Axially Chiral BODIPY DYEmers: An Apparent Exception to the Exciton Chirality Rule

Structural variety and pharmacological potential of naphthylisoquinoline alkaloids

Naphthylisoquinoline alkaloids are a fascinating class of natural biaryl compounds. They show characteristic mono- and dimeric scaffolds, with chiral axes and stereogenic centers. Since the appearance of the last comprehensive overview on these secondary plant metabolites in this series in 1995, the number of discovered representatives has tremendously increased to more than 280 examples known today. Many novel-type compounds have meanwhile been discovered, among them naphthylisoquinoline-related follow-up products like e.g., the first seco-type (i.e., ring-opened) and ring-contracted analogues. As highlighted in this review, the knowledge on the broad structural chemodiversity of naphthylisoquinoline alkaloids has been decisively driven forward by extensive phytochemical studies on the metabolite pattern of Ancistrocladus abbreviatus from Coastal West Africa, which is a particularly "creative" plant. These investigations furnished a considerable number of more than 80-mostly new-natural products from this single species, with promising antiplasmodial activities and with pronounced cytotoxic effects against human leukemia, pancreatic, cervical, and breast cancer cells. Another unique feature of naphthylisoquinoline alkaloids is their unprecedented biosynthetic origin from polyketidic precursors and not, as usual for isoquinoline alkaloids, from aromatic amino acids-a striking example of biosynthetic convergence in nature. Furthermore, remarkable botanical results are presented on the natural producers of naphthylisoquinoline alkaloids, the paleotropical Dioncophyllaceae and Ancistrocladaceae lianas, including first investigations on the chemoecological role of these plant metabolites and their storage and accumulation in particular plant organs.

Axially-chiral boramidine for detailed (chir)optical studies

The inclusion of boron atoms into chiral π-conjugated systems is an effective strategy to unlock unique chiroptical properties. Herein, the preparation and characterization of a configurationally stable axially-chiral boramidine are reported, showcasing absorption in the UV domain, deep-blue fluorescence (Φ up to 94%), and ca. |10-3| gabs and glum values. Detailed photophysical studies and quantum-chemical calculations clearly elucidate the deactivation pathways of the emissive state to triplet excited states, involving increased spin-orbit coupling between the lowest singlet excited state and an upper triplet state.

BODIPY Dimers with a Fused and Coplanar Structure: Photophysical Comparison, Low Threshold for Amplified Spontaneous Emission, and Deep-Red Bio-Imaging/Photodynamic Therapy Application

Boron dipyrromethene (BODIPY)-derived dyes are generally superior emitters, but their absorption and emission fail to match the bio-active optical window (650-900 nm). In this work, we explored four bisBODIPY dyes (PB1-PB4) with easy-to-go synthesis, good solubility, high photostability, and high emission quantum yield in the deep-red region. Methyl and ethyl groups were introduced in these BODIPY dyes to improve their solubility. PB4 having a fused coplanar plane was synthesized and compared to PB1-PB3 having a non-fused structure. Their geometric structure was confirmed by single-crystal analysis, and their electronic structure, along with one-photon and two-photon absorptions, was analyzed by time-dependent functional theory calculation. Their absorption/emission spectra, emission quantum yields, and lifetimes were compared. It was found that the fused coplanar structure successfully red shifted PB4 absorption/emission to the deep-red region (698/720 nm), with a quantum yield of 0.58. PB4 showed an amplified spontaneous emission effect with an output efficiency of 6.0% at a pumping power of 3000 μJ. An improved photodynamic therapy (PDT) performance was observed from PB4 via in vitro and in vivo experiments. The practical PDT performance was evaluated by cell availability. Upon a 980 nm laser radiation of 5 min, the cell viability was decreased to ∼15%.

Enantiopure J-Aggregate of Quaterrylene Bisimides for Strong Chiroptical NIR-Response

Chiral polycyclic aromatic hydrocarbons can be tailored for next-generation photonic materials by carefully designing their molecular as well as supramolecular architectures. Hence, excitonic coupling can boost the chiroptical response in extended aggregates but is still challenging to achieve by pure self-assembly. Whereas most reports on these potential materials cover the UV and visible spectral range, systems in the near infrared (NIR) are underdeveloped. We report a new quaterrylene bisimide derivative with a conformationally stable twisted π-backbone enabled by the sterical congestion of a fourfold bay-arylation. Rendering the π-subplanes accessible by small imide substituents allows for a slip-stacked chiral arrangement by kinetic self-assembly in low polarity solvents. The well dispersed solid-state aggregate reveals a sharp optical signature of strong J-type excitonic coupling in both absorption (897 nm) and emission (912 nm) far in the NIR region and reaches absorption dissymmetry factors up to 1.1 × 10^-2. The structural elucidation was achieved by atomic force microscopy and single-crystal X-ray analysis which we combined to derive a structural model of a fourfold stranded enantiopure superhelix. We could deduce that the role of phenyl substituents is not only granting stable axial chirality but also guiding the chromophore into a chiral supramolecular arrangement needed for strong excitonic chirality.

