Toshiyuki Hamura

Invited for the cover of this issue are Toshiyuki Hamura and co‐workers at Kwansei Gakuin University. The image depicts solid‐state generation of diarylisonaphthofuran from 1,3‐diaryl‐1,3‐dihydronaphthofuranol and its mechanochemical Diels–Alder reaction with epoxynaphthalene. Read the full text of the article at 10.1002/chem.202302660.

A solid‐state method was developed for generating diarylisonaphthofurans from 1,3‐diaryl‐1,3‐dihydronaphthofuranols. The generated reactive molecules were stable in the solid state and could be stored without any extra precautions. X‐ray diffraction analysis revealed a typical quinoidal structure. Furthermore, the mechanochemical Diels–Alder reaction of 1,3‐diarylisonaphthofurans with epoxynaphthalenes afforded synthetically attractive diepoxypentacenes.

Intramolecularsinglet fission (iSF) is an efficient strategy ofmultiexciton generation via a singlet exciton splitting into a correlatedtriplet pair in one organic molecule with more than two chromophores.Propeller-shaped iptycene-linked triisopropylsilyl-(TIPS)-ethynyl functionalizedpentacene oligomers (pent-monomer, pent-dimer, and pent-trimer) weresynthesized, and the iSF dynamics of pent-dimer and -trimer were monitoredby a visible-near-IR transient absorption (TA) spectroscopy.Quantum yields of the triplet pair, similar to 80%, of both estimatedby near-IR TA spectral analysis are in good agreement with the resultsof global analysis and triplet sensitization experiments. The iSFrate of pent-trimer is slightly faster than that of pent-dimer evenwith one more chromophore site. The unexpectedly weak difference indicatesthe existence of an intermediate process to realize iSF. The intermediateprocess might be determined by through-bond electronic coupling ofthe homoconjugation bridge in the pentacene oligomers. Our resultssuggest the importance of the rigid bridge to the fast iSF rate andthe elongated lifetime of the correlated triplet pair in pentaceneoligomers.

Thermal isomerization of cyclobutaphenanthrene to o‐quinodimethane was investigated. Sterically congested substituents or electron‐donating substituents on the four‐membered ring promoted the ring‐opening, affording o‐quinodimethane in a relatively stable form. Isolation of the newly prepared o‐quinodimethane allowed its structural elucidation and investigation of its potential reactivities. Dual [4+2] cycloaddition of an aryne and o‐quinodimethane afforded tetrabenzopentacene, demonstrating the synthetic application of the isolated compound.

Herein, a simple and practical method for generating isoacenofuran, a new π-extended quinoidal building block, was developed.

A new synthetic route to π-extended pyracylene was developed by hydrogen halide promoted cascade reaction of epoxytetracene.