Tomasz Jarosz

Advances in Star‐Shaped π‐Conjugated Systems: Properties and Applications

Until recently π-conjugated organic materials are based mainly on linear systems. Recent years, however, have brought about increasing interest in molecules boasting a dendritic, branched, or star-shaped architecture. This tendency is a direct result of the ongoing search for materials with progressively better properties. Such compounds, featuring novel, 3D architectures, exhibit a multitude of interesting qualities, making them stand out from well-known materials. The direction of star-shaped compound application is determined by whether they are able to form aggregates, π-stacks. This feature is a source of some astounding properties, coveted in numerous applications. Among this class of compounds high charge mobility, high fluorescence efficiency, and good charge separation are all found. Depending on the structure of the core, the molecule may adopt various types of symmetry. Similarly, the conjugation of orbitals may extend over the whole structure or be interrupted at chosen segments. The number of papers pertaining to star-shaped oligomers and polymers is ascending with each year, evidencing a growing interest in them. Consequently, this Review focuses particularly on the most recent reports concerning modification of the structure and properties of the aforementioned type of compounds, as well as on the development of devices based on them.

Living on pyrrolic foundations - Advances in natural and artificial bioactive pyrrole derivatives.

Pyrrole, a simple heterocyclic system, is an important building block for numerous biologically active compounds both natural and synthetic in origin, which boast an immense array of qualities, baleful and beneficial alike. The latter have given rise to a bountiful variety of pyrrole-based drugs, with many more being designed, developed and applied each year, as evidenced by the amount of entries in the Cambridge Structural Database skyrocketing from about six hundred in 2004 to more than a thousand over the course of the last decade. Particularly important in light of the ever-encroaching menace of drug-resistant bacteria, the vast progress in the field necessitates a sound organisational framework and summary - a task, to which we contribute this summary and checklist of the most recent developments, indicating the classes of compounds, which have attracted the most significant research attention.

A novel donor–acceptor carbazole and benzothiadiazole material for deep red and infrared emitting applications

A novel organic material (C1) with the structure D–π–A–π–D was synthesised and characterised. Carbazole was utilised as the electron donor and benzothiadiazole as the electron acceptor unit. The electrochemical, optical and electronic properties of the synthesised compound were studied. Compound C1 exhibits absorption in the visible and ultraviolet range with a high molar absorption coefficient. A strong solvatochromic effect was observed in its emission spectra. Electrochemical and spectroelectrochemical measurements were performed in order to estimate the properties of the molecule in different redox states. Electron paramagnetic resonance (EPR) measurements indicate the delocalisation of radical cations and radical anions over different moieties. Interpretations of the electrochemical and optical results are supported by DFT calculations. OLEDs based on C1 present efficient emission in red and infrared spectral ranges, with a quantum efficiency of 3.13% and a current efficiency of 6.8 cd A−1. The performance is considerably better than what has been reported for analogous devices, based on other carbazole and benzothiadiazole units.

Advancing the delivery of anticancer drugs: Conjugated polymer/triterpenoid composite.

Exemplifying the synergy of anticancer properties of triterpenoids and ion retention qualities of conjugated polymers, we propose a conducting matrix to be a reservoir of anticancer compounds. In this study, poly(3,4-ethylenedioxythiophene), PEDOT, based matrix for electrically triggered and local delivery of the ionic form of anticancer drug, oleanolic acid (HOL), has been investigated. An initial, one-step fabrication procedure has been proposed, providing layers exhibiting good drug release properties and biological activity. Investigation of obtained systems and implementation of modifications revealed another route of fabrication. This procedure was found to yield layers possessing a significantly greater storage capacity of OL(-), as evidenced by the 52% increase in the drug concentrations attainable through electro-assisted release. Examination of the biological activity of immobilised and released OL(-) molecules proved that electrochemical treatment has negligible impact on the anticancer properties of OL(-), particularly when employing the three-step procedure, in which the range of applied potentials is limited. PEDOT/OL(-) composite has been demonstrated to be a robust and cost-effective material for controlled drug delivery.

