Synthesis and characterization of one-handed helical oligo(o-phenylene)s: control of axial chirality by planar chiral [2.2]paracyclophane.

Optically active oligo(o-phenylene)-layered molecules were synthesized from planar chiral enantiopure [2.2]paracyclophane. Their structures and optical properties were characterized by experimental and theoretical approaches. The axial chiralities between phenylene rings of the oligo(o-phenylene)s were controlled by the planar chirality to form one-handed helical structures. The o-quinquephenyl-layered molecule was emissive, and circularly polarized luminescence was observed with a high anisotropy factor (|glum| value) of 0.012.

Aggregation-induced emission from optically active X-shaped molecules based on planar chiral [2.2]paracyclophane.

An optically active π-stacked molecule was synthesized incorporating planar chiral [2.2]paracyclophane and o-carborane units to impart circularly polarized luminescence and aggregation-induced emission properties to the molecule. The molecule exhibited a strong emission from the aggregated state in a mixed solvent system (H2O/THF) and the solid state in the PMMA matrix. In the aggregated state, weak circularly polarized luminescence was observed owing to the random intermolecular orientation. On the other hand, the circularly polarized luminescence was clearly observed in the PMMA film containing 1 wt% molecule. Theoretical studies using time-dependent density functional theory reproduced the molecule's circular dichroism and circularly polarized luminescence properties.

Direct Synthesis of ABCD-Porphyrin Platinum(II) Complexes via Dehydrative Aromatization.

Since the development of the first method for porphyrin synthesis by Rothemund in 1935, porphyrin derivatives have been widely investigated and have played an essential role in chemical sciences. Most synthetic routes of porphyrins involve oxidative aromatization. Herein, we present a synthetic method to produce ABCD-porphyrins, including chiral ones, through a one-pot reaction involving "coordination, cyclization, and dehydrative aromatization" using a mono-dipyrrinatoPt(II)Cl(COE) (COE=cyclooctene) complex as a platinum template.

Syntheses of heterotriptycenes and their Pt complexes that emit circularly polarised fluorescence and phosphorescence.

Herein, we report the synthesis and chiroptical properties of 2-azatriptycenes and their platinum(II) complexes, which represent the first examples of heterotriptycenes and metallotriptycenes that exhibit circularly polarized fluorescence and phosphorescence (CPF and CPP). Theoretical studies for CPF and CPP strongly support the experimental findings.

Synthesis of Two Novel Optically Active #-Shaped Cyclic Tetramers Based on Planar Chiral [2.2]Paracyclophanes.

This study reports the synthesis of optically active cyclic tetramers comprising four stacked π-electron systems from two enantiomerically pure [2.2]paracyclophane compounds (bis-(para)-pseudo-ortho- and bis-(para)-pseudo-meta-tetrasubstituted [2.2]paracyclophane compounds). Depending on the combination of the absolute configurations of the planar chiral pseudo-ortho- and pseudo-meta-[2.2]paracyclophane units, the cyclic tetramers formed either parallel-#- or weave-#-structures. The optical and chiroptical properties of both structures were investigated experimentally and theoretically. In particular, the weave-#-shaped cyclic tetramer exhibited good chiroptical properties and emitted circularly polarized luminescence (CPL) with a high anisotropy factor (|glum | value of the order of 10-3 ) and a CPL brightness (BCPL ) higher than 100.

Synchronous assembly of chiral skeletal single-crystalline microvessels.

Skeletal or concave polyhedral crystals appear in a variety of synthetic processes and natural environments. However, their morphology, size, and orientation are difficult to control because of their highly kinetic growth character. We report a methodology to achieve synchronous, uniaxial, and stepwise growth of micrometer-scale skeletal single crystals from planar-chiral double-decker molecules. Upon drop-casting of a heated ethanol solution onto a quartz substrate, the molecules spontaneously assemble into standing vessel-shaped single crystals uniaxially and synchronously over the wide area of the substrate, with small size polydispersity. The crystal edge is active even after consumption of the molecules and resumes stereoselective growth with successive feeding. The resultant morphology can be packed into polycyclic aromatic hydrocarbon-like microarchitectures and behaves as a microscopic container.

Synthesis of Twisted Anthracenes: Induction of Twist Chirality by the Planar Chiral [2.2]Paracyclophane.

Planar chiral [2.2]paracyclophane was employed as chiral scaffolds to twist an anthracene ring by tethering at its 1- and 8-positions; thus, twist chirality was induced in the anthracene moiety. The chiroptical properties of the resulting molecule, including circular dichroism (CD) and circularly polarized luminescence (CPL), were found to be derived from the twist chirality. An analogous molecule bearing long alkyl chains was a viscous liquid at ambient temperature, and its liquid film exhibited good CD and CPL profiles. Theoretical studies are carried out to determine the origin of these properties in the ground and excited states, which reproduced well the experimental results.

Optically Active Cyclic Oligomers Based on Planar Chiral [2.2]Paracyclophane.

