The Irreversible Photochemistry of Bianthrone

Abstract

Summary. A 4a, 4b-dihydrophenanthrene-type cyclic photoisomer, the C isomer, is the major primary photoproduct of bianthrone in protic and aprotic polar solvents, and undcrgoes solventdependent secondary reactions, including the formation of tlihydrohelianthronc in protic solvents. The C isomer was shown to be formed through the singlct cxcitcd state whilc the B isomer is formcd via the triplet manifold.

Polarity‐Dependent Isomerization of an Unsymmetrical Overcrowded Ethylene Promoted by Zwitterionic Contribution in the Twisted Isomer

“…Accordingly,t his absorption band is assignablet ot he folded isomer.T he longerw avelength peak suggests that the unsymmetrical combinationb etween the electron-donating acridane and the electron-withdrawing anthrone increases the zwitterionic character and weakens the interunit interaction. [4] Notably,w hile the twistedf orm of 1 has been reported to be unstablea gainsto xygen and light, the twisted form of 2 was found to be stable in polar solvents (t 1/2 = 570 hi nD MSO,Figure S4). Since this new absorption band is located at the near-IR region, the color change is inconspicuous and the yellow-colored solution turned only slightly red ( Figure S3).…”

“…[2][3][4][5][6][7][8][9][10] In responset oe xternal stimuli, such as photoirradiation, thermals timulation and mechanicalg rinding, 1 shows an isomerization between two isomers:t he yellow-colored folded isomer and the green-colored twisted isomer.This structural change reflects the nature of the overcrowdede thylene. In this study,a nu nsymmetrical bianthrone (2), consisting of the electron-withdrawinga nthrone and electron-donating acridane, have been synthesized and shown to exhibit as olvent-polarity-dependent isomerization reaction between the folded and twisted isomers.…”

“…[2][3][4][5][6][7][8][9][10] In responset oe xternal stimuli, such as photoirradiation, thermals timulation and mechanicalg rinding, 1 shows an isomerization between two isomers:t he yellow-colored folded isomer and the green-colored twisted isomer.This structural change reflects the nature of the overcrowdede thylene. [2][3][4][5][6][7][8][9][10] In responset oe xternal stimuli, such as photoirradiation, thermals timulation and mechanicalg rinding, 1 shows an isomerization between two isomers:t he yellow-colored folded isomer and the green-colored twisted isomer.This structural change reflects the nature of the overcrowdede thylene.…”

“…The stabilization of the twistedi somer in polar solvents can be interpreted as proof of its relatively large zwitterionic character.T he DMF solution of 2 displayed paramagnetically-broadened NMR signals from the thermally populated triplet state resultingf rom rotation of the weakened ethylenic double bond of the twisted isomer.Bianthrone( 1)h as been widely studied as an overcrowdede thylene, [1] and the physical and chemical properties of the bending and twisting ethylene doubleb ond have been explored. [2][3][4][5][6][7][8][9][10] In responset oe xternal stimuli, such as photoirradiation, thermals timulation and mechanicalg rinding, 1 shows an isomerization between two isomers:t he yellow-colored folded isomer and the green-colored twisted isomer.This structural change reflects the nature of the overcrowdede thylene. The structural strain due to twisting of the central double bond in the twisted isomer is larger than that due to bending of the anthrone parts in the folded isomer.T herefore, the twisted isomer of 1 is less stable than the folded isomer by 3.5 kcal mol À1 , [8] which does not allow its isolation.…”

Conformational Space and Dynamic Stereochemistry of Overcrowded Homomerous Bistricyclic Aromatic Enes − A Theoretical Study

“…[45] A metastable syn-folded conformation was generated photochemically. [39,42] The 2D structure and atom labeling of dithioxanthylene are shown in Figure 22. …”