ABSTRACT Strategic substitution of the 5 and 12 positions in pentacene with an electron‐donating nitrogen and electron‐accepting phosphine oxide, sulfone and carbonyl groups results in highly polarized para ‐quinodimethane (pQDM) derivatives with large dipole moments exceeding 10 D. These push‐pull systems feature narrow HOMO‐LUMO gaps (1.0–1.7 eV), reversible redox properties and near‐infrared (NIR) absorption and emission with maxima between 800 and 1100 nm. Remarkably, the polarization induces aromaticity switching: unlike their non‐aromatic double–donor and double–acceptor counterparts, the donor–acceptor analogues develop weak aromatic character in the central quinoidal ring, which is further enhanced in polar solvents, as confirmed by theoretical calculations, NMR spectroscopy and X‐ray crystallography. These findings demonstrate how molecular polarization can modulate aromaticity and electronic structure, providing a design platform for functional quinoidal π‐systems with tunable optical and redox properties.

We applied the exciton coupling theory (ECT) to interpret the dipolar interaction mechanism of C═O stretching and N─H bending vibrations in a new class of chiral macrocycles based on the 2,5-diaminoterephthalate scaffold. VCD and FT-Raman spectra, with the support of quantum chemistry calculations, came together to disentangle the energy level diagram resulted from the vibrational coupling of the ν(C═O) and δ(N─H) vibrations on the basis of the local symmetries. The effect of the configuration of the carbonyl groups on the chiral coupling demonstrated the prevalence of the through-space dipolar interaction mechanisms, with respect to the through-bond one, between the C═O bonds, which is of interest to investigations of the biochemical activity of pharmaceutical molecules endowed with acid groups.

By leveraging the strongly Lewis acidic nature of BBr3, we were able to control the bromination of dipyrrolonaphthyridinediones giving access to mono- to hexabrominated scaffolds, resulting in the formation of new π-expanded derivatives. Modifying specific core positions allowed us to achieve previously unattainable luminescence brightness in these systems, as well as a shift in their emission to the deep-red region.

This chapter describes the procedure for the synthesis of tetraaryl‐, pentaaryl‐, and hexaaryl‐1,4‐dihydropyrrolo[3,2‐b]pyrroles. Scope of this reaction has been broadened to embrace variety of primary aromatic amines and aromatic aldehydes including the derivatives of furan, benzofuran, thiophene, pyrrole, pyridine and quinolone. The chapter presents some of the important points to be considered, the conditions that need to be maintained, characterization data, and the reagents required, as well as the techniques used and the equipment setup that are vital to carrying out the process. It also describes the hazards associated with working with chemicals and the ways to deal with these hazards.

Color polymorphism combined with crystal packing-dependent luminescence properties of polymorphs reflects differences in intermolecular interactions in different molecular arrangements. The title compound has two polymorphic crystal structures having strikingly different absorption and luminescence spectra that result from different packing motifs in the crystal lattice. The polymorph with brick wall-like packing of molecules is white and shows very weak violet fluorescence whereas the second polymorph, where molecules are arranged in columnar stacks, is bright yellow and displays intense green fluorescence with maximum at 487 nm (20530 cm-1). In the white polymorph, where the distance between neighboring chromophores is increased, absorption and fluorescence spectra are similar to those of monomer in solution, and intersystem crossing to triplet manifold is the dominant pathway of relaxation. In the yellow polymorph, molecules within the columnar stacks are rotated which mitigates the steric hindrance and leads to closer π-stacking of the pyrene cores. That increases the ππ overlap and strengthens intermolecular interactions decreasing energy of the excited states. This affects emission spectra and photophysical processes-fluorescence yield grows whereas triplet formation yield decreases when S1 is lowered below higher triplet states and conditions for effective vibronic spin-orbit coupling are not favorable. The effect is not observed for other similar pyrene derivatives, testifying the uniqueness of the phenomenon.

Chiral macrocycles composed of dimethyl 2,5-diaminoterephthalate units (n = 2–4) can be synthesised in a simple one-pot reaction. All products exhibit fluorescence in solution and in the solid state that is dependent on the size of the macrocyclic ring—the smaller the macrocycle, the longer the emission wavelength. The macrocycles show strong chiroptical activity, with the trimer showing particularly high dissymmetry factors in ECD and CPL spectra. More information can be found in the Research Article by M. Górecki, M. Grzybowski and co-workers (DOI: 10.1002/chem.202300932).