Asian Ancistrocladus Lianas as Creative Producers of Naphthylisoquinoline Alkaloids

This book describes a unique class of secondary metabolites, the mono- and dimeric naphthylisoquinoline alkaloids. They occur in lianas of the paleotropical Ancistrocladaceae and Dioncophyllaceae families, exclusively. Their unprecedented structures include stereogenic centers and rotationally hindered, and thus likewise stereogenic, axes. Extended recent investigations on six Ancistrocladus species from Asia, as reported in this review, shed light on their fascinating phytochemical productivity, with over 100 such intriguing natural products. This high chemodiversity arises from a likewise unique biosynthesis from acetate-malonate units, following a novel polyketidic pathway to plant-derived isoquinoline alkaloids. Some of the compounds show most promising antiparasitic activities. Likewise presented are strategies for the regio- and stereoselective total synthesis of the alkaloids, including the directed construction of the chiral axis.

Photophysical properties of furan-bridged dimeric boron-dipyrromethene derivatives (BODIPYs)

In order to investigate the changes in the spectroscopic properties of dimeric boron-dipyrromethenes (BODIPYs), four BODIPY derivatives are synthesized, including a monomer BODIPY in which a furyl group is substituted at the meso position and a dimer BODIPY with a furan group as a bridge. The four synthesized BODIPY derivatives are characterized through nuclear magnetic resonance and mass spectrometry. Photophysical properties such as ultraviolet–visible absorbance and the fluorescence emission of monomers (mT1 and mT2) and dimers (biT1 and biT2) are studied in eight different solvents. In addition, the relationship of their structural properties and optical properties are also considered through density functional theory calculations. The covalent link between the two BODIPY units using a furan group has a profound effect on the optical properties of the dimeric BODIPYs. We believe that an understanding of the synthesis and physical properties of dimeric BODIPYs will have a promising perspective in designing new BODIPY derivatives and predicting their spectroscopic characteristics in the future.

Elucidating the origin of chiroptical activity in chiral 2D perovskites through nano-confined growth

Chiral perovskites are being extensively studied as a promising candidate for spintronic- and polarization-based optoelectronic devices due to their interesting spin-polarization properties. However, the origin of chiroptical activity in chiral perovskites is still unknown, as the chirality transfer mechanism has been rarely explored. Here, through the nano-confined growth of chiral perovskites (MBA₂PbI_4(1-x)Br_4x), we verified that the asymmetric hydrogen-bonding interaction between chiral molecular spacers and the inorganic framework plays a key role in promoting the chiroptical activity of chiral perovskites. Based on this understanding, we observed remarkable asymmetry behavior (absorption dissymmetry of 2.0 × 10⁻³ and anisotropy factor of photoluminescence of 6.4 × 10⁻² for left- and right-handed circularly polarized light) in nanoconfined chiral perovskites even at room temperature. Our findings suggest that electronic interactions between building blocks should be considered when interpreting the chirality transfer phenomena and designing hybrid materials for future spintronic and polarization-based devices.

In this study, Ma et al. demonstrated that asymmetric hydrogen-bonding interaction between chiral organic spacer and inorganic frameworks plays a key role in promoting the chiroptical activity of chiral perovskites.

A Boron Dipyrromethene Chiral-at-Boron and Carbon with a Bent Geometry: Synthesis, Resolution and Chiroptical Properties

We report a boron dipyrromethene chiral-at-boron and carbon (B*C*-BODIPY) accessible through a two-pot, one-step synthesis—an interrupted Knoevenagel condensation. The ECD spectra of chiral HPLC resolved enantiomers show clear Cotton effects...

