Encapsulation with the Protrusion of Cruciform 9,10-Bis(arylethynyl)anthracene Derivatives in a Self-Assembled Boronic Ester Cavitand Capsule: Photochemical and Photophysical Properties

Doubly Bridged Anthracenes: Blue Emitters for OLEDs

The photooxidative stability of a series of doubly bridged anthracenes was evaluated after their preparation via twofold macrocyclization of a bis(resorcinyl)anthracene. Lightfastness correlates with the energy levels of the highest occupied molecular orbital (HOMO), resulting in superior stability of the tetraesters compared to the tetraethers. The lengths and steric demand of the linker only plays a minor role for the ester-based compounds, which can be prepared in reasonable yields and thus tested in proof-of-concept organic light-emitting diodes. Double ester-bridging allows deep blue electro-luminescence, highlighting the importance of the choice of the functional groups used for macrocyclization.

Kinetic Stabilization of Blue-Emissive Anthracenes: Phenylene Bridging Works Best

In attempts at kinetically stabilizing blue-emissive anthracenes, a series of 9,10-diaryl substituted derivatives were tested for their photochemical and photooxidative persistence. A major breakthrough in light fastness comes from a new bis-meta-terphenylyl substituted anthracene which is much superior to industrially relevant 9,10-biarylated anthracenes. The key issue is the steric shielding of the anthracene core. Further, intramolecular ring closure via Yamamoto coupling furnished a doubly bridged anthracene as a "self-encapsulated" sky-blue emitter which is most resistant to photodegradation. The improved stabilization was corroborated by time-resolved irradiation experiments and rationalized by X-ray crystallography.

Synthesis and Properties of a Cyclohexa-2,7-anthrylene Ethynylene Derivative

The synthesis of a cyclohexa-2,7-(4,5-diaryl)anthrylene ethynylene (1) was achieved for the first time by using 1,8-diaryl-3,6-diborylanthracene and 1,8-diaryl-3,6-diiodoanthracene as key synthetic intermediates. Macrocycle 1 possesses a planar conformation of approximately D_6h symmetry, because of the triple-bond linker between the anthracene units at the 2,7-positions. It was confirmed that macrocycle 1, bearing bulky substituents at the outer peripheral positions, behaves as a monomeric form in solution without π-stacking self-association. Macrocycle 1 has an inner-cavity size that allows specific inclusion of [9]cycloparaphenylene ([9]CPP), but not [8]CPP or [10]CPP, through an aromatic edge-to-face CH-π interaction.

Cavitand-Based Pd-Pyridyl Coordination Capsules: Guest-Induced Homo- or Heterocapsule Selection and Applications of Homocapsules to the Protection of a Photosensitive Guest and Chiral Capsule Formation

A 2 : 4 mixture of tetrakis[4-(4-pyridyl)phenyl]cavitand (1) or tetrakis[4-(4-pyridyl)phenylethynyl]cavitand (2) and Pd(dppp)(OTf)₂ self-assembles into a homocapsule {1₂  ⋅ [Pd(dppp)]₄ }⁸⁺  ⋅ (TfO^- )₈ (C1) or {2₂  ⋅ [Pd(dppp)]₄ }⁸⁺  ⋅ (TfO^- )₈ (C2), respectively, through Pd-Npy coordination bonds. A 1 : 1 : 4 mixture of 1, 2, and Pd(dppp)(OTf)₂ produced a mixture of homocapsules C1, C2, and a heterocapsule {1 ⋅ 2 ⋅ [Pd(dppp)]₄ }⁸⁺  ⋅ (TfO^- )₈ (C3) in a 1 : 1 : 0.98 mole ratio. Selective formation (self-sorting) of homocapsules C1 and C2 or heterocapsule C3 was controlled by guest-induced encapsulation under thermodynamic control. Applications of Pd-Npy coordination capsules with the use of 1 were demonstrated. Capsule C1 serves as a guard nanocontainer for trans-4,4'-diacetoxyazobenzene to protect against the trans-to-cis photoisomerization by encapsulation. A chiral capsule {1₂  ⋅ [Pd((R)-BINAP)]₄ }⁸⁺  ⋅ (TfO^- )₈ (C5) was also constructed. Capsule C5 induces supramolecular chirality with respect to prochiral 2,2'-bis(alkoxycarbonyl)-4,4'-bis(1-propynyl)biphenyls by diastereomeric encapsulation through the asymmetric suppression of rotation around the axis of the prochiral biphenyl moiety.