Chiral fluorescent macrocycles consisting of two to four units of dimethyl 2,5-diaminoterephthalate can be readily synthesized in a one-pot manner from inexpensive building blocks. Depending on the concentration, either a paracyclophane-like dimer with closely stacked benzene rings or a triangular trimer is the main product of the reaction. The macrocycles exhibit fluorescence in solution as well as in the solid state with maxima that are red-shifted with decreasing size of the macrocyclic ring and are observed at wavelengths from 590 (tetramer in solution) to 700 nm (dimer in the solid state). Chirality dictates the differential absorption and emission of circularly polarized light by these molecules. The ECD and CPL effects are particularly strong for the trimer, which is characterized by relatively large dissymmetry factors g(abs)=& PLUSMN;2.8x10(-3) at 531 nm and g(lum)=& PLUSMN;2.3x10(-3) at 580 nm in n-hexane, being at the same time highly luminescent (& phi;(fl)=13.7 %). Despite the small chromophore, the circularly polarized brightness B-CPL of 2.3 dm(3) mol(-1) cm(-1) is comparable to values reported for other classes of established CPL emitters in the visible region, such as expanded helicenes or larger & pi;-conjugated systems.

This communication describes the photophysical behavior of three analogs of cyclophane bearing the dipyrrolonaphthyridinedione (DPND) core. In these molecules, intersystem crossing (ISC) can be successfully induced by distinct changes in the deviation from planarity within the DPND core, allowing at the same time the emission maximum to shift from the green to red region of the visible spectrum without any synthetic modifications of the chromophore structure. This finding may build the foundation for a new paradigm for inducing ISC-type transitions within other centrosymmetric and planar cross-conjugated chromophores.

Fluorene-based analogues of fluorescein, rhodol, and rhodamine exhibit absorption and fluorescence beyond 800-900 nm in water, 300-400 nm red-shifted compared to the original oxygen-bridged xanthene dyes, giving potential access to low molecular weight fluorescent markers for the second biological window (NIR-II, ca. 1000-1350 nm).

Oxidative aromatic coupling occupies a fundamental place in the modern chemistry of aromatic compounds. It is a method of choice for the assembly of large and bewildering architectures. Considerable effort was also devoted to applications of the Scholl reaction for the synthesis of chiral biphenols and natural products. The ability to form biaryl linkages without any prefunctionalization provides an efficient pathway to many complex structures. Although the chemistry of this process is only now becoming fully understood, this reaction continues to both fascinate and challenge researchers. This is especially true for heterocoupling, that is, oxidative aromatic coupling with the chemoselective formation of a C-C bond between two different arenes. Analysis of the progress achieved in this field since 2013 reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted (cyclo)dehydrogenation, and developing new reagents.

Synthetic chemical fluorescent dyes promise to be useful for many applications in biology. Covalent, targeted labeling, such as with a SNAP-tag, uses synthetic dyes to label specific proteins in vivo for studying processes such as endocytosis or for imaging via super-resolution microscopy. Despite its potential, such chemical tagging has not been used effectively in plants. A major drawback has been the limited knowledge regarding cell wall and membrane permeability of the available synthetic dyes. Of 31 synthetic dyes tested here, 23 were taken up into BY-2 cells, while eight were not. This creates sets of dyes that can serve to measure endocytosis. Three of the dyes that were able to enter the cells, SNAP-tag ligands of diethylaminocoumarin, tetramethylrhodamine, and silicon-rhodamine 647, were used to SNAP-tag α-tubulin. Successful tagging was verified by live cell imaging and visualization of microtubule arrays in interphase and during mitosis in Arabidopsis (Arabidopsis thaliana) seedlings. Fluorescence activation-coupled protein labeling with DRBG-488 was used to observe PIN-FORMED2 (PIN2) endocytosis and delivery to the vacuole as well as preferential delivery of newly synthesized PIN2 to the actively forming cell plate during mitosis. Together, the data demonstrate that specific self-labeling of proteins can be used effectively in plants to study a wide variety of cellular and biological processes.

A thorough investigation has enabled the optimization of the synthesis of 1,4-dihydro-pyrrolo[3,2-b]pyrroles. Although salts of such metals as vanadium, niobium, cerium, and manganese were found to facilitate the formation of 1,4-dihydro-pyrrolo[3,2-b]pyrroles from amines, aldehydes, and diacetyl, we confirmed that iron salts are the most efficient catalysts. The conditions identified (first step: toluene/AcOH = 1:1, 1 h, 50 °C; second step: toluene/AcOH = 1:1, Fe(ClO4)3·H2O, 16 h, 50 °C) resulted in the formation of tetraarylpyrrolo[3,2-b]pyrroles in a 6-69% yield. For the first time, very electron-rich substituents (4-Me2NC6H4, 3-(OH)C6H4, pyrrol-2-yl) originating from aldehydes and sterically hindered substituents (2-ClC6H4, 2-BrC6H4, 2-CNC6H4, 2-(CO2Me)C6H4, 2-(TMS-C≡C)C6H4) present on anilines can be appended to the pyrrolo[3,2-b]pyrrole core. It is now also possible to prepare 1,4-dihydropyrrolo[3,2-b]pyrroles bearing an ordered arrangement of N-substituents and C-substituents ranging from coumarin, quinoline, phthalimide to truxene. These advances in scope enable independent regulations of many desired photophysical properties, including the Stokes shift value and emission color ranging from violet-blue through deep blue, green, yellow to red. Simultaneously, the optimized conditions have finally allowed the synthesis of these extremely promising heterocycles in amounts of more than 10 g per run without a concomitant decrease in yield or product contamination. Empowered with better functional group compatibility, novel derivatization strategies were developed.