Axially chiral indolenine derived chromophore dimers and their chiroptical absorption and emission properties

Yamamoto homocoupling of two chiral oxindoles led to the atropo-diastereoselective formation of an axially chiral oxindole dimer. This building block served as the starting material for the syntheses of axially chiral squaraine and merocyanine chromophore dimers. These dimers show pronounced chiroptical properties, this is, outstandingly high ECD signals (Δε up to ca. 1500 M⁻¹ cm⁻¹) as a couplet with positive Cotton effect for the P-configuration around the biaryl axis and a negative Cotton effect for the M-configuration. All investigated dimers also exhibit pronounced circularly polarised emission with anisotropy values of ca. 10⁻³ cgs. Time-dependent density functional calculations were used to analyse the three contributions (local one electron, electric–magnetic coupling, and exciton coupling) to the rotational strength applying the Rosenfeld equation to excitonically coupled chromophores. While the exciton coupling term proves to be the dominant one, the electric–magnetic coupling possesses the same sign and adds significantly to the total rotational strength owing to a favourable geometric arrangement of the two chromophores within the dimer.

From an axially chiral oxindole, squaraine and merocyanine chromophore dimers with pronounced chiroptical properties were prepared.

Induced axial chirality by a tight belt: naphthalene chromophores fixed in a 2,5-substituted cofacial para-phenylene-ethynylene framework

We report the design of a synthetically easy accessible axial chirality-inducing framework for a chromophore of choice. The scaffold consists of two basic para-phenylene-ethynylene backbones separated by laterally placed corner units. Substitution with an inherently achiral chromophore at the 2 and 5 positions of the central phenylene excitonically couples the chromophore associated transition and thereby results in chiroptical properties. Using 6-methoxynaphthalene as a model chromophore, we present the synthesis, structural analysis and spectroscopic investigation of the framework. The chiral framework was synthesized in three straightforward synthetic steps and fully characterized. The obtained racemic compounds were resolved using HPLC and assignment of the absolute configuration was performed using the exciton chirality method, crystallography and DFT calculations. This simple yet potent framework might prove useful to enrich the structural diversity of chiral materials.

ECD exciton chirality method today: a modern tool for determining absolute configurations

The application of the exciton chirality method (ECM) to interpret electronic circular dichroism (ECD) spectra is a well‐established and still popular approach to assign the absolute configuration (AC) of natural products, chiral organic compounds, and organometallic species. The method applies to compounds containing at least two chromophores with electric dipole allowed transitions (e.g., π–π* transitions). The exciton chirality rule correlates the sign of an exciton couplet (two ECD bands with opposite sign and similar intensity) with the overall molecular stereochemistry, including the AC. A correct application of the ECM requires three main prerequisites: (a) the knowledge of the molecular conformation, (b) the knowledge of the directions of the electric transition moments (TDMs), and (c) the assumption that the exciton coupling mechanism must be the major source of the observed ECD signals. All these prerequisites can be easily verified by means of quantum‐mechanical (QM) calculations. In the present review, we shortly introduce the general principles that underpin the use of the ECM for configurational assignments and survey its applications, both classic ones and some reported in the recent literature. Based on these examples, we will stress the advantages of the ECM but also the key requisites for its correct application. Additionally, we will discuss the dependence of the couplet sign on geometrical parameters (angles α,β,γ between TDMs), which can be helpful for discerning the sign of exciton chirality in ambiguous situations. Finally, we will present a molecular orbital (MO) description of the exciton coupling phenomenon.

Bis-Palladium Complex of α-Benzimidazole 9-Pyrrolyl Dipyrromethene: Synthesis, Structure, and Spectral and Catalytic Properties

A new ligand is designed and synthesized in two steps starting from α-formyl 3-pyrrolyl BODIPY. In the first step, the α-formyl 3-pyrrolyl BODIPY was condensed with 1,2-diaminobenzene in toluene at reflux and afforded α-benzimidazole 3-pyrrolyl BODIPY in 16% yield. In the second step, α-benzimidazole 3-pyrrolyl BODIPY was decomplexed upon being treated with Lewis acid AlCl₃ and afforded the desired ligand α-benzimidazole 9-pyrrolyl dipyrromethene. However, the ligand was not very stable and reacted further with PdCl₂ in CH₃CN for 1 h at reflux followed by recrystallization and afforded a novel bis-palladium complex of α-benzimidazole 9-pyrrolyl dipyrromethene in 36% yield. The bis-palladium complex was characterized and studied by high-resolution mass spectrometry, one- and two-dimensional nuclear magnetic resonance, X-ray crystallography, absorption, and density functional theory/time-dependent DFT (DFT/TD-DFT) studies. The X-ray structure revealed that two ligands and two Pd(II) ions were involved in forming a unique complex in which each Pd(II) ion was coordinated to three pyrrole N atoms of the first ligand and the benzimidazole N atom of the second ligand in a distorted square planar geometry. The absorption spectrum of the bis-palladium complex shows ill-defined, broad, and less intense bands in the region of 345-425 nm along with split bands in the higher-wavelength region of 600-630 nm. The bis-palladium complex was nonfluorescent, and the results of DFT/TD-DFT studies were in agreement with the experimental observations. The preliminary studies indicated that the bis-palladium complex can act as an efficient catalyst for coupling different aryl bromides with phenylboronic acid.