Betulin-loaded PEDOT films for regional chemotherapy

Chemotherapy is one of the most commonly used cancer treatments. Even so, it has significant adverse effects on healthy tissues. These effects can be avoided through the use of regional chemotherapy, an approach based on delivering the anti-cancer agents locally, to the site of cancer tissue accumulation. Among the different classes of biomaterials that are used as drug carriers, conducting polymers allow reversible, electrostatic immobilization and controlled release of a variety of compounds. In this work, we describe a method for producing surfaces possessing anti-cancer activity, which are a potential tool for regional chemotherapy. Our method consists of covering the surface with a conducting polymer matrix, followed by loading that matrix with cytotoxic compounds. We have chosen betulin as the model compound for this study, as it is commonly available triterpene that exhibits cytotoxicity against a variety of tumor cell lines. The presence of betulin in the polymer matrix is confirmed by SEM, EDS and IR spectroscopy. The release of betulin is carried out using two protocols, i.e. passive mode (open circuit conditions) or active (application of constant potential) mode. The biological activity of betulin that was released from the matrix is confirmed by its toxic effect against KB and MCF-7 cancer cell lines (IC50 values of 13.34±0.88μg/mL and 12.57±1.81μg/mL for KB and MCF-7, respectively). The described method of surface modification is shown to be an effective mean of producing surfaces that possess anti-cancer activity, serving as advantageous materials for regional chemotherapy applications.

Spectroelectrochemistry of poly(3-hexylthiophenes) in solution

The first comprehensive spectroelectrochemical account of the behaviour of regioregular (RR-P3HT) and statistical (ST-P3HT) poly(3-hexylthiophenes) in solution is presented, in contrast to the many reports dealing with P3HT films merely deposited from solution. The conducted experiments revealed that the two types of P3HTs behave in sharply different ways upon the application of electrochemical stimuli: ST-P3HT readily precipitates at mildly oxidative potentials, while the precipitation of the RR-P3HT takes place to a much lesser extent, even at higher potentials. The two polymers, studied via UV–Vis–NIR–EPR spectroelectrochemistry, exhibited properties mostly in line with earlier reports. Further study revealed that RR-P3HT largely remains in solution, even in its doped form, whereas only traces of the doped ST-P3HT are observed in solution in identical conditions. The high concentration of the doped RR-P3HT in solution can be explained by its ability to form soluble polymer agglomerates, in which the positive charge of the p-doped chains is stabilised by and delocalised over neighbouring, interacting undoped chains. These conclusions are consistent with SEM micrographs, which show that after cycling the potential of the electrode in a solution of ST-P3HT, a uniform layer is formed, covering most of the surface of the electrode, whereas in the case of RR-P3HT surface coverage is marginal and formed layer has the appearance of veined blotches.Graphical abstract

Investigation of the Effects of Non-Conjugated Co-Grafts on the Spectroelectrochemical and Photovoltaic Properties of Novel Conjugated Graft Copolymers Based on Poly(3-hexylthiophene)

A new type of polysiloxane copolymers, with conjugated–regioregular poly(3-hexylthiophene) (P3HT) and non-conjugated-poly(ethylene glycol) (PEG)-grafts have been synthesised, and their properties have been studied alongside those of the parent conjugated polymer (P3HT). Spectroelectrochemical and conductometric analyses revealed an early rise of the conductance of the polymers. Once spectral changes begin taking place, the conductance is stable, implying a loss of mobility of charge carriers, even though standard doping/dedoping patterns are observed. Prototype bulk heterojunction solar cells have been fabricated, based on P3HT/[6,6]-Phenyl-C61-butyric acid methyl ester (PCBM), as well as by substituting P3HT for each of the copolymers. The prototype solar cells achieved PCEs of up to 2.11%. This is one of the highest reported power conversion efficiency (PCE) for devices based on P3HT with low average molecular weight Mn = 12 kDa. Strong correlation between the structure of the copolymer and its photovoltaic performance was found. Elongation of PEG copolymer chain and the use of methyl group instead of terminal hydroxyl groups significantly improved photovoltaic performance.

Enhancing anticancer activity through the combination of bioreducing agents and triterpenes

AIM Triterpenes are natural compounds, whose wide biological activity predestines them for application as promising new chemotherapeutics. In this paper, we report the results of our investigations into the substitution of oleanolic acid with aromatic and nitroaromatic moieties acting as bioreducing agents. RESULTS The process of reduction of nitro groups was investigated through cyclic voltammetry, UV-Vis and electron paramagnetic resonance spectroelectrochemistry. The cytotoxic activity against selected cancer cell lines was determined, showing a significant increase in cytotoxicity when the triterpene is equipped with a nitroaromatic moiety. CONCLUSION We believe this approach to the functionalization is promising in terms of enhancing anticancer activity. We also indicate electrochemical techniques as advantageous preclinical screening methods for the identification of cytotoxic agents.