Chiral Triptycenes in Supramolecular and Materials Chemistry

Reactivity and Steric Parameters from 2D to 3D Bulky Pyridines: Increasing Steric Demand at Nitrogen with Chiral Azatriptycenes

Sterically hindered pyridines embedded in a three-dimensional triptycene framework have been synthesized, and their resolution by chiral HPLC enabled access to unprecedented enantiopure pyridines exceeding the known steric limits. The design principles for new axially chiral pyridine derivatives are then described. To rationalize their associations with Lewis acids and transition metals, a comprehensive determination of the steric and electronic parameters for this new class of pyridines was performed. This led to the general parameterization of the steric parameters (percent buried volume %VBur, Tolman cone angle θ, and He8_steric descriptor) for a large set of two- and three-dimensional pyridine derivatives. These parameters are shown to describe quantitatively their interactions with carbon- and boron-centered Lewis acids and were used to predict the ΔG° of association with the prototypical B(C6F5)3 Lewis acid widely used in frustrated Lewis pair catalysis. This first parameterization of pyridine sterics is a fundamental basis for the future development of predictive reactivity models and for guiding new applications of bulky and chiral pyridines in organocatalysis, frustrated Lewis pairs, and transition-metal catalysis.

A Geometrically Flexible Three-Dimensional Nanocarbon

The development of architecturally unique molecular nanocarbons by bottom-up organic synthesis is essential for accessing functional organic materials awaiting technological developments in fields such as energy, electronics, and biomedicine. Herein, we describe the design and synthesis of a triptycene-based three-dimensional (3D) nanocarbon, GFN-1, with geometrical flexibility on account of its three peripheral π-panels being capable of interconverting between two curved conformations. An effective through-space electronic communication among the three π-panels of GFN-1 has been observed in its monocationic radical form, which exhibits an extensively delocalized spin density over the entire 3D π-system as revealed by electron paramagnetic resonance and UV-vis-NIR spectroscopies. The flexible 3D molecular architecture of GFN-1, along with its densely packed superstructures in the presence of fullerenes, is revealed by microcrystal electron diffraction and single-crystal X-ray diffraction, which establish the coexistence of both propeller and tweezer conformations in the solid state. GFN-1 exhibits strong binding affinities for fullerenes, leading to host-guest complexes that display rapid photoinduced electron transfer within a picosecond. The outcomes of this research could pave the way for the utilization of shape and electronically complementary nanocarbons in the construction of functional coassemblies.

BINOL-Based Chiral Macrocycles and Cages

Chirality, a fundamental principle in chemistry, biology, and medicine, is prevalent in nature and in organisms. Chiral molecules, such as DNA, RNA, and proteins, are crucial in biomolecular synthesis, as well as in the development of functional materials. Among these, 1,1'-binaphthyl-2,2'-diol (BINOL) stands out for its stable chiral configuration, versatile functionality, and commercial availability. BINOL is widely employed in asymmetric catalysis and chiral materials. This review mainly focuses on recent research over the past five years concerning the use of BINOL derivatives for constructing chiral macrocycles and cages. Their contributions to chiral luminescence, enantiomeric separation, transmembrane transport, and asymmetric catalysis were examined.

Triptycene-based diiron(II) mesocates: spin-crossover in solution

Triptycene-based diiron(II) and dizinc(II) mesocates were obtained using a novel rigid ligand with two pyridylbenzimidazole chelating units fused into the triptycene scaffold. Studies on the diiron(II) assembly in solution showed that the complex undergoes thermal-induced one-step spin-crossover with T1/2 at 243 K (Evans method).

Homoconjugation and Tautomeric Isomerism in Triptycene-Fused Pyridylbenzimidazoles

The facile, metal-free synthesis and characterization of three new series of triptycene-fused pyridylbenzimidazoles are reported; such compounds possess an imidazole moiety fused within the benzene rings of the trypticene and a pyridine ring installed at position 2 of the imidazole rings. The position of the nitrogen atom of the pyridyl moiety linked to position 2 of the fused benzimidazole scaffold is systematically changed from the ortho to para position. The number of substituted blades bearing the pyridyl-substituted fused benzimidazole scaffolds has been increased from one to three. Such a library of compounds allowed us to evaluate the enhancement of two main effects: tautomeric isomerism and homoconjugation. The characteristic dynamic equilibrium between different isomers induced by prototropic tautomerization was examined by 1H nuclear magnetic resonance spectroscopy. By comparison of the photophysical properties of the new compounds with those of classical planar pyridylbenzimidazoles, the presence of the homoconjugation effect between the different triptycene blades was demonstrated. Fine details of the electronic structure of the new derivatives were unraveled by a computational analysis. The novel compounds can be employed for the construction of intriguing self-assembled supramolecular architectures.