Palladium(II)-Catalyzed Dehydrogenative Strategy for Direct and Regioselective Oligomerization of BODIPY Dyes

A family of directly β,γ-linked BODIPY oligomers up to pentamers were regioselectively prepared via Pd(II)-catalyzed oxidative C-H cross-coupling. The structural integrity of β,γ-linked dimers was unambiguously confirmed by X-ray crystallography. These structurally unprecedented oligomers showed red-shifted absorptions and near-infrared emissions along with efficient intersystem crossing, giving Φ_Δ in the range of 12-43%, for potential use as heavy-atom-free photosensitizers.

Stereochemistry and chiroptical properties of bimetallic single helicates of hexapyrrole-α, ω-dicarbaldimines with high diastereoselectivity

Bimetallic complexes of hexapyrrole-[Formula: see text],[Formula: see text]-dicarbaldimines consisting of a pair of four-coordinate metal sites adopt a helical closed [Formula: see text]-symmetric form or sigmoidal open forms depending on whether the 2,2[Formula: see text]-bipyrrole subunit at the center of the hexapyrrole chain takes cis- or trans-conformation. X-ray crystallography of a bisNi complex having N-[([Formula: see text]-1-cyclohexylethyl]carbaldimine units at both ends of the hexapyrrole chain revealed a non-symmetric heterohelical open form where the metal coordination sites of opposite helical sense sit on opposite sides of the central 2,2[Formula: see text]-bipyrrole subunit. BisPd complexes preferred a closed [Formula: see text] form and a steric bulk at the 3,3[Formula: see text]-position of the 2,2[Formula: see text]-bipyrrole subunit improved the helical sense bias. A bisPd complex with N-[([Formula: see text]-1-cyclohexylethyl]carbaldimine units adopts a helical closed [Formula: see text] form exclusively with full bias for a [Formula: see text]-helical sense. These bimetallic single stranded helicates were reversibly oxidized to [Formula: see text]-cation radicals at 0.1[Formula: see text]0.3 V vs. a ferrocene/ferrocenium couple and spectroelectrochemistry revealed remarkable absorption and CD spectral changes in the Vis-NIR region.

FeCl3-promoted regioselective synthesis of BODIPY dimers through oxidative aromatic homocoupling reactions

The direct 3,3'-dimerization of BODIPYs lacking substituent groups in the 1,2,6, and 7 positions was developed by oxidative coupling with FeCl₃. This regioselective dimerization was achieved for BODIPYs substituted only in the 5-position with Cl or aryl groups. Further functionalization of the 5,5'-dichloride dimer gave the corresponding pyrrole or 4-(2-aminoethyl)morpholine disubstituted dimers 2f and 2g, respectively. While dimer 2f exhibited intense NIR absorption/emission maxima at 773/827 nm in toluene, dimer 2g showed favorable lysosome-targeting NIR fluorescence in living cells.

On the factors influencing the chiroptical response of conjugated polymer thin films

We study the influence of the physical and chemical structure on the chiroptical response of fluorene-based polymeric systems, namely poly(9,9-dioctylfluorene) (PFO) and the donor-acceptor type copolymer poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). We reveal the significance of electric-magnetic coupling, at both short (molecular-level) and intermediate (delocalised over multiple polymer chains) length scales, on the magnitude of the dissymmetry. These findings provide a framework for the design of new materials with an enhanced chiroptical response.

Pentacene-Bridge Interactions in an Axially Chiral Binaphthyl Pentacene Dimer

Molecular chirality can be exploited as a sensitive reporter of the nature of intra- and interchromophore interactions in π-conjugated systems. In this report, we designed an intramolecular singlet fission (iSF)-based pentacene dimer with an axially chiral binaphthyl bridge (2,2'-(2,2'-dimethoxy-[1,1'-binaphthalene]-3,3'-diyl) n-octyl-di-isopropyl silylethynyl dipentacene, BNBP) to utilize its chiroptical response as a marker of iSF chromophore-bridge-chromophore (SFC-β-SFC) interactions. The axial chirality of the bridge enforces significant one-handed excitonic coupling of the pentacene monomer units; as such, BNBP exhibits significant chiroptical response in the ground and excited states. We analyzed the chiroptical response of BNBP using the exciton coupling method and quadratic response density functional theory calculations to reveal that higher energy singlet transitions in BNBP involve significant delocalization of the electronic density on the bridging binaphthyl group. Our results highlight the promising application of chiroptical techniques to investigate the nature of SFC-β-SFC interactions that impact singlet fission dynamics.

