Furan-Containing Chiral Spiro-Fused Polycyclic Aromatic Compounds: Synthesis and Photophysical Properties.

Spiro-fused polycyclic aromatic compounds (PACs) have received growing interest as rigid chiral scaffolds. However, furan-containing spiro-fused PACs have been quite limited. Here, we design spiro[indeno[1,2-b][1]benzofuran-10,10'-indeno[1,2-b][1]benzothiophene] as a new family of spiro-fused PACs that contains a furan unit. The compound was successfully synthesized in enantiopure form and also transformed to its S,S-dioxide derivative and the pyrrole-containing analog via aromatic metamorphosis. The absorption and emission properties of the obtained furan-containing chiral spiro-fused PACs are apparently different from those of their thiophene analogs that have been reported, owing to the increased electron-richness of furan compared to thiophene. All of the furan-containing chiral spiro-fused PACs were found to be circularly polarized luminescent materials.

Transformation of Thia[7]helicene to Aza[7]helicenes and [7]Helicene-like Compounds via Aromatic Metamorphosis.

[n]Helicenes with helically twisted structures have attracted increasing interest owing to their unique properties. Therefore, it has been an important issue to develop facile synthetic methodologies which allow access to a variety of [n]helicenes. Here we report the synthesis of [7]helicenes and [7]helicene-like compounds from the thia[7]helicene as a common starting material. Desulfurative dilithiation of the thia[7]helicene and the subsequent reaction with silicon and phosphorus electrophiles afforded the silole- and phosphole-fused [7]helicene-like compounds, respectively. The cyclopentadiene-fused [7]helicene-like compound and the pyrrole-fused aza[7]helicenes were also successfully synthesized via twofold SNAr reactions of the thia[7]helicene S,S-dioxide with the carbon and nitrogen nucleophiles, respectively. The thia[7]helicene S,S-dioxide showed a slightly red-shifted absorption spectrum than the parent thia[7]helicene, which was well demonstrated by the theoretical calculations. The substituents on the silicon atom of silole-fused [7]helicene-like compounds have little impact on the longest absorption maximum. Such little effect of the substituents on absorption properties was also observed for cyclopentadiene-fused [7]helicene-like compounds and aza[7]helicenes and was well demonstrated by the theoretical calculations. The thia[7]helicene S,S-dioxide and the silole-fused [7]helicene-like compound exhibited bright blue emission, and the cyclopentadiene-fused [7]helicene-like compound and the aza[7]helicenes showed strong violet emission. Each single enantiomer of the aza[7]helicenes showed circularly-polarized luminescence with the dissymmetry factors of 4.2~4.4 × 10-3.

Solvent-sensitive circularly polarized luminescent compounds bearing a 9,9'-spirobi[fluorene] skeleton.

A series of chiral 9,9'-spirobi[fluorene] (SBF) derivatives with diphenylamino donor and cyano acceptor units were designed as a new family of circularly polarized luminescent materials. The designed SBF derivatives were successfully synthesized from 7,7'-dibromo-9,9'-spirobi[fluorene]-2,2'-diol. No racemization occurred in the synthetic sequence. Therefore, each enantiomer of the SBF derivatives can be prepared from the enantiomerically pure starting material. Absorption and fluorescence spectroscopy and theoretical calculations revealed that the phenylene linker between the donor/acceptor units and the SBF core has a great impact on their photophysical properties. In particular, the phenylene linker was found to induce a red shift in their emission bands. The obtained chiral SBF derivatives exhibited solvent-dependent circularly polarized luminescence owing to their donor-π-acceptor structures.

[1]Benzothiophene-Fused Chiral Spiro Polycyclic Aromatic Compounds: Optical Resolution, Functionalization, and Optical Properties.

Spiro polycyclic aromatic compounds have been known as rigid chiral scaffolds. In order to extend their applications, an efficient preparation route to enantiopure derivatives is highly required. Here, we design 10,10'-spirobi[indeno[1,2- b][1]benzothiophene]-7,7'-diol to achieve efficient optical resolution. The compound was successfully synthesized and resolved by chiral HPLC on a semipreparative scale. The absolute configuration of its enantiopure isomer was determined through single-crystal X-ray structure analysis of its derivative. The compound was also transformed into its derivatives with donor-acceptor (D-A) type systems. The obtained chiral D-A type molecules exhibited remarkable solvent-dependence fluorescence and were found to be solvent-sensitive circularly polarized luminescent materials. These results clearly demonstrated the utility of 10,10'-spirobi[indeno[1,2- b][1]benzothiophene]-7,7'-diol as a versatile building block for chiral spiro polycyclic aromatic compounds.

Circularly Polarized Luminescence from Chiral Spiro Molecules: Synthesis and Optical Properties of 10,10'-Spirobi(indeno[1,2-b][1]benzothiophene) Derivatives.

Chiral spiro polycyclic aromatic compounds with thiophene and/or thiophene S,S-dioxide units were synthesized as a new family of circularly polarized luminescence (CPL) materials. Oxidation of the thiophene unit to its S,S-dioxide provided significant changes in photophysical properties such as much higher fluorescence quantum yield and positive solvatochromism in photoluminescence spectra. Density functional theory calculations qualitatively demonstrated the observed absorption properties. The prepared chiral spiro compounds exhibit intense CPL signals with a relatively large dissymmetry factor for small organic molecules.