An o-carborane-based anthracene was synthesized, and single crystals, with incorporated solvent molecules, were obtained from the CHCl₃, CH₂Cl₂, and C₆H₆ solutions. The anthracene ring in the crystal is highly distorted by the formation of a π-stacked dimer between the anthracene units. The crystals exhibited a variety of emission behaviors such as aggregation-induced emission (AIE), crystallization-induced emission (CIE), aggregation-caused quenching (ACQ), and multichromism.

An o-carborane-based anthracene was synthesized, and single crystals, with incorporated solvent molecules, were obtained from the CHCl₃, CH₂Cl₂, and C₆H₆ solutions. The anthracene ring in the crystal is highly distorted by the formation of a π-stacked dimer between the anthracene units. The crystals exhibited a variety of emission behaviors such as aggregation-induced emission (AIE), crystallization-induced emission (CIE), aggregation-caused quenching (ACQ), and multichromism.

A series of organic dyes were synthesized that contain an o-carborane unit in combination with phenanthrene, tolane, and BODIPY moieties. In solution, compound 7 a, which has phenanthrene and tolane units, does not emit as a result of an intramolecular charge transfer (ICT) from the emitters to the C1C2 bond of the o-carborane cage, whereas, in the aggregate and solid state, 7 a emits intense green light through aggregation-induced emission (AIE). In solution, compound 7 b, which has phenanthrene, tolane, and BODIPY units, emits green light from the BODIPY moiety, whereas, in both the aggregate and solid state, it does not emit as a result of the energy transfer from the phenanthrene and tolanes to the neighboring BODIPY units and the successive aggregation-caused quenching (ACQ) mechanism. This work shows that the emission behaviors, the ICT, AIE, energy transfer, and ACQ, of these dyes can be controlled by the substituents at the o-carborane core.

Optically active through-space conjugated oligomers, namely, a dimer, trimer, tetramer, and cyclic trimer, consisting of a planar-chiral [2.2]paracyclophane skeleton were synthesized. In the ground state, observed similarities in the chiroptical properties of the oligomers were attributed to the equivalent orientations of two adjacent chromophores. In the excited state, the oligomers were folded into a form analogous to a one-handed helix by photoexcitation. All the compounds in dispersed solution exhibited intense circularly polarized luminescence with relatively large anisotropy factors on the order of 10⁻³.

A [2.2]paracyclophane-based through-space conjugated oligomer comprising three π-electron systems was designed and synthesized. The arrangement of three π-conjugated systems in an appropriate order according to the energy band gap resulted in efficient unidirectional photoexcited energy transfer by the Förster mechanism. The energy transfer efficiency and rate constants were estimated to be >0.999 and >10¹² s⁻¹, respectively. The key point for the efficient energy transfer is the orientation of the transition dipole moments. The time-dependent density functional theory (TD-DFT) studies revealed the transition dipole moments of each stacked π-electron system; each dipole moment was located on the long axis of each stacked π-electron system. This alignment of the dipole moments is favorable for fluorescence resonance energy transfer (FRET).

The synthesis and properties of biphenyl- and p-terphenyl-fused o-carboranes are described. Aryl rings in the biphenyl and p-terphenyl skeletons are highly coplanar because of the presence of the o-carborane unit. o-Carborane exhibits an electron-withdrawing character via the inductive effect, resulting in a decrease in both the HOMO and LUMO levels of oligophenyls without causing electronic perturbation.

New [2.2]paracyclophane-based through-space conjugated polymers containing fluorescence quenchers such as anthraquinone and ferrocene units at the polymer termini were designed and synthesized. Their optical properties were investigated in detail. Fluorescence emission from the stacked π-electron systems was effectively quenched by the stacked π-electron systems at the polymer termini due to the energy and electron transfer through a single polymer chain; thus, the polymers acted as the molecular wire. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Conjugated microporous polymers (CMPs) are prepared from disubstituted and tetrasubstituted [2.2]paracyclophane monomers by a Sonogashira–Hagihara coupling. The polymers obtained exhibit a type I nitrogen gas adsorption profile and H4-like hysteresis loops, indicating that the [2.2]paracyclophane-containing CMPs possess slit-like mesopores. Their Brunauer–Emmett–Teller surface areas are estimated to be above 500 m² g⁻¹. The step and stacked structure of the [2.2]paracyclophane unit affects the morphology of the polymers because of the contribution of two-dimensional expansion of the polymer network.

