Synthesis of Azadioxa-Planar Triphenylboranes Bridged by Aryl- and Alkylimino Groups and Their Photophysical Properties.

Heteroatom-bridged planar triphenylboranes, in which the three phenyl groups are bridged at the ortho positions by heteroatoms, are attracting growing attention as one of the heteroatom-containing π-conjugated molecules. Herein, we developed the synthetic method of planar triphenylboranes bridged by two oxygen atoms and one nitrogen atom, and the substituent on the nitrogen atom is derived into various aryl and alkyl groups. A key intermediate bearing an imino group (-NH-) was synthesized from a bis-triflate precursor bridged by two oxo groups via a nucleophilic aromatic substitution reaction of benzyl amine and following debenzylation. The X-ray crystallographic analysis revealed that the compound exhibits a planar molecular structure which can form a one-dimensionally π-stacked structure. The photophysical and density functional theory studies revealed that their highest occupied molecular orbitals and lowest unoccupied molecular orbitals (LUMOs) are originated from the triphenylborane moiety, while introducing strong electron-withdrawing groups such as the 4-cyanophenyl group on the nitrogen atom can induce the localization of the LUMO at the aryl groups instead of the triphenylborane moiety.

X-Shaped Cyclobutane-Linked Tetraporphyrins through a Thermal [2+2] Cycloaddition of Etheno-Fused Diporphyrins.

A nickel-mediated tandem double cyclization of ethynylene-linked dibromodiporphyrins afforded highly reactive etheno-fused diporphyrins, which undergo a thermal [2+2] cycloaddition at the fused C-C double bond to afford the cyclobutane moiety in X-shaped cyclobutane-linked tetraporphyrins. During the reaction of a Zn(II) complex precursor, the initial double cyclization product was converted into the diketodiporphyrin, which exhibits red chemiluminescence under ambient conditions.

Synthesis of bright red-emissive dicyanoetheno-bridged hexa-peri-hexabenzocoronene dimers.

The introduction of a dicyanomethyl anion group to hexa-peri-hexabenzocoronene (HBC) substantially enhanced the emission properties of HBC due to a large perturbation of its electronic structure. In addition, dicyanoetheno-bridged HBC dimers obtained from oxidation of a dicyanomethyl HBC anion exhibited bright red emission in solution and solid states. Intramolecular charge transfer interactions between the HBC units and the dicyanoethene bridge induced solvatochromic behaviour in their emission spectra. Dicyanoetheno-bridged HBC dimers exhibited cis-trans photoisomerization behaviour in the solution, affording the mixture in cis-isomer dominance in the photostationary state. Theoretical calculations revealed that the cis-isomer is more thermodynamically stable than the trans-isomer.

Silylethynyl substituents as porphyrin protecting groups for solubilization and selectivity control.

Silylethynyl substituents are proposed as protecting groups for porphyrin derivatives to enhance their solubility and enable regioselective functionalization. After usage as protecting groups, silylethynyl groups at the meso-positions can be efficiently removed upon heating with aqueous H2SO4 in the presence of a surfactant. This approach was applied to the preparation of unsymmetrically ß-substituted porphyrins and porphin-porphyrin oligomers, which were inaccessible by conventional methods.