Perylenetetracarboxy-3,4:9,10-diimide derivatives with large two-photon absorption activity

Perylenetetracarboxy-3,4:9,10-diimides with large TPA cross-sections.

Hydrogen-bonded six-component assembly for capsule formation based on tetra(4-pyridyl)cavitand and isophthalic acid linker and its application to photoresponsive capsule

Two molecules of tetra(4-pyridyl)cavitand 1 and four molecules of isophthalic acid linker 2a with a triethylene glycol monomethyl ether (TEG) group self-assembled into a six-component capsule 1₂·2a₄ through eight pyNHO₂C hydrogen bonds, which encapsulates one molecule of guest G such as bis(4-acetoxyphenyl)acetylene and hexakis(4-iodophenyl)benzene to form G@(1₂·2a₄). Guest-encapsulation ability and selectivity of 1₂·2a₄ were revealed. trans-5-(p-Substituted-phenylazo)isophthalic acid with two dichotomous branching TEG groups trans-2b serves as a photoresponsive linker to form 1₂·(trans-2b)₄, which moderately reduced guest-encapsulation ability upon photoisomerization (at the photostationary state, 10% guest release upon subunit-trans-2b/subunit-cis-2b = 18 : 82).

Effects of Supramolecular Encapsulation on Photophysics and Photostability of a 9,10-Bis(arylethynyl)anthracene-Based Chromophore Revealed by Single-Molecule Fluorescence Spectroscopy

The effects of supramolecular encapsulation on the photophysics and photostability of a highly fluorescent dimeric derivative of 2,6-diacetoxy-9,10-bis(arylethynyl)anthracene (G2) were investigated by single-molecule fluorescence spectroscopy (SMFS). The fluorescence properties of free-G2 and its self-assembled boronic ester encapsulation complex, G2@(Cap)₂, were compared in solution and a glassy polymer film. The fluorescence spectral characteristics and theoretical calculations suggest that the environment affects the excited-state conformation and subsequent fluorescence emission of G2@(Cap)₂. In particular, in the liquid and polymer environments, G2@(Cap)₂ emits a fluorescence photon in the planar and twist conformation, respectively, whereas the fluorescence-emitting conformation of free-G2 is planar in both environments. The luminous conformation differences between free-G2 and G2@(Cap)₂ in polymer are reflected in the intersystem crossing (ISC) parameters (the ISC quantum yield and triplet lifetime), as determined by fluorescence autocorrelation analysis. The photobleaching yield revealed a 3-fold enhancement in the photostability of encapsulated G2 (relative to free-G2). Under the SMFS measurement conditions, the photostability of the encapsulation complex was independent of the guest's photostability and appeared to be dominated by the thermal stability of the Cap host molecule.

Enhanced photostability of an anthracene-based dye due to supramolecular encapsulation: a new type of photostable fluorophore for single-molecule study

For single-molecule fluorescence studies, highly photostable fluorophores are absolutely imperative, because photo-induced degradation (i.e., photobleaching) limits the observation time of individual molecules. Herein, the photophysics and photostability of a highly fluorescent 9,10-bis(phenylethynyl)anthracene derivative (G) and its self-assembled boronic ester encapsulation complex (G@Cap) embedded in a glassy polymer matrix are investigated by single-molecule fluorescence spectroscopy (SMFS). The heterogeneity of the fluorescence emission wavelength and triplet blinking kinetics of the guest G are significantly decreased by supramolecular encapsulation due to conformational restriction and reduced heterogeneity in the local environment. A nearly 10-fold increase in the photostability of G due to encapsulation is quantitatively confirmed by evaluating the photobleaching yields of G and G@Cap. In addition, it is found that the G@Cap is >30-fold more photostable than rhodamine 6G, a widely used fluorescent dye in single-molecule studies. These results demonstrate that the G@Cap can serve as a very bright, long-lasting fluorescent probe for single-molecule studies.

Self-assembled capsules based on tetrafunctionalized calix[4]resorcinarene cavitands

The hemispherical structures of calix[4]resorcinarene cavitands are suitable for forming capsular assemblies with guest encapsulations through various intermolecular interactions.