Base-Catalyzed, Solvent-Free Synthesis of Rigid V-Shaped Epoxydibenzo[b,f][1,5]diazocines

A novel method for the synthesis of epoxydibenzo[b,f][1,5]diazocines exhibiting a V-shaped molecular architecture is reported. The unique approach is based on unprecedented base-catalyzed, solvent-free autocondensation and cross-condensation of fluorinated o-aminophenones. The structure of the newly synthesized diazocines was confirmed independently by X-ray analysis and chiroptical methods. The rigidity of the diazocine scaffold allowed for the separation of the racemate into single enantiomers that proved to be thermally stable up to 140 °C. Furthermore, the inertness of the diazocine scaffold was demonstrated by performing a series of typical transformations, including transition metal-catalyzed reactions, proceeding without affecting the bis-hemiaminal subunit.

Pathways to increase the dissymmetry in the interaction of chiral light and chiral molecules

The dissymmetric interaction between circularly polarised (CP) light and chiral molecules is central to a range of areas, from spectroscopy and imaging to next-generation photonic devices. However, the selectivity in absorption or emission of left-handed versus right-handed CP light is low for many molecular systems. In this perspective, we assess the magnitude of the measured chiroptical response for a variety of chiral systems, ranging from small molecules to large supramolecular assemblies, and highlight the challenges towards enhancing chiroptical activity. We explain the origins of low CP dissymmetry and showcase recent examples in which molecular design, and the modification of light itself, enable larger responses. Our discussion spans spatial extension of the chiral chromophore, manipulation of transition dipole moments, exploitation of forbidden transitions and creation of macroscopic chiral structures; all of which can increase the dissymmetry. Whilst the specific strategy taken to enhance the dissymmetric interaction will depend on the application of interest, these approaches offer hope for the development and advancement of all research fields that involve interactions of chiral molecules and light.

Extended Benzene-Fused Oligo-BODIPYs: In Three Steps to a Series of Large, Arc-Shaped, Near-Infrared Dyes

We present a straightforward, three-step synthesis engaging an oligomerization and subsequent one-pot oxidation step to form fully conjugated, benzene-fused oligo-BODIPYs from simple BODIPY precursors. FeCl3 serves as an efficient, bifunctional oxidant for a (multiple) cyclization/desaturation process, applied to ethylene-bridged dimeric, trimeric and oligomeric species to transform linking ethano units into stiff benzene fusions between unsubstituted β-positions of each BODIPY unit. The structural integrity was verified by X-ray crystallography, and all target compounds were studied in detail by photophysical, electrochemical and computational means. The main S1 excited state gradually converges to a structure-specific excitation limit, displaying a strong shift of the absorption event from about 500 nm (BODIPY monomer) to 955 nm (octamer) with attenuation coefficients up to ca. 500 000 M-1  cm-1 .

Synthesis and Functions of Oligomeric and Multidentate Dipyrrin Derivatives and their Complexes

The dipyrrin–metal complexes and especially the boron complex 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) have recently attracted considerable attention because of their interesting properties and possible applications. We have developed two unique and useful ways to extend versatility and usefulness of the dipyrrin complexes. The first one is the linear and macrocyclic oligomerization of the BODIPY units. These arrangements of the B–F moieties of the oligomerized BODIPY units provide sophisticated functions, such as unique recognition ability toward cationic guest, associated with changes in the photophysical properties by utilizing unprecedented interactions between the B–F and a cationic species. The second one is introduction of additional ligating moieties into the dipyrrin skeleton. The multidentate N2Ox dipyrrin ligands thus obtained form a variety of complexes with 13 and 14 group elements, which are difficult to synthesize using the original N2 dipyrrin derivatives. Interestingly, these unique complexes exhibit novel structures, properties, and functions such as guest recognition, stimuli-responsive structural conversion, switching of the optical properties, excellent stability of the neutral radicals, etc. We believe that these multifunctional dipyrrin complexes will advance the basic chemistry of the dipyrrin complexes and develop their applications in the materials and medicinal chemistry fields.