The o-carborane-based π-conjugated compound, benzocarborano- [2,1-b:3,4-b′]dithiophene was synthesized. Its crystal structure revealed high coplanarity for the two thiophene rings of the 2,2′-bithiophene skeleton, which is fixed in the cisoid structure by the o-carborane unit. Theoretical calculations indicated non-aromaticity for its center C₆ ring moiety as well as decreased HOMO and LUMO levels. The o-carborane moiety provides an electron-withdrawing character to the 2,2′-bithiophene unit through an inductive effect.

[2.2]Paracyclophane-based through-space conjugated oligomers and polymers were prepared, in which poly(p-arylene–ethynylene) (PAE) units were partially π-stacked and layered, and their properties in the ground state and excited state were investigated in detail. Electronic interactions among PAE units were effective through at least ten units in the ground state. Photoexcited energy transfer occurred from the stacked PAE units to the end-capping PAE moieties. The electrical conductivity of the polymers was estimated using the flash-photolysis time-resolved microwave conductivity (FP-TRMC) method and investigated together with time-dependent density functional theory (TD-DFT) calculations, showing that intramolecular charge carrier mobility through the stacked PAE units was a few tens of percentage larger than through the twisted PAE units.

The synthetic details of the P-stereogenic optically active polymer and the complexation behavior with palladium and platinum complexes are reported. The polymer consists of P-stereogenic bisphosphine units and the conjugated phenylene-ethynylene units alternately. The P-stereogenic bisphosphine moieties can coordinate to transition metals such as palladium and platinum, leading to a change in the conformation.

New aromatic ring-layered polymers consisting of carbazole as a layered aromatic group and xanthene as a scaffold were designed and synthesized via the Sonogashira–Hagihara coupling reaction. Their optical and electrochemical behaviors were investigated in detail; the results showed that these polymers could be used as hole-transporting materials. Polymers with nitrobenzene moieties at the polymer chain ends quenched the emission from the layered carbazoles to the nitrobenzene termini; thus, the polymers acted as the molecular wire that transferred photoexcited energy and/or electrons to the polymer termini. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4279–4288, 2009

New through-space cyano-substituted poly(p-arylenevinylene)s containing a [2.2]paracyclophane unit were synthesized by the Knoevenagel reaction. Polymers 5 and 7 have cyano groups at α-positions and β-positions from the dialkoxyphenylene unit, respectively. Their optical and electrochemical behaviors were investigated in detail in comparison with their model compounds. Polymers 5 and 7 exhibited through-space conjugation via the cyclophane units. Polymer 5 showed greenish blue emission (λ_max = 477 nm) in diluted solution with fluorescence quantum efficiency (ϕ_F) of only 0.007, whereas polymer 7 emitted in the bluish green region (λ_max = 510 nm) with ϕ_F of 0.32. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5979–5988, 2009

We synthesized through-space conjugated polymers with [2.2]paracyclophane and thieno[3,4-b]pyrazine units in the main chain by the Sonogashira–Hagihara coupling reaction. The obtained polymers were soluble in common organic solvents, and homogeneous thin films were readily obtained from the polymer solutions by spin-coating techniques. The polymers exhibited the extension of the conjugation length via the through-space interaction. The polymers showed orangish-red emission with peak maxima of around 610 nm in diluted solutions and their thin films, which were derived from the thieno[3,4-b]pyrazine moieties. The optical and electrochemical behaviors of the polymers containing pseudo-para- and pseudo-ortho-linked [2.2]paracyclophane were identical. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009