Activation of Solid-State Emission and Photostability through Molecular Confinement: The Case of Triptycene-Fused Quinacridone Dyes

We report the facile, metal-free convergent synthesis and the characterization of novel quinacridone dyes in which two triptycene units end-cap and sterically confine the quinacridone chromophore. A precise comparison of the confined dyes with their known homologues reveals that the reduction of π-π interactions in triptycene-fused quinacridone dyes compared to classical quinacridone results not only in an increase of solubility and processability but also in an enhancement of fluorescence quantum yield and photostability in the solid state.

Enantiospecific Syntheses of Congested Atropisomers through Chiral Bis(aryne) Synthetic Equivalents

The synthetic equivalents of the enantiopure binaphthyl bis(aryne) atropisomers derived from BINOL (1,1'-bi-2,2'-naphtol) featuring a stereogenic axis vicinal to the two reactive triple bonds can be generated for the first time in solution in an enantiospecific manner. Using a two-step sequence based on the bidirectional [4+2] cycloaddition of furan derivatives followed by an aromatizative deoxygenation reaction, several 9,9'-bianthracenyl-based atropisomers could be prepared enantiospecifically in high enantiomeric purity. Alternatively, bidirectional reactions with anthracene, 2-bromostyrene, and perylene as the arynophiles afforded very congested bis(benzotriptycene), bis(tetraphene) and bis(anthra[1,2,3,4-ghi]perylene) nanocarbon atropisomers in equally high enantiomeric purity. In complement, cross reactions with two different arynophiles revealed possible. The unusual atropisomer prototypes described in this study open the way to enantiopure nanographene atropisomers designed for functions.

HPLC Enantioseparation of Rigid Chiral Probes with Central, Axial, Helical, and Planar Stereogenicity on an Amylose (3,5-Dimethylphenylcarbamate) Chiral Stationary Phase

The chiral resolving ability of the commercially available amylose (3,5-dimethylphenylcarbamate)-based chiral stationary phase (CSP) toward four chiral probes representative of four kinds of stereogenicity (central, axial, helical, and planar) was investigated. Besides chirality, the evident structural feature of selectands is an extremely limited conformational freedom. The chiral rigid analytes were analyzed by using pure short alcohols as mobile phases at different column temperatures. The enantioselectivity was found to be suitable for all compounds investigated. This evidence confirms that the use of the amylose-based CSP in HPLC is an effective strategy for obtaining the resolution of chiral compounds containing any kind of stereogenic element. In addition, the experimental retention and enantioselectivity behavior, as well as the established enantiomer elution order of the investigated chiral analytes, may be used as key information to track essential details on the enantiorecognition mechanism of the amylose-based chiral stationary phase.

Chiral Iodotriptycenes: Synthesis and Catalytic Applications

New iodotriptycenes, including some chiral derivatives, have been synthesised, and their catalytic potential towards oxidative transformations has been investigated. The enantioselectivities observed in the products using chiral iodotriptycene catalysts are low, probably owing to the large distances between the coordinating groups and the iodine moieties in these compounds.

Design, Synthesis, and Anticancer Activity of Triptycene-Peptide Hybrids that Induce Paraptotic Cell Death in Cancer Cells

We report on the design and synthesis of triptycene-peptide hybrids (TPHs), 5, syn-6, and anti-6, which are conjugates of a triptycene core unit with two or three cationic KKKGG peptides (K: lysine and G: glycine) through a C₈ alkyl chain. It was discovered that syn-6 and anti-6 induce paraptosis, a type of programmed cell death (PCD), in Jurkat cells (leukemia T-lymphocytes). Mechanistic studies indicate that these TPHs induce the transfer of Ca²⁺ from the endoplasmic reticulum (ER) to mitochondria, a loss of mitochondrial membrane potential (ΔΨ_m), tethering of the ER and mitochondria, and cytoplasmic vacuolization in the paraptosis processes.