1 Introduction

2 Linear Oligomers of Boron–Dipyrrin Complexes

3 Cyclic Oligomers of Boron–Dipyrrin Complexes

4 A Cyclic Oligomer of Zinc–Dipyrrin Complexes

5 Group 13 Element Complexes of N2Ox Dipyrrins

6 Chiral N2 and N2Ox Dipyrrin Complexes

7 Group 14 Element Complexes of N2O2 Dipyrrins

8 Other N2O2 Dipyrrin Complexes with Unique Properties and Functions

9 Conclusion

Strategic Construction of Ethene-Bridged BODIPY Arrays with Absorption Bands Reaching the Near-Infrared II Region

An efficient strategy for the controllable synthesis of BODIPY arrays based on the Stille cross-coupling reaction has been developed, from which a family of well-defined ethene-bridged BODIPY arrays from dimer to hexamer was synthesized. These arrays showed strong absorptions reaching the near-infrared II (NIR II, 1000-1700 nm) region with maxima tunable from 702 nm (dimer) to 1114 nm (hexamer) and possessed efficient light-harvesting capabilities, excellent photostability, and good photothermal conversion abilities under NIR light irradiation.

Supramolecular chirality: a caveat in assigning the handedness of chiral aggregates

The handedness of a supramolecular chiral aggregate is often assigned based on the sign of circular dichroism spectra, adopting the exciton chirality method. However, the method does not properly account for the nature of intermolecular interactions. We introduce a generalized picture on the use of the sign of chiral signals in determining the helicity of chiral aggregates, rooted in the exciton model, supported by TD-DFT results.

Optical Activity and Helicity Enhancement of Highly Sensitive Dinaphthylmethane-Based Stereodynamic Probes for Secondary Alcohols

Chirality transfer from circular dichroism (CD)-silent secondary alcohol (inductor) to the stereodynamic bichromophoric di(1-naphthyl)methane probe (reporter) led to the generation of intense, induced exciton-type Cotton effects (CEs) in the ultraviolet-visible absorption region. The di(1-naphthyl)methane probe exhibits extraordinarily high sensitivity to even small structural variations of the alcohol skeleton, that is, the probe is able to distinguish between an oxygen atom and a methylene group in a 3-hydroxytetrahydrofurane skeleton. Signs and amplitudes of the exciton couplets of 1Bb electronic transition might be correlated with the type of stereo-differentiating parts of the molecule flanking the stereogenic center, however, not with the absolute configuration. The origin of the induced CEs was established by means of experimental and theoretical methods. As a result, a mechanism of chirality transfer from the permanent stereogenic center to the bichromophore is proposed.

An axially chiral 1,1′-biazulene and its π-extended derivative: synthesis, structures and properties

Chiral organic π-conjugated molecules have been intensively investigated in the fields of chiral electronic materials and devices.

A single-stranded coordination copolymer affords heterostructure observation and photoluminescence intensification

Few artificial systems can be exfoliated into, and observed as, single wires with lengths of more than several micrometers, and no previous example features a copolymer structure; this is in contrast with biopolymers such as single-strand DNAs. Here, we create a set of one-dimensional coordination copolymers featuring bis(dipyrrinato)zinc complex motifs in the main chain. A series of random copolymers is synthesized from two types of bridging dipyrrin proligand and zinc acetate, with various molar ratios between the proligands. Sonication of the bulk solid copolymer in organic solvent exfoliates single strands with lengths of 1.4 to 3.0 μm. Atomic force microscopy at ambient conditions visualizes the copolymer structure as height distributions. The copolymer structure improves its photoluminescence (up to 32%) relative to that of the corresponding homopolymers (3 and 10%). Numerical simulation based on a restricted random walk model reproduces the photoluminescence intensification, suggesting at the same time the existence of fast intrawire exciton hopping.

Fully Functionalizable β,β'-BODIPY Dimer: Synthesis, Structure, and Photophysical Signatures

The versatility in the synthesis of BODIPY derivatives in terms of functionalization is further demonstrated. In particular, in this work β-β'-BODIPY dimers with varied functional groups in the meso positions were synthesized in very efficient yields and short reaction times from a single platform. A photophysical study was carried out in all of the compounds. The resultant dimers show absorption bands at around 600 nm as a consequence of electronically coupled monomers disposed with a dihedral angle of around 30°, which is supported by theoretical simulations. The emission properties of these molecules are distinguished by the appearance of an ICT state as the polarity of the solvent increases.

