A new perylene bisimide dye self-assembles in an anti-cooperative process predominently into even numbered aggregates via dimers which could be interpreted by a newly developed K 2–K model.

The intriguing advantages of supramolecular chemistry and particularly the application of self-assembly for the construction of defined nanostructures from small, preferably synthetically easily accessible molecules has become a promising area of modern chemistry in the last years. However, the main focus of early work was based on H-bond induced self-assembly which is limited to nonpolar organic solvents. In the past years the field started to shift more and more towards obtaining self-assembling architectures in polar solvents and even water. This tutorial review will discuss some representative examples for self-assembling systems in polar solvents in order to illustrate the different concepts and strategies that can be used. We will also briefly discuss the special properties of water as the ultimate protic solvent from the perspective of a supramolecular chemist to elucidate the challenges that this solvent still poses even today to obtain specific self-assembled nanostructures.

In general, self-assembly in polar solutions requires a combination of several non-covalent interactions within one binding motif. Besides the combination of H-bonds and hydrophobic or aromatic stacking interactions, in the last few years H-bonded ion pairs have been proven useful in this context. Also the molecular rigidity and the extent of intra- versus intermolecular interactions within the monomer play an important role in determining the self-assembling properties of a given monomer. We present some general guidelines and illustrative examples of various approaches that have been pursued in the literature before finally concentrating on a case study from our own work, the dimerization of a guanidiniocarbonyl pyrrole carboxylate zwitterion. This zwitterion forms stable dimers with K > 10(9) M(-1) in DMSO and >10(2) M(-1) even in water and can not only be used to study the importance of various non-covalent interactions for self-assembly in polar solvents but also to construct large nanostructures.

A series of four spermine-functionalized perylene bisimide dyes without linkers (1) and with linkers (2-4) between the chromophore and the polyamine was synthesized. Protonation of the spermine moieties resulted in the formation of highly water-soluble dyes with up to six positively charged ammonium ions. The aggregation behavior of these strongly fluorescent bola-amphiphiles was studied in pure water as solvent by UV/Vis and fluorescence spectroscopy, and an astonishingly high fluorescence quantum yield of up to Phi(fl)=0.90 was observed for PBI 1. Atomic force microscopy and transmission electron microscopy were applied for the visualization of the aggregates on surfaces. Molecular modeling studies were performed by force-field calculations to explore the aggregate morphologies, which also provided valuable information on the influence of the additional alkylcarbonyl linkers. Our detailed spectroscopic and microscopic investigations revealed that the excellent optical properties of perylene bisimide chromophores can be used even in pure deionized water if their aggregation is efficiently suppressed.

Photochemical transformations of molecular building blocks have become an important and widely recognized research field in the past decade. Detailed and deep understanding of novel photochemical catalysts and reaction concepts with visible light as the energy source has enabled a broad application portfolio for synthetic organic chemistry. In parallel, continuous‐flow chemistry and microreaction technology have become the basis for thinking and doing chemistry in a novel fashion with clear focus on improved process control for higher conversion and selectivity. As can be seen by the large number of scientific publications on flow photochemistry in the recent past, both research topics have found each other as exceptionally well‐suited counterparts with high synergy by combining chemistry and technology. This review will give an overview on selected reaction classes, which represent important photochemical transformations in synthetic organic chemistry, and which benefit from mild and defined process conditions by the transfer from batch to continuous‐flow mode.

Improved contacting of TiO2 catalyst, substrate and light results in an impressive boost in reactor performance for blue light mediated C–H arylation of heteroarenes in continuous-flow mode.

Synthetic organic photochemistry has been intensively carried out in the 20th century and paved the way to the preparation of complex organic molecules, which were not yet accessible via thermal chemistry. Several photochemical synthesis routes have found their way into industrial applications for the production of everyday commodities, but photochemistry was still underutilized until recently as a synthesis method in organic chemistry. With the advent of novel photocatalytic and photophysical concepts for the use of high power visible light, the research field of synthetic organic photochemistry has evolved to become a vivid and highly recognized technique in the last years. Fortunately, continuous flow technology has also become an increasingly accepted tool and has proved to be an excellent key player for the advancement of photochemistry in academic and industrial research settings. This Review provides an overview on the recent developments of continuous flow photoreactors and their application to photochemical syntheses under mild and defined process conditions.

Abstract:We present here a systematic study of different guanidiniocarbonylpyrrole-aryl derivatives designed to interact with DNA or RNA both by intercalation of an aromatic moiety into the base stack of the nucleotide as well as groove binding of a guanidiniocarbonyl pyrrole cation. We varied 1.) the size of the aromatic ring (benzene, naphthalene, pyrene and acridine), 2.) the length and flexibility of the linker connecting the two binding groups, as well as 3.) the total number of positive charges present at different pH values. The compounds and their interaction with DNA and RNA were studied by UV/Vis-, fluorescence and CD spectroscopy. Also the antiproliferative activity against human tumour cell lines was determined. Our studies show that efficient interaction with e.g. DNA requires a significantly large aromatic ring (pyrene) connected via a flexible linker to the pyrrole moiety. However, a positive charge as in 12 is also needed. Compound 12 allows for a base pair selective recognition of ds-DNA at physiological pH. The antiproliferative activity correlates with the binding affinity of these compounds towards DNA suggesting that the biological effect is most likely due to DNA binding.