A series of phosphine oxide-bridged rhodamines (P-rhodamines) bearing various acyclic and cyclic amine moieties, including dimethyl- and diethylamine, azetidine, pyrrolidine and 7-azabicyclo[2,2,1]heptane (7ABH), have been synthesized. The photophysical properties as well as chemical and photostability of these dyes have been studied in detail. Among these dyes, the 7ABH-substituted dye shows stronger fluorescence in the near-infrared (NIR) region, relative to the other P-rhodamines. This dye could be applied to live-cell imaging, wherein lysosomes were selectively stained in a pH-independent manner. It was also found that the ring fusion of the amine moieties gives rise to remarkably redshifted spectra, with absorption and emission maxima at 770 and 820 nm, respectively, spectrally close to that of indocyanine green (ICG). Importantly, the ring-fused P-rhodamines showed much higher photostability than ICG, indicative of their promising utility as the NIR-emissive dyes.

AbstractDie oxidative aromatische Kupplung nimmt einen grundlegenden Platz in der modernen Arenchemie ein. Sie ist das Mittel der Wahl für den Aufbau großer, komplizierter Molekülarchitekturen. Auch die Scholl‐Reaktion und ihre Anwendungen in der Synthese chiraler Biphenole und Naturstoffe sind stark beforscht. Die Möglichkeit, Biarylverknüpfungen ohne Vorfunktionalisierung herzustellen, bietet einen effizienten Weg zu vielen komplexen Strukturen. Obwohl die Chemie hinter diesem Prozess erst jetzt nach und nach voll verstanden wird, ist er weiterhin eine Quelle der Inspiration. Dies trifft besonders auf Heterokupplungen zu, d. h. oxidative, aromatische Kupplungen unter chemoselektiver C‐C‐Bindungsbildung zwischen zwei verschiedenen Arenen. Eine Analyse der Fortschritte in diesem Feld seit 2013 zeigt, dass zahlreiche Gruppen hierzu beigetragen haben – durch die Entdeckung neuer struktureller Möglichkeiten, die Erweiterung zu oberflächengestützten (Cyclo)dehydrierungen und die Entwicklung neuer Reagenzien.

The far-red emissive fluorescent probe CaPF-1 based on a phospha-fluorescein scaffold enables the detection of cytosolic calcium ions in living cells. The probe can be excited in the red region (λabs = 636 nm) and exhibits a sufficiently high fluorescence turn-on response in the far-red region (λem = 663 nm) upon complexation with calcium ions. The hydrophilic and anionic characteristics of this phospha-fluorescein fluorophore allowed the cytosolic localization of CaPF-1. Moreover, it was possible to visualize histamine-induced calcium oscillation in HeLa cells using CaPF-1.

Various fluorescence microscopy techniques require bright NIR-emitting fluorophores with high chemical and photostability. Now, the significant performance improvement of phosphorus-substituted rhodamine dyes (PORs) upon substitution at the 9-position with a 2,6-dimethoxyphenyl group is reported. The thus obtained dye PREX 710 was used to stain mitochondria in living cells, which allowed long-term and three-color imaging in the vis-NIR range. Moreover, the high fluorescence longevity of PREX 710 allows tracking a dye-labeled biomolecule by single-molecule microscopy under physiological conditions. Deep imaging of blood vessels in mice brain has also been achieved using the bright NIR-emitting PREX 710-dextran conjugate.

Two diketopyrrolopyrroles containing electron-rich 3,4-dimethoxyphenyl and 2-furyl aromatic groups were decorated with N -alkyl substituents containing quaternary ammonium moieties. The obtained dyes were readily soluble in water, showed an intense visible absorption with relatively high two-photon absorption cross-sections and some of them could stain eukaryotic cells. A dye containing two tetraalkylammonium moieties in its side chains showed high fluorescence quantum yield (>50%) both in water and in acetonitrile, whereas the fluorescence of pyridinium salt was significantly quenched. The two-photon absorption peaks were located at ~720 nm.