Diquats with Robust Chirality: Facile Resolution, Synthesis of Chiral Dyes, and Application as Selectors in Chiral Analysis

Diquats with extremely high racemization barriers with ΔG^≠_theor of 233 kJ mol^-1 at 180 °C are described. Reported configurational robustness is due to a combination of two structural features: the rigid o-xylylene tether connecting the nitrogen atoms and the presence of two substituents in the bay region of the bipyridinium scaffold. The straightforward synthesis of diquats, plus facile resolution and derivatization make them attractive for chiral application studies. This is demonstrated by: 1) synthesis of the first non-racemic diquat dyes with pronounced chiroptical properties, and 2) capability of diquats to interact stereospecifically with chiral molecules. This suggests potential for diquat derivatives to be used as chiral selectors in separation methods.

Chiromagnetic nanoparticles and gels

Chiral inorganic nanostructures have high circular dichroism, but real-time control of their optical activity has so far been achieved only by irreversible chemical changes. Field modulation is a far more desirable path to chiroptical devices. We hypothesized that magnetic field modulation can be attained for chiral nanostructures with large contributions of the magnetic transition dipole moments to polarization rotation. We found that dispersions and gels of paramagnetic Co₃O₄ nanoparticles with chiral distortions of the crystal lattices exhibited chiroptical activity in the visible range that was 10 times as strong as that of nonparamagnetic nanoparticles of comparable size. Transparency of the nanoparticle gels to circularly polarized light beams in the ultraviolet range was reversibly modulated by magnetic fields. These phenomena were also observed for other nanoscale metal oxides with lattice distortions from imprinted amino acids and other chiral ligands. The large family of chiral ceramic nanostructures and gels can be pivotal for new technologies and knowledge at the nexus of chirality and magnetism.

Switch-ON Near IR Fluorescent Dye Upon Protonation: Helically Twisted Bis(Boron Difluoride) Complex of π-Extended Corrorin

A novel helically twisted π-extended corrorin derivative having two boron dipyrrin (BODIPY) moieties at the periphery, a BODIPY DYEmer (6-BF₂ ) cross-bridged with π-conjugated dipyrrinylidene unit, was synthesized and characterized. The neutral 6-BF₂ is nonfluorescent due to the internal photoinduced charge transfer (CT) character in the excited state as inferred from the femtosecond transient absorption spectroscopy. However, upon protonation, the CT process is suppressed and the species H6-BF₂⁺ becomes near infrared (IR) emissive. With the aid of rigid helical conformations in 6-BF₂ , the helical isomers (P- and M-forms) were resolved and their chiroptical property was investigated. The distinct circular dichroism (CD) spectral changes of the enantiomers were observed in the presence of acids, which demonstrates that 6-BF₂ can be utilized for potential acid-responsive chiroptical materials.

Metallocorroles as inherently chiral chromophores: resolution and electronic circular dichroism spectroscopy of a tungsten biscorrole

An inherently chiral metallocorrole has been resolved for the first time by means of HPLC on a chiral stationary phase. For the compound in question, a homoleptic tungsten biscorrole, the absolute configurations of the enantiomers were assigned using online HPLC-ECD measurements in conjunction with time-dependent CAM-B3LYP calculations, which provided accurate simulations of the ECD spectra.

Ligand-to-Ligand Interactions That Direct Formation of D2-Symmetrical Alternating Circular Helicate

This work demonstrates that ligand-to-ligand interactions between achiral bis-β-diketonate (BTP) and chiral bis(4-phenyl-2-oxazolinyl)pyridine [( R)- or ( S)-Ph-Pybox] are successfully directed to the fabrication of a D₂-symmetrical alternating circular helicate with the general formula [( R)- or ( S)-Ph-Pybox]₄(Ln^III)₄(BTP)₆. The lanthanide(III) Ln^III assemblies (Ln^III₄- RRRR and Ln^III₄- SSSS) have a nanometer-size squarelike grid (interatomic distances > 10 Å). X-ray structure analysis revealed that the circular helicate contains two double helicate Ln^III₂L₂ units, where both show ( M)-helicity for Ln^III₄- RRRR and ( P)-helicity for Ln^III₄- SSSS, where π-π stacking interaction is present between the side arm of ( R)-Ph-Pybox (Ph₁) and the adjacent BTP ligand around the Eu^III metal center ( d_ππ = 3.636 Å: the diketonate plane···Ph₁ distance). The newly obtained circular lanthanide(III) helicate exists as single and homochiral diastereomers in solution (Ln^III₄- RRRR and Ln^III₄- SSSS), exhibiting circularly dichroism (CD) and circularly polarized luminescence (CPL). Conversely, the circular helicate favors the heterochiral arrangement (i.e., Ln^III₄- RRRR/Ln^III₄- SSSS).

