic DSSC set-up using only the I-/I3 - redox mediator and standard operating conditions, outcompeting the corresponding DSSC based on the homoleptic reference complex. Transient photovoltage measurements confirmed that adding the co-sensitizer chenodeoxycholic acid helped in improving the efficiency by increasing the electron lifetime in TiO2. Time-resolved spectroscopy revealed spectral signatures for successful ultrafast (<100 fs) interfacial electron injection from the heteroleptic dyes to TiO2. However, an ultrafast recombination process results in undesirable fast charge recombination from TiO2 back to the oxidized dye, leaving only 5-10% of the initially excited dyes available to contribute to a current in the DSSC. On slower timescales, time-resolved spectroscopy also found that the recombination dynamics (longer than 40 µs) were significantly slower than the regeneration of the oxidized dye by the redox mediator (6-8 µs). Therefore it is the ultrafast recombination down to fs-timescales, between the oxidized dye and the injected electron, that remains as one of the main bottlenecks to be targeted for achieving further improved solar energy conversion efficiencies in future work.

Carbazole-based hole-transport materials for efficient solid-state dye-sensitized solar cells and perovskite solar cells.

Two carbazole-based small molecule hole-transport materials (HTMs) are synthesized and investigated in solid-state dye-sensitized solar cells (ssDSCs) and perovskite solar cells (PSCs). The HTM X51-based devices exhibit high power conversion efficiencies (PCEs) of 6.0% and 9.8% in ssDSCs and PSCs, respectively. These results are superior or comparable to those of 5.5% and 10.2%, respectively, obtained for the analogous cells using the state-of-the-art HTM Spiro-OMeTAD.