Optically active cyclic dimer, trimer, and tetramer, in which the p-arylene-ethynylenes were stacked, were prepared using enantiopure 4,7,12,15-tetrasubstituted [2.2]paracyclophane as the chiral building block. All molecules exhibited clear Cotton effects in their absorption bands with mirror image spectra, and the signals of the longest wavelengths of the (Rp )- and (Sp )-isomers were positive and negative, respectively. Their circularly polarized luminescence (CPL) signs corresponded with the those of the first Cotton effect. For all molecules, molecular orbitals were localized in one of the stacked p-arylene-ethynylenes in the excited states, resulting in a similar photoluminescence behavior. Although the cyclic dimer did not emit CPL, the cyclic trimer and tetramer exhibited intense CPL emissions with a relatively high dissymmetry factor in the order of 10-3 . Their optical and chiroptical properties were reproduced by time-dependent density functional theory calculations.

Construction of helical structures with planar chiral [2.2]paracyclophane: fusing helical and planar chiralities.

Optically active conjugated molecules bearing one-handed helical structures, in which two [4]helicenes or two phenanthrenes are stacked at terminal benzene moieties, were prepared using enantiopure [2.2]paracyclophane as a chiral scaffold. The obtained molecules exhibited excellent chiroptical properties such as circularly polarized luminescence with high disymmetry factors. Planar chiral pseudo-meta-disubstituted [2.2]paracyclophane was also optically resolved on the sub-gram-scale.

Experimental and theoretical studies on circularly polarized phosphorescence of a [2.2]paracyclophane-based platinum(ii) complex.

An optically active binuclear platinum(ii) complex based on planar chiral [2.2]paracyclophane was synthesized. The corresponding enantiomers exhibited red circularly polarized phosphorescence (CPP) with the dissymmetry factor |glum| = 1.0 × 10-3. We report, for the first time, theoretical estimation of the CPP |glum| value using relativistic calculations.

Control of Axial Chirality by Planar Chirality Based on Optically Active [2.2]Paracyclophane.

Optically active X-shaped molecules based on the planar chiral [2.2]paracyclophane building block were prepared, in which di(methoxy)terphenyl units were stacked on the central benzene rings. At 25 °C, anisolyl rings freely rotate in solution, while in the crystal form, they are fixed by intramolecular CH-π interactions, thereby leading to the expression of the axial chirality, i.e., propeller chirality was exhibited by the planar chiral [2.2]paracyclophane moiety. The X-shaped molecule exhibited good circularly polarized luminescence (CPL) profiles with moderate ΦPL and a large glum value in the order of 10-3 at 25 °C, in solution. In contrast, at -120 °C, dual CPL emission with opposite signs was observed. According to the theoretical studies, the rotary motion of the anisolyl units is suppressed in the excited states, and so emission from two isomers could be observed. These results demonstrate that the axial chirality was controlled by the planar chirality, leading ultimately to propeller chirality.

Control of Circularly Polarized Luminescence by Orientation of Stacked π-Electron Systems.

Planar chiral building blocks based on 4,7,12,15-tetrasubstituted [2.2]paracyclophanes were obtained via a synthetic route involving an optical resolution step. Planar chiral enantiomers, comprising two fluorophores that were stacked to form a V-shaped higher-ordered structure, were synthesized from these building blocks. The V-shaped molecules emitted intense circularly polarized luminescence (CPL). Their chiroptical properties were compared with those of X-shaped molecules bearing the same two fluorophores stacked together. The CPL sign of the X-shaped molecule was opposite to that of the V-shaped molecule, which is supported by the theoretical results, indicating that the CPL sign can be controlled by the orientation of the stacked fluorophores.

Design of Thermochromic Luminescent Dyes Based on the Bis(ortho-carborane)-Substituted Benzobithiophene Structure.

To obtain solid-state emissive materials having stimuli-responsive luminescent chromic properties without phase transition, benzobithiophenes modified with two o-carborane units having various substituents in the adjacent phenyl ring in o-carborane were designed and synthesized. Their emission colors were strongly affected not only by the substituents at the para-position of the phenyl ring but also by molecular distribution in the solid state. In particular, the emission colors were changed by heating without crystal phase transition. It was proposed that their thermochromic properties were correlated not with isomerization but with the molecular motion at the distorted benzobithiophene moiety.

Synthesis of enantiopure planar chiral bis-(para)-pseudo-meta-type [2.2]paracyclophanes.

A new type of planar chiral (Rp )- and (Sp )-4,7,12,15-tetrasubstituted [2.2]paracyclophanes was prepared from racemic 4,7,12,15-tetrabromo[2.2]paracyclophane as the starting substrate. Regioselective lithiation and transformations afforded racemic bis-(para)-pseudo-meta-type [2.2]paracyclophane (4,15-dibromo-7,12-dihydroxy[2.2]paracyclophane). Its optical resolution was performed by the diastereomer method using a chiral camphanoyl group as the chiral auxiliary. The diastereoisomers were readily isolated by simple silica gel column chromatography, and the successive hydrolysis afforded (Rp )- and (Sp )-bis-(para)-pseudo-meta-type [2.2]paracyclophanes ((Rp )- and (Sp )-4,15-dibromo-7,12-dihydroxy[2.2]paracyclophanes). They can be used as pseudo-meta-substituted chiral building blocks.