Excitation energies, singlet–triplet energy gaps, spin–orbit matrix elements and heavy atom effects in BOIMPYs as possible photosensitizers for photodynamic therapy: a computational investigation

Introduction of halogen atoms in different amounts and positions into the BOIMPY skeleton significantly affects its photophysical properties.

Design and Evaluation of a Boron Dipyrrin Electrophore for Redox Flow Batteries

A boron dipyrrin (BODIPY) dye was designed as a molecular single-component electrophore for redox flow batteries. All positions of the BODIPY core were assessed on the basis of literature data, in particular cyclic voltammetry and density functional calculations, and a minimum required substitution pattern was designed to provide solubility, aggregation, radical cation and anion stabilities, a large potential window, and synthetic accessibility. In-depth electrochemical and physical studies of this electrophore revealed suitable cathodic behavior and stability of the radical anion but rapid anodic decomposition of the radical cation. The three products that formed under the conditions of controlled oxidative electrolysis were isolated, and their structures were determined by spectroscopy and comparison with a synthetic model compound. From these structures, a benzylic radical reactivity, initiated by one-electron oxidation, was concluded to play the major role in this unexpected decomposition.

Electronic and vibrational exciton coupling in oxidized trianglimines

Readily available chiral trianglimine and their (poly)oxygenated congeners represent a unique class of macrocyclic rigid compounds optimal for testing electronic and vibrational circular dichroism exciton chirality methods. Electronic and vibrational circular dichroism spectra of such trianglimines are strongly affected by polar substituents in macrocycle skeletons. Double substitution by OH groups in each aromatic fragment of the macrocycle causes sign reversal of the exciton couplet in the region of the strongest UV absorption. On the other hand, electronic circular dichroism spectrum of the macrocycle having 2 methoxy groups shows 2 exciton couplets-the long-wavelength positive and the second of the negative sign, observed at the shorter wavelengths. VCD spectra of macrocyclic imines show vibrational exciton couplets in the region of strong C=N stretches. The signs of these couplets are positive and the opposite of the diamine chirality. For trianglimine macrocycles the interpretation of VCD spectra in terms of excitons is much more convincing than for electronic circular dichroism spectra. By contrast, trans-1,2-diaminocyclohexane-based vicinal diimines, being a one-third of the respective macrocycle, do not exhibit any vibrational exciton effect. Experimental data were confronted with DFT calculations. We observed good-to-excellent agreement between experimental and computed data.

Ethylene-Bridged Oligo-BODIPYs: Access to Intramolecular J-Aggregates and Superfluorophores

A versatile and rapid access to various chain lengths of ethylene-bridged BODIPY motifs was discovered. Corresponding oligomers comprising up to eight monomeric units were studied with respect to their microstructures by photophysical, X-ray crystallographic, and computational means. The investigation of three different dipyrrin cores revealed a crucial dependence on the substitution pattern of the core, whereas the nature of the meso-periphery is less critical. The impact of substituent effects on the conformational space was investigated by Monte Carlo simulations and a set of DFT methods (B3LYP, PBEh-3c, TPSS/PWPB95), including dispersion effects. Cryptopyrrole-derived oligo-BODIPYs are characterized by a tight intramolecular arrangement triggering a dominant J-type excitonic coupling with red-shifts up to 45 nm, exceptionally small line widths of the absorption and emission event (up to 286 cm^-1), outstandingly high attenuation coefficients (up to 1 042 000 M^-1 cm^-1), and quantum yields of up to unity.

Solvent-Sensitive Emitting Urea-Bridged bis-BODIPYs: Ready Access by a One-Pot Tandem Staudinger/Aza-Wittig Ureation

Herein we describe the synthesis, and computationally aided photophysical characterization of a new set of urea-bridged bis-BODIPY derivatives. These new dyads are efficiently obtained by a one-pot tandem Staudinger/aza-Wittig ureation protocol, from easily accessible meso-phenyl ortho-azidomethyl BODIPYs. These symmetric bis-BODIPYs outstand by a high absorption probability and excellent fluorescence and laser emission in less polar media. Nevertheless, this emission ability decreases in more polar media, which is ascribed to a light-induced charge-transfer from the urea spacer to the dipyrrin core, a process that can be modulated by appropriate changes in the substitution pattern of the BODIPY core. Furthermore, this ureation protocol can also be employed for the direct conjugation of our BODIPY-azides to amine-containing compounds, thus providing access to fluorescent non-symmetric ureas.