title: Double protonation of 1,5-bis(triarylaminoethynyl)anthraquinone to form a paramagnetic pentacyclic dipyrylium salt.
abstract: Protonation-induced intramolecular cyclization reactions of new donor (D)-acceptor (A) and D-A-D conjugated molecules 1-triarylaminoethynylanthraquinone (1-AmAq) and 1,5-bis(triarylaminoethynyl)anthraquinone (1,5-Am(2)Aq), respectively, were achieved. The former undergoes monoprotonation with bis(trifluoromethanesulfone)imide acid (TFSIH) to give pyrylium salt [1-AmPyl]TFSI, whereas the latter undergoes a novel double proton cyclization reaction to yield 1,5-bis(triarylamino)dipyrylium salt [1,5-Am(2)Pyl(2)](TFSI)(2) with a new pentacyclic backbone. This divalent cationic salt can be reduced to give the neutral species 2,8-bis(triarylamino)benzo[de]isochromeno[1,8-gh]chromene ([1,5-Am(2)Pyl(2)](0)), which maintains the planar pentacyclic backbone. The obtained condensed-ring compounds show unique optical, electrochemical, and magnetic properties due to the extremely narrow HOMO-LUMO gap. In particular, the dication [1,5-Am(2)Pyl(2)](2+) shows paramagnetic behavior with two spins centered on two triarylamine moieties through valence tautomerization with the pentacyclic backbone.
authors: Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors: Koya Prabhakara
authors: KP
authors: Rao
authors: Tetsuro
authors: T
authors: Kusamoto
authors: Fumiyuki
authors: F
authors: Toshimitsu
authors: Kiyotaka
authors: K
authors: Inayoshi
authors: Shoko
authors: S
authors: Kume
authors: Ryota
authors: R
authors: Sakamoto
authors: Hiroshi
authors: H
authors: Nishihara
mesh_terms: D000880:Anthraquinones / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008280:Magnetics; D008958:Models, Molecular; D011522:Protons; D011714:Pyrans / Q000737:chemistry*; D012492:Salts / Q000737:chemistry
chemical_list: D000880:Anthraquinones; D011522:Protons; D011714:Pyrans; D012492:Salts