Porous shape-persistent rylene imine cages with tunable optoelectronic properties and delayed fluorescence.

A simultaneous combination of porosity and tunable optoelectronic properties, common in covalent organic frameworks, is rare in shape-persistent organic cages. Yet, organic cages offer important molecular advantages such as solubility and modularity. Herein, we report the synthesis of a series of chiral imine organic cages with three built-in rylene units by means of dynamic imine chemistry and we investigate their textural and optoelectronic properties. Thereby we demonstrate that the synthesized rylene cages can be reversibly reduced at accessible potentials, absorb from UV up to green light, are porous, and preferentially adsorb CO2 over N2 and CH4 with a good selectivity. In addition, we discovered that the cage incorporating three perylene-3,4:9,10-bis(dicarboximide) units displays an efficient delayed fluorescence. Time-correlated single photon counting and transient absorption spectroscopy measurements suggest that the delayed fluorescence is likely a consequence of a reversible intracage charge-separation event. Rylene cages thus offer a promising platform that allows combining the porosity of processable materials and photochemical phenomena useful in diverse applications such as photocatalysis or energy storage.

Sulfone "Geländer" Helices: Revealing Unexpected Parameters Controlling the Enantiomerization Process.

The two sulfonyl-bridged Geländer helices 1a and 2a are obtained by oxidation of the corresponding sulfide bridged precursors 1b and 2b. Both Geländer structures are fully characterized by NMR, high-resolution mass spectrometry, and optical spectroscopies. X-ray diffraction with a single crystal of 2a provides its solid-state structure. Both Geländer helices 1a and 2a are separated into enantiomers, and their racemizations are monitored by circular dichroism. For 1a, consisting of two equally sized macrocycles, a substantial increase in the enantiomerization barrier is observed upon going from the sulfide to the sulfone, and only a subtle rise is detected for the constitutional isomer 2a with two macrocycles of different size during the same transformation. This results not only in 1a with the highest configurational stability in the series of hitherto investigated Geländer structures but also challenges the so far hypothesized correlations between bridging structures and the Gibbs free energy of enantiomerization. The simulation of the enantiomerization process in the macrocyclic subunits suggests the proximity of the endotopic hydrogens as parameter responsible for the heights of the enantiomerization barrier.

A New Class of Rigid Multi(azobenzene) Switches Featuring Electronic Decoupling: Unravelling the Isomerization in Individual Photochromes.

We report a novel class of star-shaped multiazobenzene photoswitches comprising individual photochromes connected to a central trisubstituted 1,3,5-benzene core. The unique design of such C3-symmetric molecules, consisting of conformationally rigid and pseudoplanar scaffolds, made it possible to explore the role of electronic decoupling in the isomerization of the individual azobenzene units. The design of our tris-, bis-, and mono(azobenzene) compounds limits the π-conjugation between the switches belonging to the same molecule, thus enabling the efficient and independent isomerization of each photochrome. An in-depth experimental insight by making use of different complementary techniques such as UV-vis absorption spectroscopy, high performance liquid chromatography, and advanced mass spectrometry methods as ion mobility revealed an almost complete absence of electronic delocalization. Such evidence was further supported by both experimental (electrochemistry, kinetical analysis) and theoretical (DFT calculations) analyses. The electronic decoupling provided by this molecular design guarantees a remarkably efficient photoswitching of all azobenzenes, as evidenced by their photoisomerization quantum yields, as well as by the Z-rich UV photostationary states. Ion mobility mass spectrometry was exploited for the first time to study multiphotochromic compounds revealing the occurrence of a large molecular shape change in such rigid star-shaped azobenzene derivatives. In view of their high structural rigidity and efficient isomerization, our multiazobenzene photoswitches can be used as key components for the fabrication of complex stimuli-responsive porous materials.

Molecular Ansa-Basket: Synthesis of Inherently Chiral All-Carbon [12](1,6)Pyrenophane.

The synthesis of inherently chiral all-carbon C2-symmetric [12](1,6)pyrenophane 1 is reported. The cyclophane 1 was obtained via a ring-closing alkyne metathesis reaction using Mortreux's catalyst molybdenum hexacarbonyl and 2-fluorophenol as a phenol additive. The M and P enantiomers of the all-carbon pyrenophane 1 were demonstrated to be very stable in their enantiopure form even upon prolonged heating at 200 °C. [12](1,6)Pyrenophane-6-yne 1 was fully characterized by high-resolution mass spectrometry, nuclear magnetic resonance, UV-vis, and measured and calculated electronic circular dichroism spectroscopy.

Molecular dynamic staircases: all-carbon axial chiral "Geländer" structures.

Herein, the syntheses of two tightly packed all-carbon "Geländer" molecules with axial chirality are described. Motivated by our previous results, we further reduced the bridge length by excluding the heteroatoms. The absolute configuration was determined by comparison of the measured and calculated circular dichroism (CD) spectra and the thermodynamic stability was determined by dynamic high-performance liquid chromatography (HPLC) and CD analysis. The cyclophanes were fully characterized by CD measurements, X-ray diffraction (XRD) analysis, NMR, UV-Vis and high resolution mass spectrometry (HRMS). Our novel all-carbon macrocycle is the most stable Geländer system reported so far.

Tuning Helical Chirality in Polycyclic Ladder Systems.

Conceptually and experimentally, a new set of helical model compounds is presented herein that allow correlations between structural features and their expression in the secondary structure to be investigated. A cross-linked oligomer with two strands of mismatching lengths connected in a ladder-type fashion serves as a model system. Compensation for the dimensional mismatch leads to the adoption of a helical arrangement. A strategically placed relay ensures the continuity and uniformity of the helix. Upon exchanging the heteroatomic linkage, the helix responds by increasing or decreasing the torsion of the backbone. Inversion of the relay's substitution pattern causes a distortion of the structure, while maintaining the directionality of the helix. Based on a short synthetic protocol with a modular precursor, four closely related "Geländer" oligomers (Geländer is the German word for bannister) were accessed and fully characterized. XRD analysis for one representative of each helical arrangement and complementary computational studies for the remaining derivatives allowed the impact of the alterations on the secondary structures to be studied. Isolation of pure enantiomers of all new Geländer oligomers provided insight into the racemization kinetics and estimation of the racemization barrier. In silico simulation of the electronic circular dichroism spectra of the model compounds enabled the helicity of the isolated samples to be assigned.