π-Stacked Polymer Consisting of a Pseudo⁻meta⁻[2.2]Paracyclophane Skeleton.

A novel π-stacked polymer based on a pseudo⁻meta⁻linked [2.2]paracyclophane moieties was synthesized by Sonogashira-Hagihara coupling. The UV-vis absorption spectra of the synthesized polymer and model compounds revealed an extension of the conjugation length owing to the through-space conjugation. The optical properties of the π-stacked dimer with the pseudo⁻meta⁻linked [2.2]paracyclophane unit were compared with those of the corresponding dimers with the pseudo⁻ortho⁻ and pseudo⁻para⁻linked [2.2]paracyclophane units.

A silver(i)-induced higher-ordered structure based on planar chiral tetrasubstituted [2.2]paracyclophane.

Optically active phenylene-ethynylene dimers with pyridine groups based on a planar chiral 4,7,12,15-tetrasubstituted [2.2]paracyclophane were synthesized. The chiral conformation was controlled by pyridine-Ag(i) coordinations. After Ag(i) coordination, the resulting higher-ordered structure dramatically enhanced the signal intensity of circular dichroism (CD) and decreased that of circularly polarized luminescence (CPL).

Luminescence Color Tuning from Blue to Near Infrared of Stable Luminescent Solid Materials Based on Bis-o-Carborane-Substituted Oligoacenes.

Aryl-substituted o-carboranes have shown highly efficient solid-state emission in previous studies. To demonstrate color tuning of the solid-state emission in an aryl-o-carborane-based system, bis-o-carborane-substituted oligoacenes were synthesized and their properties were systematically investigated. Optical and electrochemical measurements revealed efficient decreases in energy band gaps and lowest unoccupied molecular orbital (LUMO) levels by adding a number of fused benzene rings for the extension of π-conjugation. As a consequence, bright solid-state emission was observed in the region from blue to near infrared (NIR). Furthermore, various useful features were obtained from the modified o-carboranes as an optical material. The naphthalene derivatives exhibited aggregation-induced emission (AIE) and almost 100 % quantum efficiency in the crystalline state. Furthermore, it was shown that the tetracene derivative with NIR-emissive properties had high durability toward photo-bleaching under UV irradiation.

Oxygen-Bridged Diphenylnaphthylamine as a Scaffold for Full-Color Circularly Polarized Luminescent Materials.

An oxygen-bridged diphenylnaphthylamine with a helical shape was designed and synthesized as a key scaffold for circularly polarized luminescent (CPL) materials. The introduction of electron-withdrawing groups, such as formyl and 2,2-dicyanovinyl substituents at the naphthyl moiety in this skeleton effectively decreases the LUMO level and thus allows a tuning of the band gap. The prepared model compounds exhibit intense CPL signals with a dissymmetry factor (g value) of 10-3 both in CH2Cl2 solutions and in the solid states. The emission colors of these derivatives are influenced both by the substituents as well as by solvent effects, covering the whole visible region from blue to deep red.

Optically Active Phenylethene Dimers Based on Planar Chiral Tetrasubstituted [2.2]Paracyclophane.

Optically active phenylethene dimers based on a planar chiral 4,7,12,15-tetrasubstituted [2.2]paracyclophane were synthesized. We succeeded in controlling the molecular motion by binding luminophores in close proximity with the [2.2]paracyclophane scaffold. For example, aggregation-induced emission (AIE)-active luminophores were converted to show intense photoluminescence (PL) even in a diluted solution at room temperature and the resulting compound worked as a single-molecule thermoresponsible material around room temperature. Because of the AIE-active unit, the molecular motion could be easily activated by heating, leading to variable and reversible PL intensity. Furthermore, the π-conjugated systems with the planar chirality of 4,7,12,15-tetrasubstituted [2.2]paracyclophane provided excellent characteristics on circular dichroism (CD) and circularly polarized luminescence (CPL). The obtained dimers showed high CPL performances both in a diluted solution and in an aggregation state. We succeeded in proving that simple molecular designs composed of only carbon and hydrogen atoms could create versatile optical functionalities.

Solid-State Emission of the Anthracene-o-Carborane Dyad from the Twisted-Intramolecular Charge Transfer in the Crystalline State.

The emission process of the o-carborane dyad with anthracene originating from the twisted intramolecular charge transfer (TICT) state in the crystalline state is described. The anthracene-o-carborane dyad was synthesized and its optical properties were investigated. Initially, the dyad had aggregation- and crystallization-induced emission enhancement (AIEE and CIEE) properties via the intramolecular charge transfer (ICT) state. Interestingly, the dyad presented the dual-emissions assigned to both locally excited (LE) and ICT states in solution. From the mechanistic studies and computer calculations, it was indicated that the emission band from the ICT should be attributable to the TICT emission. Surprisingly, even in the crystalline state, the TICT emission was observed. It was proposed from that the compact sphere shape of o-carborane would allow for rotation even in the condensed state.