A novel class of planar, highly conjugated all-carbon macrocycles, which we christened âradiaannulenesâ, have been prepared based on acetylenic scaffolding using tetraethynylethene (TEE) building blocks; these structures are powerful electron acceptors and, upon peripheral substitution with electron-donating N,N-dialkylanilino groups, display intense intramolecular charge-transfer.
investigations (Table) demonstrated that the radiaannulenes are particularly powerful electronacceptors. Thus, bicyclic radiaannulene 11, which possesses eight peripheral 3,5-di(tert-butyl)phenyl substituents, is reversibly reduced at −0.83 V in THF (vs. Fc+/Fc), making it a betterelectronacceptorthan buckminsterfullerene C60 under comparable conditions.
perethynylated dehydro[12]- and dehydro[18]-annulenes were prepared by oxidative acetylenic coupling of cis-bisdeprotected tetraethynylethene derivatives obtained by a new photochemical route; they display strongly bathochromically shifted longest-wavelength absorption bands compared to their silyl-substituted counterparts resulting from efficient intramolecularcharge-transfer between the peripheral