Triptycene Derivatives: From Their Synthesis to Their Unique Properties

Since the first preparation of triptycene, great progress has been made with respect to its synthesis and the understanding of its properties. Interest in triptycene-based systems is intense; in recent years, advances in the synthetic methodology and properties of new triptycenes have been reported by researchers from various fields of science. Here, an account of these new developments is given and placed in reference to earlier pivotal works that underpin the field. First, we discuss new approaches to the synthesis of new triptycenes. Progress in the regioselective synthesis of sterically demanding systems is discussed. The application of triptycenes in catalysis is also presented. Next, progress in the understanding of the relations between triptycene structures and their properties is discussed. The unique properties of triptycenes in the liquid and solid states are elaborated. Unique interactions, which involve triptycene molecular scaffolds, are presented. Molecular interactions within a triptycene unit, as well as between triptycenes or triptycenes and other molecules, are also evaluated. In particular, the summary of the synthesis and useful features will be helpful to researchers who are using triptycenes as building blocks in the chemical and materials sciences.

Recent advances on triptycene derivatives in supramolecular and materials chemistry

Triptycene derivatives, a type of specific aromatic compound, have been attracting much attention in many research areas. Over the past several years, triptycene and its derivatives have been described to be useful and efficient building blocks for the design and synthesis of novel supramolecular acceptors, porous materials and luminescent materials with specific structures and properties. In this review, recent researches on triptycene derivatives in supramolecular and materials chemistry are summarized. Especially, the construction of a new type of macrocyclic arenes and organic cages with triptycene and its derivatives as building blocks are focused on, and their applications in molecular recognition, self-assembly and gas selective sorption are highlighted. Moreover, the applications of triptycene and its derivatives in porous organic materials and thermally activated delayed fluorescence (TADF) materials are also discussed.

Triptycene derivatives as chiral probes for studying the molecular enantiorecognition on sub-2-μm particle cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase

Two chiral triptycene derivatives were analyzed on the Chiralpak IB-U column packed with cellulose tris(3,5-dimethylphenylcarbamate)-based sub-2-μm diameter particles. Under normal-phase conditions, sub-minute baseline enantioseparations were obtained. Differences in structural elements and chromatographic behavior of the investigated compounds were evaluated to identify the interactions that drive the chiral discrimination process. From the evaluation of the experimental chromatographic data, it was found that hydrogen bond formation is essential for the separation of enantiomers.

Chiral Triphenylacetic Acid Esters: Residual Stereoisomerism and Solid-State Variability of Molecular Architectures

We have proven the usability and versatility of chiral triphenylacetic acid esters, compounds of high structural diversity, as chirality-sensing stereodynamic probes and as molecular tectons in crystal engineering. The low energy barrier to stereoisomer interconversion has been exploited to sense the chirality of an alkyl substituent in the esters. The structural information are cascaded from the permanently chiral alcohol (inducer) to the stereodynamic chromophoric probe through cooperative interactions. The ECD spectra of triphenylacetic acid esters are highly sensitive to very small structural differences in the inducer core. The tendencies to maximize the C-H···O hydrogen bonds, van der Waals interactions, and London dispersion forces determine the way of packing molecules in the crystal lattice. The phenyl embraces of trityl groups allowed, to some extent, the control of molecular organization in the crystal. However, the spectrum of possible molecular arrangements is very broad and depends on the type of substituent, the optical purity of the sample, and the presence of a second trityl group in the proximity. Racemates crystallize as the solid solution of enantiomers, where the trityl group acts as a protecting group for the stereogenic center. Therefore, the absolute configuration of the inducer is irrelevant to the packing mode of molecules in the crystal.

Chiral Triptycenes: Concepts, Progress and Prospects

Triptycenes have been established as unique scaffolds because of their backbone π-structure with a propeller-like shape and saddle-like cavities. They are some of the key organic molecules that have been extensively studied in polymer chemistry, in supramolecular chemistry and in material science. Triptycenes become chiral molecules when substituents are unsymmetrically attached in at least two of their different aromatic rings. This Minireview highlights the chirality of triptycenes from basics to an advanced stage for the development of functional molecules.

Enantiospecific Generation and Trapping Reactions of Aryne Atropisomers

Enantioenriched aryne atropisomers having a biaryl stereogenic axis vicinal to the reactive triple bond are demonstrated to exist. These reaction intermediates are easily produced in situ and can undergo the standard aryne cycloaddition chemistry in an enantiospecific manner. Notably, the aryne atropisomers herein have allowed the practical syntheses of a small nanographene as well as some triptycene and anthracene derivatives that embed stereogenic axes of controlled absolute configurations.